Periodic table notes

Atom

The basic unit of matter, consisting of a nucleus surrounded by electrons in shells.

Molecule

A group of two or more atoms bonded together, representing the smallest unit of a chemical compound.

Isotopes

Species with the same number of protons but different numbers of neutrons.

Protons

Positively charged particles found in the nucleus that determine the atomic number.

Neutrons

Neutrally charged particles located in the nucleus that contribute to the mass number.

Electrons

Negatively charged particles that orbit the nucleus in energy levels.

Atomic number

The number of protons in the nucleus of an atom, defining the element.

Mass number

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

Relative atomic mass (A_r)

The weighted average mass of an atom of an element relative to 1/12th the mass of a carbon-12 atom.

Periodic Table

A tabular arrangement of elements ordered by increasing atomic number.

Groups

Vertical columns in the Periodic Table where elements have similar chemical properties.

Periods

Horizontal rows in the Periodic Table where the number of protons increases across the row.

Electron configuration

The arrangement of electrons in shells around the nucleus of an atom.

Metals

Elements that generally conduct electricity well and are found on the left side of the Periodic Table.

Non-metals

Elements that do not conduct electricity well and are found on the right side of the Periodic Table.

Amphoteric oxides

Oxides that can react with both acids and bases, such as aluminum oxide.

Valence electrons

Electrons in the outermost shell that determine an element's chemical properties.

Alkali metals

Highly reactive metals in Group 1 that lose one electron to form +1 ions.

Halogens

Elements in Group 7 that gain one electron to form -1 ions.

Noble gases

Unreactive gases in Group 0 or 18 with complete outer electron shells, making them stable.