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OCR As Chemistry F321

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Alex Chung

on 10 March 2013

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Transcript of OCR As Chemistry F321

Chemistry Atomic Structure Nucleus Electrons Relative Atomic Mass - the weighted mean mass of an atom of an element compared with 1/12 of the mass of C-12 Moles and Equations Chemical Reactions Acids and bases Salts Any chemical compound formed from an acid when a hydrogen ion from the acid has been replaced by a positive ion (eg a metal) A species which is a proton donor A species that is a proton acceptor Alkali A type of base that dissolves in water forming hydroxide ions eg.
Sodium hydroxide NaOH
Potassium hydroxide KOH
Ammonia NH 3 Sulphuric acid H SO
Hydrochloric acid HCl
Nitric acid HNO 2 3 Oxidation Numbers A measure of the number of electrons that an atom uses to bond with atoms of another element. Rules for Oxidation Numbers: Uncombined element = 0 Combined Oxygen = -2 Combined Hydrogen = +1 Simple ion = charge on ion Combined Fluorine = -1 Think of which element in the compound is most likely to attract the bonding electrons. Out of the compound which is more electronegative. SO 2 +4 2 x -2 + = 0 Redox A gain of electrons or a decrease in oxidation number A loss of electons or an increase in oxidation number Oxidation
Is
Loss
Reduction
Is
Gain An oxidising agentoxidises another species A reducing agent reduces another species Mg + Cl MgCl 2 2 0 0 2+ 2 x 1- Mg is oxidised Cl is reduced Acid + Carbonate = Salt + Carbon dioxide + Water Acid + Metal = Salt + Hydrogen Acid + Base = Salt + Water First Ionisation Energy - The energy required to remove one mole of electrons from one mole of a gaseous substance to form a mole of gaseous ions. Successive Ionisation Energies - the energy required to remove each electron in turn from one mole of an ionic gaseous substance. Affected by Atomic radius - the further the electron is from the center the smaller the nuclear attraction. Affected by Nuclear charge - The greater the positive charge, the more attracted the electron is to the nucleus. Affected by Electron shielding - the inner repulsion of other electrons push the outer electrons further away. The nucleus has a smaller effect. Orbitals s-orbitals A region within an atom that can hold up to two electrons with opposite spin. Shells A group of atomic orbitals with the same principal quantum number
i.e. they are in the same main engergy level are within shells Up to 2 electrons Forms Sigma bonds P-orbital Forms Pi bonds From n=2 upwards Can hold up to 6 electrons D and F orbitals - after n=3 can hold 10 can hold 14 I can't be bothered to draw filling the shell stuff and electron spin. I know what to do with the opposite spin thing and 4s filling before 3d (expect for Cu and Cr) but when it comes to electrons being removed, the 4s go first. are responsible for... Bond(!)ing Ionic bonds Covalent bonds All of bonding is to do with electron transfer. Electron transfer is to do with Electronegativity Electronegatitivity of an element is affected by a measure of the attraction of a bonded atom for the pair of electrons in a bond atomic radius nuclear charge electron shielding The electrostatic attraction between oppositely charged ion A bond formed by a shared pair of electrons Polar bonds have a Permanent dipole a small charge difference in the electronegativities between the bonded atoms and polarity leads to... Permanent dipoles can make a molecule polar (if it is not symmetrical) Intermolecular Forces Hydrogen bonding The attractive forces between neighboring molecules A bond between an electron deficient H atom and a lone pair of a highly electronegative atom (chemistry is FON) Permanent dipole-dipole interactions A weak attractive force between permanent dipoles in neighboring polar molecules. They are a weaker version of Hydrogen bonds. Van der Waals' forces Exist due to induced dipoles VdWs forces become stronger with: More electrons (so the induced dipoles are larger) A larger surface area for interactions to take place Metallic bonding The strongest of the intermolecular forces The electrostatic attraction between positive metal ions and delocalised electrons a giant ionic lattice is formed Structure Giant ion lattices Created from ionic bonds They have a high melting point Can't conduct electricity as a solid but can when it's molten or dissolved in a polar solvent Covalent compounds Simple covalent a three dimensional structure of molecules bonded together by weak intermolecular forces No free particles to move around so can't conduct electricity Low melting and boiling points due to weak intermolecular forces If they are not polar, they are insoluble in polar molecules Example: Oxygen is a diatomic molecule Simple covalent molecules often take up different... Giant covalent a three-dimensional structure of atoms bonded together by strong covalent bonds they have a high melting and boiling point due to the bonds there are no free electrons so they don't conductor electricity they are insoluble in both polar and non-polar substances as there are no intermolecular forces or free electrostatic attractions example: Diamond Metallic structures Metals are held together by metallic bonds They have high melting and boiling points Good electrical conductors S Don't forget H E P A VSEPR Electron pairs repel each other The electron pairs want to move as far away from each other as possible They take up specific shapes around the main bonded atom Carbon is the main bonded atom here Lone pair > Bonded pair Greater repulsion This affects the bond angles 109.5 107 180 120 117 109.5 107 104.5 90 Note the change in bond angles with the extra lone pairs Isotopes - atoms of the same element but with a different number of neutrons The amount of any substance containing as many particles as there are in carbon atoms in exactly 12g of C-12 Avogadro constant - 6.02x10 mol 23 -1 Mol = Mass/Mr Mol = Conc x Vol Mol = Vol/24.0 Empirical formula - the simplest whole number ratio of atoms of each element present in a a compound Molecular formula - the actual number of atoms of each element in a molecule Enthalpy The heat content of a system Enthalpy Change - the heat added to a system at constant pressure Exothermic - when the energy added is negative (i.e. it releases heat) Endothermic - when the energy added to the system is positive Oxidation Photosynthesis Activation energy The minimum energy molecules must be given to react This can be lowered by a catalyst Iron catalyst used in the Haber process
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