Glossary
Anions
Negatively charged ions formed when an atom gains one or more electrons.
Example:
A sulfide ion (S2-) is an anion that is larger than a neutral sulfur atom because it has gained electrons, increasing electron-electron repulsion.
Atomic Radius
The distance from the nucleus to the outermost electron shell of a neutral atom.
Example:
Cesium has a much larger atomic radius than lithium because it has more electron shells.
Cations
Positively charged ions formed when an atom loses one or more electrons.
Example:
When a magnesium atom loses two electrons, it forms a Mg2+ cation, which is smaller than the neutral magnesium atom.
Effective Nuclear Charge (Zeff)
The net positive charge experienced by an electron in an atom, accounting for the shielding effect of inner electrons.
Example:
As you move from left to right across a period, the increasing effective nuclear charge pulls the valence electrons closer, reducing atomic size.
Electronegativity
The ability of an atom to attract electrons towards itself in a chemical bond.
Example:
Oxygen has a high electronegativity, causing it to strongly pull shared electrons towards itself in a water molecule, creating a polar bond.
Groups (Columns)
Vertical columns on the periodic table where elements share the same number of valence electrons, leading to similar chemical properties.
Example:
Elements in Group 1, like lithium and cesium, are alkali metals and all have one valence electron, making them highly reactive.
Ionic Radius
The distance from the nucleus to the outermost electron shell of an ion.
Example:
The ionic radius of a chloride ion (Cl-) is larger than that of a neutral chlorine atom due to increased electron-electron repulsion.
Periods (Rows)
Horizontal rows on the periodic table where elements share the same number of electron shells.
Example:
All elements in the fourth period, such as potassium and bromine, possess four occupied electron shells.