Give the number of valence electrons for Cd.
A) 8
B) 10
C) 12
D) 2
E) 6
The correct answer and explanation is :
The correct answer is:
D) 2
Explanation:
Cadmium (Cd) is a chemical element with atomic number 48, meaning it has 48 electrons arranged in energy levels around the nucleus. To determine the number of valence electrons, we analyze its electron configuration.
Electron Configuration of Cadmium (Cd):
The full electron configuration of Cd is:
[ 1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^6 4d^{10} 5s^2 ]
The valence electrons are the electrons in the outermost energy level (highest principal quantum number). For cadmium, the outermost energy level is n = 5, which contains only the 5s² electrons.
Why is the Answer 2?
- Valence electrons are the electrons available for bonding and chemical reactions.
- The 5s² electrons are the outermost electrons, making 2 valence electrons for Cd.
- The 4d^10 electrons are in a lower energy level (n=4) and are considered part of the core, not valence electrons.
Comparison with Other Elements in the Same Group
Cadmium belongs to Group 12 (Transition Metals) along with Zinc (Zn) and Mercury (Hg). These elements typically have two valence electrons (s² in their outermost shell).
For example:
- Zn (Zinc, 30): [Ar] 3d¹⁰ 4s² → 2 valence electrons
- Hg (Mercury, 80): [Xe] 4f¹⁴ 5d¹⁰ 6s² → 2 valence electrons
Since cadmium behaves similarly, it follows the same pattern, confirming that Cd has 2 valence electrons.