An atom of carbon has an atomic number of 6, an atomic weight of 13, and a charge of +1. How many neutrons does the atom have?
The correct answer and explanation is:
The atom has 7 neutrons.
Here is the explanation:
The atomic number of an element represents the number of protons in its nucleus. For carbon, the atomic number is 6, so this atom has 6 protons.
The atomic weight (more accurately called the mass number in this context) is the sum of protons and neutrons in the nucleus. In this problem, the atomic weight is given as 13, which means the total number of protons plus neutrons is 13.
To find the number of neutrons, subtract the number of protons from the mass number:
Number of neutrons = Mass number – Number of protons = 13 – 6 = 7 neutrons.
The charge of the atom is +1, which means the atom is ionized and has lost one electron compared to the neutral state. Normally, a neutral carbon atom has 6 electrons, equal to the number of protons. Because of the +1 charge, this atom has only 5 electrons (6 protons – 1 electron = +1 net charge).
The charge does not affect the number of neutrons or protons in the nucleus; it only indicates the balance of electrons around the nucleus. Therefore, the number of neutrons is unaffected by the charge.
In summary:
- Atomic number 6 → 6 protons
- Atomic weight (mass number) 13 → protons + neutrons = 13
- Neutrons = 13 – 6 = 7 neutrons
- Charge +1 → 5 electrons, but this does not affect the neutron count
Thus, this carbon atom has 7 neutrons.