Key Chemistry Concepts: Atomic Structure, Periodic Table, and Reactions

alkali metal

A metal in Group 1 of the periodic table.

alpha particle scattering experiment

The experiment that suggested that the mass of an atom was concentrated in the centre (nucleus) and that the nucleus was charged.

aqueous

A substance dissolved in water. Shown as (aq) in chemical equations.

aqueous solution

The mixture made by adding a soluble substance to water.

atom

The smallest part of an element that can exist.

atomic model

A model to represent the structure of the atom. This model has been revised over time as new evidence has become available.

atomic number

The number of protons in an atom of an element.

boiling

The process that happens at the boiling point of a substance when the rate of evaporation is at its maximum.

boiling point

The temperature at which a substance changes from liquid to gas (evaporates). It is also the temperature at which a substance changes from gas to liquid (condenses).

charge

A property of a particle that causes it to experience a force in an electric field.

chemical formula

A series of chemical symbols showing the number of atoms of each element in a compound.

chemical reaction

A process that involves rearrangement of atoms to produce new substances.

chemical symbol

A letter or series of letters used to represent an element, e.g. C for carbon, Na for sodium.

chromatography

A technique used to separate substances based on their solubility in a particular solvent.

compound

A substance made up of two or more different elements chemically bonded together, e.g. water is a compound of hydrogen and oxygen.

conservation of mass

No atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants.

crystallisation

A separation technique used to obtain a sample of pure salt from a salt solution.

displacement reaction

A reaction in which a more reactive substance displaces a less reactive substance.

dissolve

To mix a solute with a solvent to form a solution.

electron

A particle with a relative charge of -1 and a very small relative mass. It orbits the nucleus of an atom or ion in energy levels (shells).

electronic structure

The number of electrons in each energy level (shell) of an atom, e.g. a sodium atom has an electronic structure of 2, 8, 1.

element

A substance made of only one type of atom.

energy level

The distance from the nucleus of an atom where electrons orbit. Also called a shell.

evidence

The available information or facts that either support or counter a scientific theory or hypothesis.

filtration

A technique used to separate substances that are insoluble in a particular solvent from those that are soluble in the solvent.

fractional distillation

A separation technique used to separate miscible liquids with different boiling points.

groups

A column of the periodic table that contains elements with similar chemical properties.

halogen

An element in Group 7 of the periodic table.

ion

A charged particle formed when an atom or molecule loses or gains one or more electrons.

isotopes

Atoms of the same element with different numbers of neutrons.

James Chadwick

The scientist who provided experimental evidence to show the existence of neutrons within the nucleus of an atom.

mass number

The total number of protons and neutrons in the nucleus of an atom.

melting

A change of state from solid to liquid.

melting point

The temperature at which a substance changes from solid to liquid (melts). It is also the temperature at which a substance changes from liquid to solid (freezes).

Mendeleev

The scientist who developed the periodic table. He left gaps for elements he predicted had not yet been discovered.

metal

An element that forms positive ions.

miscible

Liquids that dissolve in each other.

mixture

A substance consisting of two or more substances not chemically combined together, e.g. air is a mixture of nitrogen, oxygen, carbon dioxide and small amounts of other gases.

neutron

A particle with no charge found in the nucleus of the atom. It has the same mass as a proton.

Niels Bohr

The scientist who adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances.

noble gas

An unreactive gas found in Group 0 of the periodic table.

non-metal

An element that forms negative ions.

nuclear model

The model of the atom suggested by Rutherford. In this model, the mass of the atom is concentrated at the nucleus, which is positively charged.

nucleus (plural: nuclei)

The centre of the atom, consisting of protons and neutrons. It is positively charged.

outer shell

The energy level of an atom furthest from the nucleus.

periodic table

A table of all the known elements arranged in order of atomic number so that elements with similar properties are in columns, known as groups.

plum pudding model

Thomson's model of the atom that suggested that the atom is a ball of positive charge with negative electrons embedded in it.

product

A substance that is formed in a chemical reaction.

proton

A particle with a charge of +1 found in the nucleus of the atom. It has the same mass as a neutron.

radius

The distance from the centre to the circumference of a circle or sphere.

reactant

A substance that takes part in a chemical reaction.

reactivity

A measure of how reactive a substance is.

relative atomic mass (Ar)

The average mass of an atom of an element that takes into account the abundance of the isotopes of the element.

shell

The distance from the nucleus of an atom where electrons orbit. Also called an energy level.

simple distillation

A technique used to separate a solvent from a solution.

solute

The substance that dissolves in a solvent to make a solution. In salt water, this substance is the salt.

solution

A homogenous mixture of two or more substances, formed when a solute dissolves in a solvent. Salt water is an example.

solvent

The substance in which a solute dissolves. In salt water, this substance is the water.

symbol equation

An equation that uses the chemical formulae of the reactants and products to model a chemical reaction.

transition metal (chemistry only)

An element positioned in the central block of the periodic table, between Group 2 and Group 3.

word equation

An equation that uses only the names of the reactants and products to model a chemical reaction.