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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:
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)