How many protons are in the nucleus of an aluminum atom?

The atomic no., #Z#, defines the number of protons, and hence the identity of the atom.

Explanation:

Aluminum has (by definition) 13 protons, 13 positively charged particles. Because aluminum is neutral (as is all matter), it therefore has 13 negatively charged particles, electrons. Aluminum has an atomic mass of about #27# amu; how many neutrons are present in the aluminum nucleus?

Aluminium-27 is an isotope of aluminium characterized by the fact that is has a mass number equal to #27#.

Now, an atom's mass number tells you the total number of protons and of neutrons that atom has in its nucleus. Since you're dealing with an isotope of aluminium, it follows that this atom must have the exact same number of protons in its nucleus.

The number of protons an atom has in its nucleus is given by the atomic number. A quick looks in the periodic table will show that aluminium has an atomic number equal to #13#.

This means that any atom that is an isotope of aluminium will have #13# protons in its nucleus.

Since you're dealing with a neutral atom, the number of electrons that surround the nucleus must be equal to the number of protons found in the nucleus.

Therefore, the aluminium-27 isotope will have #13# electrons surrounding its nucleus.

Finally, use the known mass number to determine how many neutrons you have

#color(blue)("mass number" = "no. of protons" + "no. of neutrons")#

#"no. of neutrons" = 27 - 13 = 14#

How many electrons does an aluminum atom have?

Is aluminum 12 or 14 protons?

How many protons and electrons are in aluminum?

How many protons and neutrons are in aluminium?