Module 1 of the Unit F321 which is built on the foundations of GCSE work covered in Year 11.
ATOMS
ATOMIC STRUCTURE
atoms are made up of protons, neutrons and electrons
protons and neutrons are located in the nucleus
protons have a
positive 1+ charge
protons have a mass of 1
neutrons have
no charge
neutrons have a mass of 1
the atomic mass of an atom is the
mass of both neutrons and protons
in the nucleus
electrons have a
charge of negative 1-
electrons have a
mass of 0.0005
the atomic number of an
atom is the number of
electrons in the element and also
the number of protons
however an ion is an atom
that has lost or gained
electrons to complete its outer
shell
electrons are located in
energy levels
an energy level is
sometimes known as a shell
these shells hold electrons in orbitals
each orbital can
hold only 2 electrons
of opposite spin
s-orbitals are
spherical and
hold 2
electrons
p-orbitals are dumbbell
shaped and hold 2 electrons,
but there are three p-orbitals
in each shell so they hold six
all together
the order of relative
energies of the orbitals
goes as follows; 1s 2s 2p
3s 3p 4s 3d 4p 4d
4s is slightly more energised
than 3d
elements in the
periodic table are in
certain blocks due to
the orbital that is in
their outer shell
ELECTRON
STRUCTURE
BONDING STRUCTURE
ionic bonding
is
electrostatic
attraction
between
oppositely-
charged ions
you can
predict the
charges of
elements as
ions by their
position in
the periodic
table
dot and cross diagrams are
used to show ionic bonding
with ionic charges outside
the brackets
covalent bond is a
shared pair of electrons
between non metals
dot and cross
diagrams
showing the
shared electron
pair(s) can be
used
single covalent is like the
bonds in H20, HCl, etc
dative covalent is where only
one element shares electrons
with the other.
multiple covalent
bonds exist in
molecules like O2 etc.
electronegativity is the
ability of an atom to attract
the bonding electrons in a
covalent bond
a permanent dipole may
arise when
covalently-bonded atoms
have different
electronegativities,
resulting in a polar bond
intermolecular forces within
permanent dipole covalent
bonds are stronger than
temporary or induced or no
dipole
van de waals forces exist in covalent bonds
hydrogen bonds can form between hydrogen and elements such as oxygen
and other high electronegative elements. these bonds are very strong.
water is anomalous in its properties because of the hydrogen bonds
between hydrogens and oxygens in the molecule, such as the density of
ice compared to water is lesser because the bonds are able to slide
together and it has high freezing and boiling points due to the strong
forces in hydrogen.
the shape of a simple molecule is determined by repulsion
between electron pairs surrounding a central atom
lone
pairs of
electrons
repel
more
than
bonded
pairs
the shapes of these molecules are either:
tetrahedral (like CH4), trigonal planar (like BF3),
etc etc. there are lots of shapes but these are
most common
bond angles in
tetrahedrals are
typically 90 degrees
bond angles in trigonal
planars are typically
120 degrees
METALLIC BONDING
metallic bonding as the attraction of positive ions to delocalised electrons
structures are either: giant ionic lattices with strong ionic bonding, giant
covalent lattices such as graphite or diamond, giant metallic lattices, or
simple molecular lattices
The melting points of polar substances are higher than the
melting points of non-polar substances with similar sizes.
The boiling points of ammonia, water and hydrogen fluoride
are higher than predicted due to the presence of hydrogen
bonding between the molecules.
d and f orbitals don't need to be
known about until A2, but d holds 10
electrons and f holds 14
an orbital must be full
before another can be filled
an orbital is as a region that
can hold up to two
electrons, with opposite
spins
IONS
ions are formed when
an atom takes part in an
ionic reaction
an ionic reaction is the reaction
between a non-metal and a metal
where electrons are lost and
gained in order to create ions
first ionisation energy is the energy
required to remove 1 electron from
each atom of 1 mole of gaseous
atoms to form positive +1 ions
successive ionisation energy
is the energy required to
remove 1 electron from each
atom of 1 mole of gaseous
ions
ionisation energies
are influenced by
nuclear charge,
electron shielding and
the distance of the
outermost electron
from the nucleus
the higher the
nuclear charge, the
higher the
ionisation energy
the higher the
electron shielding, the
lower the ionisation
energy
the higher the
atomic radii the
lower the
ionisation energy
first ionisation energies decrease down a group as one goes
down a group, the outer electrons are found in shells further
from the nucleus and are more shielded so the attraction of
the nucleus becomes smaller
there is a general increase in first ionisation energy because as
one goes across a period the electrons are being added to the same
shell , electrons pulled closer to nucleus and same shielding effect.
