Short Answer 
Isotopes are variations of the same element that have the same atomic number but different mass numbers due to differing numbers of neutrons. Each isotope is denoted by the element’s symbol followed by its mass number, which reflects the total number of protons and neutrons. Examples include Na-24, O-32, and U-238, highlighting the differences in neutron count among isotopes.
Step 1: Understanding Isotopes
Isotopes are atoms of the same element that have the same atomic number but differ in their mass numbers. The primary reason for this difference is the varying number of neutrons present in the nucleus of the atom. This unique characteristic of isotopes allows them to have different physical properties while still being part of the same element.
Step 2: Identifying Isotope Characteristics
Each isotope is represented with a notation that includes the element symbol, along with its mass number. The mass number indicates the total count of protons and neutrons in the nucleus. The difference in neutrons leads to varying mass numbers among isotopes. For example:
- Na-24 has 11 protons and 13 neutrons (mass number 24).
- O-32 has 16 protons and 16 neutrons (mass number 32).
- U-238 has 92 protons and 146 neutrons (mass number 238).
Step 3: Examples of Isotopes
To grasp the concept better, here are some common examples of isotopes with their respective data:
- Ca-44: 20 protons, 24 neutrons.
- Mg-24: 12 protons, 12 neutrons.
- Zn-64: 30 protons, 34 neutrons.
- Pb-207: 82 protons, 125 neutrons.
These examples illustrate how different isotopes of elements show variance in neutron numbers, leading to differences in their mass numbers while maintaining the same atomic number.