Multiple Choice
Which of the following represents the complete ground state electron configuration for a manganese (Mn) atom?
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10. Periodic Properties of the Elements
The Electron Configuration
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How many unpaired electrons are present in a neutral beryllium (Be) atom?
A
0
B
2
C
4
D
1
Verified step by step guidance1
Identify the atomic number of beryllium (Be), which tells you the number of electrons in a neutral atom. Beryllium has an atomic number of 4, so it has 4 electrons.
Write the electron configuration for beryllium by filling the orbitals in order of increasing energy. The order starts with 1s, then 2s, then 2p, etc. For Be, the configuration is $1\mathrm{s}^2 2\mathrm{s}^2$.
Recall that each orbital can hold a maximum of 2 electrons with opposite spins, so the 1s orbital is fully filled with 2 electrons, and the 2s orbital is also fully filled with 2 electrons.
Determine the number of unpaired electrons by checking if any electrons occupy orbitals singly. Since both 1s and 2s orbitals are fully paired, there are no unpaired electrons in a neutral Be atom.
Conclude that the number of unpaired electrons in a neutral beryllium atom is 0.
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