krit.club logo

Atomic Structure - Electronic Configuration and Valency

Grade 9IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

Electrons revolve around the nucleus in fixed circular paths called orbits or shells, designated as K,L,M,N...K, L, M, N... or n=1,2,3,4...n = 1, 2, 3, 4...

•

The maximum number of electrons in a shell is governed by the 2n22n^2 rule, where nn is the shell number. For example, the KK shell (n=1n=1) can hold 2(1)2=22(1)^2 = 2 electrons.

•

The outermost shell can accommodate a maximum of 88 electrons (except the KK shell, which holds 22), known as the Octet Rule.

•

Electronic configuration is the systematic arrangement of electrons in different shells of an atom based on increasing energy levels.

•

Valence electrons are the electrons present in the outermost shell of an atom, determining its chemical properties.

•

Valency is the combining capacity of an atom. It is determined by the number of electrons gained, lost, or shared to achieve a stable octet configuration.

•

If the number of valence electrons (vv) is 44 or less, the valency is usually equal to vv. If vv is more than 44, the valency is calculated as 8−v8 - v.

📐Formulae

Max electrons in a shell=2n2\text{Max electrons in a shell} = 2n^2

Valency=Valence electrons(for 1,2,3,4 electrons)\text{Valency} = \text{Valence electrons} \quad (\text{for } 1, 2, 3, 4 \text{ electrons})

Valency=8−Valence electrons(for 5,6,7,8 electrons)\text{Valency} = 8 - \text{Valence electrons} \quad (\text{for } 5, 6, 7, 8 \text{ electrons})

💡Examples

Problem 1:

Determine the electronic configuration and valency of Magnesium (Z=12Z = 12).

Solution:

  1. Atomic Number (ZZ) = 1212.
  2. Distribution of electrons:
  • KK shell (n=1n=1): 22 electrons.
  • LL shell (n=2n=2): 88 electrons.
  • MM shell (n=3n=3): 12−(2+8)=212 - (2 + 8) = 2 electrons.
  1. Electronic Configuration: 2,8,22, 8, 2.
  2. Number of valence electrons = 22.
  3. Since valence electrons ≤4\leq 4, Valency = 22.

Explanation:

Magnesium has 22 electrons in its outermost shell. To achieve a stable octet, it is easier to lose 22 electrons than to gain 66. Thus, its valency is 22.

Problem 2:

Determine the electronic configuration and valency of Chlorine (Z=17Z = 17).

Solution:

  1. Atomic Number (ZZ) = 1717.
  2. Distribution of electrons:
  • KK shell: 22
  • LL shell: 88
  • MM shell: 77
  1. Electronic Configuration: 2,8,72, 8, 7.
  2. Number of valence electrons = 77.
  3. Since valence electrons >4> 4, Valency = 8−7=18 - 7 = 1.

Explanation:

Chlorine has 77 valence electrons. It needs 11 more electron to complete its octet (88 electrons). Therefore, its combining capacity or valency is 11.

Problem 3:

Calculate the maximum number of electrons that the NN shell can hold.

Solution:

  1. For the NN shell, the principal quantum number n=4n = 4.
  2. Using the formula 2n22n^2: 2×(4)2=2×1632\begin{array}{r} 2 \times (4)^2 \\ = 2 \times 16 \\ \hline 32 \end{array}
  3. The maximum number of electrons is 3232.

Explanation:

According to Bohr-Bury scheme, the capacity of any shell is defined by 2n22n^2 where nn is the shell number.