Covalent Bonding

• A covalent bond forms when two non-metals share electrons to fill up their outermost electron shell
• A covalent bond is the strong attraction between the shared pair of electrons and the nuclei of atoms.

👇 Frequently asked on IGCSE Chemistry is..... 👇 

Representing Covalent Bond with Dot-and-Cross Diagrams

• Only outermost electrons are represented in the dot-and-cross diagrams.
• Electrons from one atom are drawn as dots, and electrons from other atom are drawn as crosses.
• Circles represent the outer shell of atoms.
• Circles overlap where there is a sharing of electrons.

Let's try to draw dot-and-cross diagrams for some examples 😄

Example 1. Hydrogen (H₂)

• Each hydrogen atom has one outer electron.
• A full electron shell for a hydrogen atoms has two electrons.
• Each hydrogen atom needs one more electron to fill its outer electron shell.
• When one electron from each hydrogen atom is shared between the two atoms, it will be as if each hydrogen atom had two electrons in its outer shell.

Example 2. Hydrogen fluoride (HF)

• Hydrogen atom has one outer electron, so it needs one more electron to fill its outer electron shell.
• Fluorine atom has seven outer electrons, so it needs on more electron to fill its outer electron shell.
• If one electron from each atom is shared between the two atoms, it will be as if both atoms have a full outer electron shell.

Example 3. Chlorine (Cl₂)

• Each chlorine atom has 7 outer electrons, so it needs one more electron to fill its outer electron shell.
• If one electron from each atom is shared between the two atoms, it will be as if both atoms have a full outer electron shell.

Example 4. Carbon dioxide (CO₂)

• Carbon atom has 4 outer electrons, so it needs 4 more electrons to fill its outer electron shell.
• Oxygen atom has 6 outer electrons, so it needs 2 more electrons to fill its outer electron shell.
• If carbon atom shares two electrons with each oxygen atom, carbon atom and both oxygen atoms have a full outer electron shell.

Example 5. Ethene (C₂H₄)

• Carbon atom has 4 outer electrons, so it needs 4 more electrons to fill its outer electron shell.
• Hydrogen atom has 1 outer electron, so it needs 1 more electron to fill its outer electron shell.
• If each carbon atom shares 2 electrons with the other carbon atom and 1 electron each with 2 hydrogen atoms, all atoms will have a full outer electron shell.

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