F331 - EL
- Created by: Jo D
- Created on: 18-05-13 16:26
Amount of 'stuff'
Avogadro constant - number of particles in 1 mole of a substance
Relative atomic mass - how much heavier an atom of an element is than 1/12 of a carbon-12 atom
Relative formula mass - sum of relative atomic masses in a molecule
Empirical formula - The simplest ratio of atoms in a compund
Molecular formula - the actual number of atoms of each element in a compound
for example: ethane has the molecular formula C2H6 but the empirical formula CH3
Working out the amount of moles in a substance: mass/Ar OR mass/Mr
A model of the atom
mass number = number of protons + neutrons
atomic number = number of protons
Isotopes
What? atoms of the same element - same atomic number but different mass number
working out the relative atomic mass: need to know relative istopic mass and relative abundance
average relative atomic mass =
(relative isotopic mass x relative abundance) + (relative isotopic mass x relative abundance)/100
Nuclear reactions
radioactive isotopes have unstable nuclei
alpha radiation - helium nuclei, charge +2, nucleus changes with 2 fewer neutrons and protons, stopped by paper or skin, low deflection in electric field
beta radiation - an electron, charge -1, nucleus changes with 1 fewer neutrons and 1 more proton, stopped by aluminium foil, high deflection in electric field
gamma radiation - electromagnetic radiation, charge 0, no change in nucleus, stopped by lead sheet, no deflection in electric field
Half-life: time taken for half the radioactive nuclei to decay
Tracers: the decay is monitored - used in medicine and decay is measured using Geiger Counter. Needs to be long enough to be traced but not long enough to cause harm to body tissues
Nuclear fusion: joining of two or more nuclei - forms heavier nucleus
Light and electrons
energy levels - at ground state, electrons are closest to nucleus. Gap between levels decreases further away from nucleus
Atomic absorption spectrum: black lines on a coloured background. Appear when electrons absord energy (a photon) and jump up to a higher energy level, producing the lines
Atomic emission spectrum: coloured lines on a black background. Appear when electrons absorb a photon and jump up an energy level, when they fall back down a frequency of light is emitted, producing the lines
Electron shells: 1st shell can hold 2 electrons, 2nd shell can hold 8 electrons, 3rd shell can hold 18 electrons, 4th shell can hold 32 electrons
Electron configuration shows how many electrons in each shell
eg. K = 2.8.8.1 Ca = 2.8.8.2 Cu = 2.8.18.1 Fe = 2.8.14.2
Bonding and properties
Metal + Non-metal = Ionic Transfers electrons to create full outer shells
Non-metal + Non-metal = Covalent Shares pair of electrons to create full outer shells
Metal + Metal = Metallic Pool of delocalised electrons and positive metal ions
Ionic lattice: high melting point, soluble, conducts if molten or in solution
Giant covalent network: high melting point, insoluble, does not conduct
Simple molecular covalent: low melting point, insoluble, does not conduct
Metallic lattice: high melting point, insoluble, conducts
Molecule shapes
Four groups of electron density: bond angle 109 4 bonding pairs = tetrahedral 3 bonding pairs, 1 lone pair = pyramidal 2 bonding pairs, 2 lone pairs = bent
Three groups of electron density : bond angle 120 3 bonding pairs = planar triangular 2 bonding pairs, 1 double bond = planar triangular
Two groups of electron density: bond angle 180 2 bonding pairs = linear 1 triple bond, 1 bonding pair = linear 2 double bonds = linear
Periodicity
- Mendeleev arranged elements according to relative atomic mass
- fitted due to chemical and physical properties
- left gaps for new elements to be discovered
- predicted properties of those elements
Periodicity - a regular pattern repeated across a period and in other periods eg. melting points and boiling points
Balanced equations
There should be the same number of each element on both the reactant and product sides of the equation
eg. Ca + H2O --> Ca(OH)2 + H2 is balanced to Ca + 2H2O --> Ca(OH)2 + H2
Reactions of elements in group 2
Metal + Water --> Metal Hydroxide + Hydrogen
The Oxides
- metal oxide + water --> metal hydroxide
- metal oxide + acid --> salt + water
The hydroxides
- metal hydroxide + acid --> salt + water
The carbonates
- metal carbonate --> metal oxide + carbon dioxide
Mass Spectrometery
- sample inlet: gas or liquid injected
- ionisation area: bombarded with electrons
- acceleration area: electric field used to give all ions same kinetic energy
- drift region: a vacuum - heavier molecules travel slower than lighter molecules
- ion detector: detects positive ions and converts into mass spectrum
The mass spectrum
greatest mass = molecular ion
most intense peak = base peak
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