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Intramolecular Forces

Key Concepts

  • An intramolecular force is the force that holds the atoms or ions together in a compound.

  • There are 3 main types of intramolecular force:

    1. Metallic Bonding

    2. Ionic Bonding

    3. Covalent Bonding

  • Intramolecular forces are much stronger than intermolecular forces (the forces that act between discrete molecules).

  • The physical properties of metals and ionic substances are dependent ONLY on strong intramolecular forces (metallic bonding and ionic bonding)

  • The physical properties of three dimensional covalent network substances are determined by strong intramolecular forces (covalent bonding)

  • The physical properties of molecular covalent substances are determined by weaker intermolecular forces.

Comparison of Intramolecular Forces

Metallic Bonding Ionic Bonding Covalent Bonding
occurs when metal atoms bond to each other cations and anions bond 2 atoms share a pair of electrons and each atom provides 1 electron for the bonding pair.
A coordinate covalent bond (dative bond) forms when 2 atoms share a pair of electrons but one of the atoms provides both electrons for the bonding pair
occurs between metal atoms metal and non-metal ions non-metal atoms
bond characteristics delocalised electrons shared between atoms cations and anions are held together by electrostatic attraction or forces electrons are shared between two atoms
typical example Group I (alkali) Metals, eg, Na
Group II (alkali earth) Metals, eg, Mg
Transition Metals, eg, Fe
Group I Metal + Non-metal, eg, NaCl
Group II Metal + a non-metal, eg, MgCl2
Molecular Substances:
Group VII elements, eg, Cl2,
Group VI non-metals, eg, O2
hydrogen + non-metal, eg, H2O
Coordinate covalent bond examples: NH4+, H3O+
Three dimensional covalent networks: Si, C (graphite and diamond), B, SiO2(quartz)
melting/boiling point high high Molecular Substances: low
Three dimensional covalent networks: high
solubility in water insoluble soluble Molecular Substances: dependent on the intermolecular forces
Three dimensional covalent network solids are insoluble.
conductivity of solid good poor usually poor
conductivity of liquid good good usually poor
conductivity of aqueous solution N/A good usually poor unless the substance reacts with water to form ions (eg, HCl reacts with water to form hydrogen ions and chloride ions)

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