The neutron, atomic number, mass number, isotopes and isobars sheet3-mark answer frameDefine atomic number and mass number. Find the protons, electrons and neutrons in ⁵⁶₂₆Fe, and say what isotopes are.
How to lay out the answer. Follow the frame, then write it in your own words.
- 1 · Atomic number. Z = number of protons in the nucleus; in a neutral atom it also equals the number of electrons.
- 2 · Mass number. A = number of protons + number of neutrons.
- 3 · Apply to iron. Z = 26, so protons = 26 and electrons = 26.
- 4 · Neutrons. Neutrons = A − Z = 56 − 26 = 30.
- 5 · Isotopes. Atoms of the same element with the same Z but different A, such as ¹²C and ¹⁴C.
- 6 · In real life. Isotopes such as cobalt-60 are used to treat cancer.
- 7 · Close. So Z fixes the element, and A − Z gives the neutrons.
Scoring tip: Always show 'neutrons = A − Z' as a line of working before the number.
