Familiarize yourself with the atom structure of each element in the periodic table. Use flashcards or refer to a textbook to ascertain the differences and study the atomic numbers. Study the elements using repetition exercises to help with memorization for testing.
Look at an illustration depicting the basic structure of an atom. Electrons are active particles that move around a nucleus; these will look like they're moving around the structures in the center of an atom. Protons and neutrons are nestled next to each other inside the nucleus and are often different colors.
Determine the element to which the atom belongs to help you define the structure of the atom's nucleus.
Find the atom's atomic number. This is equal to the number of protons in the atom. The atomic number is located in the upper left-hand corner of the element's square on the periodic table.
Find the mass number of the isotope, or element, by rounding up the atomic weight to the nearest whole number. The number at the bottom of the element's square in the periodic table shows its atomic weight.
Subtract the atomic number from the mass number; the difference is the number of neutrons in the atom.