# How do valence electrons affect the properties of atoms?

Jan 22, 2014

Valence electrons determine whether an atom forms cations, anions, or covalent compounds.

#### Explanation:

Atoms with:

• One to three valence electrons — tend to form positive ions.
• Five to seven valence electrons — tend to form negative ions.
• Four valence electrons — form covalent bonds

The number of electrons in an atom's outermost valence shell governs its chemical properties.

Elements react to form a closed shell, corresponding to the electron configuration ${s}^{2} {p}^{6}$.

This tendency is called the octet rule, because the atoms have eight valence electrons.

METALS

The most reactive metallic elements are metals from Group 1 (e.g., $\text{Na}$ or $\text{K}$) or Group 2 (e.g., $\text{Mg}$ or $\text{Ca}$).

These elements can lose one or two valence electrons to form a positive ion with an ${s}^{2} {p}^{6}$ configuration.

NONMETALS

The most reactive nonmetals are in Groups 17 (e.g., $\text{F}$ and $\text{Cl}$) and 16 (e.g., $\text{O}$).

They need only one or two additional valence electrons to form a negative ion with an ${s}^{2} {p}^{6}$ configuration.

GROUP 14 ELEMENTS

Elements in Group 14 (e.g., $\text{C}$ and $\text{Si}$) have four valence electrons. They would have to gain or lose four electrons to form stable ions.

This requires too much energy.

Instead, they gain their octets by sharing electrons in covalent bonds with other nonmetals (e.g., ${\text{CH}}_{4}$ or ${\text{SiCl}}_{4}$).