Question

Help me with these questions please!

1)
A teacher shows the class a neutral atom of Bromine that has an atomic number of 35 and has 45 neutrons.

Jackie said, "I think the atomic mass would be 45, because there are 45 neutrons and neutrons make up the mass of the atom"

Pauly said, "I think the atomic mass would be 80, because there are 45 neutrons and 35 protons. Both of these have a mass of about 1."

Sam said, "There would be 45 electrons and 45 protons, because of the atomic number."

Who is correct?

Both Sam and Pauly are correct.


Only Sam is correct.


Both Sam and Jackie are correct.


Only Pauly is correct.

Answer 1

1) Answer:- Only Pauly is correct.

Solution:- In an atom, there is a nucleus in the center and the electrons are present around it in different shells. Neutrons and protons are present in the nucleus and the mass of the atom is mainly because of these neutrons and protons.

So, Mass number = number of protons + number of neutrons

Also, a neutral atom has equal number of protons and neutrons and atomic number is same as the number of protons.

So, atomic number = number of protons

Atomic number of the neutral atom of bromine is given as 35 and it has 45 neutrons.

So, mass number = 35 + 45 = 80

Jackie said, the atomic mass would be 45 which is not correct as the atomic mass is 80.

Pauly is correct as the proton and neutron both have a mass of about 1 and so the atomic mass of the bromine atom is around 80 as the sum of protons and neutrons is 80.

Sam is not correct as there are 35 protons and 35 electrons for the neutral bromine atom.

So, only the last option is correct, " Only Pauly is correct."

2) Answer:- 33 amu is the mass of the nucleus.

Solution:- from given info, there are 15 protons and 18 neutrons.

Mass of nucleus = number of protons(mass of proton) + number of neutrons(mass of neutron)

Let's plug in the values in the formula:

mass of nucleus = 15(1.0073) + 18(1.0087)

mass of nucleus = 15.1095 + 18.1566

mass of nucleus = 33.2661 amu

If we round it off then it's 33 amu.

So, the last choice is correct. mass of nucleus is 33 amu.