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Chemical Changes and Structure (Atomic Structure (Electron (Charge =…
Chemical Changes and Structure
Rates of Reaction
Several factors can affect the rate of reaction, e.g. temperature, concentration, particle size, catalyst
The higher the temperature the faster the reaction and vice versa
the higher the concertration, the faster the reaction and vice versa
The smaller the particle size the faster the reaction and vice versa
Catalysts alter the rate of reaction but are not used up.
A biological catalyst is called an enzyme.
rate = change in volume or mass / change in time
Covalent Bonding
Molecular
Low m.p and b.p
Liquid gas or low m.p solid at room temperature
Never conducts electricity
Network
Very high m.p and b.p
Solid at room temperature
Never conducts electricity except carbon in the form of graphite.
Graphite, diamond and silicon are the three covalent network substances
A molecule is two or more elements joined by covalent bonds
A covalent bond is a shared pair of electrons between two non-metal atoms
Atomic Structure
Electron
Charge = Negative
Location = Energy Levels
Mass = negligible
Proton
Charge = Postive
Location = Nucleus
Mass = 1
Neutron
Location = nucleus
Mass = 1
Charge = no charge
atomic number = number of protons
mass number = number of protons + number of neutrons
Isotopes - atoms with the same atomic number but different mass numbers
An ion is a charged particle that has lost or gained electrons to become stable
Metals - gain electrons
Non-metals - lose electrons
Ionic Bonding
An ionic bond is an elctrostatic force of attraction between a positive metal ion and a negative non-metal ion
Ionic Lattice
High m.p and b.p
solid at room temperature
Conducts electricity when molten or in solution
A diatomic element is made up of molecules that contain two atoms
Shapes of Molecules
Tetrahedral
Pyramidal
Linear
Bent
Valency is the number of bonds that an element or ion can form
The gram formula mass of a substance is the mass of one mole of that substance
Mass = number of moles x gram formula mass
Number of moles = concetration x volume
Volume always has to be in litres. To convert cm3 to litres divide by 1000
The pH scale is a measure of the concentration of hydrogen ions and it is a continuous scale from 0-14.
<7 = alkali, >7 = acid, 7 = neutral solution
Acids contain more H+ ions than OH- ions
Alkalis contain more OH- ions than H+ ions
A base is a soluble metal oxide that when dissolved in water produces an alkaline solutution
Soluble non-metal oxides produce acids when dissolved in water
Spectator ions are ions that are present during the reaction but are unchanged by the reaction
Titration is a procedure which is used to determine the concentration of an acid.
An indicator is usually added to provide a colour change at the point when neutralisation is complete
