2.2.2

• ionic bonding: the electrostatic attraction between positive and negative ions.
• Giant ionic lattice: when oppositely charged ions strongly attract in all directions in a regular structure with strong ionic bonds
• ionic compound properties: high melting + boiling points which increase as size of charge increases or size of ionic radius decreases, in liquid form conduct electricity, soluble in water, crystalline in normal conditions
• covalent bond: sharing of a pair of electrons from non- metal elements
• number of covalent bonds= 8 - group number
• Average bond enthalpy: a measure of the average energy of a bond, increases with less shells or more bonds
• if an average bond enthalpy is positive it is an endothermic reaction
• Dative covalent bonds: when some atoms share more electrons than others in a covalent bond
• octet rule: an atoms aim to achieve a full outer shell usually of 8 electrons
• octet rule exceptions: BF3 , SF6
• Simple molecular lattice: held together by weak intermolecular forces
• giant covalent lattice: bonded together by strong covalent bonds
• simple covalent molecule properties: soluble in non-polar substances, does not conduct electricity, low melting+ boiling points
• giant covalent structure properties: does not dissolve, does not conduct electricity, high melting + boiling points
• Simple covalent molecule property explanation: Van Der Waals forces cause weakness, no free charged Particles
• Giant covalent structure properties explanation: covalent bonds require a lot of energy to break, no free charged particles
• electron repulsion theory: electron pairs arrange themselves to minimise electron repulsion
• linear: 1 or 2 pairs of electrons with bond angles of 90 or 180
• trigonal planar: 3 pairs of electrons with bond angle of 120
• tetrahedral: 4 pairs of electrons with a bond angle of 109.5
• trigonal bipyramidal: 5 pairs of electrons with bond angles of 90 and 120
• octahedral: 6 pairs of electrons with bond angle of 90
• NH3 bond angle: 107
• H2O Bond angle = 104.5
• CH4 Bond angle = 109.5
• Filled wedge = in front of the central molecule
• dashed wedge = behind central molecule
• Each lone pair of electrons reduces a bond angle by 2.5
• 3 bonding pairs + 1 lone pair = pyramidal 107
• 2 bonding pairs + 2 lone pairs = non-linear 104.5
• Electronegativity: The ability of an atom to attract the pair of electrons in a covalent bond.
• on the Pauling scale the higher the number the higher the electronegativity
• Fluorine has the highest electronegativity
• polar bond : the electronegative charge difference between atoms causing the shared pair of electrons to be more closely attracted to 1 of the bonding atoms
• polar molecule: a molecule with uneven distribution of electrons in the covalent bond
• a non polar molecule is structurally symmetrical
• a polar molecule is structurally asymmetrical
• permanent dipole - permanent dipole: dipoles are attracted to one another
• permanent dipole - induced dipole : the permanent dipoles electrons repel the non polar molecule inducing a dipole
• London forces: electrons randomly move into an uneven distribution forming an instantaneous dipole which causes an induced dipole in the molecule next to it. the more surface contact / electrons the more likely and stronger to occur