The number of protons increases, however, making the effective
attraction of the nucleus greater.
ISOTOPES
isotopes are atoms of the same
element with the same number
of protons but a different
number of neutrons and have
similar chemical properties but
are not identical
the isotope
carbon-12 is used as
the standard
measurement of
relative mass
relative isotopic mass is the mass
of an isotope compared to the mass
of 1/12th of the isotope carbon-12
relative atomic
mass is the
weighted mean
mass of all
isotopes of an
element compared
to the mass of
1/12th of the mass
of the isotope
carbon-12
to calculate the weighted mean mass of all
isotopes you take all isotopes of an element,
add them together and divide by the amount
of isotopes there are. usually to the 1 or 2 dp
relative molecular mass is the ratio of the average mass of
one molecule of an element or compound to one twelfth of
the mass of an atom of carbon-12
The relative formula mass of a substance is
the weighted average of the masses of the
formula units relative to 1/12 of the mass of
a carbon-12 atom
MOLES
the mole is the amount of a
substance which contains as
many particles as there are in
12g in carbon-12
the Avagadro constant is 6.02 x 10^23
this is the
number of
atoms in 1
mole
molar mass is the mass of a substance which
contains 1 mole e.g. CH4= (12x1) + (1x4) =
16.0gmol-1
molar volume states that 1 mole of gas always
occupies a volume of 24dm3 or 24000cm3 at room
temperature and pressure (RTP)
Avagadro's Law states that equal
volumes of gases at the same
temperature and pressure contain an
equal number of particles
mole questions will always
involve one of these:
moles (mol) =
mass (g) divided
by molar mass
(gmol-1)
moles= volume in
cm3 or dm3 divided
by molar volume
(24dm3 or 24000cm3)
concentration= moles
divided by volume
empirical formula is the simplest whole
number ratio of the atoms of each element
present in a compound
calculate empirical and molecular formulae, using
composition by mass and percentage compositions
molecular formula is the actual
number of atoms of each element
in a compound
REMEMBER TO
ALWAYS BALANCE
EQUATIONS !!!!!!
use the terms concentrated
and dilute as qualitative
descriptions for the
concentration of a solution.
ACIDS AND BASES
an acid is a H+ ion donor, and it is
this ion that makes it acidic
common acids: hydrochloric, sulfuric
acids (HCl, H2SO4, etc.)
a salt is produced when the H+ ion
of an acid is replaced by a metal ion
or NH4+;
ACIDS REACT WITH
CARBONATES TO
FORM A SALT,
CARBON DIOXIDE
AND WATER
ACIDS REACT WITH
ALKALIS TO FORM
A SALT AND WATER
ACIDS REACT WITH
BASES TO FORM A SALT
AND WATER
water of crystallisation is necessary for
the maintenance of some crystal
structures. Anhydrous means a crystal
without water and hydrated means a
crystal with water
you can calculate the
formula of the salt within a
hydrated crystal by taking
the mass of the whole
crystal and the mass of the
water to se what the mass
was to begin with, and can
from there work out the
ratio of water to compound
etc.
REMEMBER HOW TO CARRY OUT A TITRATION
AS IT WILL BE MENTIONED IN THE EXAM AND
IS PART OF YOUR COURSEWORK !!!!
a base is a H+ acceptor
common bases are:
metal oxides, metal
hydroxides and
ammonia
an alkali is a soluble
base that releases OH–
ions in aqueous solution;
common alkalis: sodium
hydroxide, potassium
hydroxide and aqueous
ammonia
a base readily
accepts H+ ions
from an acid
REDOX
Oxidation state shows the
total number of electrons
which have been removed
from an element (a positive
oxidation state) or added to an
element (a negative oxidation
state) to get to its present
state.
Oxidation
involves an
increase in
oxidation state
Reduction
involves a
decrease
in
oxidation
state
The oxidation state
of an uncombined
element is zero.
