What is What is a single covalent bond??

One shared pair of electrons between two atoms

Covalent Bonding — GCSE Chemistry Revision

The basics

The Art of Sharing

📖 The Art of Sharing

Imagine two people who each have half a pizza. Neither has enough for a full meal. But if they sit together and share, they can BOTH enjoy a complete pizza by taking slices from both halves! That's a useful starting image for covalent bonding — but with an important difference: in H₂ the sharing really is equal, like two identical halves. In molecules like HCl or H₂O, one atom attracts the shared electrons more strongly than the other, so the "pizza" is tilted — both atoms still count the shared electrons, but they are not evenly distributed. This unequal sharing is the basis of polarity, which you will meet in later topics.

🧲 Bilateral Attraction

What actually holds a covalent bond together is simultaneous attraction from two nuclei. When two non-metal atoms are close enough, both positive nuclei attract the same pair of electrons at the same time. The shared electron pair sits between both nuclei, pulled toward each simultaneously. Neither atom "owns" the electrons outright — both nuclei exert a continuous pull on them. This dual attraction is what creates the bond. The stronger each nucleus's pull on electrons (electronegativity), the more the shared pair tilts toward that atom.

We've seen how metals give electrons to non-metals in ionic bonding. But what happens when TWO non-metals meet? Both nuclei have a strong pull on electrons. Neither will donate electrons to the other, because both are attracted to electrons strongly enough to hold onto them.

The result is not a compromise between competing desires — it is simultaneous attraction. Both nuclei can hold onto the same shared pair of electrons at the same time. The shared electrons sit between the two nuclei and are attracted to both of them at once. This bilateral attraction — two nuclei pulling on the same electron pair — is what holds the atoms together and constitutes the covalent bond.

Take hydrogen (H₂) as the simplest example. Each hydrogen atom has just 1 electron, but needs 2 to fill its outer shell. When two hydrogen atoms approach each other, they each contribute their single electron to a shared pair. Now both atoms can "claim" 2 electrons — the shared pair belongs to both of them. This shared pair of electrons IS the covalent bond.

The key insight: In covalent bonding, electrons are SHARED, not transferred. Neither atom becomes an ion — they stay neutral. They form a MOLECULE — a distinct particle with a fixed number of atoms held together by covalent bonds.

And here's something crucial for understanding properties: the covalent bonds within a molecule are incredibly strong. But the forces BETWEEN different molecules are very weak. This is why water (covalent molecules) boils at just 100°C, while salt (ionic lattice) needs 801°C to melt!

What is a covalent bond?: A shared pair of electrons between two non-metal atoms

Key terms

Chemistry glossary

What is a covalent bond?: A shared pair of electrons between two non-metal atoms
What is a single covalent bond?: One shared pair of electrons between two atoms

Spotlight

Understanding Different Types of Covalent Bonds

Single, Double, and Triple Bonds:

Exam tip

Earn the mark scheme marks

🧠 Memory Aids

CO-valent = CO-operate = SHARE: The "co" prefix means "together" — co-operative means working together. Covalent bonds work by atoms cooperating (sharing), not by one taking from the other.

Number of bonds from the periodic table:

Group 4 (C, Si) → 4 bonds (need 4 to reach 8)
Group 5 (N, P) → 3 bonds (need 3 to reach 8)
Group 6 (O, S) → 2 bonds (need 2 to reach 8)
Group 7 (F, Cl) → 1 bond (need 1 to reach 8)
Group 1 (H) → 1 bond (need 1 to reach 2)

Dot-cross rule: "No brackets for covalent, only overlap" — covalent diagrams use overlapping circles without square brackets. Brackets and charges are only for ionic compounds.