Question 7.PS.8: Valence Electrons (a) Using the noble gas notation, write th......

Principles of Chemistry The Molecular Science [1096176]

Valence Electrons

(a) Using the noble gas notation, write the electron configuration for bromine. Identify its core and valence electrons.
(b) Write the Lewis dot symbol for bromine

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(a) $[Ar] 3d^{10}4s^24p^5$ Core electrons are $[Ar]3d^{10}$ ; valence electrons are $4s^24p^5$ .

(b) $:\overset{..}{\underset{..}{Br}}⋅$

Strategy and Explanation Bromine is element 35, a Group 7A element. Its first 18 electrons are represented by [Ar], as shown in Table 7.6. These, along with the ten $3d$ electrons, make up the core electrons. Because it is in Group 7A, bromine has seven valence electrons, as given by $4s^24p^5$ and shown in the Lewis dot symbol.

Table 7.6 Lewis Dot Symbols for Atoms
	1A $ns^1$	2A $ns^2$	3A $ns^2np^1$	4A $ns^2np^2$	5A $ns^2np^3$	6A $ns^2np^4$	7A $ns^2np^5$	8A $ns^2np^6$
Period 2	$Li\cdot$	$\cdotBe\cdot$	$⋅\overset{.}{B}⋅$	$⋅\overset{.}{\underset{.}{C}}⋅$	$⋅\overset{..}{\underset{.}{N}}⋅$	$:\overset{..}{\underset{.}{O}}⋅$	$:\overset{..}{\underset{..}{F}}⋅$	$:\overset{..}{\underset{..}{Ne}}:$
Period 3	$Na\cdot$	$\cdotMg\cdot$	$⋅\overset{.}{Al}⋅$	$⋅\overset{.}{\underset{.}{Si}}⋅$	$⋅\overset{..}{\underset{.}{P}}⋅$	$:\overset{..}{\underset{.}{S}}⋅$	$:\overset{..}{\underset{..}{Cl}}⋅$	$:\overset{..}{\underset{..}{Ar}}:$

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