Chapter-5 Periodic Classification of Elements Extra Questions

Explanation:

(d) Calcium

The law of octaves was found to apply to calcium (element 20).

The octave law is a periodic observation made by British chemist John Newlands in 1864, which states that when elements are arranged in order of increasing atomic weight, their properties repeat every eight elements. This trend was observed for calcium (element 20) at

Newlands. However, due to some inconsistencies, his octave law was not widely accepted at the time, and it was later refined and extended to modern elements by Dmitri Mendeleev The Periodic Table, which includes all known elements up to the potassium (element 19).

Explanation:

(a) Increasing atomic mass

According to Mendeleev's periodic law, the elements of the periodic table are arranged in order of increasing atomic mass.

Mendeleev's original periodic table, published in 1869, was listed by atomic mass, which is the total number of protons and neutrons in an atomic nucleus. He observed that when elements are arranged in ascending order of atomic mass, their chemical and physical properties exhibit periodic patterns. However, when the periodic table was later revised by Henry Moseley in 1913, it was based on increasing atomic numbers, the number of protons in the nucleus, as this provided a more precise and consistent ordering of elements.

Explanation:

(c) Germanium

Germanium was found in the periodic table later.

Mendeleev's periodic table left gaps for elements that had not yet been discovered. In particular, Mendeleev predicted the existence of an element he called eka-silicon, which would fill the gap under silicon in group 4 of the periodic table. This element was later discovered by Clemens Winkler in 1886 and named germanium. Germanium has similar chemical and physical properties to silicon and tin and is a widely used semiconductor in electronic devices. Therefore, option (a) germanium will later find its way into the periodic table.

Explanation:

The correct answer is (d) (i), (ii) and (iv).

(i) The first statement is false. Elements in the modern periodic table are ordered by increasing atomic number rather than decreasing atomic number.

(ii) The second statement is also incorrect. Elements in the modern periodic table are ordered by increasing atomic number rather than increasing atomic mass.

(iii) The third statement is correct. The elements of the modern periodic table are ordered according to their increasing atomic number.

This arrangement allows the elements to be divided into groups and periods based on their electronic configuration, which determines their chemical and physical properties.

(iv) The fourth statement is incorrect. Isotopes are not located in adjacent groups in the periodic table of elements. An element's position in the periodic table is determined solely by its atomic number and electron configuration.

Explanation:

The correct statement is (b) It has 18 vertical columns called groups.

The modern periodic table is a list of chemical elements arranged in tabular form according to their atomic structure and chemical properties. It consists of 18 vertical columns called groups and 7 horizontal rows called periods. Elements of the same family have similar chemical and physical properties due to the similar configuration of electrons, while elements of the same period have the same number of electron shells.

Each group has a number ranging from 1 to 18 and a letter representing the elements of the group. For example, group 1 is called the alkali metals and includes elements like lithium, sodium, and potassium, while group 18 is called the noble gases and includes elements like helium, neon, and argon.

Explanation:

The correct answer is (c) B, C , D.

The elements A, B, C, D and E have the atomic numbers 2, 3, 7, 10 and 30 respectively.

To determine which of these elements belong to the same period, it is necessary to find common features between them.

The period of element is determined by the main energy level (shell) where its valence electrons are located. The dominant energy level is equal to the number of cycles. Thus, to find elements belonging to the same period, we need to find elements with the same valence shell. The atomic number of element A is 2, i.e. it has two electrons, and its valence shell is the first shell (K shell).

Element B has atomic number 3, which means it has three electrons, and its valence shell is the second shell (L-shell). Element C has an atomic number of 7, which means it has seven electrons, and its valence shell is the second shell (L-shell). The atomic number of element D is 10, which means it has 10 electrons, and its valence shell is the third shell (M-shell). Element E has an atomic number of 30, which means it has thirty electrons, and its valence shell is the fourth shell (N-shell).

It can be seen from the above analysis that elements B, C and D belong to the same period, because their valence electrons are all in the second shell (L-shell).

So the correct answers are (c) B, C, D.

Explanation:

The correct answer is (d) A and C.

The elements A, B, C, D, and E have atomic numbers of 9, 11, 17, 12, and 13, respectively. To identify which pairs of elements belong to the same group, we need to examine their chemical properties. Elements in the same group have similar chemical properties because they have the same number of valence electrons and similar electron configurations.

Element A has an atomic number of 9 and an electron configuration of 2,7. Element B has an atomic number of 11 and an electron configuration of 2, 8, 1. Element C has an atomic number of 17 and an electron configuration of 2, 8, 7. Element D has an atomic number of 12 and an electron configuration of 2, 8, 2. Element E has an atomic number of 13 and an electron configuration of 2, 8, 3.

