topic 2 Flashcards
octet rule?
tendency for an atom to lose or gain electrons in order to achieve noble gas electron configuration
Ionic bond
strong electrostatic attraction between oppositely charged ions
what do ionic compounds form?
giant ionic lattices
factors affecting ionic bond strength
ionic charge and ionic radius
ionic properties (5)
conduct electricity when molten or dissolved, ions free to move
Hard brittle crystalline
doesn’t conduct when solid - ions fixed in place
insoluble in non polar solvent
soluble inn polar solvents
prove ionic solids have charged particles
dissolve KMnO4 onto wet filter paper, place on microscope slide and attach a current
purple MnO4- ions are observed to migrate towards positive terminal
Covalent bond
strong electrostatic attraction between shared pairs of electrons and the two nuclei
dative bond
a dative covalent bond involves one atom providing both the electrons in the shared pair
Mixed bonding
compounds contain both ionic and covalent bonds
NH4Cl
Factors affecting covalent bonds length
size of atom
number of pairs of e shared
electron deficient atoms
Be, Al, B
expanded octets can be….
P
S
Cl
Br
biggest repulsion order in shapes of molecules
L.P to L.P repulsion greater than
L.P to B.P repulsion which is greater than
B.P to B.P repulsion
polar covalent bond
shared e are drawn to atom with stronger pull on e
electronegativity?
ability for an atom to attract bonding in the covalent bond
Dipole
difference in electronegativity when polarisation occurs
cation attracts e of the anion
what increases polarising power
high charge density
electronegativity increases across group bc
increases N.C, constant shielding = increased attraction between valence e and nucleus
electronegativity down group decreases bc
increased shielding and increased atomic radius = decreased attraction
where do London forces exist
exist between all molecules
how do London forces work
random electron movement in molecule to one side of molecule
creates temporary dipole
this temporary dipole created induced dipole for neighbouring molecule
two molecules now attracted
what affects L.F
more electrons = more random e movement so bigger dipoles so stronger london forces
increased branching weakens london forces as molecules have less contact points and cant get as close to each other
P:D to P;D
attraction between the partially positive and partially negative ends of a molecule
due to polar bonds
Hydrogen bonding
attraction between the lone pair of electrons on an O,N or F atom and an electron deficient hydrogen bonded to an O, N or F atom
why do alcohols have higher B.P than alkanes
alcohols have H.B, PD:PD bonding and London forces
alkanes only london forces
boiling point of hydrogen halides
HF highest BP as it has H.B
increased BP from HCl to HI due to increased number of electrons creating stronger london forces
how many hydrogen bonds does water form
4 HB forming a rigid 3d lattice
why can ice float
ice forms an open lattice structure with molecules being further apart in solid state than in liquid
ice is less dense so it can float
metallic bonding
electrostatic attraction between metal ion and sea of delocalised electrons creating a lattice
properties of metallic bonding
good electrical conductor - delocalised e can carry current
good thermal conductor - energy transferred to delocalised e that move around rapidly conducting heat
High MP
Malleable - layers of atoms can slide over each other into different shapes
Diamond structure
giant covalent structure with each c having 4 hydrogen bonds
diamond properties (3)
hard - network of atoms
high mp
poor electric conductor as e fixed in place
good thermal conductor atoms pass vibrations rapidly along bonds in rigid structure
Graphite structure
giant covalent structure each c contains 3 C.B
delocalised e form weak london forces between layers
graphite properties
soft - weak L.F easily overcome - layers can slide over each other
high MP - alot of eneegry to overcome 3 covalent bonds
good electrical conductor - delcoalsied e can move throughout
allotrope
different forms of the same element
fullerene
simple covalent
each c has 3 covalent bonds
