Periodic Table Trends and Properties: Atomic Radius, Electronegativity, and Ions

Atomic radius

Distance from the nucleus to the outermost electron.

Electronegativity

The ability of an atom to attract electrons in a bond.

Ionization energy

Energy needed to remove an electron from an atom.

Metallic character

How easily an element loses electrons; metals have high metallic character.

Metalloid

Element with properties of both metals and nonmetals (e.g., Si, Ge).

Nonmetal

Usually gains electrons in reactions; poor conductors.

Cation

Positive ion (atom loses electrons).

Anion

Negative ion (atom gains electrons).

Period trend (left → right)

Atomic radius decreases, electronegativity increases, ionization energy increases.

Group trend (top → bottom)

Atomic radius increases, electronegativity decreases, metallic character increases.

Group 1 (Alkali metals)

1 valence electron, react vigorously with water, form +1 ions.

Group 2 (Alkaline earth metals)

2 valence electrons, less reactive than Group 1.

Group 15

5 valence electrons, contains nonmetals, metalloids, metals.

Group 16

6 valence electrons, contains nonmetals and metalloids.

Allotropes

Same element, different structure, different properties (e.g., O2 and O3).

STP

Standard Temperature and Pressure (0°C, 1 atm).

Stable electron configuration

Full valence shell (noble gases).

Periodic Table Groups

Vertical columns with similar chemical properties.

Periodic Table Periods

Horizontal rows, trends across a period.

Metal properties

Malleable, ductile, good conductor of heat/electricity, reacts with oxygen.

Nonmetal properties

Brittle (if solid), poor conductor, gains electrons in reactions.

Electronegativity trend across a period

Increases left → right.

Electronegativity trend down a group

Decreases.

Ion radius trend

Cations smaller than atoms, anions larger than atoms.

Diatomic elements at STP

H2, N2, O2, F2, Cl2, Br2, I2.