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Question 4.1: Determine the number of valence electrons in atoms of each o......

Determine the number of valence electrons in atoms of each of the following elements.

a.   _{12}Mg             b.   _{14}Si             c.   _{33}As

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a. Atoms of the element magnesium have two valence electrons, as can be seen by examining magnesium’s electron configuration.

The highest value of the electron shell number is n = 3. Only two electrons are found in shell 3: the two electrons in the 3s subshell.
b. Atoms of the element silicon have four valence electrons

Electrons in two different subshells can simultaneously be valence electrons. The highest shell number is 3, and both the 3s and the 3p subshells belong to this shell. Hence all of the electrons in both of these subshells are valence electrons.
c. Atoms of the element arsenic have five valence electrons.

The 3d electrons are not counted as valence electrons because the 3d subshell is in shell 3, and this shell does not have maximum n value. Shell 4 is the outermost shell and has maximum n value.

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