Question

A certain particle X has 17 protons, 17 electrons and 18 neutrons.
i) What is the mass number of X? ii) What is the atomic number of X? iii) What is valency of X?

Answer 1

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GiveN:

• No. of protons = 17
• No. of electrons = 17
• No. of neutrons = 18

To FinD:

• Mass no. of X?
• Atomic number of X?
• Valency of X?

Step-wise-Step Explanation:

1) Mass no. = No. of protons + No. of neurons

Or simply, No. of nucleons inside the nucleus.

Mass no. of this element X:

= No. of protons + No. of neutrons

= 17 + 18

= 35

2) Atomic no. = No. of protons inside Nucleus.

Atomic no. of this element X:

= 17

3) Valency of the element X can be determined by the no. of electrons to be gained/lost to complete the octet configuration.

Electronic configuration of X:

• 2,8,7

There are more than 4 valence electrons in the outermost shell. Valency will be 8 - 7 = 1

Need one more electron in the last shell to complete octet, hence valency will be -1 because it needs to gain 1 electron.

Answer 2

Answer:-

Given:

A particle X has :-

• 17 protons

• 17 electrons

• 18 neutrons.

• Mass number is nothing but the sum of number of electrons or protons and number of neutrons.

So, Mass number = 17 + 18 = 35 a.m.u

• Atomic number is the number of protons or electrons.

So, Atomic number of X (Z) = 17

Atomic number is 17 , So the required element is Chlorine (Cl)

Now,

Number of electrons = 17

So, Electronic configuration = 1s² 2s² 2p⁶ 3s² 3p⁵

We observe that,

Number of Valence electrons [ Electrons in the outermost shell ] (n > 4) i.e., 7 > 4

So, Valency of Cl (X) = 8 - n = 8 - 7 = 1.