High melting and boiling points
Both 4s and 3d electrons join the bond
1. General properties: mass, radius and metallic property
2. Two places apart
Calcium melts at 842 °C. Titanium, two places later in period 4, melts at 1680 °C.
Pick the right answer
Predict: what makes titanium's metallic bond so much stronger?
- A. Its atoms are heavier
- B. More of its electrons join the metallic bond
- C. Only its 4s electrons bond, just like calcium's
الشرح
More of titanium's electrons join the metallic bond: the book says both the 4s and the 3d electrons share in it. Calcium has no 3d electrons, so its bond uses its 4s electrons and is weaker.
3. The melting point column
| Element (period 4) | Melting point (°C) |
|---|---|
| K | 63 |
| Ca | 842 |
| Sc | 1397 |
| Ti | 1680 |
| V | 1710 |
| Cr | 1890 |
| Mn | 1247 |
| Fe | 1538 |
| Co | 1490 |
| Ni | 1492 |
| Cu | 1083 |
Book point 3b: the transition elements have high melting and boiling points.
See both columns from the book
| Element | Melting point (°C) | Boiling point (°C) |
|---|---|---|
| Sc | 1397 | 3900 |
| Ti | 1680 | 3130 |
| V | 1710 | 3530 |
| Cr | 1890 | 2480 |
| Mn | 1247 | 2087 |
| Fe | 1538 | 2800 |
| Co | 1490 | 3520 |
| Ni | 1492 | 2800 |
| Cu | 1083 | 2582 |
4. Which electrons bond?
↑↓
4s3d
↑↓
4s↑↑
3dCalcium has only its two 4s electrons for the metallic bond. In titanium, both the 4s and the 3d electrons share in it.
More bonding electrons make a strong metallic bond, so more heat is needed to melt it.
5. Switch on the 3d electrons
A model of a titanium crystal. Switch the 3d electrons on and off. The atoms stay the same mass.
3d electrons in the bond (0 = off, 1 = on) 0
bonding electrons per Ti atom 2
6. Not about heavy atoms
| Element | Atomic mass | Melting point (°C) |
|---|---|---|
| Cr | 52 | 1890 |
| Cu | 63.5 | 1083 |
7. A student's claim
Pick the right answer
A student says: "Scandium (45) melts higher than calcium (40) because scandium is heavier." Which reply fits the book?
- A. Scandium's 3d electron joins its 4s electrons in the metallic bond, so the bond is stronger
- B. Agree: heavier atoms always melt higher
- C. Scandium has more 4s electrons than calcium
الشرح
The reply that fits the book: scandium's 3d electron joins its 4s electrons in the metallic bond, so its bond is stronger than calcium's, which uses 4s electrons. Being heavier is not the reason.
True or false?
In the transition metals, only the 4s electrons take part in the metallic bond.
الشرح
Book point 3b: the strong metallic bond forms by sharing both 4s and 3d electrons.
8. Write the reason
Fill in the blanks
Transition elements have high melting points due to the strong _____ bond, formed by sharing both 4s and _____ electrons.
الشرح
Book point 3b: the strong metallic bond is formed by sharing both 4s and 3d electrons.
Need a hint?
- The bond holds metal atoms together.
- Write titanium's configuration: [Ar] … Which sublevel appears after 4s?
9. Summary
- The first transition elements have high melting and boiling points.
- Reason: a strong metallic bond, formed by sharing both 4s and 3d electrons.
- Potassium and calcium have only 4s electrons to bond, so they melt much lower.
- Heavy atoms are not the reason: Cu is heavier than Cr but melts lower.
Back to the hook: can you explain why titanium melts so much higher than calcium?
Reveal
| Element | Electrons in the metallic bond | Melting point (°C) |
|---|---|---|
| Ca | 2 (4s only) | 842 |
| Ti | 4 (4s and 3d) | 1680 |
Calcium has only its two 4s electrons for the metallic bond. In titanium both the 4s and the 3d electrons share in it, so its metallic bond is stronger and more heat is needed to melt it.