By examining their electron configurations, we can see that elements A and C have the same number of valence electrons (7), and they both belong to group 17 (halogens). Elements D and E have the same number of valence electrons (2) and belong to group 2 (alkaline earth metals). Therefore, the correct answer is (d) A and C, as they both belong to group 17 (halogens) due to having the same number of valence electrons.

Explanation:

The correct answer is (b) Group 18

An element's electron configuration describes how its electrons are arranged at different energy levels or shells. The valence shell, which is the outermost shell, determines the chemical behavior of the element.

In this case, the given electron configuration is 2,8, which means that the element has 2 electrons in its first energy level (K shell) and 8 electrons in its second energy level (L shell). Because the valence shell of this element is the second energy level (L shell), it belongs to the second period of the modern periodic table of elements. Elements with similar valence electron configurations have similar chemical properties and belong to the same group.

In this case, the element has 8 valence electrons, which corresponds to group 18 (noble gases) of the modern periodic table.

Explanation:

The correct answer is (c) Group 14

Carbon is an essential component of all organic compounds. It has an atomic number of 6 and is classified as a group 14 element in the modern periodic table. This group, also referred to as the carbon group, contains five elements: carbon (C), silicon (Si), germanium (Ge), tin (Sn), and lead (Pb).

Group 14 elements possess 4 valence electrons, which allows them to form stable octet configurations by sharing electrons in covalent bonds with other atoms. The unique electronic configuration of these elements makes them important in various chemical applications, including semiconductor manufacturing and metallurgy.

Explanation:

The correct answer is (c) L shell.

Elements of period 2 have electrons of valence in the second energy level which has 2 sublevels - 2s and 2p sublevels. This means that the outermost shell of a period 2 element is shell L, which contains the 2s and 2p sublevels.

Explanation:

The correct answer is (c) P.

In the given element, the electronic configuration of sodium (Na) is 2,8,1. The electronic configuration of aluminum (Al) is 2,8,3. Silicon (Si) has an electron configuration of 2,8,4. Phosphorus (P) has an electron configuration of 2.8.5.

Explanation:

The correct answer is (c) F, O, N.

The atomic radius of an element refers to the half the distance between the centers of two atoms of that element that are just touching. When comparing O, F, and N, F has the smallest atomic radius due to its small size and strong attraction to electrons, resulting in a larger effective nuclear charge. As a consequence, its electrons are more tightly bound. On the other hand, N has the largest atomic radius because it has the lowest effective nuclear charge and the highest number of electron shells. O has a slightly smaller atomic radius than N due to its higher effective nuclear charge, which pulls its outer electrons closer to the nucleus.

Explanation:

The correct option is (c) Potassium (K).

Atomic radius generally increases as we move down a group and decreases as we move across a period from left to right.

Among the given elements Na, Mg, K, and Ca, they all belong to the same period (period 3) of the periodic table. Therefore, the atomic radius trend is not affected by the period number and we need to compare the atomic radii based on the positions in the modern periodic table.

Since K is located at the bottom of the same group as Na, it has the largest atomic radius among the given elements.

Explanation:

The correct answer is (b) K.

The elements of group 1 (alkali metals) and group 2 ( earth metals) have low ionization energies, which means they easily lose electrons.

Of the options offered, all are alkaline earth metals.

However, Na and K are in group 1 and have lower ionization energies than group 2. Therefore, Na and K lose electrons more easily than Mg and Ca.

Among Na and K, K is more large in size and has an electron in its outer shell which is farther from the nucleus than the outer electron of Na. Therefore, K loses electrons more easily than Na.

Explanation:

The correct answer is (a) F

Elements of the noble gas family (Group 18) have energies of ionization relatively higher. It is stable due to its filled outer electron shell. Among the proposed options, no element belongs to the group of noble gases.

Mg and Al are two metals that tend to lose electrons to achieve a stable electron configuration. However, Al has a higher ionization energy than Mg due to its smaller atomic size and greater effective nuclear charge.

Na is a metal with a lower ionization energy than Al due to its larger atomic size and lower effective nuclear charge.

Fluorine (F) has a higher electron affinity and tends to easily gain electrons to achieve a stable octet configuration. Hence, F is unlikely to easily lose electrons.

Explanation:

The correct answer is (a) (i) and (iii).

The atomic number of isotopes of an element is the same because it represents the number of protons in their nuclei, while the number of neutrons may vary. Therefore, statement (ii) is false.

Due to the difference in the number of neutrons, isotopes may have slightly different physical properties such as melting and boiling points, so statement (iv) is false.

Isotopes of an element have the same number of electrons and hence the same electron configuration, which determines their chemical properties. Thus, statement (iii) is correct.

Explanation:

Therefore option (d) Na > Mg > Al > Si > Cl is the correct answer.

The metallic nature of an element refers to the ease with which the atoms of the element lose their outer electrons to form cations. The more easily an atom loses electrons, the more metallic it is.

