Question

1. in nature, 94.72% of all bromine exists as bromine - 80, 2.82% exists as bromine - 79, 2.41% exists as bromine - 81, and 0.05% exists as bromine - 78. based on this data, calculate the average atomic mass of bromine. show all work.
2. calculate the average atomic mass of sulfur if its abundance in nature is 95% sulfur - 32, 0.76% sulfur - 33, and 4.22% sulfur - 34. show all work.

for each of the ions listed, identify the total number of electrons for each.

1. cr+3
2. mg+2
3. pt+2
4. co+3

Explanation:

Step1: Recall average atomic mass formula

$Average\ atomic\ mass=\sum (isotope\ mass\times relative\ abundance)$

Step2: Calculate average atomic mass of bromine

$(80\times0.9472)+(79\times0.0282)+(81\times0.0241)+(78\times0.0005)=79.9035$

Step3: Calculate average atomic mass of sulfur

$(32\times0.95)+(33\times0.0076)+(34\times0.0422)=32.066$

Step4: Find electrons in ions

• For $Cr^{+3}$: Chromium has 24 protons. $24 - 3=21$ electrons.
• For $Mg^{+2}$: Magnesium has 12 protons. $12 - 2 = 10$ electrons.
• For $Pt^{+2}$: Platinum has 78 protons. $78 - 2=76$ electrons.
• For $Co^{+3}$: Cobalt has 27 protons. $27 - 3 = 24$ electrons.

Answer:

Average atomic mass of bromine: 79.9035
Average atomic mass of sulfur: 32.066
Electrons in $Cr^{+3}$: 21
Electrons in $Mg^{+2}$: 10
Electrons in $Pt^{+2}$: 76
Electrons in $Co^{+3}$: 24