Difficult/memory Flashcards
Describe electron pair repulsion theory
Each pair of electrons around an atom will repel all other electrons.
The pairs will therefore take up position as far apart as possible to minimise repulsion.
Shape of molecule: two pairs of electrons
Linear. 180°
Shape of molecule: three pairs of electrons
Trigonal planar. 120°
Shape of molecule: four pairs of electrons
Tetrahedron. 109.5°
Shape of molecule: five pairs of electrons
Trigonal bipyramid. 90° (same plane) 120° on different.
Shape of molecule: six pairs of electrons
Octahedral. 90°
What is the effect of a lone pair of electrons.
Reduces the bond angle by 2.5°
What is the order of electron pair repulsion.
bp-bp< bp lp< lp lp
Name the classification rule for the period table (s,p,d)
S block- highest energy electrons are in the s- orbitals (eg. Li 1s2, 2s1)
P block- highest energy electrons are in the p- orbitals (eg. C 1s2, 2s2, 2p2)
D block- highest energy electrons are in the d- orbitals (eg. Fe 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d6)
Relative atomic msss
average mass of an atom relative to 1/12 of 1 atom of carbon-12.
Why is a mass spec kept under a vacuum
To prevent the ions that are produced colliding with molecules from the air.
Describe electrospray ionisation
The sample is dissolved in a volatile solvent
Then forced through a fine hollow needle which is connected to a + terminal.
Produces tiny + charged droplets that have gained a proton.
Solvent evaporates.
Describe electron impact ionisation
Sample is vaporised
High energy electrons fired from an electron gun.
This knocks off one electron from each ion forming +1 ions.
X(g) + e- ——-> X+(g) + 2e-
What happens in a mass spec
Ionisation
Acceleration- + ions are attracted to - charged plate and accelerate towards it. Lighter ions travel faster.
Ion drift- ions pass through hole in - charged plate, called flight tube to the detector
Detection- flight times of each ion is recorded, + ions pick up electrons from the detector causing currently to flow
What is the electron arrangement for Cr
1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d5
What is the electron arrangement for Cu
1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d10
Define first ionisation energy
energy required to remove one mole of electrons from an atom in a gaseous state.
What is Avogadro constant
The number of atoms in 12g of carbon-12.
6.022x10^23. A mole has 6.022x10^23
Ideal gas equation
PV=nRT.
Pa x m3 = n x JK-1mol-1 x K
What is 0 K in °
-273
What is an empirical formula
The formula that represents the simplest whole number ratio.
What is a molecular formula
The actual number of atoms of each element in a molecule.
What are the forces holding ionic compounds.
electrostatic forces
Describe an ionic structure
Giant ionic lattice
Does ionic bonding conduct.
Conducts when molten or dissolved.
Describe ionic compounds melting and boiling points
High m and b points due to strong electrostatic forces
What is a co-ordinate bond/ dative covalent bond
When an atom in a covalent bond donates a pair of electrons, rather than one electron.
What are the bonds in a covalent molecule
covalent bonds
Describe the structure of a metallic compound.
Positive ions in a sea of delocalised electrons. Giant structure.
Define electronegativity
Electronegativity is the power of an atom to attract the electron density in a covalent bond towards itself.
Describe the trends in electronegativity
Increases going up a group: there is less shielding.
Increases going across a period: nuclear charge increases without extra shielding so atoms get smaller.
Name 3 intermolecular forces in order of strength
Van der Waals, dipole dipole forces, hydrogen bonds.
What are dipole dipole forces
Forces that act between molecules that have permanent diapoles
What are Van der Waal forces
Forces that act between all molecules. They are forces that act between an instantaneous diapole and an induced dipole.
What makes Van der Waal forces larger
More electrons= larger force. As the diapoles are caused by moving electron clouds, the more elctrons, the stronger the diapole.
What is enthalpy change
heat change at constant pressure
Standard molar enthalpy of formation
enthalpy change when one mole of substance is formed from its constituent elements under standard conditions, all reactants and products being in their standard states.
standard molar enthalpy of combustion
enthalpy change when one mole of substance is burned in oxygen under standard conditions, all reactants and products being in their standard states.
enthalpy change equation
q=mCAT (mass in grams)
bond disassociation enthalpy
enthalpy change required to break a covalent bond, with all species in a gaseous state.
Name the 5 things that affect a rate of reaction.
