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Oxygen has an atomic number of 8 and an atomic mass of 16. How many valence electrons does it have?
A
6
B
2
C
4
D
8
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1
Identify the atomic number of oxygen, which is 8. This number tells us the total number of electrons in a neutral oxygen atom.
Recall that electrons are arranged in energy levels (shells) around the nucleus. The first shell can hold up to 2 electrons, and the second shell can hold up to 8 electrons.
Distribute the 8 electrons of oxygen into the shells: fill the first shell with 2 electrons, then place the remaining electrons in the second shell.
Determine the number of electrons in the outermost shell (the second shell in this case). These are the valence electrons responsible for chemical bonding.
Conclude that the number of valence electrons in oxygen is the number of electrons in its outermost shell, which is the total electrons minus those in the inner shells.