Zusammenfassung der Ressource
Foundations in Chemistry
- Atoms Ions & Compounds
- Atomic Structure and isotopes
- Definitions
- Isotopes: atoms of the same element with
different numbers of neutrons and
different masses
- Relative isotopic mass: mass of an
element compared with 1/12th mass of
carbon 12
- relative atomic mass: weighted mean
mass of an element compared with
1/12th mass of carbon 12
- Relative mass
- Definitions
- Mass Defects: the mass lost by
the strong nuclear forces holding
protons and neutrons together
- 1 u is approximately the mass of 1 proton or neutron
- u is the unit for atomic mass unit
- carbon-12 is exactly 12 u
- mass to charge ratio M/Z = relative mass of an
ion/relative charge on an ion
- weighted mean mass takes into account 1) The
percentage abundance of each isotope 2) relative
isotonic mass of each isotope
- The Mole
- 1 mole is 6.02*10^23 of something
- avogadros constant
- Number of particles = mass (g) /
molar mass (g mol^-1)
- Amounts of Substance
- Amount of Substance
- Gas
- Volume
Moles x 24
- 1 mole of gas has a
volume of 24dm^3
- Solid
- Mass
Moles x Mr
- Determination of formulae
- Definitions
- Empirical formula: the simplest smallest whole
number ratio of atoms of each element in a
compound
- Mr = Ar+Ar+Ar
- Hydrated salts
- blue colour from water, when water is removed so is
the colour so only a white powder remain that is
anhydrous, but still slightly blue, as difficult to
remove all the water
- Assumptions
have to be made
- 1) All the water is lost - to make sure heat
repeatedly until weight no longer changes,
showing all the water has been removed
- 2) No further decomposition - many salts
decompose further when heated, which would be
difficult to notice if theres no colour change
- Moles and Volumes
- In a solution
- Moles = concentration x volume
- May need to convert from cm to dm^3
- A standard solution is
a solution of a known
concentration
- Made by dissolving an
exact mass of solute a
solvent and making it to
an exact volume
- A molar gas volume is the
volume per mole of gas at a
stated temperature and pressure
- RTP
- 101KPa
- 20ºC
- Molar gas volume is
always 24 dm^3 at RTP
- Volume = moles x 24
- Ideal Gas
Equation
- pV = nRT
- P is Pressure in pascals
- V is volume in m cubed
- n is moles of gas
- R is ideal gas constant = 8,31 J mol^-1 K^-1
- T is Temperature in K
- Reacting Quantities
- Percentage
yield
- Maximum possible is
theoretical yield
- 1) reaction may not
have been completed
- 2) Side
reactions
may have
taken place
- 3) Purification of the
product may cause a
loss in product
- Limiting Reagents
- Reagents that
is not in excess
- Whatever has the
most moles as it will
be used up first
- Atom Economies
- How well atoms
have been utilised
- If high then lots of desired
products and sustainable
- Atom economy = sum of molar mass of desired products
/ sum of molar masses of all products
- Acids and Redox
- Acids Bases & Neutralisation
- A strong acid releases all its
H+ ions &completely
dissociates in aqueous solution
- e.g. HCl
- A weak acid only releases a
proportion of it's H+ atoms
as it only partially dissociates
- e.g Ethanoic acid
- most organic acids are weak
- Bases neutralises an
acid to form a salt
- e.g. metal
oxides/hydroxides/carbonates
& ammonia
- An Alkali is a base that
dissolves in water realising
hydroxide ions into the solution
- Acid+Base=Salt+Water
- Only Carbonates produce
anything other than
water and salt (CO2)
- Acid-Base titrations
- Can be used for
- Identifying chemicals
- finding concentrations
- finding purity of a substance
- important for quality control
- e.g medicine food ect.
- Volumetric flasks are used to create standard solutions
- Titration Calculations
- You will know V1 and C1 and V2
- 1) Work out the mol of the solution that you know C1 and V1
- 2) Use ratios to find the mol of the other substance
- 3) Use the mol and V2 to work out C2
- Redox
- Definitions
- Oxidation Number: a measure of the
number of electrons that an atoms uses to
bond with atoms of another element.
