Covalent vs Ionic Bond

Quick Answer

A covalent bond is sharing of electrons between atoms. An ionic bond is transfer of electrons followed by electrostatic attraction.

What Each One Really Means

The easiest way to remember the difference is to ask: are the atoms sharing or giving? In a covalent bond, two atoms share a pair of electrons. Neither one fully owns the electrons. They hold on together. In an ionic bond, one atom gives electrons away completely and the other takes them. The result is two ions, one positive and one negative, and they stick together because opposite charges attract. Now, the rule of thumb most textbooks give is metals bond ionically with non-metals, and non-metals bond covalently with non-metals. That works most of the time, but not always. The real deciding factor is electronegativity difference. If the difference is large, the bond is ionic. If it is small, the bond is covalent. In between, it is polar covalent, which is a whole topic on its own. Here is what I tell my students. Do not just memorise the metal and non-metal rule. Understand that it is a shortcut. If you want the true test, look at the electronegativity values. But for secondary school exams, the shortcut will usually serve you well. Also remember that covalent compounds tend to have low melting points and do not conduct electricity, because there are no free ions. Ionic compounds have high melting points and conduct electricity when molten or dissolved, because the ions are free to move. That practical difference is often what examiners are testing.

Side-by-Side Comparison

Memory Device

Covalent means co-owning. Ionic means one gives and one receives.

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