i. Sample is VAPOURISED
ii. sample is bombarded with high energy electrons and this IONISES
iii. ions are ACCELERATED by an ELECTRIC FIELD
iv. ions are the DEFLECTED by a MAGNETIC FIELD
v. the recorder indicates mass/charge ratio and relative abundance.
1st Ionisation energy
* the energy required to remove one mole of electrons from one mole of atoms in their gaseous state to produce one mole of gaseous 1+ ions
*general trend Na-Ar >higher the atomic number, the higher the ionisation energy. The more protons and electrons, the stronger the electrostatic attraction therefore the greater the energy required to remove one electron.
2 s p
3 s p d
4 s p d
5 s p d
Completely full shells and subshells >> completely full inner shells and subshells >> completely full inner shells and half filled subshells >> completely full inner shells and incomplete subshells
Amount of substance
1) Ar (Relative atomic mass) is the weighted average mass of an atom of an element taking into account its naturally occuring isotopes relative to 1/12th the Ar of an atom of carbon-12
2) Mr (relative molecular mass) the relative mass of a molecule compared to 1/12th of the mass of an atom of carbon-12
3) Avogadro's constant 6.022 x10²³ is the number of atoms in 12g of carbon 12. The amount of substance that contains 6.022 x10²³ particles is called a mole. The Ar of any element in grams contains one mole of atoms
4) Calculating moles number of moles= mass/molar mass
Ideal gas equation
Avogadro's law states that: equal volumes of gases at the same temperature and pressure contain equal numbers of molecules
p=pressure in Pa
V=volume in m³ (1m³=1000dm³=1000000cm³)
n=number of moles
R= gas constant = 8.31
T= temperature in Kelvins (add 273)
Empirical & molecular formula & molarity
Empirical formula represents the simplest ratio of atoms of each element present in a compound
1. Find the masses of each element present
2. Work out the number of moles present
3. Convert the number of moles of each element into a whole number ratio
Molecular formula gives the actual number of atoms of each element in one molecule of the compound
1. Divide the Mr by he relative mass of the empirical formula
Concentration= (number of moles/volume)x1000
Atom economy & percentage yield
% atom economy=(mass of desired product/total mass of reactants)x100
It is impossible to get 100% yield because:
* reactions may be reversible
* reactants may react to give unexpected products
* some product may be left behind in apparatus
* reactants may not be pure
Percentage yield= (actual amount/expected amount)x100
Water has an exceptionally high boiling point because it can hydrogen bond. To hydrogen bond, we need at least one H atom covalently bonded to a sufficiently electronegative atom (N, O, F) with at least one lone pair of electrons. H bonds occur between H bonds and lone pairs. The attractive force is greater than expected because H atoms are so small, so the charge: surface area ratio is high. Only N, O & F are electronegative enough to make the H atom positive enough.
Ice floats on water because it has an open structure as the H bonds are stronger than the intermolecular forces so there are not huge forces attracting the molecules to one another.
Bonding and structure
Dative covalent bonding: a bond resulting from two atoms sharing a pair of electrons in which both electrons came from one of the atoms involved.
Bond breaking is endothermic
Bond making is exothermic
Van der Waals: when electrons are more dense in one area of a molecule, a temporary dipole is formed. From this, induced dipoles are formed in other molecules, forming a Van der Waal.
Displayed formula: shows every atom and bond
Structural formula: shows the unique arrangement of atoms in a molecule in a simplified form without the bonds. Each carbon atom is written separately with the atoms of groups that are attached. Branches are shown in brackets.
Molecular formula: shows the number and type of atoms present in a substance.
Homologous series: a series of chemically similar compounds which conform to a general formula. Each member of the series differs from the last by CH₂. The length of the carbon chain has little effect on chemical properties yet has an effect on physical properties mp. bp. etc.
IUPAC: the rules linking systematic names and structure are used by all chemists using the same conventions.
Roots 1= meth 2=eth 3=prop 4=but 5=pent 6=hex
ane=no double bonds
ene=there is a double bond
Side chains are shown by a prefix whose name shows the number of carbons
Most organic compounds have one or more reactive groups attached:functional group. When naming, always count in from the functional group end of the chain. These are shown by a suffix, with the exception of haloalkanes which are shown by a prefix.
