Chemistry Notes

Atomic Theory

Modern atomic theory states that all matter is made up of atoms.

Subatomic particles

Atoms are composed of protons (+), electrons (-), and neutrons (neutral).

Atomic number

The atomic number is equal to the number of protons in the nucleus and dictates what the element is.

Neutral atom

A neutral atom has the same number of protons and electrons.

Atomic mass

The atomic mass is the combined number of protons and neutrons in an atom's nucleus.

Particle

A particle can refer to any small unit of matter, including atoms, molecules, compounds, and ions.

Ion

An ion is a positively or negatively charged particle, having more protons than electrons (+) or more electrons than protons (-).

Cation

A positive ion, which has more protons than electrons.

Anion

A negative ion, which has gained electrons, thus becoming more negatively charged.

Octet rule

Atoms strive to have eight valence electrons for stability.

Chemical reaction

A process that leads to the chemical transformation of one set of chemical substances into another.

Synthesis reaction

A reaction where two or more reactants combine to create one new substance.

Decomposition reaction

A reaction where a compound breaks down into simpler substances.

Single replacement

A reaction where one element replaces another in a compound.

Double replacement

A reaction where ions from two compounds exchange places to form new compounds.

Combustion reaction

A rapid reaction with oxygen, always resulting in carbon dioxide and water, usually releasing heat and light.

Acid-base reaction

A reaction between an acid and a base where hydrogen ions are exchanged.

Isotopes

Two of the same element with different masses due to a different number of neutrons.

Mass number

The total number of protons and neutrons in an atom.

Bohr diagram

A model showing the arrangement of electrons surrounding the nucleus of an atom.

Chemical symbol

A one or two-letter representation of an element, always beginning with a capital letter.

Physical change

A change that alters appearance or state but does not change the substance's chemical identity.

Chemical change

A change at the molecular level that alters the nature and properties of a substance, forming a new substance.

Balancing equations

Adjusting the coefficients in a chemical equation to ensure the number of atoms on both sides are equal.

Stoichiometry

The study of the quantitative relationship between reactants and products in a chemical reaction.

Mole

A unit used to measure the amount of a substance, containing exactly 6.022 x 10²³ elementary entities.

Avogadro’s number

The number of particles in one mole, which is 6.022 x 10²³.

Molar mass

The mass of one mole of a substance, found by adding the atomic masses of all the elements in the compound.

Covalent bonding

A type of bonding where two atoms share electrons to achieve stability.