Periodic Trends: Valence Electrons, Radius, Ionization Energy, and Electronegativity

Vocabulary flashcards covering key periodic trends: valence electrons, atomic radius, ionization energy, and electronegativity.

Valence electrons

Electrons in the outermost energy level (usually in the S and P subshells) that participate in bonding; main-group elements tend to have up to eight valence electrons.

Octet rule

Atoms tend to have eight valence electrons in their outer shell to achieve stability.

Atomic radius

One-half the distance between the nuclei of two identical atoms; trend: decreases across a period, increases down a group.

Shielding effect

Inner electron shells shield outer electrons from the full positive charge of the nucleus, reducing the effective nuclear charge felt by valence electrons; shielding increases down a group.

Nuclear charge

The total positive charge of the nucleus (equal to the number of protons); higher nuclear charge pulls electrons more strongly.

Ionization energy

Energy required to remove the most loosely bound electron from a gaseous atom; trend: increases across a period, decreases down a group.

Electronegativity

Ability of an atom to attract electrons in a chemical bond; trend: increases across a period, decreases down a group; noble gases have little or no electronegativity.

Noble gases

Group 18 elements with full valence shells; generally unreactive and have very low electronegativity.

Period

A horizontal row in the periodic table; properties change gradually across the row.

Group

A vertical column in the periodic table; elements in a group have similar valence electron configurations and chemical properties.

Outer energy level

The electron shell farthest from the nucleus that contains the valence electrons.

S and P subshells

Valence electrons reside in the outermost S and P subshells (e.g., ns2 and np6 configurations).

Across a period trend

Across a period, nuclear charge increases with more protons, pulling electrons closer and typically decreasing atomic radius while increasing ionization energy and electronegativity.

Down a group trend

Going down a group adds electron shells, increasing atomic radius and typically lowering ionization energy and electronegativity due to shielding.

Electron shielding

Another term for shielding effect; inner electrons block the nucleus' pull on outer electrons.