Chemical Bonding

• giant metallic lattice structure, metal cations arranged in a lattice and surrounded by a ‘sea’ of delocalised electrons • electrostatic attraction between metal cations and the ‘sea’ of delocalised electrons form metallic bonds

• no. of delocalised e- : due to more valence electrons • high charge density : due to higher charge and smaller ionic radius • leads to: greater electrostatic attraction between metal cation and delocalised electrons → stronger metallic bond strength. • greater electrical conductivity: more valence electrons → more mobile charge carriers

(NaCl) has a giant ionic structure with electrostatic attraction b/w oppositely charged ions

increase in Lattice Energy: higher charge, decrease in ionic radius, decrease in interionic distance b/w cation and anion → stronger electrostatic attractions between cation and anion, more energy to overcome

due to presence of charge carriers: * describe structure of metal and ionic cpd * metals have sea of delocalised e- to act as mobile charge carriers in both solid and molten * ionic cpd cation and anion are held in fixed position in solid state * able to conduct in molten state as ionic lattice is broken down to form mobile ions which act as charge carriers

(graphite) has a giant molecular structure with c atoms held tgt by strong electrostatic attraction b/w the 2 +ve nuclei and shared pair of electrons (covalent bond)

• size of valence orbital increases • orbital overlap becomes less effective • strength of covalent bond decreases • less energy needed to overcome covalent bond

simple covalent structure, held together by weak id-id

id-id: * Electrons constantly moving at any moment * electron density of molecule unsymmetrical, * resulting in instantaneous dipole and induces a dipole in a neighbouring molecule * resulting in id-id interactions pd-pd: * Molecules are polar with permanent dipoles * pd-pd interactions arise due to electrostatic attraction between the partial +ve charge of one phosgene molecule and partial –ve charge of the other phosgene molecule.

Structure→Polarity→IMF→Energy • CF 4 and water have simple molecular structure • CF 4 is non-polar with id-id interactions between the molecules • Water is polar and hydrogen bonds exist between H2O molecules. • energy evolved when CF 4 molecules form id-id interactions with water molecules insufficient to overcome the hydrogen bonds between H2O molecules and the id-id interactions between the CF4 molecules

Structure→Polarity→IMF→Energy • Both have simple molecular structure and are polar with pd-pd interactions and id-id interactions between molecules • CH3SCH3 has a larger electron cloud than CH3OCH3 and electron cloud is polarised to a larger extent → stronger id-id interactions between molecules • more energy needed to overcome stronger id-id bond, higher bp

extensiveness of h2 bond: * hydrazine (contains 2 N atom), able to form more extensive, 2 intermolecular hydrogen bonds per molecule * ammonia can only form 1 intermolecular hydrogen bonds per molecule * more energy is required to break the more extensive intermolecular hydrogen bonding present in hydrazine electonegativity of N,O,F in H2 Bond: * F more electronegative, dipole moment of H-F larger * stronger intermolecular h2 bond formed in H-F bond * large amt of E required to overcome presence of INTRAmolecular H2 bond: * INTRAmolecular H2 bond limit no.of sites for INTERmolecular h2 bond * INTERmolecular less extensive, less energy required to overcome hydrogen bonding based on lone pair e- on N!! NOT H bonded to N!!!

• e- in random motion,→ uneven distribution of electrons in molecule → separation of charges and creates an instantaneous dipole in the CO2 molecule • instantaneous dipole induces formation of dipoles in the neighbouring unpolarised CO2 molecules • weak electrostatic forces of attraction (instantaneous dipole – induced dipole interactions) forms between two dipoles

• e- in random motion,→ uneven distribution of electrons in molecule → separation of charges and creates an instantaneous dipole in the CO2 molecule • instantaneous dipole induces formation of dipoles in the neighbouring unpolarised CO2 molecules • weak electrostatic forces of attraction (permanent dipole – permanent dipole interactions) forms between two dipoles • Molecules are polar with permanent dipoles ??

• N atom more electronegative than H atom, attracts bonding e- in the N−H bond • N atom gains a partial negative charge, H atom acquires a partial positive charge • electrostatic attraction (hydrogen bond) between the e- deficient H atom of one NH3 molecule and the lone pair of e- on N atom on another NH 3 molecule

• e- pairs arranged as far apart to minimise e- repulsion • lp-lp repulsion > lp-bp > bp-bp > lone e- -bp • increase in repulsion, bond angle decreases

bond strength increases: * s-chracter of the hybrid orbital increases * hybrid orbital is less diffused, * e- more tightly held by the nuclei —> 1) (link to basicity) e- less available for dative bonding with H+ and is a weaker base OR 2) (normal elab) e- overlap with the orbital of another atom more effective, bond is stronger and bond length is shorter

sp hybridisation results when one 2s and one 2p orbital of C mix to form two sp hybrid orbitals. There are two unhybridised p-orbitals in C. (unhybridised p orbital forms the pi bond) make sense there is 2 unhybridised as there are c triple bonds in SP

one atom provides lone pair of e-, other atom has vacant low lying orbital to accept e-

Branching: * less surface area of contact * less extensive id-id interactions b/w molecules * id-id weaker, less energy needed to overcome id-id interactions

BE decreases down the group: * size of valence orbital of atoms increases down the grp * less effective overlap b/w orbitals from Cl2 to I2 * covalent bond formed b/w the halogen atoms weaker, BE decreases Boiling pt increase down the group: * all have simple molecular structure, non-polar, with id-id interaction b/w molecule * size of e- cloud increases and becomes more polarisable * strength of id-id interactions increases, more energy need to overcome from Cl2 to I2

• simple molecular structure, weak id-id interactions b/w molecules • larger e- cloud, more polarisable • strength id-id interactions increases, more energy needed to overcome strong id-id