Alkanes: -ane, CnH2n + 2 , no double bond
Alkenes: -ene, CnH2n, double bond
Alcohols: -ol, CnH2n+1, -OH hydroxyl functional group
Haloalkanes: chloro-, bromo-, iodo-, fluoro-,
Aldehydes: -al, RC(=O)H, at the end of a carbon chain
Ketones: -one, RC(=O)R, in between two carbons
Carboxylic acids: -oic acid, C(=O)OH, carboxyl group present
Positional: have the same functional group attached to the main chain at different points
Functional group: structural isomers can have functional groups that are different
Chain: have a different arrangement of the hydrocarbon chain, such as branching
Periodicity:Trends in Period 3 elements
Na>Al- metallic structure but bond strength increases, more energy required therefore melting/boiling points increase.
Si- highest-macro molecular structure and covalent bonding, very high melting point.
P₄ >>Cl₂ much lower because only weak Van der Waals so less energy is required to break the bonds
S₈ is higher because the molecules are bigger, therefore more electrons and stronger Van der Waals.
Ar is very low because it consists of free atoms, only very very weak Van der Waals between atoms
Periodicity:Trends in Period 3 elements continued
Atomic radius decreases >> as the electrostatic attraction between the growing number of protons and electrons increases yet the shielding remains the same, therefore the attraction between the nucleus and the outer shell increases.
1st ionisation energy- there is an overall increase due to increase in effective nuclear charge, however Mg higher than Al because it has a full 3s subshell
P is higher than S because it has an exactly half full 3p orbital, providing extra stability compared to S.
- non polar due to similar electronegativities
-mp/bp increase as alkanes get bigger as the Van der Waals increase
- dont dissolve in polar substances but are soluble in non polar liquids
- strong C-C & C-H bonds= fairly unreactive
-don't react with acid/base/oxidising/reducing agents
- burn when lots of O₂ present to produce H₂O and CO₂> exothermic
-react with halogens to form haloalkanes via free radical substitution reactions
Fractional distillation of oil
Petrol- complex mixture of many compounds, mostly C₈H₁₈, carefully blended to give the correct properties
1. crude oil is heated in a furnace (650K)
2. this is passed into a tower which is cooler at the top than at the bottom
3. the vapours pass up the tower until they reach a tray which is sufficiently cool for it to condense.
4. the mixtures on each tray are piped off, with shorter chain hydrocarbons condensing nearer the top of the tower.
5. thick residue that doesn't vaporise is called tar/bitumen and is used for road surfacing.
Problems with fractional distillation
1. straight run gasoline from primary distillation makes poor petrol so has to be processed further
2. Crude oil contains a surplus of high bp fractions but not enough of the shorter chained hydrocarbons for demand. Oil refineries then have to convert crude oil into useful components, to produce different hydrocarbons, such as alkenes, cycloalkanes & arenes
To meet demand, longer Carbon chains are cracked into shorter hydrocarbon chains. More useful shorter chains are produced, as well as alkenes. Cracking takes place when a long chain saturated hydrocarbon is heated with a catalyst & decomposes to form a shorter long chain saturated hydrocarbon molecule and a short unsaturated molecule.
* involves heating to 700-1200K and under pressures of 7000kPa & keeping them in these conditions for only around one second
* Homolytic fission occurs producing two shorter chains each ending in a Carbon free radical. These are highly reactive and react to form a variety of shorter chain molecules, some of which have to be alkenes as there are not enough hydrogens in the original hydrocarbons
* Test with bromine water: alkene will decolourise (orange> colourless), alkane has no effect on the bromine water
- takes place at a lower temperature around 720K and a lower pressure, on the surface of a zeolite catalyst (silicon dioxide and aluminium oxide) which have active sites which can favour the desired product.
- products are mostly branched alkanes, alkenes, cycloalkanes & aromatic compounds
- the catalyst gradually becomes coated with carbon so is burnt in air. The energy released from this heats up the catalyst and the heat is transferred to the feedstock so cracking occurs without any additional heating.
Catalytic converters are fitted in all new cars, to reduce the output of CO, nitrogen oxides and hydrocarbons.
2CO + 2NO >> N₂ + 2CO₂
C₈H₁₈ + 25NO >> 12.5N₂ + 8CO₂ + 9H₂O