Module 2: Foundations in Chemistry

Electron Relative Mass

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Relative Isotopic Mass

The mass of the atom of an isotope compared to 1/12th of the mass of a Carbon-12 atom

Relative Atomic Mass

The weighted mean mass of the atom of an element compared to 1/12th of the mass of a Carbon-12 atom

Mole

The amount of any substance that contains as many particles as there are C atoms in exactly 12g of the Carbon-12 isotope

Avogadro Constant

The amount of particles in 1 mole-

6.02×10²³

Molar Mass

The mass of one mole of a substance

Stoichiometry

The ratio of moles of each substance in a chemical equation

Reaction Observation Examples

Effervescence

Solid getting smaller

Colour change

Steam let off

Oxidation Number

A measure of the number of electrons used to bond with the atom of another element

Hydrogen Oxidation Number

+1 (except in metal hydrides where it is -1)

Group 7 Oxidation Number

-1 (except in molecules like chlorates)

Roman Numerals In Elements

The number of electrons in the outer shell, can be used to indicate oxidation number of an atom with variable oxidation states

Nitrate Ions

Carbonate Ions

Sulfate Ions

Hydroxide Ions

Ammonium Ions

Zinc Ions

Silver Ions

Redox Reaction

A chemical reaction where both oxidation (loss of electrons, increase in oxidation number) and reduction occurs

Disproportionation

When the same element is both oxidised and reduced in a chemical reaction

Shell

A group of atomic orbitals with the same principle quantum number

Formula for amount of electrons in a shell

2n²

Atomic orbital

a region around the nucleus that can hold up to 2 electrons with opposite spins

S orbitals

Spherical

All shells have one

P orbitals

3d dumbbell shaped

Each shell from the second shell has 3 of these at right angles to each other

D orbitals

Has a more complex shape

Each shell from the 3rd shell has 5 of these

Chromium and copper electronic configuration

3d orbital fills fully or halfway before 4s orbital due to the enhanced stability of the full/half full orbital

Giant Lattice

A structure resulting from the attraction of oppositely charged ions in an ionic substance happening in all direction, causing many strong ionic bonds

Factors affecting boiling points of ionic compounds

atom size

ion charge

Solubility rules

ionic lattice must break down

water molecules must be attracted to the ions and surround them

attraction between H2O and individual ions > electrostatic attraction between oppositely charged ions

Electrical conductivity

requires mobile charge carriers

Covalent bond

the strong electrostatic attraction between a negatively charged shared pair of electrons and the positive nuclei of the bonded atoms that is formed when their orbitals overlap

Octet rule

When the central atom of a covalently bonded molecule has 4 pairs of electrons

Dative bond

When both electrons in a shared pair in a covalently bonded molecule are donated by one atom

Average bond enthalpy

The energy required to break 1 mole of a specified type of bond in a gaseous molecule

Linear molecule shape

180 degrees- has 2 bonding pairs

Trigonal planar

120 degrees- has 3 bonding pairs

Tetrahedral

109.5 degrees- has 4 bonding pairs

Octahedral

90 degrees- has 6 bonding pairs

Trigonal pyramidal

107 degrees- has 3 bonding pairs and 1 lone pair

Non linear

104.5 degrees- has 2 bonding pairs and 2 lone pairs

Molar volume 

The volume per mole of gas (24dm³mol^-1)

Gas volume & mole equation

Moles=volume/24

Ideal gas equation 

pV=nRT

Converting from degrees Celsius to Kelvin

+273

Assumptions made about the molecules making up a gas in the ideal gas equation

They have random motion,

elastic collisions,

negligible molecule size,

no intermolecular forces between them

Mass Spectrometry

An instrumental method of analysis that can be used to:

Find the abundance and mass of each isotope allowing us to determine its Ar

Find the relative molecular mass of substances made of molecules

Mass spectrometry process

Sample placed in spectrometer

Vaporised & ionised to form + ions which are then accelerated → heavier ions are slower and harder to deflect so the ions of each isotope are separated

Ions are detected on a mass spectrum as a mass to charge ratio (m/z) → the greater the abundance, the larger the signal given off