Elements, compounds and mixtures

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Lesson notes

Elements

An **element** is made from **only one type of atom**.
There are over 100 known elements, listed on the **periodic table**.
Examples: argon (monatomic gas – single atoms not joined), oxygen (diatomic gas – two atoms chemically joined).

Compounds

A **compound** is a substance where **two or more different atoms** are **chemically joined**.
Example: carbon dioxide contains carbon and oxygen atoms bonded together.
Compounds have different properties from their constituent elements.

Mixtures

A **mixture** contains **two or more elements or compounds** that are **not chemically joined**.
Components can be separated by physical methods.
Examples: nitrogen gas mixed with oxygen gas (mixture of elements); carbon dioxide mixed with carbon monoxide (mixture of compounds).

Key Differences

**Element vs compound**: element has one type of atom; compound has two or more types chemically joined.
**Compound vs mixture**: in a compound, atoms are chemically bonded; in a mixture, substances are not chemically joined and can be separated physically.
A mixture can contain elements, compounds, or both.

Identifying Elements, Compounds, and Mixtures from Diagrams

**Element**: only one type of atom (same colour/size spheres).
**Compound**: two or more different atoms chemically joined (different spheres bonded together).
**Mixture**: two or more different atoms or molecules not bonded (different spheres or groups mixed but not joined).

Examples of Elements and Compounds

**Elements**: iron, nitrogen, oxygen, aluminium.
**Compounds**: iron oxide (iron + oxygen), carbon dioxide (carbon + oxygen), hydrochloric acid (hydrogen + chlorine), water (hydrogen + oxygen).

Atomic structure of oxygen (element). Two oxygen atoms bond to form O₂ (diatomic element).

Atomic structure of argon (monatomic element).

Particle arrangement in solids, liquids, and gases – useful for understanding mixtures of different states.

Slides

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Practice questions

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1.Which of the following best describes an element?
Easy
- AA substance made from only one type of atom
- BA substance made from two or more different types of atom chemically joined
- CA substance containing two or more elements or compounds that are not chemically joined
- DA substance that can be separated by physical methods
2.What is a compound?
Easy
- AA substance where two or more atoms of different elements are chemically joined
- BA substance containing only one type of atom
- CA substance where two or more elements are mixed but not chemically joined
- DA substance that consists of only molecules
3.Which of the following is a mixture?
Easy
- AOxygen gas (O₂)
- BCarbon dioxide (CO₂)
- CAir (a mixture of gases)
- DWater (H₂O)
4.Which of the following substances is an element?
Medium
- AIron oxide
- BNitrogen
- CCarbon dioxide
- DWater
5.Which of the following is a compound?
Medium
- AOxygen
- BArgon
- CHydrochloric acid
- DNitrogen gas mixed with oxygen gas
6.What is the difference between an element and a compound?
Medium
- AAn element contains only one type of atom, while a compound contains two or more different types of atom chemically joined
- BAn element can be separated by physical methods, while a compound cannot
- CAn element is always a gas, while a compound is always a solid
- DAn element contains molecules, while a compound contains atoms
7.Which statement correctly describes the difference between a compound and a mixture?
Hard
- AIn a compound, different substances are chemically joined; in a mixture, they are not chemically joined
- BIn a compound, substances are physically combined; in a mixture, they are chemically combined
- CA compound can be separated by filtration, but a mixture cannot
- DA mixture always contains elements only, while a compound contains compounds only
8.Which of the following diagrams represents an element? (Assume different shapes represent different types of atoms)
Easy
- AA diagram showing only one type of atom (e.g., all circles the same)
- BA diagram showing two different types of atoms bonded together
- CA diagram showing two different types of atoms not bonded together
- DA diagram showing many different types of atoms all bonded

