Phosphorus has the atomic number 15 and an atomic mass of 31 amu. How many protons, neutrons, and electrons are in a neutral phosphorus atom? (Chapter 4)
The correct answer and explanation is:
Correct Answer:
- Protons: 15
- Neutrons: 16
- Electrons: 15
Explanation:
To determine the number of protons, neutrons, and electrons in a neutral phosphorus atom, begin by understanding the meaning of atomic number and atomic mass.
The atomic number represents the number of protons in an atom. For phosphorus, the atomic number is 15, which means there are 15 protons in the nucleus. In a neutral atom, the number of protons is equal to the number of electrons to balance the electrical charge. So phosphorus also has 15 electrons.
The atomic mass or mass number is the total count of protons and neutrons in the nucleus. Phosphorus has an atomic mass of 31 atomic mass units (amu). To find the number of neutrons, subtract the number of protons from the atomic mass:
Number of neutrons = Atomic mass – Atomic number
Number of neutrons = 31 – 15 = 16
So a neutral phosphorus atom contains:
- 15 protons (positively charged particles)
- 15 electrons (negatively charged particles)
- 16 neutrons (neutral particles)
Each component plays a specific role in atomic structure. The protons determine the identity of the element. The electrons determine chemical behavior and bonding characteristics. The neutrons contribute to the atomic mass and help stabilize the nucleus.
Understanding these numbers helps in studying isotopes, chemical reactions, and nuclear stability. For example, isotopes of phosphorus would have the same number of protons but different numbers of neutrons. In this case, phosphorus-31 is the most common and stable isotope, containing 16 neutrons. This atomic makeup is essential in biological and chemical processes, including phosphorus’s role in DNA, ATP, and cell membranes.