Safety and evidence boundary
Use supplied notation, datasets, and simulations. No physical procedure is required for this lesson.
Explicit science instruction
Isotopes are atoms of the same element with the same proton number but different neutron numbers. Because element identity is tied to atomic number, carbon-12 and carbon-14 are both carbon.
Neutron differences change mass number and can affect nuclear stability, but they do not automatically change ordinary chemical identity. Electron count can vary separately when atoms form ions.
Keep isotope notation and ionic charge as separate bookkeeping layers: one describes the nucleus, the other describes electron imbalance.
Vocabulary: isotope; mass number; atomic number; nuclear composition; nuclide.
Worked example with reasoning
For ³⁷Cl: Z=17, so the nucleus contains 17 protons and 20 neutrons. For ³⁵Cl⁻, the nucleus contains 17 protons and 18 neutrons, while the −1 charge means 18 electrons.
Guided question
Compare ²⁴Mg, ²⁵Mg, and ²⁶Mg. What stays constant, what changes, and which quantity defines the element?
Independent work
- Create a table for three isotopes of one element with proton, neutron, and electron counts.
- Write one example showing that isotopes and ions are different concepts.
- Explain why isotope abundance can affect periodic-table atomic mass without changing atomic number.
Misconception check
Isotopes do not have different proton numbers. If proton number changes, the atom is a different element.
Formative understanding check
Can two isotopes of the same element have different mass numbers and still share the same chemical symbol?
Reveal worked response
Yes. Their proton numbers are the same; neutron numbers differ.
Public self-check only.
Mentor evidence conference
Ask Archaemenes to inspect your isotope/ion table for any place where nuclear and electron bookkeeping became mixed.
Teacher guidance
Foundation: Identify protons and neutrons from supplied isotope notation.
Core: Compare isotope and ion notation and explain the distinction.
Extended: Construct a valid nuclide symbol from particle counts and defend the notation.