---
marp: true
theme: default
html: true
---

# What is an element?

Year 8 Chemistry · Elements and compounds

<!-- Speaker note: Students define an element as a pure substance of only one type of atom, tell elements from compounds by their particles, and use chemical symbols (AC9S8U06, node 2). About 24 minutes (Engage and Explore 7 min · Explain 10 min · Evaluate 3 min · Typical adds 3 min, Wider about 4 min). -->

---

## Today

**We are learning to** an element is a pure substance made of only one type of atom. Its particles can be single atoms (helium) or atoms joined together (O₂), but every atom is the same type. Each element has a symbol of one or two letters, and the periodic table lists them all.

- I can define an element.
- I can tell an element from a compound by the atoms in its particles.
- I can use chemical symbols, including two-letter ones.

<!-- Speaker note: Before class: A concept tutorial for introducing or revising the idea. Set the width with `?width=minimum`, `typical` (default) or `wider`. It builds on What are particles made of? (node 1) and comes before Why isn't salt poisonous? (compounds, node 3). Not a hinge node, but two ideas trip students up here: "pure" taken to mean "element", and "element" taken to mean "single atoms" (so O₂ looks like a compound). The prediction tests both. Board notes: every substance is drawn as a gas in a box, including metals' atoms in other lessons; real metals are solids made of atoms packed together. Molecules are rigid, in 2D. The board names each kind of particle (element or compound) once inspected. Teacher: In your own words: the three labelled particle drawings are the evidence. -->

---

## Why it matters

> Everything around you, from your phone to your fingernails, is built from fewer than a hundred kinds of atom. Each kind is an element.

<!-- Speaker note: Last lesson: atoms come in types. This lesson: substances made of just one type. -->

---

<span style="background:#dbeafe; color:#1a1a1a; border:1.5px solid #3b82f6; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">💬 Discussion</span>

## Engage: predict

**A jar of pure oxygen and a jar of pure water. Both are pure substances. Which is an element?**

- Only the oxygen
- Neither: oxygen particles have two atoms
- Only the water
- Both: they are pure

<!-- Speaker note: What happens: Only the oxygen. Every oxygen particle (O₂) is two oxygen atoms: one type of atom, so oxygen is an element. Water is pure too, but each particle has hydrogen and oxygen atoms: two types, so water is a compound. Take two or three predictions before anyone runs it. -->

<!-- Speaker note: Teacher: tally the predictions. 'Both' means pure = element; 'neither' means element = single atoms. -->

---

<span style="background:#fef3c7; color:#1a1a1a; border:1.5px solid #f59e0b; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✍️ Activity</span>

## Explore it

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fchemistry-8%2Felements%2Fstep-2&code=widget%3A+atoms%0Ashow%3A+O2+x10%0Acaption%3A+A+jar+of+pure+oxygen%2C+enlarged+millions+of+times.%0A}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/chemistry-8/elements/?full=step-2#step-2)

<!-- Speaker note:  -->

<!-- Speaker note: Teacher: ask what was the same about every atom in the oxygen jar, and what was different in water. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 25px; }</style>

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## What happened?

* Only the oxygen. Every oxygen particle (O₂) is two oxygen atoms: one type of atom, so oxygen is an element. Water is pure too, but each particle has hydrogen and oxygen atoms: two types, so water is a compound.

<!-- Speaker note: Reveal after running. Ask who predicted it, and what made them think so. -->

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## What an element is

**What is an element?**

- A pure substance made of only one type of atom
- Any substance made of single atoms
- Any pure substance

* Answer: A pure substance made of only one type of atom

<!-- Speaker note: One type of atom, and nothing else. The atoms may be single (helium) or joined (oxygen, O₂). -->

<!-- Speaker note: Teacher: the definition, the sort and the symbols are the node's success criteria; Co and CO is the two-letter rule. -->

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Element or compound

**Element or compound?**

Groups: Element · Compound

O₂ (oxygen) · He (helium) · N₂ (nitrogen) · O₃ (ozone) · H₂O (water) · CO₂ (carbon dioxide) · NaCl (salt)

* Answer: O₂ (oxygen) → Element; He (helium) → Element; N₂ (nitrogen) → Element; O₃ (ozone) → Element; H₂O (water) → Compound; CO₂ (carbon dioxide) → Compound; NaCl (salt) → Compound

<!-- Speaker note:  -->

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Symbols

**Match each symbol to its element.**

| | |
|---|---|
| `O` | A. Copper |
| `C` | B. Carbon |
| `Fe` | C. Iron |
| `Na` | D. Oxygen |
| `Cu` | E. Sodium |
| `Au` | F. Gold |

* Answer: O → D. Oxygen; C → B. Carbon; Fe → C. Iron; Na → E. Sodium; Cu → A. Copper; Au → F. Gold