In a given element, the order of metallicity from large to small is: Na > Mg > Al > Si > Cl.

Therefore, the correct order of metal properties from top to bottom is: Na > Mg > Al > Si > Cl. 

Explanation:

(c) is the correct answer.

The nonmetallic character of an element refers to the propensity of the atoms of this element to gain electrons to form anions. The greater the tendency of an atom to gain electrons, the more non-metallic it is.

Within a given element, the non-metallic properties increase in the order: Li < Be < C < O < F.

Therefore, the correct order of increasing non metallicity is: Li < Be < C < O < F.

Explanation:

The correct answer is (c) 

Eka Aluminum is a hypothetical element predicted by Mendeleev with properties similar to aluminum. The oxides that aluminum Eka will form can be predicted from the periodic trend of the group to which it belongs (Group 13).

Aluminum belongs to group 13 and forms oxides with a metal/oxygen ratio of 2:3. Aluminum Eka also falls into this category and should therefore form oxides with a metal to oxygen ratio of 2:3.

Explanation:

The correct answer is (b) metalloids.

Boron (B), silicon (Si) and germanium (Ge) are considered metalloids because they have both metallic and non-metallic properties. They are moderately conductive and can act as conductors or insulators depending on the environment.

Boron is a hard and brittle material used to make ceramics, semiconductors and alloys. Silicon is a versatile semiconductor material that is also used to make computer chips and solar cells. Germanium is a shiny, hard material used to make transistors and other electronic devices.

Explanation:

The correct answer is (d) element of atomic number 7.

Acid oxides are oxides that react with water to form acidic solutions. The atomic number 7 element is generally a non-metallic element and tends to form acidic oxides when reacting with oxygen. Nitrogen (N) with atomic number 7 is an example of an element that forms acid oxides. Nitrogen dioxide (NO2) and nitrogen trioxide (NO3), which are acid oxides, are formed when nitrogen reacts with oxygen.

Elements with atomic numbers 3, 12, and 19 are metals that tend to form basic oxides when reacting with oxygen.

Basic oxides react with water to form basic solutions. For example, magnesium (Mg), atomic number 12, reacts with oxygen to form magnesium oxide (MgO), a basic oxide.

Explanation:

The answer is (c) metalloids.

The element with atomic number 14 is silicon (Si), which belongs to the metalloids.

Metalloids have properties intermediate between those of metals and nonmetals, they show a mixture of properties of metals and nonmetals. Silicon is a shiny, grayish, hard and brittle material with metallic and non-metallic properties.

Silicon forms the acid oxide SiO2, the main component of sand and quartz. It also forms covalent halides such as SiCl2, which is a colorless volatile liquid.

Explanation:

The correct answers are (d) (ii) and (iii).

In pictures iii) and ii), the atomic radius is clearly depicted as the distance between the nucleus and the outer orbit, while in pictures i) and iv), this distance is not shown.

Explanation:

The correct answer is (d) valence.

Valence is the number of electrons in the outermost shell of an atom, which remains constant for all elements in a group. Going down the group, the atomic radius and the number of shells increase due to the addition of new electron shells. The metallic character also increases as the group descends, because the outer shell electrons are farther from the nucleus, making them more likely to be lost and form positive ions.

Explanation:

The correct answer is (c) decreases.

As one moves from left to right in a period of the periodic table, the size of atoms decreases.

This tendency is due to the increase in nuclear charge, which more strongly attracts electrons from the outer shell to the nucleus. This stronger attraction reduces the size of the atom. Also, the increase in nuclear charge causes the number of electrons to remain the same during this period, but they are added at the same main energy level, making the atom more compact.

Explanation:

The correct answer is (d) Be, Mg , Ca

The metallic nature of element increases as we go down a group in the periodic table and over a period from right to left. Using this information, we can rank a given set of elements in increasing order of metallicity as follows:

(a) C, O, N - This set contains elements from period 2 of the periodic table, with progressively less metallic character as we move through the period from left to right. So C > O > N. So the correct order is N < O < C.

(b) Mg, Al, Si - This set contains elements from period 3 of the periodic table, and as and as we advance in the period from left to right, the metallic properties gradually decrease. Therefore, Mg > Al > Si. The correct order is therefore Si < Al < Mg.

(c) Na, Li, K - This set contains elements of the alkali metal group, with increasing metallic properties as one descends in the band.

Therefore, K > Na > Li. Therefore, the correct order is Li < Na < K.

(d) Be, Mg, Ca - This set contains elements from the alkaline earth group, and the metallicity increases as we rise And rises descend in the group. Therefore, Ca > Mg > Be. Therefore, the correct order is Be < Mg < Ca.

Explanation:

The arrangement of elements in which the atomic mass of one element is approximately equal to the average of the atomic mass of the other two elements with similar properties is called the law of triads.

