Types of Chemical Bonds — Chemistry Mnemonic
Target: mnemonic for types of chemical bonds ionic covalent metallic
Why is this hard to memorize?
Chemical bonding is the foundation of all chemistry — why and how atoms join together determines every property of every material. The three main types are: Ionic bonding (transfer of electrons, Na⁺Cl⁻), Covalent bonding (sharing of electrons, H₂O), and Metallic bonding (sea of delocalized electrons, Fe). NEET and JEE test you on identifying bond types from properties (high melting point → ionic, low melting point → covalent), predicting properties from structure, and understanding intermediate cases like polar covalent bonds. Fajan's rules (when ionic bonds have covalent character) are a JEE favourite.
Classic mnemonics you should know
"Ionic = I Transfer (metal → non-metal). Covalent = C Share (non-metal + non-metal). Metallic = M Pool (metal + metal)"
Ionic: electrons are TRANSFERRED from metal to non-metal. Covalent: electrons are SHARED between non-metals. Metallic: electrons are POOLED in a "sea" shared by all metal atoms. The type depends on who's bonding.
"Ionic: High MP, conducts when molten/dissolved. Covalent: Low MP, doesn't conduct. Metallic: Variable MP, always conducts."
Each bond type has signature properties. If a substance has high melting point AND conducts when dissolved but not solid → ionic. Low MP, doesn't conduct at all → covalent molecular. Conducts in solid state → metallic (or graphite).
"Small cation + Large anion + High charge → More covalent character in ionic bond"
Fajan's rules predict when an "ionic" bond becomes more covalent: (1) smaller cation, (2) larger anion, (3) higher charge on either. LiI is more covalent than NaF because Li⁺ is smaller and I⁻ is larger. This explains why LiCl is soluble in organic solvents.
The complete list
- Ionic bond (electron transfer)
- Covalent bond (electron sharing)
- Metallic bond (electron sea)
- Polar covalent (unequal sharing)
- Coordinate/dative bond (one-sided sharing)
- Hydrogen bond (intermolecular)
- Van der Waals forces (weak intermolecular)
Frequently asked questions
How do I decide if a bond is ionic or covalent?
Use electronegativity difference (ΔEN): ΔEN > 1.7 → ionic. ΔEN 0.4-1.7 → polar covalent. ΔEN < 0.4 → non-polar covalent. As a shortcut: metal + non-metal → usually ionic. Non-metal + non-metal → usually covalent. There are exceptions (AlCl₃ is covalent despite being metal + non-metal).
What is a coordinate bond and how is it different from covalent?
In a normal covalent bond, both atoms contribute one electron each. In a coordinate (dative) bond, ONE atom provides BOTH electrons. Example: NH₃ + BF₃ → H₃N→BF₃ (nitrogen donates its lone pair to boron). Once formed, a coordinate bond is identical to a regular covalent bond in terms of strength and properties.
Why do ionic compounds have high melting points?
Ionic compounds form a crystal lattice where each cation is surrounded by anions and vice versa. The strong electrostatic attraction between oppositely charged ions in all directions requires a LOT of energy to overcome → high melting point. NaCl melts at 801°C. Covalent molecules (like CH₄, −162°C) have only weak intermolecular forces to overcome.
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