Question

Two elements A and B belong to group 1 and 2 respectively in the same period.compare them in respect to (a) number of valence electron, (b) valency

Answer 1

The one in 1st group has one valance electron whereas the one in 2 nd group has 2 valance electrons.

And valancy of the 1st one is 1 and that of the 2nd is 2

Answer 2

$\bold{MODERN \: PEROIDIC \: TABLE }$

◼In modern peroidic table ,the elements are arranged in the increasing order of their atomic number according to law

$\textit{Properties \: of \: elements \: are \: periodic}$ $\textit{function \: of \: their \: atomic \: number}$

◼The elements are arranged in 7 horizontal peroids and 18.vertical groups.

$\bold{PEROIDIC \: PROPERTIES}$

Properties that reoccurs at a fixed interval of time is the peroidic property and this phenomenon is called periodicity in properties of elements.

Ex :-Atomic radius , Ionisation Potential ,electron negativity. etc

$\boxed{ \bold{GROUP \: 1 }}$

▶Group 1 elements are called alkali metals.

▶They have one valence electron in the outermost shell.

▶These elements are strong reducing agent ,highly reactive ,electropositive metals.

$\boxed{ \bold{GROUP \: 2 }}$

▶Group 2 elements are called alkaline earth metals.

▶They have two electrons in the outermost shell.

$\boxed{ \bold{VALENCE ELECTRONS}$

The number of electrons a element loses or gains to be stable like nearest noble gas.

▶They have all properties similar to alkaki metals but are less reactive.

◼VARIANCE IN NUMBER OF VALENCE ELECTRONS

▶Moving across a peroid the number of valence electrons increases by 1.

▶Moving down a group the number of valence electrons remains same.

◼VARIANCE IN NUMBER OF SHELLS

▶The number of shells remains same across a peroid.

▶The number of shells increases by one moving down a group.

COMPARASION OF ELEMENT A AND B.

▶A belongs to group 1 so the valence electron will be +1.

▶Valency will be +1.

Which means element A will lose one electrons to be stable like nearest noble gas.

▶B belongs to group 2 ,since the number of valence electron increases by one across a peroid and it lies after element A its valence electrons will be +2.

▶Hence , Valency will be +2.

Which means element B will lose two electrons to be stable like nearest noble gas.