Education Always

Level: JHS, Basic 9  |  Subject: Integrated Science  |  Strand: Diversity of Matter  |  Topic: Chemical Bonding (Ionic and Covalent)

Curriculum reference: B9.1.1.1 Demonstrate understanding of chemical bonding. Indicator B9.1.1.1.1: Explain how ionic and covalent bonds are formed. All the exemplars are merged into one set of notes.

1. Why Atoms Bond

Atoms join to become stable. An atom is stable when its outer shell is full. For the first shell this is 2 electrons (the duet rule). For the other shells it is usually 8 electrons (the octet rule). Noble gases like helium, neon and argon already have full outer shells, so they do not easily react.

A chemical bond is the force that holds atoms together. Atoms bond by losing, gaining or sharing electrons.

2. Electron Arrangement (Configuration)

Electrons fill shells in order: 2 in the first, 8 in the second, 8 in the third (for the first 20 elements).

Element	Atomic number	Electron arrangement
Hydrogen (H)	1	1
Carbon (C)	6	2,4
Nitrogen (N)	7	2,5
Oxygen (O)	8	2,6
Sodium (Na)	11	2,8,1
Magnesium (Mg)	12	2,8,2
Chlorine (Cl)	17	2,8,7
Calcium (Ca)	20	2,8,8,2

3. Ionic Bonding (Transfer of Electrons)

An ionic bond forms between a metal and a non-metal. The metal atom gives away its outer electrons and becomes a positive ion (cation). The non-metal atom takes the electrons and becomes a negative ion (anion). The opposite charges attract each other strongly.

Example: sodium chloride (common salt, NaCl)

• Sodium (2,8,1) loses 1 electron and becomes Na+ (2,8).
• Chlorine (2,8,7) gains 1 electron and becomes Cl- (2,8,8).
• The Na+ and Cl- ions attract to form NaCl.

Other examples: magnesium oxide (Mg2+ and O2-), calcium chloride (Ca2+ and two Cl-).

Properties of ionic compounds:

• Hard crystals with high melting and boiling points.
• Do not conduct electricity as solids, but conduct when melted or dissolved in water.
• Most dissolve in water.

4. Covalent Bonding (Sharing of Electrons)

A covalent bond forms between non-metal atoms. The atoms share pairs of electrons so that each gets a full outer shell. The result is a molecule.

Molecule	Sharing
Hydrogen chloride (HCl)	1 shared pair (single bond)
Water (H2O)	Oxygen shares one pair with each of 2 hydrogen atoms
Methane (CH4)	Carbon shares one pair with each of 4 hydrogen atoms
Chlorine (Cl2)	1 shared pair
Oxygen (O2)	2 shared pairs (double bond)
Nitrogen (N2)	3 shared pairs (triple bond)
Carbon dioxide (CO2)	Carbon forms a double bond with each oxygen

Properties of covalent compounds:

• Low melting and boiling points (many are gases or liquids).
• Do not conduct electricity.
• Many do not dissolve in water, for example methane and cooking oil.

5. Ionic and Covalent Compared

Feature	Ionic	Covalent
Formed between	Metal and non-metal	Non-metals
Electrons	Transferred	Shared
Particles	Ions	Molecules
Melting point	High	Low
Conducts electricity	When molten or dissolved	No
Example	NaCl, MgO	H2O, CH4, CO2

Remember: Metals lose electrons, non-metals gain or share them. Transfer gives ionic bonds and sharing gives covalent bonds.

Education Always (education.inspiringalways.com). Original notes written to follow the NaCCA Basic 9 Integrated Science curriculum.