Question

An element 'X' has mass number 35 and number of neutrons 18. Write atomic number and electronic configuration of 'X'. Also write group number, period number and valency of 'X'.(All India - 2016)

Answer 1

Answer:

Mass no=35

no of neutrons=18

thus,atomic no=35-18=17

therefore,w.c=2,8,7

group no=17

period no=3

valency=-1

Answer 2

Atomic number, Electronic configuration, Group number, period number and Valency of element X.

Given:

Mass number of element 'X' = 35

Number of neutrons present in 'X' = 18

To find:

Atomic number, Electronic configuration, Group number, period number and Valency.

Explanation:

Atomic number:

• To find the atomic number the following formula must be used:

N = M - A

Where,

N - Number of neutrons

M - Mass number

A - Atomic number

• From the given values, the atomic number can be calculated as

A = M - N

A = 35 - 18

A = 17

• Thus the atomic number of element 'X' is identified as 17.

Electronic configuration:

• To write the electronic configuration, atomic number is required. As the atomic number of element 'X' is 17. its electronic configuration is as follows:

$1s^22s^22p^63s^23p^5$

Group and period number:

• As the atomic number of element 'X' is identified as 17, its group number and period number are 17 and 3 respectively.

Valency:

• The formula used for calculation of valency is:

Valency = 8 - valence electrons

• As there as 7 electrons in the outermost orbital, it contains 7 valence electrons.
• Thus the valency is

Valency = 8 - 7

Valency = 1

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