# Original model cards · atoms, isotope names and ion counts

Every display label below is a **fictional teaching context**, not a tested sample, measured spectrum, safety claim or material recipe. The element symbols, atomic numbers and example isotope mass numbers were independently checked against [CIAAW's tables](SOURCE-AND-RIGHTS.md); the arithmetic is audited in the worked key. A model is useful without being a literal picture of electron paths.

## Card A · what this early atom model can and cannot show

An atom's nucleus contains **protons** (positive) and **neutrons** (no charge); electrons (negative) are outside it. For this starter, represent electrons in **distinct energy levels**, as the QCAA first atomic-structure point says. A drawn ring is a teaching convention, **not a measured circular orbit** or a full orbital/electron-configuration description. The element's identity follows its proton count, not the colour, context name or the number of drawn dots.

## Card B · count rules for one isotope or ion

- **Atomic number Z = number of protons.** Find the element symbol from Z; changing protons means changing element.
- **Mass number A = protons + neutrons** for one nuclide; therefore **neutrons = A − Z**. A is a whole number, not the decimal standard atomic weight in a periodic-table tile.
- A **neutral atom** has electrons = protons = Z.
- A **positive 1+ ion** has lost one electron from that neutral atom; electrons = Z − 1. A **2+** ion has Z − 2 electrons.
- A **negative 1− ion** has gained one electron; electrons = Z + 1. A **2−** ion has Z + 2 electrons.
- In these electron-only changes, proton and neutron counts, Z, A and isotope name **stay fixed**. Count = bookkeeping, not a claim about an actual reaction or a stable free ion.

## Card C · how to read a nuclear symbol

Write `A` above `Z` to the **left of the element symbol X**: `^{A}_{Z}X` in plain text, and put charge at the upper right if needed: `^{24}_{12}Mg^{2+}`. Read the first as “magnesium-24, atomic number 12, charge two plus.” The accessible full-word alternative is always **symbol/name, A, Z, charge**. In this pack, a missing charge means a **neutral atom by the task's explicit convention**, not a claim that every printed isotope symbol in science implies an atom rather than a nuclide.

## Card D · original comparison inventory

| Label for a fictional display | Symbol/name and given status | Count to derive |
| --- | --- | --- |
| Recycled carbon-fibre exhibit | carbon-12, Z 6, **neutral** | p 6, n 6, e 6 |
| Archive paper-fibre exhibit | carbon-13, Z 6, **neutral** | p 6, n 7, e 6 |
| Wetland oxygen-label panel | oxygen-16, Z 8, **neutral** | p 8, n 8, e 8 |
| Coastal salt-ion card | chlorine-35, Z 17, **1− ion** | p 17, n 18, e 18 |
| Bicycle-frame metal card | magnesium-24, Z 12, **neutral** | p 12, n 12, e 12 |
| Same isotope, charged model | magnesium-24, Z 12, **2+ ion** | p 12, n 12, e 10 |

The context names are **story labels only**. They do not prove the composition, safety, manufacturing route or origin of a real fibre, wetland, salt or frame. The rows are not abundance data. For a quick classroom set use [the count mat](print/count-mat.svg) and [isotope/ion fork](print/isotope-ion-fork.svg).

## Card E · same element, different isotope; same isotope, different charge

Carbon-12 and carbon-13 both have **Z 6**, so both are carbon; their neutron counts **6 and 7** differ, so they are isotopes. Neutral carbon atoms each have six electrons in this task. Magnesium-24 atom and magnesium-24 **2+ ion** both have **12 protons and 12 neutrons**, so they are the *same isotope*; their electron counts **12 and 10** differ. Calling these two magnesium records “different isotopes” would mistake charge for a change in nucleus. A third example, chlorine-35 versus chlorine-37, has Z 17 and neutron counts 18 versus 20.

## Card F · model claim discipline

`given symbol/status → Z and A → proton/neutron/electron count → bounded claim`. Do not infer isotope abundance from one sample card, a material's composition from a context label, safety from an element symbol, or real electron trajectories from a ring diagram. A correct count can still be paired with a false claim if it silently changes **neutral** to **ion**, uses a rounded decimal atomic weight for A or treats a story as a laboratory result.

SubjectNest original model cards © NeuroForgeIO Pty Ltd 2026, [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/).