Comprehensive Chemistry Notes

Atom

• The smallest part of an element that can exist.

Element

• A substance made of one type of atom only.

Molecule

• A collection of two or more atoms held together by chemical bonds.

Compound

• A substance formed by the chemical union of two or more elements.

Simple distillation

• A separation method used to separate a solvent from a solution.

Fractional distillation

• In fractional distillation, a mixture of several substances, such as crude oil, is distilled, and the evaporated components are collected as they condense at different temperatures.

Chromatography

• Used to separate different substances dissolved in a liquid.

Proton

• A subatomic particle with a positive charge and a relative mass of 1.
• The relative charge of a proton is +1.

Neutron

• An uncharged subatomic particle, with a mass of 1 relative to a proton.
• The relative charge of a neutron is 0.

Electron

• A subatomic particle with a negative charge and a negligible mass relative to protons and neutrons.

Period

• A horizontal row in the periodic table.

Group

• A vertical column in the periodic table.

Alkali metals

• The first vertical column of elements in the periodic table, starting with lithium and ending with francium.
• Also called group 1.

Transition element

• A metal that is located in between groups 2 and 3 of the periodic table and has colored compounds.

Catalyst

• A substance that changes the rate of a chemical reaction without being changed by the reaction itself.

Particle model

• The scientific theory used to explain the properties of solids, liquids and gases.
• It involves the arrangement and movement of the particles in a substance.

Evaporation

• The process in which a liquid changes state and turns into a gas.

Boiling

• Changing from the liquid to the gas state, in which bubbles of gas form throughout the liquid.

Sublimation

• When a solid turns straight into a gas on heating, without becoming a liquid first - or when a gas turns straight into a solid, without becoming a liquid.

Ion

• An electrically charged particle, formed when an atom or molecule gains or loses electrons.

Ionic bonding

• Ionic bonding forms between two atoms when an electron is transferred from one atom to the other, forming a positive-negative ion pair.

Ionic lattice

• The regular arrangement of ions in an ionic substance.

Ionic compound

• An ionic compound occurs when a negative ion (an atom that has gained an electron) joins with a positive ion (an atom that has lost an electron).

Covalent bond

• A bond between atoms formed when atoms share electrons to achieve a full outer shell of electrons.

Giant covalent structure

• A structure in which very large numbers of atoms are joined together by covalent bonds in a regular network.

Fullerenes

• Molecules of carbon with hollow shapes.
• Their structures are based on hexagonal rings of carbon atoms.

Polymer

• A large molecule formed from many identical smaller molecules known as monomers.

Delocalise

• Electrons that are not associated with a particular atom, e.g. in a metal, outer electrons can be free to move through the solid.

Alloy

• An alloy is a mixture of two or more elements, at least one of which is a metal.

Nanoparticles

• Tiny particles which are between 1 and 100 nanometres (nm) in size.

Formula

• A combination of symbols that indicates the chemical composition of a substance.

Relative formula mass

• The sum of the relative atomic masses of the atoms in a chemical formula.

Non-enclosed system

• A system in which gases or other substances can enter or leave during a reaction.

Uncertainty

• The interval within which the true value of a quantity can be expected to lie.

Range

• A measure of spread found by subtracting the smallest number from the biggest number.
• In other words, the difference between the highest and lowest values in a set of data.

Resolution

• For a measuring instrument, the smallest change in a quantity that gives a change in the reading that can be seen.

Atom economy

• A measure of how many reactant atoms form a desired product.

Percentage yield

• A measure of how much product is made, calculated using the formula:
  100 × \frac{\text{actual yield}}{\text{theoretical yield}}

Mole (Higher)

• The amount of substance that contains the same number of particles as there are atoms in 12 g of carbon-12 (contains the Avogadro's constant 6.02 ×10^{23} number of particles).

Avogadro constant (Higher)

• The number of particles in one mole of particles, 6.02 × 10^{23} per mole.

Concentration (Higher)

• A measure of the mass or amount of solute dissolved in a given volume of solvent or solution.

Limiting reactant (Higher)

• The reacting substance that is completely used up in a chemical reaction, which determines how much product is made.

Reactivity

• A measure of how vigorously a substance will react.
• The more reactive it is, the greater its reactivity and the more vigorous its reactions will be.

