Science Test Revision

Element

A pure substance made of one type of atom.

Atom

The smallest unit of an element.

Proton

A subatomic particle with a +1 charge located in the nucleus.

Neutron

A subatomic particle with 0 charge located in the nucleus.

Electron

A subatomic particle with a -1 charge located around the nucleus.

Atomic number (Z)

The number of protons in an atom.

Mass number (A)

The sum of protons and neutrons in an atom.

Isotopes

Atoms of the same element that have different numbers of neutrons.

Ions

Charged atoms, which can be cations (positive) or anions (negative).

Cations

Positively charged ions that have lost electrons.

Anions

Negatively charged ions that have gained electrons.

Periodic Table

A table arranging elements by increasing atomic number.

Group

Columns in the periodic table that indicate similar chemical properties.

Period

Rows in the periodic table corresponding to the number of electron shells.

Alkali metals

Elements in Group 1, characterized by +1 ions and high reactivity.

Halogens

Group 17 elements that form -1 ions and are diatomic.

Noble gases

Group 18 elements that are unreactive and found in the atmosphere.

Transition metals

Elements in Groups 3–12, known for their hardness and high melting points.

Electron Shells

Concentric regions around the nucleus where electrons are found.

Maxwell–Boltzmann distribution

Describes the distribution of energies among particles in a substance.

Chemical Symbol

A one or two-letter representation of an element.

Coefficient

A number placed before a chemical formula to indicate the number of molecules.

Subscript

A small number in a chemical formula indicating the number of atoms of an element.

Precipitation reaction

A reaction where two aqueous solutions form a solid.

Solubility rules

Guidelines to determine the solubility of compounds in water.

Stoichiometry

The calculation of reactants and products in chemical reactions.

Collision theory

A theory stating that reactions occur when particles collide with sufficient energy and proper orientation.

Activation energy

The minimum energy required for a reaction to occur.

Exothermic reaction

A reaction that releases energy, resulting in lower energy products.

Endothermic reaction

A reaction that absorbs energy, resulting in higher energy products.

Rate of reaction

The speed at which a reactant is consumed or a product is formed.

Catalyst

A substance that increases the rate of a reaction without being consumed.

Chemical equation

A representation of a chemical reaction using symbols and formulas.

Acid-base reaction

A reaction where an acid reacts with a base to produce salt and water.

Combustion reaction

A reaction where a substance combines with oxygen to produce energy, CO₂, and H₂O.