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-
Periodic table block | Periodic table group | Valence electrons |
|---|---|---|
s- block | Group 1 | 1 |
Group 2 | 2 | |
p-block | Group 13 (Boron family) | 3 |
Group 14 (Carbon Family) | 4 | |
Group 15 (Nitrogen family) | 5 | |
Group 16 (Oxygen family) | 6 | |
Group 17 (Halogen family) | 7 | |
Group 18 (Noble gases) | 8 | |
d-block | Group 3-12 (Transition metals) | 3-12 |
f-block | Lanthanides and actinides | 3-16 |
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
