Question

which element has atoms with valence electrons in a higher energy than those of calcium
A. cesium
B. bromine
C. oxygen
D. lithium

Answer 1

To determine which element has atoms with valence electrons in a higher energy level than those of calcium (Ca), we need to consider the electron configuration and the principle energy level of the outermost electrons.

Calcium has the atomic number 20 and its electron configuration is:

\[ \text{Ca: [Ar] 4s}^2 \]

This means that the valence electrons of calcium are in the 4s orbital.

Now let's analyze the options:

A. **Cesium (Cs)** - Atomic number 55, electron configuration: \[ \text{Cs: [Xe] 6s}^1 \]
- Valence electrons are in the 6s orbital, which is higher than the 4s of calcium.

B. **Bromine (Br)** - Atomic number 35, electron configuration: \[ \text{Br: [Ar] 4s}^2 3d^{10} 4p^5 \]
- Valence electrons are in the 4p orbital, which is at the same principal energy level (n=4) but not higher than calcium's 4s.

C. **Oxygen (O)** - Atomic number 8, electron configuration: \[ \text{O: [He] 2s}^2 2p^4 \]
- Valence electrons are in the 2s and 2p orbitals, which are at a much lower energy level than calcium's 4s.

D. **Lithium (Li)** - Atomic number 3, electron configuration: \[ \text{Li: [He] 2s}^1 \]
- Valence electrons are in the 2s orbital, which is also at a lower energy level than calcium's 4s.

Among these options, **cesium (A)** has valence electrons in a higher energy level (6s) than those of calcium (4s).

Thus, the correct answer is:

**A. cesium**