Year 9 Science · Unit 2 · Lesson 9
Foundation Worksheet
Learning Goals
Match each term to its meaning
Write the letter of the matching meaning in the middle column.
| Term | Letter | Meaning |
|---|---|---|
| Covalent bond | A. Two shared pairs of electrons between the same two atoms, as in O=O. | |
| Double bond | B. A weak attraction between separate molecules. | |
| Intermolecular force | C. Atoms joined by covalent bonds in one continuous 3D network, with no separate molecules, as in diamond. | |
| Triple bond | D. One shared pair of electrons between two atoms, as in H–H. | |
| Giant covalent structure | E. Three shared pairs of electrons between the same two atoms, as in N≡N. | |
| Single bond | F. Two non-metal atoms sharing a pair of electrons so that both reach a full outer shell. |
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
In the H–H bond, each hydrogen atom provides one electron to the shared pair.
Correct it:
A water molecule (H₂O) contains one double bond.
Correct it:
Diamond has a very low melting point because carbon is a non-metal.
Correct it:
Nitrogen gas (N₂) contains a triple bond: three shared pairs between the two nitrogen atoms.
Correct it:
Simple molecules like CO₂ and H₂O have high melting points because their covalent bonds are very strong.
Correct it:
1. Explain how a covalent bond forms between two hydrogen atoms. What does each atom give, and what does each atom gain?
2. Draw dot-and-cross diagrams, showing outer-shell electrons only, for (a) hydrogen chloride, HCl, and (b) methane, CH₄. Hints: H has 1 outer electron, Cl has 7 and C has 4.
Scenario: six covalent substances
Every substance in Table 1 has its atoms held together by covalent bonds, yet their melting points differ by thousands of degrees.
| Substance | Formula | Melting point (°C) |
|---|---|---|
| Hydrogen chloride | HCl | −114 |
| Silicon dioxide (quartz) | SiO₂ | 1713 |
| Methane | CH₄ | −182 |
| Glucose | C₆H₁₂O₆ | 146 |
| Diamond | C | above 3500 |
| Water | H₂O | 0 |
Source: data book values.
3. Which substances in Table 1 are already melted (liquid or gas) at a room temperature of 25 °C? Which two are giant covalent structures?
4. Diamond and methane both contain carbon joined to other atoms by strong covalent bonds. Explain the key structural difference that makes diamond’s melting point thousands of degrees higher.
5. Dry ice is solid carbon dioxide. It turns straight into a gas at −78.5 °C, so it is used to keep vaccines cold in transport. A student says: “When dry ice turns to gas, the CO₂ molecules break apart.” Explain why this is wrong and what actually happens.