Variation of atomic radii in periodic table ~ NEET chemistry

Over all Variation in atomic size can be explained based on two factors:-

Nuclear attractions
Interelectronic repulsion

:---when one factor decrease in atomic radii and the other factor increase in atomic radii.

For s Block element:----

In cass of s block elements as we move from up to down in a group atomic size increases and the number of shells increases.

Increasing order of atomic size for s block elemnts :---@

1st group elements order =

H>Li>Na>K>Rb>Cs>Fr

2nd group elements order =

Be>Mg>Ca>Sr>Ba>Ra

For d block elements :---

In case of d block elements as we move from left to right the nuclear charge increases. But the electrons are added to penultimate(n-1) shell, hence the electron cloud density of inner shells increases which increases the screening effect. Thus nuclear charge increases and the screening effect increases .

Therefore, decreases in the atomic radius but the extent of Variation is very small compared to s block and p block element.

:--- moving from Sc to Zn, initially one factor nuclear charges increases but screening effect decreases hence the atomic radii decreases.

:--- In the middle, these two factors mostly operating equal, hence the atomic radii almost equal.

:---- In the end, the number of electrons in the inner orbitals increases therefore the electronic repulsion factor operate, hence atomic radii increases. (Ni to Zn)

Sc>Ti>V>Cr>Mn=Fe=Co=Ni<Cu<Zn

For p block elements:----

In case of p block elements ,moving up to down the atomic size of elements increases due to increasing number of shells.

13 group elements:---

B>Al>Ga>In>Tl

14 group elements :---

C>Si>Ge>Sn>Pb

15th group elements :---

N>P>As>Sb>Bi

16th grpup elements:---

O>S>Se>Te>Po

16th group elements :---

F>Cl>Br>I>At

18th group elements:---

He>Ne>Ar>Kr>Xe>Rn

Across period:----

Moving left to right across the period the atomic size of elements decreases.

For f block elements:---

Lanthanoid elements:---

Due to lanthanoid contraction, size of f block elements decreases with increase in number of f electrons.

:-- the lanthanoid contraction is caused by a poor shielding effect of the 4f electrons.

Actinoid elememts:---

The general trend in actinoid is a gradual decrease in the size of atoms due to actinoid contraction resulting from poor shielding by 5f electrons.

The actinoid are radioactive element and the earlier members have relatively long half lines, the later ones have half life value ranging from a day to 3 min for lawrencium (Z = 103) .The later member could be prepared only in nanogram quantity. These facts render their study more difficult.

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