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a) 6 

b) 8 

c) Same group

In 1869 Mendeleev arranged the known 63 elements in horizontal and vertical columns and gave shape to the periodic table. He found that the chemical and physical properties of elements repeat at a regular intervals when they were arranged in the increasing order of atomic masses. Based on this Mendeleev proposed the periodic law of elements. The law states that physical and chemical properties of elements are periodic function of their atomic masses.

(a) Period 1 has 2 elements while period 2 and period 3 have 8 elements each.

(b) Hydrogen and helium

(c) The elements at the end of period 2 and Period 3 have 8 electrons in its outermost shell.

(d) if an element is in group 17, it is likely to be Non metallic (Metallic / non-metallic) in character while with one electron in its outermost energy level (shell), then it is likely to be metallic (Metallic / Non-metallic)

(a) Since it belongs to group II, it has 2 valence electrons and hence it is a metal.

(b) Barium is placed below calcium in the group. Since, it has more number of shells; it is easier for it to lose its valence electrons to complete its octet configuration. Hence it is more reactive than calcium.

(c) It needs to lose its 2 valence electrons to complete its octet configuration; therefore its valency is also 2.

(d) The formula of its phosphate will be (Ba)₃ (PO₄)₂

(e) As we move from left to right in a period, the size decreases, therefore, it will be smaller than Cesium

The vertical columns in the periodic table are known as groups and the horizontal rows are called periods.

i. Group of X and Y is IA. 

ii. X belongs to 3^rd period and Y belongs to 5^th period. 

iii. Valence electrons of X and Y is 1. 

iv. Valency of X and Y is 1. 

v. X and Y are alkali metals. 

Separate position at the bottom of the periodic table

Yes. These elements are called inner transition elements.

The horizontal rows in the modern periodic table are called as periods and the vertical columns are called as groups. The modern periodic table consists of seven periods and eighteen groups

i. D 

ii. P 

iii. Halogen 

iv. A - Lithium, X - Carbon, Q - Chlorine, S - Iodine 

v. a. Valency of X,Y and Z is 4. 

b. Valency of L and M is 2. 

c. Valency of P, Q, R and S is 1. 

vi. a. D has larger radius (out of A and D). 

 b. A has larger radius (out of A and P). 

vii. Group 1 is known as alkali metals. 

 Group 2 is known as alkaline earth metals. 

i. Phosphorous 

ii. 15 

iii. 5 

iv. 3 

v. Non-metal 

vi. Electronic configuration (2, 8, 5) 

Eka-boron was named as Scandium 

Eka-aluminium was named as Gallium 

Eka-silicon was named as Germanium 

The first period is the shortest period containing only 2 elements. The sixth period is the longest and it contains 32 elements in it. 

i. Lithium 

ii. Neon 

iii. Carbon 

iv. Fluorine 

v. Beryllium 

vi. Boron 

i. This law is known as Mendeleev’s periodic law. 

ii. Mendeleev’s periodic law means that if elements are arranged in the order of increasing atomic masses, then the properties of the elements are repeated after certain intervals or periods. 

iii. It differs in the following way - The Modern periodic law states that “The chemical and physical properties of elements are a periodic function of their atomic numbers”. 

On moving from left to right in a period of the periodic table 

 i. Atomic size decreases 

 ii. Metallic character decreases 

 iii. Non-metallic character increases 

 iv. Number of valence electrons increases

The outermost shells of the elements belonging to group 18 contain eight electrons (except helium), so they are already completely filled with electrons. They have no tendency to lose or gain electrons and hence have a stable electronic configuration with zero valency. Therefore, group 18 of modern periodic table is also known as group zero. 

(a) Increases

(b) Increases

(c) Increases

(d) Decreases

(e) Increases

Atom becomes charged when there is transfer of electrons [Lose or gain electrons] they are called ions.

On moving from top to bottom in a group of the periodic table 

 i. Metallic character of elements increases. 

 ii. Non-metallic character decreases. 

 iii. Size of atoms increases 

 iv. All elements will have the same number of valence electrons. 

Answer is Decrease

The amount of energy required to liberate the most loosely bound electrons from the outermost shell of an isolated gaseous atom of an element is called ionization energy.

Atomic size increases as we move from top to bottom.

Every ionic compound have some percentage of covalent character according to Fajan’s rule. The percentage of ionic character in a compound having some covalent character can be calculated by the following equation.

Percentage ionic character \(=\frac{\textit { Obsereed dipole moment }}{\textit { Calculated dipole moment }} \times 100\)

(a)  Na, Mg, Al, Si, P, S, Cl

(b)  (i) The element below sodium in the same group would be expected to have a Lower (lower/higher) electro-negativity than sodium and the element above chlorine would be expected to have a higher (lower/ higher) ionization potential than chlorine.

(ii)  remains the same

(iii)  remains the same

Size of the atom

Ionization energy increases

Ionization energy decreases.

According to Mullikan scale:

Electronegativity = Ionisation enthalpy + Electron gain enthalpy / 2
When IE and electron gain enthalpy are expressed in eV.
Electronegativity = Ionisation enthalpy + Electron gain enthalpy / 540 When ionization enthalpy and electron gain enthalpy are expressed in kJ/mol.
χ_pauling = χ_mullikan/2.8
χ_pauling = Ionisation enthalpy + Electron gain enthalpy /5.6

On moving from left to right in a period, as nuclear charge increases, the size of the atom decrease hence ionization energy increase.

As the size of the atom increases metallic character also increases.

Non-metallic

As the size of an atom increases the distance between the nucleus and the outermost electron increases, hence the electronegativity decreases. As we move in the same period form left to right size of atom decrease hence electronegativity increases.

Non-metals are more electronegative.

Electronegativity across the period is Increases.

(a) The element fluorine has the highest electronegativity and Caesium has the lowest electronegativity.

(b) The nature of oxides changes from basic to acidic as we move from left to right in third period. Hence sodium forms most basic oxide while oxide of Aluminum is amphoteric and oxides of phosphorus, sulphur and chlorine are progressively acidic