How many valence electrons does a calcium (Ca) atom have?

• A. 4
• B. 6
• C. 8
• D. 2

Answer: (D)

Verified step by step guidance

1. Identify the atomic number of calcium (Ca), which is 20. This means a neutral calcium atom has 20 electrons.
2. Determine the electron configuration of calcium by filling the orbitals in order: 1s, 2s, 2p, 3s, 3p, and then 4s.
3. Write the electron configuration for calcium: \$1s^2 2s^2 2p^6 3s^2 3p^6 4s^2$.
4. Recognize that valence electrons are the electrons in the outermost shell (highest principal quantum number). For calcium, this is the 4th shell.
5. Count the electrons in the 4th shell (4s orbital), which gives 2 valence electrons for calcium.