PERIODIC TRENDS

Periodic Table

An organized map of all known elements.

Basis of the Periodic Table

Atomic number and electron configuration of elements.

Purpose of the Periodic Table

Allows scientists and chemists to predict elements’ properties, behavior, and reactivity.

Periods

The 7 horizontal rows of the periodic table.

Groups or Families

The 18 vertical columns of the periodic table.

Bohr’s Diagram

A model with a nucleus in the middle, surrounded by electrons in specific energy levels.

Principal Quantum Number (n)

The highest principal energy level containing electrons.

Energy Level

Another name for the principal number.

Groups and Families — Similar Properties

Elements in the same group share similar physical and chemical properties because they have the same number of valence electrons.

Group 1

Alkali metals with 1 valence electron.

Group 2

Alkaline earth metals with 2 valence electrons.

Metallic Character Across a Period

Decreases from left to right.

Periodic Trends

Predictable patterns in element properties across a period or down a group.

Nuclear Charge

The positive charge of the nucleus determined by the number of protons.

Nuclear Charge Across a Period

Increases as protons are added, pulling electron shells closer.

Electron Shielding

Inner electron shells reduce the effective pull of the nucleus on valence electrons.

Atomic Radius

The distance from the center of an atom’s nucleus to its outermost electron shell.

Atomic Radius Across a Period

Decreases from left to right because increasing nuclear charge pulls electrons closer.

Atomic Radius Down a Group

Increases because new electron shells increase the distance from the nucleus.

Ionization Energy (IE)

The energy required to remove an electron from a gaseous atom.

Ionization Energy Across a Period

Increases from left to right because atoms hold electrons more tightly.

Ionization Energy Down a Group

Decreases because valence electrons are farther from the nucleus and more shielded.

Electronegativity

An atom’s ability to attract shared electrons in a chemical bond, measured on the Pauling scale.

Most Electronegative Element

Fluorine.

Electronegativity Across a Period

Generally increases from left to right, excluding noble gases.

Electronegativity Down a Group

Generally decreases from top to bottom.

Metallic Character

How readily an atom loses electrons to form positive ions (cations).

Strong Metallic Character

Associated with low ionization energy and low electronegativity.

Metallic Character Across a Period

Decreases from left to right; metals tend to lose electrons while nonmetals tend to gain electrons.

Metallic Character Down a Group

Increases because electrons farther from the nucleus are easier to lose.

Cation

A positive ion formed when an atom loses electrons.

Anion

A negative ion formed when an atom gains electrons.

Two Major Factors Driving Periodic Trends

Nuclear charge and electron shielding.