Covalent Bonding Flashcards
covalent bond
electrostatic attraction between a pair of electrons and positively charged nuclei
How does covalent bonding come about?
- 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
How are the forces of attraction between the nuclei and shared electrons balanced?
by forces of repulsion between two nuclei
octet rule
tendency of atoms to form a stable arrangement of eight electrons in their outer shell
lone pairs
pairs of electrons no involved in forming the bond
bond length
measure of distance between two bonded nuclei
bond strength
measure of energy required to break bond (described in terms of bond enthalpy)
short bonds are – bonds
- strong
- atomic radius increases down group
- atoms form molecules with longer bonds
- shared electron pair further from pull of nuclei so bond weaker
multiple bonds are — and — than single bonds
- 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
structure of graphite
- 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
electrical conductivity of graphite
- good electrical conductor
- contains one non-bonded delocalised electron per atom that gives electron mobility
thermal conductivity of graphite
not a good thermal conductor unless heat can be force to conduct in direction parallel to crystal layers
appearance of graphite
- non-lustrous
- grey
- crystalline solid
special properties of graphite
- soft and slippery due to slippage of layers over each other
- brittle
- very high melting point
- most stable allotrope of carbon
structure of diamond
- each C atom is covalently bonded to four others
- arranged in tetrahedral with bond angles 109.5
electrical conductivity of diamond
- non-conductor
- all electrons bonded therefore non-mobile
thermal conductivity of diamond
- very efficient thermal conductor
- better than metals
appearance of diamond
- highly transparent
- lustrous crystal
special properties of diamond
- hardest known natural substance
- cannot be scratched by anything
- brittle
- very high melting point
structure of fullerene (C60)
- 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
electrical conductivity of fullerene
- semi conductor at normal temperature and pressure
- some electron mobility
- easily accepts electrons to form negative ions
thermal conductivity of fullerene
very low thermal conductivity
appearance of fullerene
yellow crystalline solid
special properties of fullerene
- soluble in benzene
- very light and strong
- reacts with K to make superconducting crystalline material
- low melting point
