Question

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Answer 1

Question

$\sf{For \: an \: element \: { }^{35}T_{17} \: find \:- }$

(a) Group number

(b) period number

(c) Number of valence electrons

(d) Is T a metal or non - metal

Answers

(a) Group no. = 17

(b) period no. = 3

(c) No. of valence electrons = 7

(d) T is a non - metal

Explanation

$\rule{202}1$

When an element X is represented in the form

$\huge{\bf{{ }^{A}X_Z}}$

then,

A is the mass number of element X and Z is the atomic number of element X.

so,

Atomic no. of element T is 17

and its mass no. is 35.

$\rule{202}1$

Now,

Let us write electronic configuration of element T

$\bf{K\:\:\: L \:\:\: M} \\ \bf{ 2 \: \: \; \: 8 \: \; \: \: 7}$

$\rule{202}1$

so,

Group no. of an element can be decided by the no. of valence electrons the element have

Group no. | no. of valence electrons

1 | 1

2 | 2

13 | 3

14 | 4

15 | 5

16 | 6

17 | 7

18 | 8

since, element T have 7 valence electrons

therefore, group no.of element T is 17 .

$\rule{202}1$

Now,

Period no. is given by the no. of electron shells in the element .

Since, element T has 3 electron shells ( K , L , M )

therefore, period no. of element T is 3 .

$\rule{202}1$

As we can see in the electronic configuration of element T that , the no. of electrons in its outermost shell is 7

therefore, its no. of valence electrons will be also 7 .

$\rule{202}1$

An element having less than 4 electrons in its outermost shell is considered as a metal and element having more than 4 electrons in its outermost shell is considered non - metal.

since, element T has 7 electron in its outermost shell therefore , Element T is a non - metal.

$\rule{202}1$

● The element with atomic no. 17 and mass no. 35 is Chlorine.