Temperature Concentration of a solution Pressure of a gas SA of solid reactants Catalyst
Define activation energy
The minimum energy that a particle needs in order to react
What effect does temperature have on a Maxwell Boltzmann distribution graph.
Flattens the curve and pushes it to the right, with more particles over Ea.
The total area under the curve is the same.
Average and most probable energy increases.
What is a catalyst
Catalysts are substances that increase the rate of reaction (by offering an alternate reaction pathway with a lower activation) without being chemically changed themselves at the end of the reaction.
Describe a catalytic converter
a honeycomb, made of a ceramic material, coated with platinum and rhodium metals (the catalysts). honeycomb to increase surface area.
catalytic converters reactions
carbon monoxide +nitrogen oxides——> nitrogen and carbon dioxide
hydrocarbons + nitrogen oxides——> nitrogen +carbon dioxide + water
describe the steps of the reaction that take place on the catalytic converter
- adsorption - gases form weak bonds with metals atoms of the catalyst. The gases react on the surface.
- desorption- the products break away from the metal atoms.
Define dynamic equilibrium
When concentration of reactants and products remain constant because the forward and backward reaction are moving at the same rate.
State Le Châtelier’s principle
If a system is distributed, the equilibrium moves in the direction that tends to reduce the disturbance.
Define an isomer
molecules that have the same molecular formula but whose atoms are arranged differently.
Name 3 structural isomers
Positional, functional, chain
Describe positional isomerism
isomers where the same functional groups are attached to the main chain at different points.
Describe functional isomerism
isomers where the functional group is different
Describe chain isomerism
isomers where the hydrocarbon chains are branched differently.
Name a type of stereoisomerism/geometric
E-Z isomerism
Describe E-Z isomerism
Arrangement of bonds in space, around a double bond as there is no rotation around a double bond.
Describe thermal cracking
Heating alkanes to a high temperature under high pressure. Produces alkanes and alkenes.
Describe catalytic cracking
Takes place at lower temperatures and pressure. Uses zeolite catalyst. Produces branched alkanes, cycloalkanes and aromatic compounds.
What is incomplete combustion
When a substance burns in a limited supply of oxygen so CO is formed.
What are the products when an alkane burns
carbon dioxide and water
Why are CFC’s destroying the ozone
When CFC’s are exposed to UV light they can form chlorine free radicals which reacts with the ozone and breaks it down into O2.
Show the equations for the breakdown of ozone
C. +O3 —-> ClO. + O2
ClO. +O3 ———> 2O2 + Cl.
Overall: 2O3—-> 3O2
Describe and explain the trend in atomic radius across period three
Atomic radii decrease due to increased nuclear attraction with no increased shielding ng.
Describe and explain the trend in first ionisation energy.
Increases across a period as it requires more energy to get rid of an electron as the nuclear attraction also increases across a period.
Describe and explain the trend in melting points across period 3.
Giant structures (left) have high melting points whereas molecular structures (right) have lower boiling points. Molecular structures mp depends on how packed the electrons are (Van der Waal forces). For this reason S8>P4>Cl2
Group 2 reaction with water
M(s) + 2H2O (l) —-> M(OH)2 + H2 (g)
Magnesiums reaction with steam
Mg (s) +H2O (g) ——> MgO (s) +H2 (g)
Describe the trend in solubility of group 2 hydroxides.
As you go down the group they become more soluble.
Describe the trend in solubility of group 2 sulfates
As you go down the group they become less soluable.
Name a use of barium sulfate
When ingested outlines gut so it can be seen in an xray
Describe the trend in oxidising ability in the halogens
The oxidising ability of the halogens increases going up a group.
Reaction of NaCl and conc. sulphuric acid
NaCl (s) + H2SO4 (l) ——> NaHSO4 (s) + HCl (g)
Reaction of NaBr and conc. sulphuric acid
Two Reactions
NaBr (s) + H2SO4 (l) ——> NaHSO4 (s) + HBr (g)
But then HBr reacts with H2SO4 to produce sulfur dioxide water and bromine
2H+ +2Br + H2SO4 (l) ——> SO2 (g) + H2O (l) + Br2 (l)
Reaction of sodium iodide
Nal (s) + H2SO4 (l) ——> NaHSO4 (s) + HI (g)
But then the HI reacts with the acid to produce hydrogen sulfide water and iodine.
8H+ +8I- +H2SO4 (l)—-> H2S (g) + 4H2O (l) + 4I2 (s)
