Multiple Choice
Which of the following best describes the core electrons in a phosphorus (P) atom?
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10. Periodic Properties of the Elements
Valence Electrons of Elements
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In the molecule Br2 and the ion Br-, how many pairs of valence electrons does each bromine atom possess?
A
Br2: 3 pairs; Br-: 3 pairs
B
Br2: 3 pairs; Br-: 4 pairs
C
Br2: 4 pairs; Br-: 3 pairs
D
Br2: 2 pairs; Br-: 3 pairs
Verified step by step guidance1
Identify the number of valence electrons for a single bromine (Br) atom. Bromine is in group 17 of the periodic table, so it has 7 valence electrons.
For Br2 (a bromine molecule), consider that two bromine atoms share one pair of electrons in a single covalent bond. Each bromine atom contributes one electron to this bond.
Calculate the number of lone pairs on each bromine atom in Br2. Since each bromine has 7 valence electrons and uses 1 electron for bonding, the remaining 6 electrons form lone pairs. Divide these 6 electrons by 2 to get the number of lone pairs.
For the bromide ion (Br⁻), add one extra electron to the 7 valence electrons because of the negative charge, giving a total of 8 valence electrons.
Determine the number of lone pairs on the bromide ion by dividing the 8 valence electrons by 2, since all electrons are non-bonding in this ion (no bonds to other atoms).
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