Question

An element A atomic number 7 mass number 14
B electronic configuration 2, 8, 8
C electrons 13, neutrons 14
D Protons 18 neutrons 22
E electronic configuration 2, 8, 8, 1
State (i) valency of each element (ii) which one is metal (iii) which is non-metal (iv) which is inert gas.

Answer 1

Valency: Valency is the combining capacity of an element.

• Metals are electropositive. i.e.; they have a tendency to lose electrons. Metals have 1, 2, or 3 electrons in their valence shell which when lost help to attain stability by the octet rule.
• Non-metals are electronegative. i.e.; they have a tendency to gain electrons. Non-metals have 5,6 or 7 electrons in their valence shell. If these non-metals gain electrons, it helps them to attain stability due to the octet rule.

Octet rule: It states that the atoms that have a complete octet (8) of electrons in its valence shell like noble gases are stable.

• Valence electrons are the electrons present in the outermost shell of an atom.
• For metals, Valency= valence electrons
• For non-metals, Valency= 8-valence electrons

For element A:

• Atomic number 7 mass number 14 (Given)
• For a neutral atom of an element,
• Atomic number= Number of electrons= Number of protons
• Therefore, the number of electrons= 7
• To write valency, number of valence electrons is required. This can be found out from electronic configuration.
• Electronic configuration is the arrangement of electrons in orbits around the nucleus of an atom.
• Electronic configuration of A= 2, 5
• Therefore, Number of valence electrons= 5
• As number of valence electrons is more than 4, therefore valency= 8-5= 3
• Also, number of valence electrons is 5 which makes it easier for the element to gain electrons i.e.; the element is electronegative in nature and therefore a non-metal.

For element B:

• Electronic configuration 2, 8, 8 (Given)
• From the electronic configuration, number of valence electrons= 8
• As this value is more than 4, therefore valency= 8-8= 0
• Also, the number of valence electrons=8 meaning that the octet is complete. As inert gases have a complete octet of electrons, therefore B is an inert gas.

For element C:

• Electrons 13, neutrons 14 (Given)
• Electronic configuration of 13 electrons is 2, 8, 3
• Number of valence electrons= 3
• As the number of valence electrons is 3 which is less than 4, therefore Valency= Valence electrons.
• So Valency= 3
• Also, the number of valence electrons is 3 which makes it easier for the element to lose electrons i.e.; element is electropositive in nature and therefore a metal.

For element D:

• Protons 18 neutrons 22 (Given)
• Atomic number= Number of protons= Number of electrons
• Therefore Number of electrons= 18
• Electronic configuration= 2, 8, 8
• From the electronic configuration, number of valence electrons= 8
• As this value is more than 4, therefore valency= 8-8= 0
• Also, the number of valence electrons=8 meaning that the octet is complete. As inert gases have a complete octet of electrons, therefore D is an inert gas.

For element E:

• Electronic configuration 2, 8, 8, 1 (Given)
• Number of valence electrons= 1
• As the number of valence electrons is 1 which is less than 4, therefore Valency= Valence electrons.
• So Valency= 1
• Also, the number of valence electrons is 1 which makes it easier for the element to lose electrons i.e.; element is electropositive in nature and therefore a metal.

Element	Total number of electrons	Electronic configuration	Valence electrons	Valency	Metal/Non-metal/ Inert gas
A	7	2, 5	5	3	Non-metal
B	18	2, 8, 8	8	0	Inert gas
C	13	2, 8, 3	3	3	Metal
D	18	2, 8, 8	8	0	Inert gas
E	19	2, 8, 8, 1	1	1	Metal