How Ionic and Covalent Bonds Hold Atoms Together

Electrons occupy regions around an atom's nucleus. The electrons farthest from the nucleus are called valence electrons, and they play the largest role in chemical bonding. Atoms often become more stable when their outer electron arrangement resembles that of a noble gas.

This idea is sometimes taught as the octet rule, because many atoms become stable with eight electrons in their outer level. It is a helpful starting model, but it is not a perfect rule for every atom and compound. Hydrogen is stable with two outer electrons, and several elements form structures that do not fit a simple set of eight.

Bonding is not driven by atoms thinking about neat electron diagrams. The arrangement forms when the combined system has lower energy and is more stable than the separated particles. The simple electron model helps you predict the result without pretending atoms hold committee meetings.

In ionic bonding, one atom transfers one or more electrons to another. The atom that loses electrons becomes a positively charged ion, while the atom that gains electrons becomes a negatively charged ion. Opposite charges attract, holding the ions together.

Sodium chloride is a common example. A sodium atom can lose one outer electron, and a chlorine atom can gain one. The resulting sodium and chloride ions attract in a repeating three-dimensional lattice. A crystal of salt is therefore not made from separate little sodium chloride pairs lined up politely. It is a large organised structure of alternating ions.

Ionic substances often have high melting points because many strong attractions must be overcome. When melted or dissolved in water, their ions can move and may carry electric current. In a solid crystal, the ions are fixed in place and cannot flow freely.

In covalent bonding, atoms share pairs of electrons. The shared electrons are attracted to more than one nucleus, helping hold the atoms together. Two hydrogen atoms can share a pair to form hydrogen gas, while oxygen atoms can share two pairs in an oxygen molecule.

Water contains covalent bonds between oxygen and hydrogen. The sharing is unequal because oxygen attracts the shared electrons more strongly. This gives different parts of the molecule slight charges and helps explain many of water's unusual properties.

Compare the basic patterns:

• •Ionic bonding transfers electrons.
• •Covalent bonding shares electrons.
• •Ionic bonds create charged ions.
• •Covalent bonds often create molecules.
• •Both arrangements can lower the system's energy.

Chemical bonds form through the behaviour of outer electrons. Ionic bonding creates attracting positive and negative ions, while covalent bonding holds atoms together through shared electrons. Learn the electron story first, and formulas begin to describe a pattern instead of a pile of symbols.