Chemical Bonding — Part 1: Electrovalent (ionic) bonding: visual lesson, ICSE Class 10 Chemistry (Science Paper 2)

Lesson

Why do atoms join?

Part 1 — atoms bond to reach a stable arrangement of electrons like a noble gas. One way is to transfer electrons and form ions.

In this lesson you will

Explain why atoms combine, using the octet and duplet rules
Draw electron dot diagrams for the formation of NaCl, MgCl₂ and CaO
State the conditions that favour an electrovalent bond
Explain the properties of electrovalent compounds

Table of helium, neon and argon with their stable duplet or octet configurations
Noble gas	Configuration	Outer shell
Helium	2	Duplet (2 electrons)
Neon	2, 8	Octet
Argon	2, 8, 8	Octet

Concept

Octet rule and the electrovalent bond

Atoms tend to gain, lose or share electrons to get eight electrons in the outer shell (an octet), or two in the first shell (a duplet, as for H, Li). An electrovalent (ionic) bond forms when one atom transfers electrons to another: the atom that loses electrons becomes a cation, the one that gains becomes an anion, and the opposite charges attract strongly. The number of electrons lost or gained is the electrovalency.

Diagram

Electron dot diagrams: NaCl, MgCl₂ and CaO

NaCl: Na (2, 8, 1) gives 1 electron to Cl (2, 8, 7) → Na⁺ (2, 8) and Cl⁻ (2, 8, 8). MgCl₂: Mg (2, 8, 2) gives 1 electron to each of 2 Cl atoms → Mg²⁺ and 2Cl⁻. CaO: Ca (2, 8, 8, 2) gives 2 electrons to O (2, 6) → Ca²⁺ (2, 8, 8) and O²⁻ (2, 8). Show the metal’s electrons as crosses and the non-metal’s as dots, and put each ion in square brackets with its charge.

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