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Chemical quantities and formulae
Definitions
Elements are substance which cannot be broken down by chemical means into other
substances
Atoms are the smallest part of any element that can take part in chemical reaction
Ions are formed when an atom gains or loses electrons ­ charged particles
Compounds are formed…

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however due to rounding to the nearest mole the balanced equations may not be
entirely accurate
Practice the calculations



Reactions with gases
Molar volumes is the volume occupied by 1 mol of any gas= 24dm3 at standard
pressure and temp
Ratio of gas volumes used to calculate reacting masses.
E.g.…

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Between a systems and surroundings
H = HProducts Hreactants
Enthalpy level diagrams show relative energy levels of reactants and products
Exothermic reactions have a negative H and give out energy into surroundings
Endothermic reactions have a positive H and take in energy from surroundings

Reactants Products


Products Reactants


Definitions
H°f…

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They are average values which may be different in certain environments
Values given are gaseous bond enthalpies
o If a liquid is in the calculation the energy of vapourization must be included.
They are calculated under standard conditions
H°c = bonds broken (left) ­ Bonds made (right)

You can input…

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Na [1s12s22p63s1]
1st ionization energy trend increases across a
period but decreases down a group.

Evidence for electron subshells

Drop between Be and B show that B has
a new subshell which is less stable and
therefore more easily ionized.



N has relatively high ionization energy
due to it having…

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Electron density maps will show separate ions with zero density between
Electrolysis and separate attraction to anode and cathode
Ions try and achieve noble gas configuration (octet rule or isoelectronic) either as an anion (+)
by gaining electrons or a cation (+) by losing electrons
Dot and cross diagrams (easy)…

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Covalent bond is the strong electrostatic attraction between the nucleus' of the two atoms
involved and the shared pair of electrons
Dative covalent bond are formed when both shared electrons are from one atom
Double/triple bonds
Lone pairs of electrons affect the shape of the molecule as they contribute to…

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Cl + CH3 CH3Cl
CH3 + CH3 C2H6
Alkenes are unsaturated HC's which contain double bonds, general formula is CnH2n
CarbonCarbon double bonds have a sigma and pi bond and are not rotational
o p orbitals overlap to produce 2 areas of
electron density, above and below the sigma
bond…

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Potassium manganite (VII) reacts the same way, decolorized with the presence of
double bonds

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