4.3 Covalent structure Flashcards
what is the octet rule?
where each outer atom has 8 valence electrons
what is the only exception where a covalent compound does not follow the octet rule?
hydrogen, because it only needs 2 valence electrons
what types of elements follow the octet rule?
- all covalent compounds
- period 1 elements
- period 2 elements
- period 3 elements
what is the difference between an octet rule and an expanded octet rule?
- octet rule is when each outer atom has 8 valence electrons
- expanded octet rule is when the central atom can have more than 8 valence electrons (note that this only applies to the central atom)
when does a structure get termed the word ‘resonance structure’?
when the double bond in a molecule can exist in multiple locations
define electron domains
bonds and lone pairs on the central atom
list the 3 domain geometries and state their molecular geometry
- linear 90
- trigonal planar 120
- tetrahedral 109.5
what are the 2 forms of molecular geometry when a molecule has 3 domains (talk about the lone pairs as well)?
- trigonal planar
- bent (which has 1 lone pair)
what are the 3 forms of molecular geometry when a molecule has 4 domains (talk about the lone pairs as well)?
- tetrahedral 109.5
- trigonal pyramidal 107
- bent
what are allotropes?
different crystalline forms of carbon
what are the 4 different allotropes?
- diamond
- graphite
- graphene
- buckminsterfullerene
describe the structure and properties of diamonds
- giant tetrahedral
- each carbon is thus bonded to 4 other carbons, forming a hexagonal ring
- which makes it very hard
- since it only contains covalent bonds, it has a high melting and boiling point
- no valence electrons = cannot conduct electricity
describe the structure and properties of graphite
- a layered structure composed of carbon atoms bonded with 3 other carbons
- forms a hexagonal ring
- with a sea of delocalized electrons between layers
- forms weak intermolecular forces
- due to their free valence electrons, graphite can conduct within layers but not through them
what is graphene?
- a single layer of graphite
- flexible
- conducts electricity
describe the structure and properties of buckminsterfullerene
- gigantic molecular carbon structure
- each molecule is composed of 60 carbons each bonded to 3 carbons
- forming alternating hexagons and pentagons
- weak intermolecular forces between molecules
- has low melting point
- no valence electrons are free to move so it can’t conduct
