The atomic number and
Mass number describe
different features of an
atom.
Relative atomic masses
An isotope is: ' A different atomic form of the same
element, with the same number of protons and
electrons, but a different number of neutrons.
same atomic number- different mass number
Ionic Bonding
Transferring Electrons
Atoms lose or gain electrons to
form charged particles (ions)-
strongly attracted to each other
Group 1 and 2 metals
only have to lose
one/two electrons to
become stable ions (+ charge)
Elements in Groups 6 and 7
only have to gain one/two
electrons to become stable
ions (- charge)
Latch onto atoms
that the gave/gained
electron from
Regular Giant Ionic Lattices
Very Strong electrostatic forces of
attraction between oppositely
charged ions in all directions
Properties
High melting and
boiling points- strong
attraction between
ions
When molten, ions
are free to move-
will carry electric
current
Dissolve easily in water.
Ions separate- free to move-
carry electric current
Ions and
Formulas
Ions have the structure
of a noble gas
Groups 1,2,6 and 7
most readily form
ions.
Group 1 and 2
elements = metals - form +
ions Group 1 elements( alkali
metals) form ions with non
metals where metal has 1+
charge
Group 6 and 7 elements = non-metals-
gain electrons to form - ions Group 7
elements (halogens) form ionic
compound with alkali metals where
halide ion has 1- charge
Charge on
positive ions is
the same as
group number
e.g. Group 1 + LI+
Group 7 = F-
Charges must
balance each
other e.g. MgCl2
Covalent Bonding
Sharing electrons
Covalent Bond =
shared pair of electrons
Dot and Cross diagrams
Simple Molecular
Substances
Very strong
covalent bonds to
form small
molecules of
several atoms.
Intermolecular forces =
very weak - Melting and
boiling points are very
lows - molecules easily
parted
Most molecular
substances are
gases/ liquids at room
temperature but can
be solids
Don't conduct
electricity - no
ions, no
electrical
charge
Giant Covalent
(Macromolecules)
Similar to giant ionic
lattices except no charged
ions
All atoms bonded to each
other by strong covalent
bonds- very high
melting/boiling points
Don't conduct electricity-
except graphite
Main examples = Diamond and Graphite
Diamond- Each
carbon atom forms
four covalent bonds
in a v. rigid giant
covalent structure.
Diamond = hardest
natural substance
-used for drill tips
Graphite- Each carbon atom has
3 covalent bonds. Creates layers-
free to slide over each other.
Graphite soft and slippery. Layers
can be rubbed off onto paper e.g.
a pencil. Weak intermolecular
forces between layers. Only
non-metal that's a good conductor
of heat and electricity. Delocalised
electrons that conduct heat and
electricity
Metallic Structures
Giant Structure
Metallic bonds involve 'free electrons'-
come from outer shell of the metal atoms
and produce the properties of metals
Electrons free to move-
good conductors of heat
and electricity
These electrons hold atom together in regular
structure- strong forces of electrostatic
attraction between + metal atoms and -
electrons
Electrons allow layers of
atoms to slide over each
other - metals can be
bent/shaped
Alloys
Harder than pure metals-different
sized atoms distorting layers- more
difficult to slide over each other =
harder
New Materials
Smart
Materials
Behave
differently
depending on
conditions e.g.
temperature
Nitinol = shape memory alloy- when
cool bends and twist like rubber.
When heatedit goes back to a
'remembered' shape- used for braces
Nanoparticles
Between 1-100
nanometres across
1nm=0.000000001m
Contain roughly a few
hundred atoms
Include fullerenes-
molecules of carbon,
shaped like hollow balls or
closed tubes- arranged in
hexagonal rings. Different
fullerenes have different
numbers of carbon atoms
A nanoparticle has v. different
properties from the bulk
chemical e.g. fullerenes have
different properties from big
lumps of carbon
Fullerens can be joined
together to make
nanotubes. All the covalent
bonds make nanotubes v.
strong- Can be used to
reinforce graphite in tennis
rackets
Nanoscience
Huge surface area
to volume ratio-
could help make
new catalysts
Nanotubes can
make stronger,
lighter building
materials
Sun cream can
include nanoparticles-
do't leave white
marks
Nanomedicine-
fullerenes absorbed
more easily by the
body - could deliver
drugs into the cells
where they're needed