<!-- Speaker note: Some symbols come from Latin names: Fe from ferrum (iron), Na from natrium (sodium), Cu from cuprum (copper), Au from aurum (gold). -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 21px; }</style>

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Co or CO

**Why is the symbol for cobalt written Co, not CO?**

- It doesn't matter how you write it
- A symbol is one capital letter, or a capital and a small letter; CO means a carbon atom joined to an oxygen atom
- CO is the symbol for cobalt gas

* Answer: A symbol is one capital letter, or a capital and a small letter; CO means a carbon atom joined to an oxygen atom

<!-- Speaker note: Each symbol starts with a capital. Co is one element (cobalt); CO is two symbols, C and O: carbon monoxide. -->

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## The periodic table

**What does the periodic table show?**

- Only the elements found in living things
- Every substance, including compounds
- Every element, one box each, in order of atomic number, with similar elements in columns

* Answer: Every element, one box each, in order of atomic number, with similar elements in columns

<!-- Speaker note: About 118 elements are known; around 90 occur naturally. Everything else is made from them. -->

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Reading a box

**A box on the periodic table shows 26, Fe and Iron. What does each part tell you?**

- 26 is the temperature iron melts at
- 26 is the atomic number (its place in the table), Fe is the symbol and Iron is the name
- 26 is the number of atoms in one particle of iron
- Fe is the formula of a compound of iron

* Answer: 26 is the atomic number (its place in the table), Fe is the symbol and Iron is the name

<!-- Speaker note: Each box gives an element's atomic number, symbol and name (often its atomic mass too). Find the name and you have the symbol, or the other way round. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 25px; }</style>

---

<span style="background:#fef3c7; color:#1a1a1a; border:1.5px solid #f59e0b; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✍️ Activity</span>

## Elaborate: Co or CO?

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fchemistry-8%2Felements%2Fstep-4&code=widget%3A+atoms%0Ashow%3A+CO+x10%0Acaption%3A+%22CO%3A+carbon+monoxide.%22%0A}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/chemistry-8/elements/?full=step-4#step-4)

<!-- Speaker note: What this step is for: Inspecting carbon monoxide makes the capital-letter rule concrete: two capitals, two elements, a compound. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 25px; }</style>

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Two capitals

**CO is a poisonous gas from faulty heaters. Cobalt (Co) is a hard, shiny metal. How does the board show CO is not an element?**

- The particles are moving
- It has two letters
- Each particle has a carbon atom and an oxygen atom: two types

* Answer: Each particle has a carbon atom and an oxygen atom: two types

<!-- Speaker note: Two types of atom joined: a compound. Two capital letters in a formula mean two elements. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 28px; }</style>

---

<span style="background:#fef3c7; color:#1a1a1a; border:1.5px solid #f59e0b; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✍️ Activity</span>

## Elaborate: two forms of oxygen

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fchemistry-8%2Felements%2Fstep-5&code=widget%3A+atoms%0Ashow%3A+O3+x6%2C+O2+x6%0Acaption%3A+Oxygen+and+ozone%2C+high+in+the+atmosphere.%0A}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/chemistry-8/elements/?full=step-5#step-5)

<!-- Speaker note: What this step is for: Ozone and oxygen are the same element in two forms, which breaks the idea that one element means one substance. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 25px; }</style>

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## One element, two substances

**Ozone (O₃) and oxygen (O₂) are both made of only oxygen atoms, but ozone protects us from ultraviolet light high in the atmosphere and is harmful to breathe. What does this show?**

- Ozone must be a compound
- One element can form different substances when its atoms join in different ways
- O₃ contains a different type of oxygen atom

* Answer: One element can form different substances when its atoms join in different ways

<!-- Speaker note: Carbon does the same: diamond and graphite are both pure carbon. How the atoms are joined changes the properties. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 26px; }</style>

---

## Evaluate: look back

Write one sentence: "At first I thought… Now I think… because…"

**Revision summary**

- An **element** is a pure substance made of only one type of atom. Its particles can be single atoms (He) or atoms joined together (O₂, O₃).
- A **compound** has two or more types of atom joined (H₂O, CO₂).
- Each element has a **symbol**: one capital letter, or a capital and a small letter (C, Co, Na). Some come from Latin names (Fe, Na, Cu, Au).
- The **periodic table** lists all the elements, about 118.

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 26px; }</style>

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Exit ticket

**Nitrogen gas is N₂ and ammonia is NH₃. Which is an element, and how can you tell from the formula?**

* Nitrogen: only one symbol (N), so one type of atom. Ammonia has two symbols (N and H): a compound.

<!-- Speaker note: Students answer on paper or a mini whiteboard before the reveal. Anyone who cannot answer needs the main idea again next lesson. Where this leads: Next: Why isn't salt poisonous? (compounds, node 3). In class: element samples (copper, sulfur, carbon, aluminium foil) beside compounds (salt, water, sugar); a periodic table hunt for the elements in everyday objects; symbol bingo. -->