Chemical bonds are formed only by valence electrons through electron transfer (ionic bond) or electron sharing (covalent bond), enabling atoms to achieve a stable duplet or octet electron arrangement. (p.110)
5.2 Ionic Bond
Ionic bond forms between a metal atom and a non-metal atom by transfer of electrons: the metal donates electrons to form a cation, and the non-metal accepts electrons to form an anion. (p.111)
Ions of opposite charge attract each other by strong electrostatic attraction force, known as the ionic bond. (p.113)
5.3 Covalent Bond
Covalent bond forms between non-metal atoms by sharing electrons. A single bond shares one pair of electrons. (p.114)
A double bond shares two pairs of electrons (e.g. O=O); a triple bond shares three pairs of electrons (e.g. N≡N). (p.115)
5.4 Hydrogen Bond
Hydrogen bond: the attraction force between a hydrogen atom bonded to a highly electronegative atom (N, O or F) and an N, O or F atom in another molecule (e.g. between water molecules). (p.117)
5.5 Dative Bond
Dative (coordinate) bond is a type of covalent bond where the shared pair of electrons comes from one atom only (e.g. formation of H3O+ or NH4+). (p.120)
5.6 Metallic Bond
Metallic bond: electrostatic attraction force between the delocalised sea of electrons and the positively-charged metal ions in a metal’s closely-packed structure, which allows metals to conduct electricity. (p.121)
5.7 Properties of Ionic Compounds and Covalent Compounds
Electrical conductivity: ionic compounds conduct electricity when molten or in aqueous solution (ions move freely) but not as solids; covalent compounds do not conduct electricity in any state (molecules are neutral). (p.125)
Solubility: most ionic compounds are soluble in water but not in organic solvents; most covalent compounds are soluble in organic solvents but not in water. (p.126)
Melting/boiling point: ionic compounds have high melting and boiling points (strong electrostatic forces to overcome); covalent compounds with simple molecules have low melting and boiling points (only weak Van der Waals forces between molecules to overcome). (p.126)
Covalent compounds can have a simple molecular structure (low melting/boiling point, weak Van der Waals forces between molecules) or a giant molecular structure (very high melting/boiling point, strong covalent bonds throughout, e.g. SiO2, diamond). (p.128)