Molecules and Compounds - Free Printable

Let's go through each question on the "Elements, Compounds and Mixtures" worksheet step by step and provide clear explanations and answers.

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1. Which of the boxes contains:

We have three boxes with different arrangements of particles:

- Box 1: Five black dots (individual atoms).
- Box 2: Four pairs of white circles (diatomic molecules).
- Box 3: Three molecules made of one black and one white circle (heteronuclear diatomic molecules).

#### a) Molecules of an element?
> Answer: Box 2
> Explanation: The molecules in Box 2 are made of two identical white atoms bonded together (e.g., O₂ or N₂). This represents molecules of an element, because they consist of only one type of atom.

#### b) Molecules of a compound?
> Answer: Box 3
> Explanation: Each molecule in Box 3 consists of two different types of atoms (one black and one white), meaning it is a compound (e.g., like CO or HCl). A compound is formed when two or more different elements chemically bond.

#### c) Atoms of an element?
> Answer: Box 1
> Explanation: Box 1 shows individual black dots — these represent atoms of an element that are not bonded into molecules. For example, this could be a sample of noble gas atoms like helium or argon.

#### d) Do any of the boxes contain a mixture? Explain your answer.
> Answer: No, none of the boxes show a mixture.
> Explanation:
> - A mixture would involve two or more substances (elements or compounds) that are not chemically bonded and can be physically separated.
> - Box 1: Only one type of atom → pure element.
> - Box 2: Only one type of molecule → pure element (diatomic).
> - Box 3: Only one type of molecule → pure compound.
>
> Since all boxes contain only one type of particle, they are pure substances, not mixtures.

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2. Look at the following substances. Circle the elements and underline the compounds.

a) Li
b) N₂
c) CO
d) Cl₂
e) S₈
f) NaCl

> Elements (circle):
> - Li (lithium – single atom)
> - N₂ (nitrogen gas – diatomic molecule of same atoms)
> - Cl₂ (chlorine gas – diatomic molecule)
> - S₈ (sulfur – molecular form of sulfur)

> Compounds (underline):
> - CO (carbon monoxide – carbon + oxygen)
> - NaCl (sodium chloride – sodium + chlorine)

✔ Final Answer:
- Circle: a) Li, b) N₂, d) Cl₂, e) S₈
- Underline: c) CO, f) NaCl

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3. How many elements make up each compound?

a) HCl → Hydrogen (H) + Chlorine (Cl) → 2 elements
b) CaCO₃ → Calcium (Ca) + Carbon (C) + Oxygen (O) → 3 elements
c) HNO₃ → Hydrogen (H) + Nitrogen (N) + Oxygen (O) → 3 elements
d) H₂SO₄ → Hydrogen (H) + Sulfur (S) + Oxygen (O) → 3 elements
e) CH₃OH → Carbon (C) + Hydrogen (H) + Oxygen (O) → 3 elements

✔ Answers:
a) 2
b) 3
c) 3
d) 3
e) 3

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4. How many atoms are there in each of these molecules?

a) N₂ → 2 nitrogen atoms → 2 atoms
b) CO₂ → 1 C + 2 O → 3 atoms
c) O₃ → 3 oxygen atoms → 3 atoms
d) CH₄ → 1 C + 4 H → 5 atoms
e) SO₂ → 1 S + 2 O → 3 atoms
f) C₂H₄ → 2 C + 4 H → 6 atoms

✔ Answers:
a) 2
b) 3
c) 3
d) 5
e) 3
f) 6

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5. Circle the molecule with the most atoms in each pair:

a) HCl vs POCI
- HCl: 1 H + 1 Cl = 2 atoms
- POCl: P + O + Cl = 3 atoms → ✔ POCl

b) NH₃ vs HNO₃
- NH₃: 1 N + 3 H = 4 atoms
- HNO₃: 1 H + 1 N + 3 O = 5 atoms → ✔ HNO₃

c) C₃H₈ vs C₂H₅OH
- C₃H₈: 3 C + 8 H = 11 atoms
- C₂H₅OH: 2 C + 6 H + 1 O = 9 atoms → ✔ C₃H₈

d) CH₃COCH₃ vs C₆H₆
- CH₃COCH₃ (acetone): 3 C + 6 H + 1 O = 10 atoms
- C₆H₆ (benzene): 6 C + 6 H = 12 atoms → ✔ C₆H₆

✔ Answers:
a) POCI
b) HNO₃
c) C₃H₈
d) C₆H₆

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6. What is the formula for each molecule shown below?

We have four diagrams:

1. Two white circles labeled "O" → O–O → O₂
2. One "C" between two "O" → O–C–O → CO₂
3. One "O" bonded to two "H" → H–O–H → H₂O
4. One "N" bonded to three "H" → H–N–H with third H → NH₃

✔ Formulas:
- O₂
- CO₂
- H₂O
- NH₃

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✔ Summary of Answers:

#### 1.
a) Box 2 – molecules of an element
b) Box 3 – molecules of a compound
c) Box 1 – atoms of an element
d) No, no box contains a mixture; all are pure substances.

#### 2.
Circle: Li, N₂, Cl₂, S₈
Underline: CO, NaCl

#### 3.
a) 2
b) 3
c) 3
d) 3
e) 3

#### 4.
a) 2
b) 3
c) 3
d) 5
e) 3
f) 6

#### 5.
a) POCI
b) HNO₃
c) C₃H₈
d) C₆H₆

#### 6.
- O₂
- CO₂
- H₂O
- NH₃

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