Chemistry worksheet on elements, compounds, and mixtures with student diagrams.

Let's solve this step by step.

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Part 1: Complete the following sentences using the word bank.

Word Bank:
- two or more
- two or more
- only one
- not chemically joined
- chemically joined

1. An element is made up of only one type of atom.
→ Elements consist of atoms that are all the same (e.g., oxygen atoms in O₂).

2. A compound is made up of two or more different atoms, chemically joined together.
→ Compounds form when different types of atoms bond chemically (e.g., H₂O – hydrogen and oxygen).

3. A mixture is made up of two or more different atoms, not chemically joined together.
→ In mixtures, substances are physically combined but not bonded (e.g., salt and sand).

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Part 2: State whether each statement is true or false.

1. False – Elements can exist as atoms, but also as molecules (e.g., O₂, N₂). So they don't *only* exist as single atoms.

2. False – Compounds can exist as molecules (like H₂O), but also as ionic lattices (like NaCl), which aren't discrete molecules.

3. True – Mixtures can contain atoms, molecules, or both (e.g., air contains O₂ molecules, N₂ molecules, and individual atoms like noble gases).

4. False – Compounds must be broken down chemically, not physically. Physical methods won’t break chemical bonds.

5. True – Elements cannot be broken down into simpler substances by chemical means; they are already pure.

6. False – Mixtures are separated physically (e.g., filtration, distillation), not by chemical reactions.

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Part 3: Evaluate the diagrams for soda water (a mixture of CO₂ and H₂O)

Soda water is a mixture of:
- Carbon dioxide (CO₂) – molecule with 1 carbon (black) and 2 oxygen (grey)
- Water (H₂O) – molecule with 2 hydrogen (white) and 1 oxygen (grey)

In a mixture, these molecules are not chemically bonded to each other — they just coexist.

Let’s analyze each student’s diagram:

#### Phillip:
- Shows separate atoms (single grey, black, white circles).
- No molecules formed.
- ✘ Incorrect.
- Error: He drew individual atoms instead of molecules. CO₂ and H₂O should be shown as molecules, not as free atoms. Also, there's no indication of CO₂ or H₂O molecules.

#### Caroline:
- Shows CO₂ molecules (black + two grey) and H₂O molecules (one grey + two white).
- Molecules are present and not joined to each other.
- ✔ Correct.
- She correctly shows a mixture of CO₂ and H₂O molecules, not chemically bonded.

#### Roderick:
- Shows molecules where carbon (black) is bonded to hydrogen (white) and oxygen (grey) — forming something like CH₂O or other hybrid molecules.
- These are not real molecules in soda water.
- ✘ Incorrect.
- Error: He incorrectly showed atoms from CO₂ and H₂O bonding together to form new molecules, implying a chemical reaction has occurred. But in a mixture, no new compounds form — the molecules remain intact.

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✔ Final Answers:

#### Complete the sentences:
1. only one
2. two or more, chemically joined
3. two or more, not chemically joined

#### True or False:
1. False
2. False
3. True
4. False
5. True
6. False

#### Evaluate student diagrams:

Phillip:
✘ Incorrect. He showed individual atoms rather than molecules of CO₂ and H₂O. In reality, CO₂ and H₂O exist as discrete molecules in the mixture.

Caroline:
✔ Correct. She correctly represented CO₂ and H₂O molecules separately, showing a physical mixture without chemical bonding.

Roderick:
✘ Incorrect. He incorrectly showed atoms from CO₂ and H₂O chemically combining into new molecules, suggesting a chemical reaction, which does not occur in a mixture.

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