What is atomic density ? give the periodicity of atomic density in periods and groups.

Atomic Density:

Density is the ratio of mass and volume. Higher the atomic volume leads to lower density as vice versa lower the atomic volume leads to higher density.

(A) Trends in group:

When we move top to bottom in a group the atomic density generally increases, it is due to increasing in atomic volume and atomic mass because top to bottom in group, number of shells increases but mass is more and more increases with respect to volume, so finally the atomic density in a group increases.

(B) Trends in period: 

When we move from left to right along with a period, the atomic density increases and become maximum at mid period , and after that decrease.

(C) Atomic density depends upon two factors these are given as.

(i) The electronic configuration of inner most shells

(ii) Packing capacity 

Exception:

(1) Density of Na > Density of K

Reason: 

The density of 'Na' is greater than the density of 'K' .It is due to the inner shells of 'Na' atom is fully filled but the shells the inner most shells of 'K' not full filled.

₁₁Na= 1s² 2s² 2p⁶ 3s¹ (Completely filled Inner shell s)

₁₉K= 1s² 2s² 2p⁶ 3s¹ 3p⁶ 3d⁰, 4s¹ (incomplete inner shells)

(2) Density of Mg > Density of Ca 

Reason:

The density of 'Mg' is greater than the density of of 'Ca' .It is due to the inner shells of 'Mg' atom is fully filled but the shells the inner most shells of 'Ca' not full filled.

₁₂Mg= 1s² 2s² 2p⁶ 3s²(Completely filled Inner shell s)

₂₀Ca= 1s² 2s² 2p⁶ 3s¹ 3p⁶ 3d⁰, 4s² (incomplete inner shells)

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(4) What is Mendeleev's periodic table ? give important features and draw back of Mendeleev's table.

(5) What is atomic volume ? and what is periodicity of atomic volume in groups and periods ?

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(11) Li2CO3 decomposes on heating but other alkali metal carbonates don’t. Explain.

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