# High melting and boiling points

> Both 4s and 3d electrons join the bond


## Objectives

- Read the melting and boiling point columns of the book's table (for illustration only).
- Explain the high values: a strong metallic bond formed by sharing both 4s and 3d electrons.
- Contrast with potassium and calcium, where only 4s electrons take part, and reject the 'heavy atoms' idea.

## 1. General properties: mass, radius and metallic property




## 2. Two places apart

Predict: what makes titanium's metallic bond so much stronger?

- Its atoms are heavier
- Only its 4s electrons bond, just like calcium's
- More of its electrons join the metallic bond ✓

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.

[ar-EG] الـ titanium عنده electrons أكتر بتشارك في الـ metallic bond: الكتاب بيقول إن الـ 4s والـ 3d electrons الاتنين بيشاركوا فيه. الـ calcium مفيهوش 3d electrons، فالـ bond بتاعه بيعتمد على الـ 4s electrons وبيبقى أضعف.
## 3. The melting point column

K and Ca: common data values. Sc to Cu: book's table, p.12 (for illustration only). The values do not rise steadily. Book point 3b: the transition elements have **high melting and boiling points**. See both columns from the book Book's table, p.12 (for illustration only)


## 4. Which electrons bond?

$\ce{_{20}Ca}$: [Ar] $4s^2$, only 4s electrons bond $\ce{_{22}Ti}$: [Ar] $4s^2\ 3d^2$, 4s and 3d electrons bond Calcium 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) 4s only: 2 free electrons per atom. A weaker bond, like calcium's. 4s and 3d: 4 free electrons per atom. A strong metallic bond. bonding electrons per Ti atom bonding electrons per Ti atom


## 6. Not about heavy atoms

From the book's table, p.12 (for illustration only) Transition elements melt high because their atoms are heavy.


## 7. A student's claim

A student says: "Scandium (45) melts higher than calcium (40) because scandium is heavier." Which reply fits the book?

- Scandium's 3d electron joins its 4s electrons in the metallic bond, so the bond is stronger ✓
- Scandium has more 4s electrons than calcium
- Agree: heavier atoms always melt higher

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.

[ar-EG] الرد اللي ماشي مع الكتاب: الـ 3d electron بتاع الـ scandium بيشارك مع الـ 4s electrons في الـ metallic bond، فالـ bond بتاعه بيبقى أقوى من بتاع الـ calcium اللي بيستخدم الـ 4s electrons. إنه أتقل مش هو السبب.
## 8. Write the reason

Transition elements have high melting points due to the strong ___ bond, formed by sharing both 4s and ___ electrons.


## 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. Give reasons: transition elements have high melting and boiling points Due to the **strong metallic bond**, formed by the **sharing of both 4s and 3d electrons**. Back to the hook: can you explain why titanium melts so much higher than calcium? 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.



Chapter: Transition Elements (https://yaani.ai/en/learn/chemistry/chem-s3-en.ch1)
Source: https://yaani.ai/en/lesson/chem-s3-en.lesson-te.high-melting-points