Chem Paper 1

3.1.1 Atomic Structure

• mZ = number of protons
• In time of flight mass spectrometer, samples are ionised, accelerated to constant kinetic energy, allowed to drift and detected
• A mass spectrum can be used to find the relative isotopic mass and abundance of isotopes in a sample
• Relative atomic mass is the average mass of an atom compared to 1/12 the mass of a carbon 12 atom
• There are 4 types of sub-shells: s, p, d and f
• An orbital consists of two electrons spinning in opposite directions
• The first ionisation energies decrease down Group 2 as the outermost electrons are increasingly shielded from the attraction to the nucleus
• There is an increase in the first ionisation energy across a period as the nuclear charge increases 

3.1.2 Amount of Substance

• Relative molecular mass is the sum of the relative atomic masses of all the atoms in a molecule
• Relative formula mass is the sum of the atoms that make up a formula unit in a giant structure
• Ideal gases have point like particles in random motion, the particles do not react on collision, undergo elastic collisions and there are no intermolecular forces
• Ideal gas equation: pV=nRT
• The empirical formula is the simplest whole ratio of atoms in a compound
• The molecular formula is the actual number of atoms in a compound
• The chemical formula is the number of atoms of each element in a formula unit in a giant structure
• Concentration = mole/volume
• A volumetric solution is one in which the concentration is known
• A titration is used to find an unknown volume or concentration of a reactant

3.1.3 Bonding

• Ionic bonding is the electrostatic attraction between two oppositely charged ions
• A covalent bond is the electrostatic attraction between the nuclei of two atoms that share a pair of electrons
• Dative or co-ordinate bonds are covalent bonds in which both bonding electrons originate from the same atom
• A metallic bond is the electrostatic attraction between positively charged metal ions and the surrounding delocalised electrons
• Ionic crystals have high melting points and only conduct when molten
• Macromolecular crystals have high melting points and do not conduct
• Molecular crystals have low melting points and do not conduct
• Lone pair = -2.5 from bond angle
• Linear = 180, Trigonal planar = 120, Square Planar = 90, Tetrahedral = 109, Trigonal bipyramidal = 90, Octahedral = 90
• Electronegativity is an atom's ability to draw the electron density from a covalent bond towards itself
• Permanent dipole dipole forces are caused by differences in electronegativity
• Hydrogen bonds form between hydrogen and oxygen/ fluorine/ nitrogen
• Van der Waals are between all molecules and increase with the size of the molecule

3.1.4 Energetics

• Enthalpy change of a reaction is the energy transferred to or from the number of moles in the equation
• Standard enthalpy change is measured under standard conditions: 100kPa, 298K and all substances in standard states
• The standard enthalpy of combustion is the enthalpy change when one mole of a substance is completely burnt in oxygen under standard conditions
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