The Periodic Table

Periodicity

Refers to trends in properties of elements across a period and down a group.

Alkali metals

Group 1 elements that are soft, highly reactive, and have low melting points.

Alkaline earth metals

Group 2 elements that are harder and less reactive than alkali metals.

Transition metals

Groups 3-12 elements that have unique properties and are found in the d-block.

Halogens

Group 17 elements that are very reactive non-metals needing one electron to complete their octet.

Noble gases

Group 18 elements that are inert due to having a full valence shell.

Lanthanides and actinides

F-block elements usually displayed separately at the bottom of the periodic table.

S-block

Includes groups 1-2; elements whose valence electrons occupy an s sublevel.

P-block

Includes groups 13-18; elements with valence electrons in p orbitals.

D-block

Contains transition metals; made up of elements with electrons in d orbitals.

F-block

Includes lanthanides and actinides; elements with outer electrons in f orbitals.

Effective nuclear charge

Increases across a period, affecting the attraction of outer electrons.

Atomic radius

Decreases across a period due to increasing nuclear charge.

Ionization energy

Energy needed to remove an electron; increases across a period and decreases down a group.

Electron affinity

Energy change when an electron is added to a gaseous atom; usually negative for the first addition.

Electronegativity

An atom's ability to attract electrons in a covalent bond.

Cations

Positively charged ions formed by metals losing electrons.

Anions

Negatively charged ions formed by non-metals gaining electrons.

Ionic bonds

Formed when electronegativity difference (ΔEN) is greater than 1.8.

Covalent bonds

Formed when ΔEN is less than 1.8; polar covalent bonds fall between 0.5 and 1.8.

Transition metals colors

Transition metals form colored complexes due to partially filled d-orbitals.

Reactivity trend in alkali metals

Increases down the group due to decreasing ionization energy.

Reactivity trend in halogens

Decreases down the group for reduction reactions.

Oxides across periods 2 & 3

Range from basic (Na₂O) to acidic (SO₂) across a period.

Acidic oxides

Produce low pH solutions in water; character increases across a period.

Metalloid

Elements with properties between metals and non-metals, e.g., silicon.

Phase changes of halogens

Increase with size: F₂ (gas), Cl₂ (gas), Br₂ (liquid), I₂ (solid).

Bonding behavior

Based on the drive to achieve a complete outer shell (octet).

Metals vs Non-metals

Metals lose electrons (form cations); Non-metals gain/share electrons (form anions).

Orbital filling

Periodic table blocks indicate types of orbitals being filled: s, d, p, f.

Intermolecular forces

Weak forces between non-metals in simple molecular structures, leading to low melting points.

Giant covalent structure

High melting point and brittleness, e.g., silicon.