This law was proposed by Johann Dobereiner at the beginning of the 19th century.

An example of a group of elements that obeys the triplet law is the alkali metal triplet. This triad consists of lithium (Li), sodium (Na), and potassium (K), which have atomic masses of approximately 7, 23, and 39, respectively. According to the law of the triads, the atomic mass of sodium is approximately equal to the average of the atomic masses of lithium and potassium. These elements also have similar chemical properties and form similar compounds.

Explanation:

(a) The two groups of elements with similar properties in the order given are:

1. Na, Mg, Al: This is a group of metals of increasing atomic mass. They are located in groups 2, 13 and 14 of the periodic table of elements.

They have low electronegativity, form cations in chemical reactions, and have metallic bonds.

2. P, S, Cl: This is a group of nonmetals of increasing atomic mass. They belong to groups 15, 16 and 17 of the periodic table of elements. They are highly electronegative, form anions in chemical reactions, and have covalent bonds.

(b) The sequence given represents the law of octaves, proposed by John Newlands in 1864.

This law states that when the elements are arranged in increasing order of their atomic mass, each eighth element has similar properties to the first element. In this sequence, the eighth element is F and the ninth element is Na, whose properties are similar to F. Similarly, the sixteenth element is S, which has similar properties to the seventh element, Cl. This pattern, which repeats after every eighth element, is known as the octave rule.

Explanation:

A Dobereiner triad is a group of three elements in which the atomic mass of the middle element is approximately equal to the average of the atomic masses of the other two elements.

(a) Na, Si, Cl: The atomic masses of

Na, Si and Cl are 23, 28 and 35, respectively. The average atomic mass of Na and Cl is (23+35)/2=29, which is close to the atomic mass of Si. But this group of elements cannot be classified as Doberina triples because the properties of Na, Si and Cl are too different.

(b) Be, Mg, Ca:

The atomic masses of Be, Mg and Ca are 9, 24 and 40 respectively. The average atomic mass of Be and Ca is (9+40)/2=24.5, which is close to the atomic mass of Mg. Therefore, this group of elements can be classified as the Dobelena Triad.

In addition, Be, Mg and Ca behave similarly.

They are both metals, they have similar reactivity and form similar types of compounds. Therefore, this triplet satisfies both the criterion of similar chemical properties and the criterion that the atomic mass of the intermediate element is close to the average of the atomic masses of the other two elements.

Explanation:

Mendeleev classified the elements of his periodic table according to their chemical and physical properties and tried to keep elements with similar properties in the same vertical column (group). He also listed them in order of increasing atomic mass, but he made some adjustments to keep the periodic properties.

Cobalt (Co) and nickel (Ni) are two transition metals with very similar chemical and physical properties.

Cobalt has an atomic mass of 58.93 amu while nickel has an atomic mass of 58.71 amu. In order of increasing atomic mass, nickel should come before cobalt. However, Mendeleev placed cobalt before nickel in his periodic table to keep the periodic properties.

Indeed, cobalt has certain properties closer to those of the first group of elements (iron, Fe) than nickel. Mendeleev also observed that the atomic mass of cobalt was closer to the average atomic mass of iron and nickel than that of nickel. He therefore decided to place cobalt before nickel in his periodic table to maintain the periodicity of the properties.

Explanation:

1. Hydrogen (H) occupies a unique place in the modern periodic table for the following reasons:

It has an electron configuration of 1s1 and is the only group 1 element (alkali metals) with a valence state of a single electron shell. Its position in the periodic table indicates that it must have properties similar to other alkali metals such as lithium (Li), sodium (Na), potassium (K), etc. However, its chemical and physical properties are quite different from other alkali metals, such as its melting and boiling points are much lower, and it is a gas at room temperature.

2. Hydrogen can also act as a nonmetal and gain electrons to form negative ions (H-). This is a similar property to halogens, which are nonmetals in group 17 of the periodic table.

This means that hydrogen can exhibit similar properties to alkali metals and halogens, making it a unique element.

3. Hydrogen is the only element that does not fit neatly into a particular group on the periodic table. It has similarities to alkali metals and halogens, but also has properties distinct from these two groups. It is therefore difficult to predict the properties of hydrogen based solely on its position in the periodic table.

4. Hydrogen is also unique in that it can form a variety of compounds, both ionic and covalent.

It can even form compounds with itself, such as molecular hydrogen (H2), which distinguishes it from other elements.

Therefore, due to its unique properties and position in the periodic table, hydrogen is generally considered a separate class of elements rather than grouped with any other specific group of elements.

Explanation:

Eka-silicon and Eka-aluminum are the names Mendeleev gave to the elements that he thought would fill in the gaps in the periodic table. Eka silicon was later identified as germanium (Ge) and Eka aluminum was identified as gallium (Ga).

