Covalent Bonding - 4th

• they share pairs of electrons to get a full outer-shell

• by drawing arrows or using highlighters on the unpaired electrons on each atom • an atom will make a shared pair for each electron missing from its outer shell • e.g. N always shares 3 times and O always shares 2 times (how many electrons they need are how many bonds they make) • once known how many they share, draw in its other electrons

• some molecules contain double or triple pairs

• S has 6 in the outer shell - needs to share two pairs • F has 7 in the outer-shell - needs to share one pair • So we need 2 * F and 1*S

• the electrostatic attraction between protons in two nuclei and a shared pair of electrons between them • the shared pair of electrons effectively pull the nuclei of the atoms closer together • very strong attraction • a small group of atoms held together by covalent bonds is called a simple molecule.

• a small group of atoms held together by covalent bonds is called a simple molecule • have strong covalent bonds • weak intermolecular forces

• weak intermolecular forces break, not the bonds!!

• as molecular mass increases • so does the strength of the weak intermolecular forces • boiling point increases

• charged particles that can move freely

• electrical conductivity requires charged particles that can move freely, but in a simple molecular substance, there aren’t any charged particles • they can never conduct electricity because molecules are neutral.

• a unique simple molecule composed of sixty carbon atoms in a ball • low boiling point - not as low as other molecules - has a high molecular mass -mm - 720 • bp - +600 • soft and slippery solid -> molecules can roll over each other easily • electrical insulator - molecules are neutral

• form of pure carbon arranged into a giant lattice • every C makes 4 covalent bonds • tetrahedral shape • strong, grid like arrangement • sublimes (s->g) at v.h temperatures • cannot conduct electricity -> no freely moving charged particles • all atoms are neutral, and all electrons are stuck inside an atom/bond

• covalent bonds are very strong • there are lots of bonds in the giant lattice • lots of energy is required to break all the bonds • therefor is one of the hardest substances -> used in cutting

• graphite is another form of pure carbon arranged into a different giant lattice • layers of hexagons of C atoms • every C makes 3 covalent bonds • weak intermolecular forces between layers • delocalised electrons inside each layer • sublimes at v.h. temperatures • soft and slippery because the layers can slide easily, so it used as a solid lubricant • conducts electricity -> delocalised electrons that can move freely

• covalent bonds are very strong • there are lots of bonds in the giant lattice • lots of energy is required to break all the bonds

• also known as silica • giant covalent structure • every Si makes 4 covalent bonds • every O makes 2 covalent bonds • tetrahedral shape (like diamond) • strong, grid-like arrangement. • similar properties to diamond due to similar bonding and structure • much less expensive -> less rare

• ionic • giant lattice • high MP/BP, insulator when (s), conductor when (l) and (aq) • brittle, usually soluble in water, crystalline

• covalent • simple molecules • low MP/BP, insulator • usually insoluble in water, dull

• metallic • giant lattice • high MP/BP, conductor • malleable, ductile, shiny