Covalent Bonding

electrostatic attraction between a pair of electrons and positively charged nuclei

• when two non-metals react together • each want to gain an electron • able to achieve this by sharing electron pair • shared pair of electrons concentrated in region between two nuclei and is attracted to both atoms

by forces of repulsion between two nuclei

tendency of atoms to form a stable arrangement of eight electrons in their outer shell

pairs of electrons no involved in forming the bond

measure of distance between two bonded nuclei

measure of energy required to break bond (described in terms of bond enthalpy)

• strong • atomic radius increases down group • atoms form molecules with longer bonds • shared electron pair further from pull of nuclei so bond weaker

• shorter and stronger • greater number of shared electrons • stronger force of electrostatic attraction between bonded nuclei • greater pulling power of nuclei bringing them closer together

• each C atom is covalently bonded to three others • forms hexagons in parallel layers with bond angles of 120 • layers only held together by weak London dispersion forces so can slide over each other

• good electrical conductor • contains one non-bonded delocalised electron per atom that gives electron mobility

not a good thermal conductor unless heat can be force to conduct in direction parallel to crystal layers

• non-lustrous • grey • crystalline solid

• soft and slippery due to slippage of layers over each other • brittle • very high melting point • most stable allotrope of carbon

• each C atom is covalently bonded to four others • arranged in tetrahedral with bond angles 109.5

• non-conductor • all electrons bonded therefore non-mobile

• very efficient thermal conductor • better than metals

• highly transparent • lustrous crystal

• hardest known natural substance • cannot be scratched by anything • brittle • very high melting point

• bonded in sphere of 60 carbon atoms - consists of 12 pentagons and 20 hexagons • closed spherical cage • each carbon bonded to three others • not a giant molecule because has fixed formula

• semi conductor at normal temperature and pressure • some electron mobility • easily accepts electrons to form negative ions

very low thermal conductivity

yellow crystalline solid

• soluble in benzene • very light and strong • reacts with K to make superconducting crystalline material • low melting point