Two different atoms have 11 protons each, but one has 12 neutrons, and the other has 13 neutrons. How do their atomic numbers and mass numbers compare? Are they the same element or different elements?
Both atoms have 11 protons each. Since the atomic number is equal to the number of protons, both atoms have the same atomic number of 11. However, their mass numbers are different. The mass number is the total number of protons and neutrons. For the first atom, the mass number is 11 + 12 = 23. For the second atom, the mass number is 11 + 13 = 24. Because they have the same atomic number but different mass numbers, they are atoms of the same element. Such atoms are called isotopes.
Explanation
The atomic number defines the identity of an element. Since both atoms have 11 protons, their atomic number is the same, making them the same element. The mass number depends on the total nucleons (protons + neutrons), which differs (23 vs 24). Atoms of the same element with different mass numbers are defined as isotopes in the chapter.
Solution Steps
Step 1: Calculate atomic numbers. Atom 1: 11 protons = 11. Atom 2: 11 protons = 11. They have the same atomic number.
Step 2: Calculate mass numbers. Atom 1: 11 protons + 12 neutrons = 23. Atom 2: 11 protons + 13 neutrons = 24. They have different mass numbers.
Step 3: Determine element identity. Since atomic numbers are the same, they are the same element (isotopes).