Oxidation

• The gain of oxygen, or loss of electrons, by a substance during a chemical reaction.

Reduction

• The loss of oxygen, gain of electrons, or gain of hydrogen by a substance during a chemical reaction.

Displacement reaction

• A reaction that occurs when a more reactive element replaces a less reactive element in a compound.

pH

• Scale of acidity or alkalinity.
• A pH (power of hydrogen) value below 7 is acidic, a pH value above 7 is alkaline.

Neutralisation

• The reaction between an acid and a base to form a salt plus water.

Base

• A substance that reacts with an acid to neutralise it and produce a salt.

Alkali

• A base which is soluble in water.

Titration

• A quantitative procedure in which two solutions react in a known ratio, so if the concentration of one solution is known and the volumes of both are measured, the concentration of the other solution can be determined.

End-point

• In a titration, the point at which the indicator first permanently changes color.

Concentration

• A measure of the mass or amount of solute dissolved in a given volume of solvent or solution.

Electrolysis

• Decomposition (of a liquid electrolyte) using (a direct current of) electricity.

Electrolyte

• Liquid which conducts electricity and is decomposed by it.

Anode

• Positive electrode.

Cathode

• Negative electrode.

Energy

• The capacity of a system to do work or the quantity required for mechanical work to take place.
• Measured in joules (J).
• For example, a man transfers 100 J of energy when moving a wheelbarrow.

Endothermic

• Reaction in which energy is taken in.

Thermal decomposition

• Type of reaction in which a compound breaks down to form two or more substances when it is heated.

Exothermic

• Reaction in which energy is given out to the surroundings.
• The surroundings then have more energy than they started with so the temperature increases.

Combustion

• The process of burning by heat.

Reaction profile

• Chart showing how the energy of reactants and products changes during a reaction.

Energy level diagram

• Chart showing the energy in the reactants and products, and the difference in energy between them.

Reactant

• A substance that reacts together with another substance to form products during a chemical reaction.

Product

• A substance formed in a chemical reaction.

Activation energy

• The minimum amount of energy that colliding particles must have for them to react.

Cell

• A store of internal energy that can be transferred as an electric current in a circuit.

Voltage

• The potential difference across a cell, electrical supply or electrical component.
• It is measured in volts (V).

Fuel cell

• Device that produces a voltage continuously when supplied with a fuel and oxygen.

Particle

• A general term for a small piece of matter.
• For example, protons, neutrons, electrons, atoms, ions or molecules.

Successful collision

• A collision between reactant particles that has enough energy for a reaction to happen.

Surface area

• The total area of all sides on a 3D shape.

Burette

• Long glass tube with a tap and marked with volume measurements, used in titrations.

Frequency

• The total number of times an event occurs.

Gradient

• Another word for steepness.
• On a graph, the gradient is defined as being the change in the 'y' value divided by the change in the 'x' value.
• It defines how steep a line is.

Tangent

• A straight line that just touches a point on a curve.
• A tangent to a circle is perpendicular to the radius which meets the tangent.

Enzyme

• A protein which catalyses or speeds up a chemical reaction.

Reaction pathway

• The sequence of reactions needed to produce a desired product from a particular set of raw materials.

Reversible reaction

• A chemical reaction in which the products can change back into the reactants.

Equilibrium

• In chemical reactions, a situation where the forward and backward reactions happen at the same rate, and the concentrations of the substances stay the same.

Alkane

• Saturated hydrocarbon.
• A compound of hydrogen and carbon only, with no C=C bonds.

Saturated

• A saturated hydrocarbon contains no carbon-to-carbon double bonds, only single bonds.

Alkene

• Unsaturated hydrocarbon with a double bond between the carbon atoms.

Unsaturated

• An unsaturated compound contains at least one double or triple bond.

Addition reaction

• Type of reaction in which two substances react together to form one new substance.

Alcohol

• An organic compound containing a hydroxyl group, -OH.
• The 'alcohol' in alcoholic drinks is ethanol, produced by the fermentation of sugars and found in wines, spirits and beers.

Hydrocarbon

• A compound that contains hydrogen and carbon only.

Crude oil

• Mixture of hydrocarbons, mainly alkanes, formed over millions of years from the remains of ancient dead marine organisms.