The chlorides of these elements can be written:

1. Eka Silicon chlorides (germanium): germanium has an atomic number of 32 and belongs to group 14 of the periodic table. Its chloride molecular formula can be written as GeCl4.

2. Eka aluminum chloride (gallium): gallium has an atomic number of 31 and belongs to group 13 of the periodic table. The molecular formula of its chloride can be written GeCl3.

Explanation:

There are 3 electrons in the outer shell of element A, which belongs to group 13 of the modern periodic table (also called the boron group). Element B has 4 electrons in its outer shell, which means it belongs to group 14 (also known as the carbon group) of the modern periodic table. Element C has 2 electrons in its outer shell, which means it belongs to group 2 (also known as alkaline earth metals) of the modern periodic table.

The valences of the three elements are:

• Element A: Valence 3 (because its outer shell has 3 electrons)

• Element B: Valence 4 (because its outer shell has 4 electrons)

• Element C: Valence 2 (because its outer shell outer shell has 4 electrons) It has 2 electrons in its outer shell)

Explanation:

If element X is in group 14 of the periodic table, it has 4 electrons in its outer shell. The electronic configuration of X will be written [valence shell] ns²np², where n is the number of shells.

When X reacts with chlorine (Cl2) to form chloride, it loses 4 electrons for a stable configuration and each chlorine atom will gain one electron for a stable configuration. This leads to the formation of XCl₄.

The nature of the bond in XCl₄ is covalent because the X and Cl atoms share electrons to form the molecule. Each chlorine atom shares one electron with atom X to form a single bond, and atom X shares its remaining 2 electrons with two other chlorine atoms to form the other two single bonds. This results in the formation of a tetrahedral structure, with each chlorine atom at the vertices of a tetrahedron surrounding the central X atom.

Therefore, the chemical formula of chloride of element X of group 14 of the periodic table is XCl₄, and its bonding property is a covalent bond.

Explanation:

The radius of an atom is determined by the size of its electron cloud, which in turn is determined by two main The influence of factors becomes factors: the number of electrons and the number of protons in an atom.

(a) X has 12 protons and 12 electrons. This means that the number of positive charges in the nucleus equals the number of negative charges in the electron cloud, making it a neutral atom.

12 electrons will occupy the first three shells of the atom, with 2 electrons in the first shell, 8 electrons in the second shell, and 2 electrons in the third shell. The size of the electron cloud will mainly be determined by the repulsion between the negatively charged electrons and the force of attraction between the positively charged nuclei and the electrons. Since the number of protons in X is equal to the number of electrons, the attractive and repulsive forces balance each other, resulting in an intermediate radius.

(b) Y has 12 protons and 10 electrons. This means that the number of positive charges in the nucleus is greater than the number of negative charges in the electron cloud, resulting in positively charged ions.

10 electrons will occupy the first two layers of the atom, with 2 electrons in the first layer and 8 electrons in the second layer. The size of the electron cloud is mainly determined by the force of attraction between the positively charged nucleus and the remaining 10 electrons. Since there are fewer electrons in Y than protons, the attractive force will be greater than the repulsive force, resulting in a smaller radius.

Substances X and Y will therefore have different radii, X having an intermediate radius due to the balance between attractive and repulsive forces, and Y having a smaller radius due to the stronger attraction of positively charged ions .

Explanation:

(a) F < N < Be < Li

From left to right is due to the increase in effective nuclear power charge, which attracts electrons to the nucleus and reduces the size of the electron cloud. Li has the largest atomic radius because it has only one electron in its outer shell which is farthest from the nucleus. Be has a smaller radius because it has a larger effective nuclear charge due to the addition of a proton to the nucleus. The radius of F is smaller than that of N because the effective nuclear charge in F is larger, which can attract electrons more strongly to the nucleus.

(b) Cl < Br < I < At

The atomic radius generally decreases within a group due to the addition of new shells of electrons, increasing the size of the electron cloud.

Cl has the smallest atomic radius among the given elements because it has the most efficient nuclear charge of the group. As we descend, the atomic radius increases due to the addition of new layers of electrons. It has the largest atomic radius among the given elements due to the addition of new electron shells. The atomic radius of At is larger than that of I due to relativistic effects leading to an increase in atomic size.

Explanation:

(a) 2, 8, 2 is magnesium ( Mg)

has a total of 12 electrons, 2 in the first shell, 8 in the second shell, and 2 in the third shell.

Magnesium is a group 2 metal of the periodic table.

(b) 2, 8, 1 corresponds to sodium (Na)

has a total of 11 electrons, 2 in the first shell, 8 in the second shell and 1 in the third shell.

Sodium is a metal in group 1 of the periodic table of elements.

(c) 2, 8, 7 corresponds to chlorine (Cl)

has a total of 17 electrons, 2 in the first shell, 8 in the second shell and 7 in the third shell.

