U1- Bonding and shapes Flashcards
metallic bond
a lattice of positively charged ions (cations) surrounded by free-moving ‘delocalised’electrons
metals are good conductors of heat because
the fact that they have delocalised electrons flowing through the lattice which can collide with the metal ions and pass on heat energy
metals are good conductors of electricity because
sea of delocalised electrons flowing through the lattice are free to move and carry electrical charge
metals are malleable and ductile because
the fact that the attraction between the metal lattice and delocalised electrons can take a fair amount of force before the lattice breaks and so it maintains its properties whilst changing shape
metals generally have high melting and boiling points because
the fact that the electrostatic force of attraction between the metals cations and the delocalised electrons is strong and requires a lot of energy to break
alloys
combinations of two or more metals
alloys vs pure metals
because when two or more metals form an alloy, the arrangement of the ions is disturbed tf alloys are:
harder than pure metals
less malleable
poorer conductors
metals are lustrous because
delocalised electrons form a barrier to reflect the light from the surface
galvanising/ galvanisation
the process of applying a protective zinc coating to steel or iron to prevent rusting
protects iron or steel by preventing corrosive substances from reaching the underlying steel/iron and protects iron by corroding first
extraction of iron
1) coke reacts in oxygen to form carbon dioxide
C + O2 –> CO2
2) CO2 is reduced by carbon to form carbon monoxide
CO2 + C –> 2CO
3) CO reduces iron oxide to form iron
Fe2O3 + 3CO –> 2Fe + 3CO2
4) Limestone breaks down in heat calcium oxide ad carbon dioxide
CaCO3 –> CaO + CO2
5) calcium oxide reacts with sand to form slag
CaO + SiO2 –> CaSiO3
extraction of aluminium
1) Bauxite is purified and crushed then dissolved in NaOH
2) Dissolved in cryolite (Na3AlF6) as this lowers the boiling point to 1000C compared to AL2O3 2040C boiling point
3) At cathode: Al3+ + 3e –> Al (red)
4) At anode: 2O2 –> O2 + 4e (ox)
5) Then at anode (as anode made of C):
C + O2 –> CO2
so anode needs replacing
formula unit
smallest whole number ratio of atoms in an ionic compound
why do atoms gain or lose electrons?
to form a stable configuration
polyatomic ions symbol for: acetate (ethanoate) permanganate cyanide chromate dichromate peroxide
CH3COO-1 MnO4-1 CN-1 CrO4-2 Cr2O7-2 H2O2
*molecular formular
smallest unit of a substrate that retains the chemical and physical properties of a substrate.
they have a known formula
2 or > non metals
covalent bond
shared pair of electrons between. two non-metallic atoms
dative covalent bond
covalent bond in which both of the shared electrons are contributed by one atom only
eg NH4
valence structure vs lewis structure
valence = lone pairs have dots, bonds have lines lewis = all dots
octet rule
covalent bonds form so that the bonded atoms obtain a noble gas configuration generally having 8 e- in outer shell
(hw) not always true eg boron or sulfur
Valence Shell Electron Pair Repulsion (VSEPR) Theory
electron pairs within a molecule have a repulsive effect on each other
shape of a molecule is determined by the number of electron pairs surrounding the central atom
shape affects melting point, boiling point, hardness and solubility
(double bond pair behaves as a single region of electron density)
(lone pair is more repulsive than bonding pair)
shape: linear
4 total e-
2 bp
0lp
OR
3 lp
shape: trigonal planar
6 total e-
3 bp
0lp
shape: tetrahedral
8 total e-
4 bp
0 lp
shape: trigonal bipyramidal
10 total e-
5 bp
0 lp
shape: octahedral
12 total e-
6 bp
0 lp
shape: pyramidal
8 total e-
3 bp
1 lp
shape: bent
8 total e-
2 bp
2 lp
buckyballs
allotrope of carbon
C60 soccer balls- spherical arrangement of hexagons and pentagons
diamond properties
giant lattice structure
tetrahedral arrangement
strong covalent bonds
can’t conduct electricity
SiO2 properties
tetrahedral arrangement
high melting point
X conduct electricity
Graphite properties
C bonded to 3 C
high melting point- bc strong covalent bonds require lots of nrg 2 break
insoluble in water
conduct electricity- spare e becomes delocalised bw layers and r able to carry electrical charge
hexagonal layers
soft- layers can slide over each other (dispersion forces bw layers)
carbon nanotubes
semiconductors in electrical circuits
act as a component of industrial catalysts
fibres are v strong tf used in ‘composite materials’
can cage other molecules
by what angle does each lone pair reduce the bond angle?
2.5 degrees. default is 109.5 degrees
intramolecular forces
bonds within the elements
eg covalent, ionic, metallic
properties of covalent molecules
low melting and boiling point
can’t conduct electricity excluding water
low solubility in water
diamond properties + explanation
C allotrope w ea C covalently bonded to 4 C –> tetrahedral shape
Strong covalent bonds
high melting point bc strong c bonds require lots of nrg to break
X conduct elect bc no delocalised e that can carry elect charge
insoluble in water
hard
SiO2 properties
tetrahedral shape
high melting point bc strong covalent bonds require lots of nrg 2 break
X conduct elect bc no delocalised e can carry a charge
insoluble in water
hard
dispersion forces
temporary fluctuating dipoles caused by the constant movement of electrons giving rise to electrostatic forces of attraction
bigger molecule, greater SA tf stronger dispersion forces
more electrons in a sample, a greater di[pole can exist tf greater strength of dispersion force
polar
an uneven distribution of charge
dipole dipole
permanent dipole
occurs bw polar molecules (if intermolecular bonds are polar and shape= asymmetrical)
hydrogen bonding
extra strong dipole dipole attraction between molecules with hydrogen bonded to a NOF and attracted to a NOF
what makes a bond more polar
the larger the difference in electronegativity the more polar a molecule is (the further they are from each other in the periodic table).
most electronegative= top right Fluorine
least electronegative= bottom left Caesium
valence structure (drawing)
lines for shared pairs, dots for lone pairs
lewis structure
dots for ALL electrons
