Chemistry
Ionic vs covalent bonds — quick study summary
Atoms bond to achieve a stable (usually full) outer electron shell. Ionic bonds form when one atom transfers electrons to another, producing oppositely charged ions held together electrostatically. Covalent bonds form when atoms share electron pairs. Metals + non-metals usually form ionic; non-metals + non-metals form covalent.
Key points
- Ionic: electron transfer between metal and non-metal (e.g. NaCl)
- Covalent: electron sharing between non-metals (e.g. H₂O, CO₂)
- Ionic compounds: high melting/boiling points, conduct when molten or dissolved
- Covalent compounds: lower melting points (usually), don't conduct electricity
- Polar covalent: unequal sharing (electronegativity difference 0.4–1.7)
In more depth
How each bond forms
Ionic bonds form when a metal transfers electrons to a non-metal, creating oppositely charged ions held together by strong electrostatic attraction in a giant lattice. Covalent bonds form when non-metal atoms share pairs of electrons: a single bond shares one pair, a double bond two. Dot-and-cross diagrams show where each electron came from.
Linking structure to properties
Ionic compounds have high melting points because many strong bonds must break, and they conduct electricity only when molten or dissolved, when the ions can move. Simple covalent molecules have low melting points because only the weak forces between molecules break, not the covalent bonds. Giant covalent structures such as diamond and silicon dioxide have very high melting points.
Electronegativity and polarity
Bonding is a scale rather than two separate boxes. When one atom is more electronegative, shared electrons sit closer to it and the covalent bond is polar, as in water. A large difference in electronegativity moves the bond towards ionic.
Common mistakes
- Saying simple covalent substances melt easily because covalent bonds are weak. The bonds are strong; the forces between molecules are weak.
- Thinking solid ionic compounds conduct electricity. The ions cannot move until the compound is melted or dissolved.
- Describing ionic bonding as sharing electrons rather than transferring them.
Practice quiz
Click each question to reveal the answer.
1. What type of bond holds Na⁺ and Cl⁻ together in salt?
- Covalent
- Ionic
- Hydrogen
- Metallic
Answer: Ionic
2. What type of bond is in a water molecule (H₂O)?
Answer: Covalent (polar)
3. Which compound has a higher melting point — NaCl or H₂O?
Answer: NaCl
Ionic lattices require breaking many strong electrostatic bonds.
Last reviewed: May 2026