Chlorine is a nonmetal in group 17 of the periodic table.

(d) 2, 1 corresponds to lithium (Li)

has a total of 3 electrons, 2 in the first shell and 1 in the second shell.

Lithium is a metal in group 1 of the periodic table of elements.

Explanation:

Element A with atomic number 19 is potassium (K) and element B with atomic number 17 is chlorine (Cl). The chemical formula of the product composed of

potassium and chlorine is KCl.

And the electronic structure of KCl is:

The nature of the bond formed between potassium and chlorine is an ionic bond. Potassium loses an electron to form a 1+ charged cation, while chlorine gains an electron to form a 1- charged anion.

The electrostatic attraction between cations and anions leads to the formation of ionic bonds.

Explanation:

The order of metallicity from large to small is:

Ge < Ga < Mg < Ca < K

The metallic properties increase as one goes down in a group and from right to left in a period of the periodic table. Ge and Ga are metalloids, Mg and Ca are metals, and K is a highly reactive alkali metal. Therefore, K has the highest metallic character followed by Ca, Mg, Ga, and Ge.

Explanation:

(a) The soft, reactive metal described here could be potassium (K) or sodium (Na).

These metals are both soft and very reactive, especially with water and oxygen.

(b) The metal which is an important constituent of limestone is calcium (Ca). Limestone is mainly composed of calcium carbonate (CaCO3).

(c) The metal that exists in a liquid state at room temperature is mercury (Hg).

The order of increasing reactivity of

is:

Mercury (Hg) < Calcium (Ca) < Potassium (K) or Sodium (Na)

Explanation:

(a) The soft metals stored in kerosene belong to group 1 and period 3 or 4 of the periodic table and contain alkali metals. The softness and reactivity of this metal suggest it may be sodium (Na) or potassium (K)

(b) Elements with variable valence and stored underwater will be in group 15, period 3 of the periodic table.

These metals are often stored under water to prevent them from reacting with oxygen and forming oxides or hydroxides on their surface.

(c) The tetravalent elements that form the basis of organic chemistry are in group 14 of the periodic table, which contains the carbon group elements. Phase 2(c) carbon is the most well-known element of this group and is essential for all forms of organic life.

(d) The noble gas element with atomic number 2 is helium (He), which belongs to group 18, period 1, of the periodic table. This group contains noble gases, which are characterized by low reactivity due to their stable electronic configuration.

(e) An element whose thin oxide layer is used to make other elements corrosion resistant by the process of "anodizing" will be in group 13 of the periodic table, which includes the boron group of elements . The most famous element in this group is 3rd period aluminum (Al), which forms a thin layer of aluminum oxide when exposed to air. This oxide layer is highly corrosion resistant and serves to protect the underlying metal from further corrosion.

Explanation:

(a) The group 2, period 3 element of the periodic table that burns in the presence of oxygen to form basic oxides is magnesium (Mg).

(b) The electron configuration of magnesium is 1s² 2s² 2p⁶ 3s².

(c) When magnesium burns in air, it reacts with oxygen to form magnesium oxide (MgO), a white powdery solid. The equilibrium equation for this reaction is:

2Mg + O2 → 2MgO

(d) When magnesium oxide dissolves in water, it forms magnesium hydroxide (Mg(OH)2 ), which is a weak base. The equilibrium equation for this reaction is:

MgO + H2O → Mg(OH)2

(e) The electron point structure for the formation of magnesium oxide (MgO) involves the transfer of two electrons from magnesium to oxygen to form Mg²⁺- and O²⁻. The electron point structure is shown in the figure below:

Explanation:

(a) Element X with atomic number 17 is chlorine (Cl) and belongs to group 17 ( Halogen ) ) group) of the periodic table of the elements. Element Y with atomic number 20 is calcium (Ca), which belongs to group 2 (alkaline earth metals) of the periodic table.

(b) Chlorine (Cl) is a nonmetal and calcium (Ca) is a metal.

(c) Calcium oxides are basic oxides which react with water to form a strong base (calcium hydroxide). The nature of the bond in calcium oxide is an ionic bond, where calcium donates two electrons to oxygen to form the ionic compound CaO.

(d) The divalent halide formed from chlorine (Cl) and calcium (Ca) is calcium chloride (CaCl2). The electron point structure of calcium chloride is as follows:

Explanation:

(a) The elements with atomic numbers 10, 20, 7 and 14 are neon (Ne), calcium (Ca), nitrogen (N) and silicon (Si), respectively.

(b) Neon (Ne) belongs to group 18 (noble gases), calcium (Ca) belongs to group 2 (alkaline earth metals), nitrogen (N) belongs to group 15 (pnictogens) and Silicon (Si) belongs to the Periodic Elements Table na 14 group (carbon group).

