lesson
Protons identify the element
1 · Learn
Atomic number counts protons. Mass number counts protons plus neutrons. Isotopes of one element have the same proton number but different neutron numbers; ions have gained or lost electrons.
Changing electron count changes charge, not the element's identity. Do not confuse a mass number for one isotope with a relative atomic mass that reflects an isotopic mixture.
2 · Worked example
A neutral atom with 6 protons and 8 neutrons has mass number 14 and 6 electrons. Losing one electron gives charge +1 without changing its six protons.
3 · Your turn
An atom has atomic number 11 and mass number 23. How many neutrons?
Check your answer
12.
4 · Apply your learning
Build a labelled particle-count table and check charge separately from mass number.
Adult guidance and safety
Use supplied data and approved diagrams. Laboratory work requires qualified supervision, suitable equipment and a risk assessment. No independent chemical, electrical, heating, radiation or biological-culture experiments. Human biology is general education, not personal diagnosis or treatment.
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Check a calculation · Year 5 onward
Use this only when your teacher or adult allows a calculator for the task. Show your thinking first. It does not replace mental or written arithmetic and does not mark your lesson answer.
Powers, roots and trigonometry · Year 7 onward
Use only when the task allows a calculator. Choose one operation at a time and record your working. Trigonometry here always uses degrees (DEG), not radians. Inverse sine, cosine and tangent return an angle, not a reciprocal. Keep exact fractions and π in answers when requested.
Approximate numerical results use up to 12 significant digits. Inverse sine returns −90° to 90°, inverse cosine 0° to 180°, and inverse tangent −90° to 90°; these are principal values, not every possible solution of a trigonometric equation.
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