# SCIENCE/CHEM

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Bromine exists as a mix of bromine 79 and bromine 81 isotopes. an atom of bromine 79 contains:

35 prot.44.neutr.35 electrons
35 prot.and 35 electrons only
44 prot.44 elect and 35 neutr.
35 prot.79 neutr. and 35 electrons
79 protons 79 electrons and 35 neutr.
which is correct please thanks Andy

• SCIENCE/CHEM -

# protons = atomic number. Look it up on the periodic table.
#protons + #neutrons = mass number (in this case 81 or 79)

• SCIENCE/CHEM -

does that narrow it down to 35 prot,79 neutrons and 35 electrons?
Soory bit lost on electrons...
Andy
why was there two choices for mass number???

• SCIENCE/CHEM -

aha....# of prot and electrons =35 same as atomic number.
#of neutons=mass number - atomic number=44 neutrons...
so 35 protons,44 neutrons and 35 electrons .....hows that???

• SCIENCE/CHEM -

very good. Why are there two mass numbers? Because the problem tells you Br comes in two flavors; i.e., mass number 79 and 81. But they only asked about the 79 isotope.

• SCIENCE/CHEM -

thanks...... andy

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