Topic 1

Aton

Single particle, smallest part of an element that can participate in a chemical reaction

Element

An atom or group of atoms of only one type which can be chemically joined or not. A substance that cannot be broken down into simpler substances

Ion

An atom that has gained or lost electrons to become electrically charged

Molecule

Two or more atoms chemically joined together

Compound

A substance with 2 or more elements chemically joined together

Empirical formula

Smalled whole number ratio of atoms in a

Molecular formula

The actual number of atoms (of each element) in a compound/molecule

Relative isotopic mass

• Relative isotopic mass is defined as the mass of an isotope relative to 112 of a carbon-12 atom

Relative atomic mass

The relative atomic mass is the weighted mean / average mass of an atom relative to 112 of the mass of a carbon-12 atom

Relative formula mass

The symbol for the relative formula mass is M_r and it refers to the total mass of the substance.
If the substance is molecular you can use the term relative molecular mass

• 
  

Avogadro constant

The Avogadro constant (N_A or L) is the number of particles equivalent to the relative atomic mass or molecular mass of a substance

• The value of N_A is 6.02 x 10²³ mol^-1

Equation with mass of substance, molar mass and mol

n = mass, m / Molar mass, M

Neutralization reactions

• These can be identified by the presence of reactant acids and bases as well as the formation of a neutral solution salt and water (and sometimes other compounds such as carbon dioxide)

HCl (aq) + NaOH (aq) → NaCl (aq) + H₂O (l)

Na₂CO₃ (aq) + 2HNO₃ (aq) → 2NaNO₃ (aq) + H₂O (l) + CO₂ (g)

•  The ionic equations can more clearly demonstrate the neutralisation of an acid and a base:

H⁺ (aq) + OH^- (aq) → H₂O (l)

2H⁺ (aq) + CO₃^2- (aq) → H₂O (l) + CO₂ (g)

Displacement reactions

(aq) + 2KI (aq) → I₂ (aq) + 2KBr (aq)

•  In this reaction, the more reactive bromine displaces the less reactive iodide in potassium iodide

• This can also be seen in the ionic equation for the reaction

 Br₂ (aq) + 2I^- (aq) → I₂ (aq) + 2Br^- (aq)

Precipitation reaction

• These are shown by the reaction of two aqueous solutions to form products which include one solid

BaCl₂ (aq) + Na₂SO₄ (aq) → BaSO₄ (s) + 2NaCl (aq)

•  The ionic equation shows the precipitation reactions more clearly as there are no other products considered

Ba²⁺ (aq) + SO₄^2- (aq) → BaSO₄ (s)

Percentage composition by mass formula

% mass of an element = Ar× number of atoms of the elementMr of the compound × 100

Ideal gas equation

• The ideal gas equation is:

PV = nRT

• P = pressure in pascals (Pa)

  • V = volume in cubic metres (m³)

  • n = the amount of substance in moles (mol)

  • R = the gas constant, which is given in the Data Booklet as 8.31 J mol^-1 K^-1 

  • T = temperature in Kelvin (K)

Formula for moles, concentration and volume

Moles, n = concentration x volume

Formula linking moles, particles and avogrados constant

Moles, n = number of particles / Avogrado’s constant

PPM: Parts per million

• 1 ppm is defined as

  • A mass of 1 mg dissolved in 1 dm³ of water

Concentration in PPM equation

concentration in ppm=volume of gas×1000000/volume of air

The kinetic theory of gases states that molecules in gases are constantly moving, what assumptions does the theory make?

• That gas molecules are moving very fast and randomly

• That molecules hardly have any volume

• That gas molecules do not attract or repel each other (no intermolecular forces)

• No kinetic energy is lost when the gas molecules collide with each other (elastic collisions)

• The temperature of the gas is related to the average kinetic energy of the molecules

Atom economy

• The atom economy of a reaction shows how many of the atoms used in the reaction become the desired product

  • The rest of the atoms or mass is wasted

• It is found directly from the balanced equation by calculating the M_r of the desired product

Atom economy equation

Atom economy = molecular mass of desired product / sum of molecular masses of ALL reactants × 100

What are allotropes?

Allotropes of carbon are substances that contain ONLY carbon atoms due to high physical difference in bonding

Giant convalent lattices mp and bp

• Very high melting and boiling point

• These compounds have large number of covalent bonds linking the whole structure so alot of energy id required to break the lattice

Are allotropes hard or soft?

• Can be hard or soft

• Eg: graphite is soft as forces between the carbon layers are weak. Diamond / silicon oxide is hard because its difficult to break 3d network of strong covalent bonds

Are most compounds soluble or insoluble in water?

Most compounds are insoluble with water

Do most compounds conduct electricity

• Graphite has delocalised electrons between carbon layers which can move along the layers when a voltage is applied

• Diamond and silicon oxide do not conduct electricity as all four outer electrons on every carbon or silicon atom are involved in covalent bonds so there are no freely moving electrons available

Graphite delocalised electrons

• Each carbon atom is bonded to 3 others forming layers of hexagons leaving one free electrons per carbon atom

• These free electrons migrate along the layers and free to move and carry charge so graphite can conduct electricity

Graphite malleable

The covalent bonds within the layers are very strong but the layers are held together by weak intermolecular forces of attraction which are easily overcome allowing the layers to slide over each other making graphite soft and slippery. This property makes graphite useful as a lubricant and in pencils and its ability to conduct electricity makes it useful for electrodes

Diamond structure

In diamond, each carbon atom bonds with 4 other carbons forming a tetrahedron. All the covalent bonds are identical, very strong and no intermolecular forces. Diamond is very hard so used in cutting jewellery and drilling tools. Its brilliance makes it useful in jewellery.

Graphene

• Single layer of graphite which is a sheet of carbon atoms covalently bonded forming a continuous hexagonal layer

• 2D molecule

• Unusual properties making it useful in fabricating composite matrrials and in electronics

Drawing of diamond structure

Drawing of graphite structure

Drawing of graphene structure