Atom “Cheat Sheet”
Frequently asked questions
Q: How do I find the number of protons?
A: The number of protons is the same as the atomic
number.
13
Al
26.982
Q: What is the atomic number?
A: The top number : look at the periodic table!
Q: How do I find the number of electrons?
A: In a neutral atom the number of electrons is the
SAME as the number of protons.
Q: How do I know if an atom is neutral.
A: There is NO charge written so if the problem says
Aluminum it is neutral. If the problem says Aluminum +2 then it is not
neutral it has a +2 charge.
Q: How do I find neutrons?
A: You find neutrons by doing Atomic mass - # of protons.
Q: Where is the atomic mass?
A: It’s the bottom number on the periodic table.
Q: But the atomic mass is a decimal. What do I do?
A: Round it to a whole number.
Q: How do I know how many protons there are?
A: I’VE ALREADY ANSWERED THAT
Q: Why is that how you find neutrons?
A: Well the atomic mass is the total number of protons and neutrons.
So if Protons +Neutrons = Atomic Mass
you would have 13 + neutrons = 27.
Do some algebra to solve for neutrons
Q: What if a problem says Aluminum-30?
A: That I am telling you which isotope it is. Use 30 as the atomic mass.
Q: How come protons can’t change?
A: If you change the number of protons it’s not Aluminum anymore.
Protons are in Prison
Q: What if a problem says Aluminum +2
A: Then the Aluminum atom has a charge of positive 2.
Q: So how do I find Protons?
A: Protons don’t change, refer to the first questions.
Q: How do I find electrons?
A: For an atom to have a positive charge of 2 that means there are two
more protons than electrons. So if Aluminum normally has 13 electrons
then an Aluminum atom with a +2 charge has only 11 electrons.
For more basic practice I would check this out