CHEMISTRY UNIT 1
- Created by: charlie
- Created on: 16-02-14 21:48
triangles
DIAGRAM
empirical formula from percentage
-
working out chemical formulae
- find valency then use the 'cross method'
DIAGRAM
strong + weak acids
STRONG
H2SO4 --> 2H + + SO4 2-
0% 100%
strong acids disassociate fully
WEAK
CH3COOH <--> H + +CH3COO-
40% 60%
weak acids partial ionization in water
neutralisation
ACID + ALKALI --> SALT + WATER
e.g. HCL (aq) + KOH (aq) --> KCL (aq) + H2O (l)
IONIC EQUATION = H+(aq) + OH-(aq) --> H2O (l)
salt making
ACID + BASE --> SALT + WATER
ACID + METAL --> SALT + HYDROGEN
ACID + CARBONATE --> SALT + WATER + CARBON DIOXIDE
water of crystallisation
.
calculating R.A.M
DIAGRAM
3 factors affecting nucleus attraction
1. ATOMIC RADIUS
- GREATER DISTANCE = WEAKER ATTRACTION
2. ELECTRON SHIELDING
- 'repulsion between electrons in different inner shells which reduces net attractive force from the positive nucleus on the outer shell electron'
- MORE INNER SHELLS = LARGER SHEILDING EFFECT
3. NUCLEAR CHARGE
- GREATER NUCLEAR CHARGE = GREATE ATTRACTIVE FORCE ON OUTER ELECTRON
electron arrangement
Electrons arranged in shells (energy levels) --> sub shells (sub-levels) --> orbitals (hold 2 e-) ORBITALS S orbital
- spherical
- 1 section X 2e-
P orbital
- 8 shape
- 3 sections X 2e-
D orbital
- 5 sections X 2e-
F orbital
- 7 sections X 2e-
ions
electrons gained or lost from highest energy orbitals
BUT... transition ions lose from 4S first
e.g.
- Fe = [Ar] 4s2 3d6
- Fe 2+ = [Ar] 3d6
- Fe 3+ = [Ar] 3d5
filling orbital rules
DIAGRAM
shapes of molecules
'depend on total number of electron pairs around the central atom'
- electron pairs repel each other as fair apart as possible
- lone pairs repel more apart than electron pairs
3D MOLECULE
diagram...
- every lone pair reduces bonding angle by 2.5 d.c
- N.B (treat double bonds as single bonds when working out shape)
3 types of inter molecular bonding
1. VAN DER WAALS
- temporary dipole to dipole attraction induced
- uneven distribution of electrons (constant movement)
- BIGGER MOLECULE = GREATER V.D.W
2. PERMANENT DIPOLE - DIPOLE ATTRACTION
- molecules with overall dipole
- attractions between peramanent dipoles of neighbouring molecules
3. HYDROGEN BONDING
- permanent dipole - dipole attraction where H atom bonded to very elctronegative atom (F,O,N)
- polar bond leaves H nucleus expose (1 electron)
- strong attraction between lone pair on F,O,N molecule to exposed nucleus
hydrogen bonding properties
H2O
- anomalously high BP
- high surface tension
- FROZEN WATER - less dense than liquide water - h-bonds hold water in open lattice (relatively long)
- good solvent for solutes that can h-bond with water - ionic + covalent molecules
ionic, covalent + metallic bonding
IONIC
- bond isnt directional
COVALENT
- bond is directional - acting soley between 2 atoms in bond
METALLIC
- form GIANT METALLIC LATTICE - strong metallic bonds
- INC ATTRACTION (+3 ions) = INC BP + MP
- E.G. metals in group 1 form 1+ ions provide 1 electron to mobile sea
- metals in gorup 3 form 3+ ions provide 3 electrons to moblie sea (STRONGER)
metallic bonding properties
malleable/ductile
- bendy - made into wire
- DUE TO... free electron still attract metal ions even if they are shifted
high MP/BP
CONDUCT electricity
- delocalised electron cane move throughout 3D lattice + carry charge
giant covalent lattices
- huge networks of covlently bonded atoms