(c) Neon (Ne) is placed in period 2, Calcium (Ca) is placed in period 4, Nitrogen (N) is placed in period 2, and Silicon (Si) is placed in period 3 of the periodic table.

(d) The electronic structures of the four elements are as follows:

• Neon (Ne): 1s² 2s² 2p⁶

• Calcium (Ca): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²

• Nitrogen (N): 1s² 2s² 2p³

• Silicon (Si): 1s² 2s² 2p⁶ 3s² 3p²

(e) The valence of an element is determined by the number of valence electrons it has.

Valence is the ability of an element to bond with other atoms. The valences of these elements are:

1. Neon (Ne) has a valence of 0 (since it is an inert gas and the envelope is completely filled).

2. Calcium (Ca) has a valence of 2 (because it loses two electrons from its outer shell to form the Ca²⁺ ion).

3. Nitrogen (N) has a valence of 3 or 5 (because it can gain or share three electrons to complete its octet).

4. Silicon (Si) has a valence of 4 (because it can share four electrons to complete its octet).

Explanation:

Across:

1) Magnesium

3) Tin

4) Iodine

Down:

2) Sodium

5) Lithium

6) Neon

7) Astatine

8) Iron

9) Boron

Explanation:

(a) Their increasing atomic number order:

H < He < Li < Be < B < C < N < O < F < Ne < Mg < Al < Si < P < S < Cl < Ar < K < Ca

(b) Group 1: H (hydrogen), Li (lithium), Na (sodium), K (potassium)

Group 2: Be (beryllium), Mg (magnesium), Ca (calcium)

Group 13: B (boron) , Al (aluminum)

Group 14: C (carbon), Si (silicon)

Group 15: N (nitrogen), P (phosphorus)

Group 16: O (oxygen), S (sulfur)

Group 17: F ( Fluorine), U(Uranium)

Group 18: He(Helium), Ne(Neon), Ar(Argon)

Explanation:

(a) Silicon Eca was discovered later and named germanium (Ge), while aluminum eca was discovered later and named gallium (Ga).

(b) Germanium (Ge) belongs to group 14 (also known as the carbon group) and period 4 of the modern periodic table of elements. Gallium (Ga) belongs to group 13 (also known as the boron group) and period 4 of the modern periodic table.

(c) Germanium (Ge) is a metalloid, which means it has both metallic and non-metallic properties. Gallium (Ga) is a metal.

(d) Germanium (Ge) has four valence electrons, while gallium (Ga) has three valence electrons.

Explanation:

(a) The most electropositive element is lithium (Li).

Lithium is a chemical element with symbol Li and atomic number 3.

It is a soft, silvery-white metal that belongs to the alkali metal group of the periodic table. Lithium is the lightest metal and the least dense solid element. It is highly reactive and flammable and should be stored under oil or in an inert atmosphere. Lithium has many uses, including batteries, ceramics, glass, and medicine. It also has applications in nuclear technology and is used as a coolant in some types of reactors.

(b) Among them, the most electronegative element is fluorine (F).

Fluorine is a chemical element with symbol F and atomic number 9. It is the lightest halogen in the periodic table and the most electronegative element. It is a highly reactive, yellowish, corrosive gas found in nature as the mineral fluorite. It is widely used in the production of many chemicals including refrigerants, solvents and plastics.

Fluoride is also commonly used in toothpastes as it helps prevent tooth decay. Due to its high reactivity, fluorine does not occur naturally in its elemental form and must be made from its compounds.

(c) The element with the smallest atomic size is fluorine (F).

Fluorine is a chemical element with symbol F and atomic number 9. It is the lightest halogen in the periodic table and the most electronegative element.

It is a highly reactive, yellowish, corrosive gas found in nature as the mineral fluorite. It is widely used in the production of many chemicals including refrigerants, solvents and plastics. Fluoride is also commonly used in toothpastes as it helps prevent tooth decay. Due to its high reactivity, fluorine does not occur naturally in its elemental form and must be made from its compounds.

(d) where the metalloid element is boron (B).

Boron is a chemical element with symbol B and atomic number 5. It is a metalloid, that is, it has both metallic and non-metallic properties. Boron is a relatively rare element found in the earth's crust, oceans and some meteorites. It has a wide range of uses, including as a component of heat-resistant glass, as a dopant in semiconductors, and as a neutron absorber in nuclear reactors. Boron is also an important plant nutrient and is used as a fertilizer in agriculture.

Its abundance in the earth's crust is low, but its compounds are widely present in nature.

(e) The element with the highest valence is carbon (C) with a valence of 4.

Carbon is a chemical element with symbol C and atomic number 6. It is a nonmetal and one of the few elements known to man since antiquity. Carbon is the basis of all known life on Earth and is an essential building block of organic compounds such as proteins, DNA and carbohydrates.