- Oxidation Numbers
- Pure elements are always 0
- Sign is placed before the number
- O = -2
- H = +1
- F = -1
- Will match charge
- e.g. Mg2+ = +2
- Special cases
- H in hydrides = -1
- O in peroxides = -1
- O bonded to F = +2
- Sum of Oxidation Numbers = Total charge
- Group 1 = +1
- Group 2 = +2
- Al = +3
- Roman numerals shows the oxidation
state of the element without a sign
- Which will be the same as the charge
- NO2- is nitrite
- NO3- is nitrate
- SO4^2- is sulfate
- OIL RIG
- of electrons
- gaining oxygen is oxidation
- Reduction is decrease to oxidation number
- Oxidation is increase in oxidation number
- Some Dilute Acids undergo redox
reactions with metals to produce
salts and hydrogen gas
- Electrons and Bonding
- Electron strucure
- Shells are energy levels within the atom. The
energy increase as the shell number (principle
quantum number0 increases
- An Atomic Orbital is a region around
the nucleus that can hold two electron
of opposite spins. they are visualised as
areas of probability for finding an
electron.
- S-orbitals can hold 1 or 2 electrons,
the greater the wheel number, the
greater its s-orbital radius, spherical
shape.
- There are 3
P-orbitals, each
holding 2 electrons,
have a figure of 8
shape.
- Sub-shells are within a
shell, and are the same
type of orbital.
- Orbitals fill in order of increasing energy
- 4s fills before 3d
- electrons are negatively charged so repel
each other, so have opposite spins in an
orbital, shown by up and down arrows
- Orbitals with the same
energy are occupied singly
first
- 4s fills first, but is also emptied first,
as once 3d is filled its energy falls
below 4s
- Ionic bonding & Structure
- Ionic bonding is the electrostatic attraction
between positive and negative ions
- Cations include metal
ions & ammonium ions
- Anions include non-metal
ions & polyatomic ions
- Dot and cross diagrams using square brackets
- Each ion attracts oppositley in all
directions, so an ionic compound
has a giant ionic lattice structure
- Most are solids at room
temperature.
- There is insufficient energy to overcome the
strong electrostatic attraction between the
oppositely charged ions. High angry levels are
required so they have a high melting point
- Higher melting point for greater attractions.
- Many ionic compounds dissolve
in polar solvents such as water.
- Polar molecules break down the lattice
and surround each ion in solution
- In compounds with larger charges,
the attraction may be too strong to
overcome so won't be very soluble
- As a solid ionic compounds don't conduct
electricity as the ons are fixed in position
so there are no mobile charge carriers
- As a liquid or when dissolved in an aqueous
solution the ionic lattice has broken down, so
the ions can act as mobile charge carriers
- Covalent Bonding
- Covalent bonding is the strong
electrostatic attraction between a
shared pair of electrons and the
nuclei of the bonded atoms
- A covalent bond is the overlap of atomic orbitals, each one
containing one electron to give a shared pair of electrons
- The shared pair of electrons is attracted to each of the nuclei
- Both have the same structure in the outer shell as the nearest noble gas.
- Occurs with non-metal
elements/compounds and
polyatomic ions
- The attraction is localised acting only between the shared
pair of electrons, resulting in a small unit called a molecule
- Number of bonds
- Carbon - 4
- Nitrogen - 3
- Oxygen - 2
- Hydrogen - 1
- Multiple bonds - when two atoms
share more than 1 pair of electrons
- Double bonds
- Dative or Coordinate bonds are were one
atom pzrovidesthe shared pair of electrons
which was originally a lone pair, e.g. NH4+
- Shapes of Molecules and intermolecular forces
- Shapes of Molecules
- Electrons has negative
charges so repel one another
- determines shape of molecule
- lone pair is slightly closer to the central atom & occupies
more space so repels more strongly than a bonded pair
- Angles
- 2 bonded pairs, linear, 180º
- 3 bonded pairs, trigonal planar, 120º
- 4 bonded pairs, tetrahedral, 109.5º
- 6 bonded pairs, octahedral, 90º
- 3 bonded arts, 1 lone pair,
pyramidal, 107º
- 2 bonded pairs, 2 lone pairs, non-linear, 104.5º
- Electronegativity & Polarity
- Definition
- Electronegativity is the measure of
attraction of a bonded atom for the
pair of electrons in a covalent bond
- FONCl has the highest Pauling electronegativity
value, With having the highest of 4.0
- Bond Type Electronegativity Difference
- Covalent 0
- Polar Covalent 0 to 1.8
- Ionic greater than 1.8