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Chemistry GCSE Definitions

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Introduction

UNIT 1 - Structure and Bonding Atomic structure Proton - +1 Electron - weighs 1/1836 -1 Neutron - changes for isotopes (neutral) Isotopes do not change the atomic number, but increase the mass number because of the increase in neutrons, This will change the relative atomic mass depending on spread of isotopes. Mass spectrometry, sample in gaseous state vaporised, and bombarded with electrons, forming positive ions which are accelerated and passed by a magnet which then splits apart different strengths, forming a graph showing abundance of different species. Can find isotopes Relative atomic mass can be calculated First ionisation energy The amount of energy required to remove one mole of electrons from each atom in the gas phase to form a singly positive ion. Second ionisation energy The amount of energy required to remove the next electron from an atom. Requires more energy after the first, since this will usually lead to open electrons, or electrons left in unfilled shells. Jump to between shells requires a lot more energy, and shows large peak on graph Across periodic table generally increases but then drops when starting a new row because, outer shell contains one electron an so is not held well due to nuclear shielding *Slight dips occur at between elements which have half filled shells, since the next element ...read more.

Middle

Lattice enthalpy is the energy change per mole for the process M+ + X- = MX Ignores polarisation so actual covalence can be calculated Covalence increases lattice energy P/S orbs head on lap for sigma bonds P orbs side lap for pi bond A covalent bond is polar if there is a large difference in electronegativity Electronegativity is the measure of how strongly an atom attracts electrons when in a covalent bond. Two bonded pairs - linear 180 Two bonded two lone - bent linear 104 Three bonded pairs - trigonal planer 120 Three bonded, one lone pair - pyramidal 107 Three bonded, two lone pairs - t shaped two 90 and one 180 Four bonded pairs tetrahedral - 109.5 Five bonded pairs - trigonal bipyramid 3 are 120 and two 90 Six bonded pairs - octahedron 90 Two double bonds linear 180 One double, two single - trigonal planer 120 Two double bonds, two single - tetrahedral 109.5 Two double bonds, one lone pair - bent linear 104 Noble gases increase in temperature for mpt *Hydrides also Group 7 Fluorine pale yellow gas Chlorine greenish gas Bromine brown volatile liquid Iodine dark grey lustrous solid The hydrogen halides are very soluble Produce strong acids HF has strongest bond, and decreases down the group Have high ionisation energies Produce ppts with Ag+ ions, of which chloride is soluble with NH3, bromide with conc. ...read more.

Conclusion

the pressure and physical states of the reactants and products are the same in each case Enthalpy of dissociation energy - enthalpy change when mole of a gaseous substance is broken up into free gaseous atoms Can also be called and enthalpy for covalent bonds Organic Carbon can catenate, form bonds with itself homologous series - similar chemical properties, gradual variation, formula Nucleophiles - species which seek out positive centres and must have a lone pair if electrons to donate to form a covalent bond Electrophiles - species which seek out negative centres and must be capable of accepting a lone pair of electrons to form a covalent bond Aliphatic - normal aromatic - contain rings do not obey rules Free radical (can form from breaking bonds like Cl2) homolytic fission Calculating energy per unit - moles gives g; divide kj by moles to get kgperg then times by density for calorific value (kjcm-3) A tertiary iodide will be the most reactive because the C-I bond is the weakest and is on the third carbon. Alcohols CnH2n+1OH Aldehydes and keytones - CnH2nO (keytone cant have H as second R group) CnH2n+1CO2H (INSERT SYNTHETIC PATHWAY SUMMARY) Kinetics Kinetic stability means that the reactants are thermodynamically unstable but do not have enough energy to react to react and so are kinetically stable. ...read more.

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