Proton number identifies the element; electrons determine net charge
| English | 中文 | Pinyin |
|---|---|---|
| ion/ˈaɪɒn/ | 离子 | lí zi |
| atomic number/əˈtɒmɪk ˈnʌmbə/ | 原子序数 | yuán zi xù shù |
What would explain this observation?
- A sodium atom and a sodium ion 离子 have different electron counts but still belong to the same element. Changing a neutron count also leaves the element identity unchanged.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- A proton has relative electrical charge +1, a neutron 0 and an electron −1. Protons and neutrons are in the nucleus, with electrons outside it in energy levels. Atomic number 原子序数, Z, is the number of protons. All atoms of a particular element have the same proton number; atoms of different elements have different proton numbers. In a neutral atom, electron number equals proton number, so their charges cancel.
- atomic number: The number of protons in an atom’s nucleus; ion: An atom or group of atoms carrying a net electric charge.
Which count establishes an element’s identity?
Net relative charge = proton number − electron number. Losing electrons produces a positive ion; gaining electrons produces a negative ion. Ordinary chemical ion formation changes electrons, not the nucleus. An atom with eleven protons is sodium even when it has ten electrons; its net charge is +1. A model with ten protons is neon, regardless of a similar electron arrangement.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Net relative charge = proton number − electron number. Losing electrons produces a positive ion; gaining electrons produces a negative ion. Ordinary chemical ion formation changes electrons, not the nucleus. An atom with eleven protons is sodium even when it has ten electrons; its net charge is +1. A model with ten protons is neon, regardless of a similar electron arrangement.
- Use counters labelled with charge rather than colours alone. Place protons and neutrons centrally and electrons outside, then add the signed charges. Identify the element from proton number using the periodic table. Explain neutrality as cancellation, rather than saying the atom contains no charged particles. Model distances are deliberately not to scale.
Which two habits make the investigation or model in this case more defensible?
Use counters labelled with charge rather than colours alone. Place protons and neutrons centrally and electrons outside, then add the signed charges. Identify the element from proton number using the periodic table. Explain neutrality as cancellation, rather than saying the atom contains no charged particles. Model distances are deliberately not to scale.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: a particle contains 13 protons, 14 neutrons and 10 electrons. Z=13 identifies aluminium. Net relative charge = 13 − 10 = +3, so the particle is Al³⁺. The fourteen neutrons contribute no electric charge. If it instead had thirteen electrons, the same nucleus would form a neutral aluminium atom.
A particle has 12 protons and 10 electrons. Calculate its net relative charge. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A particle has 12 protons and 10 electrons. Calculate its net relative charge.
The result is 2 . Known: a particle contains 13 protons, 14 neutrons and 10 electrons. Z=13 identifies aluminium. Net relative charge = 13 − 10 = +3, so the particle is Al³⁺. The fourteen neutrons contribute no electric charge. If it instead had thirteen electrons, the same nucleus would form a neutral aluminium atom.
Check the conclusion and its limits
- Atomic number is not the sum of every particle and cannot be read from electron count for an ion. Neutrality does not mean the proton and electron charges are individually zero. Neutrons affect mass and isotope identity without contributing to the net electric charge.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
A neutral atom contains no electrically charged particles. This claim is false: Atomic number is not the sum of every particle and cannot be read from electron count for an ion. Neutrality does not mean the proton and electron charges are individually zero. Neutrons affect mass and isotope identity without contributing to the net electric charge.
Proton number identifies the element; electrons determine net charge: Net relative charge = proton number − electron number. Losing electrons produces a positive ion; gaining electrons produces a negative ion. Ordinary chemical ion formation changes electrons, not the nucleus. An atom with eleven protons is sodium even when it has ten electrons; its net charge is +1. A model with ten protons is neon, regardless of a similar electron arrangement.
A neutral atom contains no electrically charged particles.
Atomic number is not the sum of every particle and cannot be read from electron count for an ion. Neutrality does not mean the proton and electron charges are individually zero. Neutrons affect mass and isotope identity without contributing to the net electric charge.
The number of protons in an atom’s nucleus: write the technical term.
atomic number means The number of protons in an atom’s nucleus.