The sum of the
oxidation states of all
the atoms or ions in a
neutral compound is
zero.
The sum of the oxidation
states of all the atoms in an
ion is equal to the charge on
the ion.
The more electronegative
element in a substance is
given a negative oxidation
state. The less
electronegative one is
given a positive oxidation
state. Remember that
fluorine is the most
electronegative element
with oxygen second.
PRACTICAL SKILLS NEEDED FOR F321
x Making up a standard solution. x NaOH or
Na2CO3/HCl titration. x NaOH/H2SO4 to illustrate
difference in stoichiometry. x Titration involving a
dilution – citric acid in lime juice cordial. x
Determination of the percentage of water of
crystallisation in a hydrated salt. x Determination of
the relative atomic mass of an unknown metal by
gas collection. x Determination of the concentration
of lime water. x Determination of the relative
formula mass of washing soda by titration. x
Reactions of the bases, alkalis and carbonates with
acids. x Preparation of salts from an acid and a base,
eg copper(II) sulfate, ammonium sulphate. x
Reactions of metals with acids.
x Reactions of some Group 2 metals with oxygen and water.
x Action of water on Group 2 oxides and testing pH of
resulting solutions. x Thermal decomposition of Group 2
carbonates. x Halogen displacement reactions. x Testing for
the presence of halide ions in solution using silver nitrate.
PERIODICITY
Elements are arranged
in increasing atomic
number in the periodic
table
Elements in Groups have
similar physical and chemical
properties The atoms of
elements in a group have
similar outer shell electron
configurations, resulting in
similar chemical properties
Atomic radii
decrease as you
move from left
to right across a
period, because
the increased
number of
protons create
more positive
charge
attraction for
electrons which
are in the same
shell and have
similar shielding
IN GROUP 3
For Na, Mg, Al- Metallic
bonding : strong bonding –
gets stronger the more
electrons there are in the
outer shell that are released
to the sea of electrons. A
smaller positive centre also
makes the bonding stronger.
High energy is needed to
break bonds.
Ar is monoatomic weak
van der waals between
atoms
Si is Macromolecular: many strong
covalent bonds between atoms high
energy needed to break covalent bonds–
very high mp +bp
Cl2 (g), S8 (s), P4 (S)- simple
Molecular : weak van der waals
between molecules, so little energy is
needed to break them – lowmp+bp
S8 has a higher mp than P4 because it
has more electrons (S8 =128)(P4=60) so
has stronger v der w between molecules
PERIOD 2
Similar trend in period 2 Li,Be metallic
bonding (high mp) B,C macromolecular
(very high mp) N2,O2 molecular (gases!
Low mp as small v der w) Ne
monoatomic gas (very low mp)
Periodicity is a
repeating
pattern across
different
periods
GROUP 2
Atomic radius
increases down the
Group. As one goes
down the group
the atoms have
more shells of
electrons making
the atom bigger
Down the group the melting points decrease. The metallic
bonding weakens as the atomic size increases. The distance
between the positive ions and delocalized electrons increases.
Therefore the attractive forces between the positive ions and
the delocalized electrons weaken.
The outermost electrons are held more weakly
because they are successively further from the
nucleus in additional shells In addition, the
outer shell electrons become more shielded
from the attraction of the nucleus by the
repulsive force of inner shell electrons
Reactivity of group 2
metals increases down
the group
The reactivity increases down the group as the atomic radii increase there is
more shielding. The nuclear attraction
HALOGENS
A halogen that is more reactive will displace a
halogen that has a lower reactivity from one of its
compounds
The reactivity of
the halogens
decreases down
the group as they
less easily accept
electrons.
Chlorine will displace both
bromide and iodide ions;
bromine will displace iodide
ions
Chlorine is more reactive than bromine because it will gain
an electron and form a negative ion more easily than
bromine. The is because an atom of chlorine is smaller than
bromine and the outermost shell of chlorine is less shielded
than bromine so the electron to be gained is attracted more
strongly to the nucleus in chlorine than bromine.
silver nitrate test
This reaction is used as a test to identify
which halide ion is present. The test
solution is made acidic with nitric acid, and
then Silver nitrate solution is added
dropwise.
the trend in reactivity of Group 7
elements down the group:
decreasing ease of forming
negative ions, in terms of atomic
size, shielding and nuclear
attraction;