Why do atoms stick together?
Ever wondered why table salt doesn’t fall apart in your shaker? The answer lies in chemical bonding – the invisible glue that holds atoms together.
In simple words, an ionic bond is like a game of give‑and‑take: one atom hands over an electron, the other receives it, and they become attracted. A covalent bond is more like sharing a pizza: two atoms share electrons so both get a tasty bite.
Ionic Bonding – The Electron Transfer Party
What is an ion?
An ion is an atom that has gained or lost electrons, giving it a net electric charge. Lose electrons, become positive (cation). Gain electrons, become negative (anion).
How does an ionic bond form?
Think of a metal atom as a generous neighbour who easily gives away a marble (electron). A non‑metal neighbour loves collecting marbles. When the metal hands over the marble, both become charged and pull each other together like opposite poles of a magnet.
Classic example: Sodium chloride (NaCl)
Sodium (Na) has one valence electron it wants to lose. Chlorine (Cl) needs one electron to fill its outer shell. Na gives its electron to Cl, becoming Na⁺ and Cl⁻. Their opposite charges snap together, forming the familiar salt crystal.
Covalent Bonding – The Electron‑Sharing Club
What is a covalent bond?
A covalent bond is when two non‑metal atoms share one or more pairs of electrons so each can enjoy a full outer shell. It’s like two friends sharing a single pizza slice; each gets a bite, and both stay happy.
Single, double, and triple bonds
- Single bond: one pair of electrons shared (e.g., H₂).
- Double bond: two pairs shared (e.g., O₂).
- Triple bond: three pairs shared (e.g., N₂).
Why do atoms share?
Atoms with similar electronegativity – the tendency to attract electrons – find it easier to share than to steal. When the pull is almost equal, sharing wins.
Key Differences at a Glance
| Feature | Ionic Bond | Covalent Bond |
|---|---|---|
| Typical participants | Metal + non‑metal | Non‑metal + non‑metal |
| Electron movement | Transfer (complete loss/gain) | Sharing (partial) |
| Resulting particles | Oppositely charged ions | Neutral molecules |
| Physical state at room temp. | Usually solid, high melting point | Gases, liquids or low‑melting solids |
| Electrical conductivity | Conducts when molten or dissolved | Generally poor conductor |
Quick Summary
- Ionic bonds form by full electron transfer, creating charged ions that attract.
- Covalent bonds form by sharing electron pairs, keeping atoms neutral.
- Electronegativity difference decides which type is likely.
- Properties (melting point, conductivity) differ because of the bond type.
📝 Likely Exam Questions
- Explain why NaCl has a high melting point.
Answer: NaCl is ionic; strong electrostatic forces between Na⁺ and Cl⁻ require a lot of energy to break, giving a high melting point. - Write the electron‑dot structures for H₂O and CO₂ and identify the type of bonds present.
Answer: H₂O has two single covalent bonds (O shares one electron with each H). CO₂ has two double covalent bonds (C shares two pairs with each O). - How does electronegativity difference influence bond type?
Answer: A large difference (>1.7) usually leads to electron transfer → ionic bond. A small difference leads to sharing → covalent bond. - Describe one property that distinguishes ionic compounds from covalent molecules.
Answer: Ionic compounds conduct electricity when melted or dissolved because ions are free to move; covalent molecules generally do not conduct. - Give an example of a compound that has both ionic and covalent characters and explain.
Answer: Aluminum chloride (AlCl₃) in solid form shows covalent character due to high charge density on Al³⁺, but in molten state it behaves ionically. This dual nature arises from the balance of charge and size.