Question

How does the following vary in a period? Explain. (a) Atomic Size (b) Valence Electrons​

Answer 1

Answer:

Atomic size of elements in a period first decreases and then suddenly increases on noble gas

Valence electons increases

Answer 2

The following vary in a period:  (a) Atomic Size (b) Valence Electrons​

Explanation:

Periodic table

It is tabulated form for the systematic  arrangement of elements .

It is based on modern periodic law :

According to it, properties of elements all periodic function of their atomic numbers.  

So, when elements are arranged acc. to increasing atomic no.’s their is periodicity in electronic configuration that leads to periodicity in their chemical properties.  

Modern periodic table

It consist of  :

horizontal rows (Periods)  

Vertical column (Groups  )

 

There are 7 period and 18 groups in this long form of periodic table.  

Ist period has 2 elements  

IInd period has 8 elements  

IIIrd  period has 8 elements  

IVth period has 18 elements  

Vth period has 18 elements  

VIth period has 32 elements

VIIth period hs rest of elements  

NOTE no of valence electron in atom of elements decides which elements will be first in period and which will be last.  

In group:-  

1 to 2 gp and 13 to 17 contain normal elements  

3 to 12gp – transition elements.  

        57 to 71 lanthanides  

89 to 103 Actinides.  

Left hand side – metals.  

Right hand side – non-metals  

Valence electron in period : increases by 1 and in group it remains same .

V. electron of gp I element  -- 1  

V. electron of gp 2 element  -- 2  

V. electron of gp 13 element -- 3  

V. electron of gp 14 element -- 4  

V. electron of gp 15 element -- 5

V. electron of gp 16 element --6  

V. electron of gp 17 element -- 7

V. electron of gp 18 element -- 8  

ATOMIC SIZE

I is  defined  as: " size of on atom or distance from nucleus to outermost shell of an atom. "

 ALONG GROUP

It increases.  

For example:- Consider 1st gp  

Li – 3  2,1    K,L  

Na- 11   2,8,1    K, L, M  

K- 19   2, 8, 8, 1   K,L, M, N  

As we move down the gp. , every time a new shell is being added due to which size of an atom increases.  

Along period :  it decreases.

For example:- consider 3rd period  

Na   Mg   Ar   Si  

2,8,1       2,8,2  2,8,3    2,8,4  

We see ,every time a new electron is added to the same shell due to which nuclear charge increases and size decreases.