31p, 32p, and 33p. The atomic number of phosphorus is 15. How many protons does each of the isotopes have?
The Correct Answer and Explanation is:
Each of the phosphorus isotopes — ³¹P, ³²P, and ³³P — has 15 protons.
Explanation:
Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons. The atomic number of an element tells you the number of protons in the nucleus of each atom of that element. For phosphorus, the atomic number is 15, which means that every atom of phosphorus has exactly 15 protons, regardless of which isotope it is.
The number associated with each isotope (31, 32, or 33) is the mass number, which is the total number of protons and neutrons in the nucleus. Since the number of protons remains the same for all isotopes of phosphorus, the difference in the mass number must come from the number of neutrons.
To determine the number of neutrons in each isotope, subtract the atomic number (number of protons) from the mass number:
- ³¹P has 31 – 15 = 16 neutrons
- ³²P has 32 – 15 = 17 neutrons
- ³³P has 33 – 15 = 18 neutrons
So, although the number of neutrons varies, all three isotopes — ³¹P, ³²P, and ³³P — contain the same number of protons, which is 15. This is what makes them all phosphorus atoms.
The chemical properties of an element are primarily determined by the number of protons and electrons, which means all isotopes of phosphorus behave similarly in chemical reactions. However, the difference in neutron number can influence the stability of the nucleus. For instance, ³²P is a radioactive isotope, while ³¹P is stable and is the most abundant isotope of phosphorus found in nature. Understanding isotopes is crucial in fields such as medicine, archaeology, and nuclear science.