- CARBON can form structure - 4 strong covlent bonds
DIAMOND (allotrope of carbon) - diff. form of same element in same state
- each carbon attached to another 4 in tetrahedral shape
- high MP, extrememly hard, vibrations can travel (thermal conductor)
- CAN'T CONDUCT (all electrons held in localised bonds), wont dissolve in any solvent
GRAPHITE (allotrope of carbon)
- carbon atoms in flat hexagon sheets - 3 bonds each
- 4th outer electrons delocalised between sheets
- sheets of hexagons bonded together by VDW
- slippery (Weak bonded sheets), CAN CONDUCT (delocalised electron)
- less dense (far apart layers) high MP (strong covalent bonds in hexagons)
- insoluble in any solvent (covalent bonds too hard to break)
group 2 element properties
down the group
- inc. raidus = more shells of electrons
- dec. I.E - bigger radius / more shielding / weaker attraction despite inc. protons
- inc. reactivity
MP higher than group 1
- stronger attraction between 2+ ions and more electrons
medium density
reactions with O2, water + acid
- vigourous - REDOX
- 2Sr(s) + O2(g) --> 2SrO(s)
- Sr(s) + 2H2O(l) --> Sr(OH)(aq) + H2(g)
- Sr(s) + 2HCl(aq) --> SrCl2(aq) + H2(g)
group 2 compounds
OXIDES basic + neutralises acids
- NOT REDOX instead is an ACID - BASE REACTION
- SrO(s) + 2HCl(aq) --> SrCl2(aq) + H2O(l)
forms HYDROXIDES with water
- down group hydroxides more SOLUBLE so realease more OH- ions to water (INC. PH)
- SrO(s) + H2O(l) --> Sr(OH)2(aq)
CARBONATES all undergo thermal decomposition
- down group become more THERMALLY STABLE
- SrCO3(s) --> SrO(s) + CO2(g)
group 2 elements - limestone cycle
DIAGRAM
group 2 hydroxides - uses
Mg(OH)2 pH 8.5
- non-toxic = used to NEUTRALISE excess stomach acid
- e.g. INDIGESTION TABLETS
Ca(OH)2 pH 10
- NEUTRALISE soil acidity = CROPS can grow
- NOT CaO as with water is EXOTHERMIC - producing HEAT - kills humus + dangerous
halogens
- non-metals all exist as separate diatomic moleucles e.g. Cl2
BP INC. down group
- inc. no of electrons = inc. VDW
ELECTRONEGATIVITY DEC. down group
- despite more PROTONS, INC. SHELLS (shielding), INC. RADIUS (less attraction)
OXIDISING power DEC. down group
- inc. sheilding + atmoic radius
- CHLORINE - (high electronegativity+small size) can bring highest oxidation state in elements
DISPLACEMENT REACTIONS
- Cl2 + 2Br- --> Br2 + 2Cl-
- Cl2 + 2I- --> I2 + 2Cl-
- Br2 + 2I- --> I2 + 2Br-
halogens (2)
DISPROPORTIONATE REACTION of chlorine
- chlorine is oxidised + reduced
- e.g.
- 2NaOH(aq) + Cl2(g) ---> NaCl(aq) + NaOCl(aq) + H2O(l)
USES OF HALOGENS
- Cl2: bleach, solvents, polymers, water purifiying
- F2: CFC's, polymers
- F-: prevent tooth decay
- HF: etch glass
- AgBr: photographic film
TESTING FOR HALIDE IONS (dilute nitric acid + silver nitrate + dilute ammonia+concen. amm.)
- Cl - : WHITE (soluble in both ammonia)
- Br - : CREAM (soluble in concen. ammonia)
- I - : YELLOW (insoluble in both)
- Ag+(aq) + X-(aq) ----> Ag+X-(s)
oxidation numbers
- UNCOMBINED ELEMENT : 0
- COMBINED OXYGEN : -2
- COMBINED HYDROGEN : +1
- SIMPLE ION : (charge on ion)
- COMBINED FLUORINE : -1
EXCEPTIONS
- OXYGEN + FLUORINE: oxygen has +2
- PEROXIDES : oxygen has -1 (H202)
- HYDRIDES + METAL : hydrogen has -1
most electronegative is dominant element
e.g. CuO(s) + H2(g) -----> Cu(s) + H2O(l)
+2 -2 0 0 +1 -2
Copper reduced + Hydrogen oxidised
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