Revision notes

## Elements, Compounds & Mixtures - **Element**: made from only **one type of atom**. Listed on the periodic table (over 100 known). Examples: argon (monatomic gas), oxygen (diatomic gas). - **Compound**: two or more atoms of **different elements** chemically joined. Example: carbon dioxide (contains carbon and oxygen). - **Mixture**: contains two or more elements or compounds **not chemically joined**. Example: nitrogen gas mixed with oxygen gas (mixture of elements); carbon dioxide mixed with carbon monoxide (mixture of compounds). ### Key Differences - **Element vs Compound**: Element has one type of atom; compound has two or more different atoms chemically bonded. - **Compound vs Mixture**: In a compound, atoms are chemically joined; in a mixture, substances are not chemically joined and can be separated by physical means. ### Examples from Workbook - **Elements**: Iron, Nitrogen, Oxygen, Aluminium - **Compounds**: Iron Oxide, Carbon dioxide, Hydrochloric acid, Water - Compounds contain: Iron oxide (iron, oxygen); Carbon dioxide (carbon, oxygen); Hydrochloric acid (hydrogen, chlorine); Water (hydrogen, oxygen). ### Quick Check - Diatomic gas: two atoms chemically joined (e.g., O₂). - Monatomic gas: single atoms not joined (e.g., Ar).

Element: A substance made from only one type of atom.
Compound: A substance where two or more atoms of different elements are chemically joined.
Mixture: A substance that contains two or more elements or compounds that are not chemically joined together.
Diatomic gas: A gas that contains two atoms that are chemically joined (e.g., oxygen).
Monatomic gas: A gas that contains only single atoms that are not chemically joined (e.g., argon).

Flashcards

What is an element?

An element is made from only one type of atom. There are over 100 known elements listed on the periodic table.

What is a compound?

A compound is a substance where two or more atoms of different elements are chemically joined together.

What is a mixture?

A mixture is a substance that contains two or more elements or compounds that are not chemically joined together.

What is a diatomic gas?

A diatomic gas contains two atoms that are chemically joined, e.g., oxygen (O₂).

What is a monatomic gas?

A monatomic gas contains only single atoms that are not chemically joined, e.g., argon (Ar).

Is oxygen an element, compound, or mixture?

Oxygen is an element because it contains only one type of atom.

Is carbon dioxide an element, compound, or mixture?

Carbon dioxide is a compound because it contains atoms of carbon and oxygen chemically joined.

Is a mixture of nitrogen and oxygen an element, compound, or mixture?

It is a mixture of two different elements (nitrogen and oxygen) that are not chemically joined.

Is argon an element, compound, or mixture?

Argon is an element because it contains only one type of atom.

List the elements from: iron, iron oxide, nitrogen, oxygen, carbon dioxide, aluminium, hydrochloric acid, water.

Elements: iron, nitrogen, oxygen, aluminium.

List the compounds from: iron, iron oxide, nitrogen, oxygen, carbon dioxide, aluminium, hydrochloric acid, water.

Compounds: iron oxide, carbon dioxide, hydrochloric acid, water.

What elements does iron oxide contain?

Iron oxide contains iron and oxygen.

What elements does carbon dioxide contain?

Carbon dioxide contains carbon and oxygen.

What elements does hydrochloric acid contain?

Hydrochloric acid contains hydrogen and chlorine.

What elements does water contain?

Water contains hydrogen and oxygen.

Describe the difference between an element and a compound.

An element contains only one type of atom, while a compound contains two or more different types of atoms chemically joined.

Describe the difference between a compound and a mixture.

In a compound, atoms of different elements are chemically joined; in a mixture, substances are not chemically joined and can be separated by physical means.

How many known elements are there?

There are over 100 known elements.

Where are elements listed?

Elements are listed on the periodic table.

Give an example of a mixture of compounds.

Carbon dioxide mixed with carbon monoxide is a mixture of compounds.

Give an example of a mixture of elements.

Nitrogen gas mixed with oxygen gas is a mixture of elements.

What is the key difference between a diatomic and monatomic gas?

A diatomic gas has two atoms chemically joined; a monatomic gas has single atoms not chemically joined.

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