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 .

Answer 1

atomic number of element x is 17 and electronic configuration is 2,8,7 and group number is 17 and period number is 3 and valency is 1.

Answer 2

Answer: The atomic number of the element X is 17. It belongs to group 17 and period 3. Valency of this is 1.

Explanation:

Atomic number is defined as the number of protons or number of electrons that are present in neutral atom.

Atomic number = Number of protons = Number of electrons

Mass number is defined as the sum of number of protons and number of neutrons.

Mass number = Number of protons + Number of neutrons

We are given:

Mass number of X = 35

Number of neutrons = 18

Number of protons or atomic number = 35 - 18 = 17

• Electronic configuration of element X = $1s^22s^22p^63s^23p^5$

To identify the period, we look at the highest occupied principle quantum number which is 'n'. Here, the value of 'n' is 3. Thus, it belongs to Period 3 of the periodic table.

As, the last electron in entering p-shell. Thus, it is a p-block element.

• The rule for determining the group number for p-block element is:

Group number = Number of valence electrons + 10

The number of valance electrons = 2 + 5 = 7

Group number = 7 + 10 = 17

Thus, it belongs to Group 17.

• This element requires one electron to obtain stable electronic configuration. So, its valency is 1.

Hence, the atomic number of the element X is 17. It belongs to group 17 and period 3. Valency of this is 1.