What is the difference between ionic and covalent bonding?
Short answer
Ionic bonding happens between a metal and a non-metal: the metal transfers electrons to the non-metal, forming oppositely charged ions that attract each other. Covalent bonding happens between non-metals: atoms share pairs of electrons. Ionic compounds have high melting points and conduct electricity when molten or dissolved; simple covalent substances usually have low melting points and do not conduct.
Step by step
- Look at the elements. Metal plus non-metal usually means ionic; non-metal plus non-metal means covalent.
- In ionic bonding, metal atoms lose electrons to become positive ions and non-metal atoms gain electrons to become negative ions.
- In covalent bonding, each shared pair of electrons is one bond. Atoms share until their outer shells are full.
- Link the bonding to properties: strong electrostatic forces in a giant ionic lattice explain the high melting point of salt.
Worked example
Sodium chloride and methane
- NaCl: sodium gives one electron to chlorine, forming Na⁺ and Cl⁻. Ionic.
- CH₄: carbon shares one pair of electrons with each of four hydrogen atoms. Covalent.
- Salt melts at 801 °C; methane is a gas at room temperature.
Common mistakes
- Saying ionic compounds conduct electricity when solid. The ions can only move when molten or dissolved.
- Saying that melting a simple covalent substance breaks the covalent bonds. It overcomes the weak forces between molecules.
- Drawing dot and cross diagrams with the wrong number of outer electrons.
Useful for:GCSEIGCSEWAECMatric
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