It is also a key element in many minerals such as diamond, graphite and coal. Carbon has a wide range of applications, including as a fuel source, steel production, and the production of various chemicals and materials. It comes in several allotropes, including diamond, graphite, and fullerene, each with unique properties and applications. Carbon is abundant in the earth's crust and is the fourth most abundant element by mass.

Explanation:

(a) Element X is sulfur (S).

(b) The electronic configuration of sulfur is: 1s², 2s², 2p⁶, 3s², 3p⁴.

(c) The equilibrium chemical equation for the thermal decomposition of iron(II) sulfate crystals is:

2FeSO4Fe2O3+SO2+SO3

(d) The oxides formed are sulfur dioxide (SO2) and sulfur trioxide, diacid trioxide.

(e) Sulfur (S) belongs to group 16 and period 3 of the modern periodic table of the elements.

Sulfur is a non-metallic chemical element with symbol S and atomic number 16. At room temperature, sulfur is a brittle, odorless and tasteless yellow solid. Sulfur exhibits bonding, which means it can form chains of atoms from itself, and allotropy, which means it can exist in different forms of allotropes, including rhombohedral crystals and monoclinic, and an amorphous or amorphous crystalline form.

Sulfur is an important element in the chemical industry and is used in the production of sulfuric acid, one of the most widely used industrial chemicals. It is also used to make fertilizers, dyes, and many other products. Sulfur is an essential element for all living organisms and is found in many amino acids, proteins and other organic compounds. Sulfur compounds such as hydrogen sulfide (H2S) have a strong odor and are responsible for the characteristic rotten egg smell. Sulfur is ubiquitous in nature and is found in many minerals including gypsum, Epsom salts and sulfur ores.

Explanation:

(a) Element X is nitrogen (N), which has 5 valence electrons.

Nitrogen is a non-metallic chemical element with symbol N and atomic number 7. Nitrogen is a diatomic gas at normal temperature, making up about 78% of the Earth's atmosphere. Nitrogen is a very important element for living organisms as it is a key component of amino acids, proteins and nucleic acids (DNA and RNA).

Nitrogen also plays an important role in the environment, as it is an integral part of the global nitrogen cycle. Nitrogen can exist in many different forms, including inorganic compounds such as ammonia (NH3), nitric oxide (NO) and nitrous oxide (N2O), and organic compounds such as amino acids and nucleic acids. Nitrogen is also used in the chemical industry to produce ammonia, which is used to make fertilizers, plastics, and other products. Nitrogen has 5 valence electrons and can form covalent and ionic bonds with other elements.

(b) The structure of the electronic point of the diatomic nitrogen molecule (N2) is:

This is a covalent bond, more precisely a triple bond, between two nitrogen atoms.

(c) The electron point structure of ammonia (NH₃) is:

This is also a covalent bond between a nitrogen atom and a hydrogen atom, specifically a polar covalent bond.

Explanation:

Which groups of elements in Mendeleev's periodic table cannot be perturbed in their original order are inert gases (group 18). That's because the noble gases hadn't been discovered when Mendeleev developed his periodic table, so they wouldn't mess up the original order.

In fact, the discovery of noble gases provided further support for Mendeleev's periodic law, which states that the properties of elements are periodic functions of their atomic masses. Noble gases have very low reactivity and do not easily form compounds with other elements, which sets them apart from other groups of elements in the periodic table. The position of the noble gases in the rightmost column of the periodic table corresponds to their properties, without modifying the original order formulated by Mendeleïev.

Explanation:

Mendeleev's classification of elements was based on their atomic mass, physical and chemical properties, and mode of behavior. He began by compiling a list of known elements and listed them in order of increasing atomic mass. He then grouped elements with similar properties into columns, which he called groups, and arranged these groups into horizontal rows, which he called periods. Mendeleev noticed that certain properties of the elements periodically repeated as he moved from one period to another. For example, the alkali metals (group 1) all have similar properties, and their atomic mass increases as it goes down.

Mendeleev then developed what he called the "periodic law", which states that the properties of elements are periodic functions of their atomic masses. He noticed that when the elements were arranged in order of increasing atomic mass, elements with similar properties periodically appeared. He used this law to predict the existence and properties of several new elements, including gallium and germanium, which were later discovered and whose properties closely matched his predictions.

Overall, Mendeleev's process of classifying elements was a combination of empirical observation, logical reasoning, and intuition. He was able to organize the known elements into a systematic and consistent pattern, which has since become the basis of the modern periodic table.

To arrive at the periodic law, Mendeleev had to make several adjustments to his original tables, including leaving blank spaces for elements that had not yet been discovered and reversing the order of some elements based on their chemical properties. He also had to consider the role of isotopes, then unknown, and their effect on the atomic mass of certain elements.