van der waal's forces
ionic bonding : electrostatic force of attraction hat occurs between the oppositely charged ions.
giant ionic structure / lattice:
opposite charge attract
(+) and (-) ions form a lattice. every (+) ions surrounded by (-) ions and every (-) ions surrounded by (+) ions
strength of ionic bonds depends on charges of the ion and radii of ions (smaller: stronger) (down the group : bigger, across period : smaller)
evidence for existence of ions:
- electron density map
- physical properties : high melting and boiling point, solid at room temp, often soluble in water, conduct electricity in molten state or solution, brittle
covalent bond : strong and arises from the electrostatic attraction between the nucleus and the electrons which are between the nuclei
dative covalent bond : bond in which two atoms share a pair of electrons, both the electrons being donated by one atom
evidence for existence of covalent bond:
- giant molecular structures : diamond - giant atomic structure.
- very high melting points
- very hard
lattice energy (indicates the strength of the ionic bonds in an ionic lattice):
the energy change when one mole of a solid ionic crystal is formed from its isolated gaseous ions, under standard condition.
first electron affinity : energy released when one mole of gaseous atoms each acquire electron to form one mole of singly negatively charged gaseous ions.
"higher charge, smaller size, stronger lattice energy"
smaller cation, higher charged cation, larger anion (Fajan's rule)
smaller cation : more polarizing (silicon is more polarizing than magnesium)
larger anion : more polarizable (chlorine is more polarizable than fluorine)
metallic bonding : electrostatic force of attraction between the delocalised "sea of electrons" and the postitive ions which are arranged in a regular lattice
depends on the number of outer electrons donated to the cloud and the size of the metal ion
e.g : metallic bond in potassium is weaker than in sodium because:
metallic radius of potassium is larger than sodium
force of attraction between potassuim ions and delocalised electrons are weaker
e.g : metallic bond in magnesium is stronger than in sodium because:
Mg atom donate 2 electrons to the cloud
greater electron density holds ions together more strongly
- good conductor (due to the flow of delocalised electrons)
- high thermal conductivity (metal heated > delocalised e of higher temp have higher kinetic energy and move rapidly to the cooler regions > transfer their energy to other e)
- high melting & boiling point
- malleable and ductile (positive metal nuclei can move when hammered, still will be surrounded by the sea of delocalised e