Chemical Bonds: Ionic and Covalent

Learning Objectives

Explain why atoms form chemical bonds.

Distinguish between an ionic bond and a covalent bond.

Describe how ions are formed by the gain or loss of electrons.

Explain the difference between a single, double, and triple covalent bond.

How Atoms Stick Together

Most atoms in the universe are not found by themselves. They are usually joined together with other atoms. A chemical bond is the force of attraction that holds atoms together in a molecule or compound.

Why Do Atoms Bond? The Octet Rule

Atoms form bonds to become more stable. For most of the elements we will study, an atom is most stable when it has a full outer shell of 8 valence electrons. (Remember, valence electrons are the electrons in the outermost energy level). This is called the octet rule ('octet' means a group of eight).

The atoms in Group 18, the noble gases, already have 8 valence electrons. This is why they are very stable and unreactive. Other atoms will gain, lose, or share electrons with other atoms in order to achieve a stable, noble gas configuration. This gaining, losing, or sharing is what creates chemical bonds.

There are two main types of chemical bonds: ionic and covalent.

Ionic Bonds: The Great Electron Transfer

An ionic bond is formed when one or more electrons are transferred from one atom to another. This type of bond typically forms between a metal and a nonmetal.

1.Ion Formation:

The metal atom loses one or more of its valence electrons. When an atom loses a negative electron, it becomes a positively charged ion, called a cation.

The nonmetal atom gains those electrons. When an atom gains a negative electron, it becomes a negatively charged ion, called an anion.

2.Attraction: Now we have a positive ion and a negative ion. Opposite charges attract! The strong electrostatic attraction between the cation (+) and the anion (-) is the ionic bond.

Example: Sodium Chloride (NaCl), or table salt. Sodium (Na), a metal, gives its one valence electron to Chlorine (Cl), a nonmetal. This makes a Na⁺ ion and a Cl⁻ ion. These oppositely charged ions are then strongly attracted to each other.

Covalent Bonds: The Art of Sharing

A covalent bond is formed when two atoms share one or more pairs of valence electrons. This type of bond typically forms between two nonmetal atoms.

By sharing electrons, each atom can achieve a stable outer shell. The shared pair of electrons orbits the nuclei of both atoms, holding them together. A group of atoms held together by covalent bonds is called a molecule.

Single Bond: One pair of electrons is shared (e.g., in H₂ or H₂O).

Double Bond: Two pairs of electrons are shared (e.g., in O₂ or CO₂).

Triple Bond: Three pairs of electrons are shared (e.g., in N₂).

Example: Water (H₂O). Oxygen needs two more electrons to have a full shell. Each hydrogen atom needs one more. The oxygen atom shares one electron with each of the two hydrogen atoms, forming two single covalent bonds.

Key Terms

**Chemical Bond: The force of attraction that holds atoms together.
**Valence Electrons: The electrons in the outermost shell or energy level of an atom.
**Octet Rule: A chemical rule of thumb that states that atoms tend to bond in such a way that they each have eight electrons in their valence shell, giving them the same electronic configuration as a noble gas.
**Ionic Bond: A chemical bond formed through the transfer of one or more electrons from a metal to a nonmetal, creating oppositely charged ions that attract each other.
**Covalent Bond: A chemical bond formed when two nonmetal atoms share one or more pairs of valence electrons.
**Ion: An atom or molecule with a net electric charge due to the loss or gain of one or more electrons.
**Molecule: A group of two or more atoms held together by covalent bonds.