Periodic Trends

Dmitri Mendeleev

Russian chemist who created the first periodic table organized by atomic mass.

Henry Mosley

Updated the periodic table to be organized by atomic number.

Periodic Law

Elements arranged by atomic number exhibit periodic repetition of chemical and physical properties.

Periods

Horizontal rows in the periodic table.

Groups

Vertical columns in the periodic table.

Representative Elements

Elements in the s and p orbitals.

Metals

Found on the left side of the periodic table, characterized by high electrical conductivity and luster.

Non-metals

Found on the right side of the periodic table, non-lustrous and poor conductors.

Metalloids

Elements showing properties of both metals and non-metals, located on the stair step of the periodic table.

Alkali Metals

Group 1A, the most reactive elements.

Alkaline Earth Metals

Group 2A elements.

Transition Metals

A category of metals including inner transition metals and other metals.

Lanthanide Sequence

The top row of the inner transition metals.

Actinide Sequence

The bottom row of the inner transition metals.

Halogens

Group 7A, the most reactive non-metals.

Noble Gases

The last column of the periodic table, very unreactive due to a full outer ring of electrons.

Effective Nuclear Charge (ENC)

The attraction between electrons and the positively charged nucleus.

Electron Shielding

The repulsion that occurs due to like charges, increasing down a group and constant across a period.

Atomic Size

Increases down a group and right to left across a period.

Valence Electrons

Increase from left to right across a period and remain constant down a group.

Cation

A positively charged atom.

Anion

A negatively charged atom.

Oxidation Number

The charge an element has after becoming an ion.

Ion Size

Follows the same trend as atomic size; anions are larger than cations due to increased electron repulsion.

Ionization Energy

The energy required to remove an electron from an atom, increasing up a group and left to right across a period.

Electronegativity

The tendency of an atom to attract an electron when forming bonds, increasing up a group and left to right across a period, with noble gases having an electronegativity of 0.