Calculate valence and core electrons of Carbon, Silicon, Nitrogen, Phosphorus, Oxygen, Sulfur, Magnesium and Calcium

Q) How many valence electrons do the following elements have-

a) Carbon and Silicon b) Nitrogen and Phosphorus c) Oxygen and sulfur d) Magnesium and Calcium

(Periodic table as a reference is provided at the end of the article)

Refer to the tutorial- What are valence and core electrons? How to determine a valence electron?

Reference table from the article-

The group number and atomic number is used to determine the valence electrons of an element. 

a) Carbon and Silicon:

Method 1- Group Number

Carbon and Silicon belong to the same group 14 in the periodic table. All elements belonging to the same group in the periodic table will have the same number of valence electrons (table A). The only difference will be their shell number due to the increase in atomic size. So, both Carbon and Silicon will have four valence electrons.

Method 2- Atomic Number

The atomic number of Carbon is 6. Its electronic configuration after dividing the electrons into shells and orbitals is - 1s² 2s² 2p². The outermost shell is 2, containing four valence electrons (2s² 2p²), and the two core electrons are in shell 1 (1s²).

The atomic number of Silicon is 14. Its electronic configuration is 1s² 2s² 2p⁶ 3s² 3p². The outermost shell 3 contains four valence electrons (3s² 3p²), and the remaining are Silicon's core electrons in shells 1 and 2 (1s² 2s² 2p⁶).

b) Nitrogen and Phosphorus

Method 1- Group Number

Carbon and Silicon belong to the same group 15 in the periodic table. The elements belonging to the same group have the same valence electrons. The valence electrons of both Nitrogen and Phosphorus are 5.

Method 2- Atomic Number

The Atomic Number (Z) of Nitrogen (N) is 7, and its electronic configuration is 1s² 2s² 2p³. So, the outermost shell is 2, containing five valence electrons. The two core electrons are present in shell 1 (1s²).

The Atomic Number (Z) of Phosphorus (N) is 15, with 15 electrons distributed into various shells and orbitals. The electronic configuration of P is 1s² 2s² 2p⁶ 3s² 3p³.  The outermost shell is 3, containing five valence electrons (3s² 3p³), and the core electrons are in the inner 1 and 2 shells (1s² 2s² 2p⁶).

c) Oxygen and sulfur

Method 1- Group Number

Oxygen and Sulfur belong to the same group 16 in the periodic table and therefore have the same number of 6 valence electrons.

Method 2- Atomic Number

The Atomic Number(Z) of Oxygen (O) is 8, corelating to 8 electrons. The electronic configuration of O is 1s² 2s² 2p⁴. The farthest shell from the nucleus is 2 with six valence electrons (2s² 2p⁴). The two core electrons are present in shell 1 (1s²).

The Atomic Number(Z) of Sulfur (S) is 16 with 16 electrons. The electronic configuration of S is 1s² 2s² 2p⁶ 3s² 3p⁴. The outermost shell is 3 with 6 valence electrons (3s² 3p⁴). The ten core electrons are in shells 1 and 2 (1s² 2s² 2p⁶).

d) Magnesium and Calcium

Method 1- Group Number

Magnesium and Calcium belong to Group number 2. Both have the same number of two valence electrons.

Method 2- Atomic Number

The Atomic Number(Z) of Magnesium (Mg) is 12, and the electronic configuration is 1s² 2s² 2p⁶ 3s². The outermost shell is 3 with two valence electrons (3s²). The ten core electrons are in shells 1 and 2 (1s² 2s² 2p⁶).

The Atomic Number(Z) of Calcium (Ca) is 20, and the electronic configuration of Ca is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s². The outermost and highest energy level is 4, containing two valence electrons (4s²). The 18 core electrons are in shells 1, 2, and 3 (1s² 2s² 2p⁶ 3s² 3p⁶).

Reference- Periodic table