Multiple Choice
How many valence electrons does a copper (Cu) atom have?
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10. Periodic Properties of the Elements
Valence Electrons of Elements
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How many valence electrons does a neutral atom with 15 protons have?
A
5
B
15
C
3
D
7
Verified step by step guidance1
Identify the element by its number of protons. The number of protons in a neutral atom is equal to its atomic number. Here, the atom has 15 protons, so its atomic number is 15.
Use the atomic number to find the element on the periodic table. The element with atomic number 15 is phosphorus (P).
Determine the electron configuration of phosphorus to understand how its electrons are arranged in shells and subshells. The electron configuration for phosphorus is $1s^2 2s^2 2p^6 3s^2 3p^3$.
Identify the valence electrons, which are the electrons in the outermost shell. For phosphorus, the outermost shell is the third shell, containing the $3s^2$ and $3p^3$ electrons.
Count the valence electrons by adding the electrons in the outermost shell: $2$ (from $3s^2$) plus $3$ (from $3p^3$), giving a total of $5$ valence electrons.
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