Mixture

• Two or more substances that are not joined together.
• The substances can be elements, compounds, or both.

Fraction

• In fractional distillation, such as that of crude oil, the different parts of the original mixture are called fractions.
• The substances in each fraction have similar boiling points to each other.

Viscosity

• A measure of how difficult it is for a substance to flow - the higher the viscosity, the 'thicker' it is.

Cracking

• The breaking down of large hydrocarbon molecules into smaller, more useful hydrocarbon molecules by vaporising them and passing them over a hot catalyst.

Pure

• A substance that consists of only one element or only one compound.

Impure

• A substance that consists of more than one element or compound.

Melting point

• The temperature at which a solid changes into a liquid as it is heated.

Formulation

• A mixture that is always made with the same proportions of the same substances.

Chromatogram

• The results of separating mixtures by chromatography.

Soluble

• Able to dissolve in solvent.
• For example, sugar is soluble in water because it dissolves to form sugar solution.

Mobile phase

• Phase in chromatography that moves, usually a solvent or mixture of solvents.

Solvent

• The liquid in which the solute dissolves to form a solution.

Stationary phase

• Phase in chromatography that does not move, for instance, the paper in chromatography.

Dissolved

• A substance is said to be dissolved when it breaks up and mixes completely with a solvent to produce a solution.

Precipitate

• A suspension of particles in a liquid formed when a dissolved substance reacts to form an insoluble substance, e.g. in a precipitation reaction.

Limewater

• Calcium hydroxide solution.
• It turns milky in the presence of carbon dioxide.

Halide

• A halide ion is an ion formed when a halogen atom (an atom from group 7) gains one electron.
• Halide ions have a single negative charge.
• Ionic compounds containing halide ions may be called halides.

Atmosphere

• The layers of gases that surround the Earth.
• The important gases in the atmosphere are nitrogen, oxygen and carbon dioxide.

Vapour

• Vapour is a cloud of liquid particles.
• Steam is water vapour.

Photosynthesis

• A chemical process used by plants to make glucose and oxygen from carbon dioxide and water, using light energy.
• Oxygen is produced as a by-product of photosynthesis.

Fossil fuel

• Natural, finite fuel formed from the remains of living organisms, e.g. oil, coal and natural gas.

Greenhouse effect

• The retention of heat in the atmosphere caused by the build-up of greenhouse gases.

Climate change

• Average weather conditions over longer periods and over large areas.

Weather

• The day-to-day condition of the atmosphere.

Acid rain

• Rain that contains dissolved acidic gases such as nitrogen oxides and sulfur dioxide.

Fuel

• Material that is used to produce heat, like coal, oil or gas.

Pollutant

• A toxic chemical or object that causes damage to the land, air or water.

Smog

• A type of air pollution that appears as a visible smoky fog which is very harmful to health.

Greenhouse gas

• The gases responsible for global warming - carbon dioxide, methane, nitrous oxide and CFCs (chlorofluorocarbons).

Global warming

• The rise in the average temperature of the Earth's surface.

Finite

• Something that has a limited number of uses before it is depleted.
• For example, oil is a finite resource.

Sterilise

• To kill any living organisms, usually microbes that might cause disease, on an object or in a substance.

Desalination

• The removal of salt from water.
• This is an energy-intensive process.
• Also known as desalinisation.

Distillation

• A separation technique which involves a solution being heated so that the solvent evaporates before being cooled to form a pure liquid.

Natural resources

• Minerals that have been made through the formation of the world that can be used for human benefit.

Reverse osmosis

• A method of purifying water by forcing it under pressure through a membrane which has tiny holes in it.
• The molecules of water pass through the holes but most ions and molecules of dissolved substances do not pass through.

Life-cycle assessment (LCA)

• A 'cradle-to-grave' analysis of the impact of a manufactured product on the environment.
• Also known as a life-cycle analysis.

Properties

• The characteristics of something.
• In chemistry, chemical properties include the reactions a substance can take part in.
• Physical properties include colour and boiling point.

Malleable

• Capable of being hammered or pressed into a new shape without being likely to break or return to the original shape.

Unreactive

• A substance is unreactive or inert if it does not easily take part in chemical reactions.

Composite material

• Material made from two or more different materials with contrasting properties.

Matrix

• The substance that binds the reinforcement together in a composite material.