Atoms, Elements and Compounds Worksheet - KS3 - Intermediate

Atoms, Elements and Compounds worksheet for KS3 (Key Stage 3 / Year 7-9 (Ages 11-14)). Intermediate level science practice, aligned to the UK National Curriculum. Print-ready with answer key included.

Science•Key Stage 3 / Year 7-9 (Ages 11-14)•Atoms, Elements and Compoundsintermediate

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Atoms, Elements and Compounds: The Building Blocks of Matter

Key Stage 3 Science | Ages 11–14 | Intermediate

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Instructions: Work through the activities in order, using the information in each question and your knowledge of particle models and the periodic table. Write clearly in the answer boxes and show any reasoning needed. Chemical symbols use a capital letter first; a second letter, when present, is lower case.

Sort the substances

Classify each substance as an element, compound or mixture. An element contains one type of atom; a compound contains different elements chemically joined; a mixture contains substances together without them being chemically joined. Write one classification for each item.

1. Copper wire (Cu)

2. Pure water (H₂O)

3. Air, containing nitrogen, oxygen and other gases

4. Sodium chloride (NaCl)

5. Sulphur powder (S)

Read the particle descriptions

Use each description to decide what kind of substance is represented. A particle may be a single atom or a group of atoms joined together. Explain your classification briefly in each answer.

1. Every particle is one oxygen atom; no other type of atom is present. Is the substance an element, compound or mixture?

2. Every particle contains one carbon atom chemically joined to two oxygen atoms. Is the substance an element, compound or mixture?

3. The sample contains separate helium atoms and oxygen molecules, with no chemical bonds between the different particles. Is the sample an element, compound or mixture?

4. Every particle contains two hydrogen atoms chemically joined to one oxygen atom. Is the substance an element, compound or mixture?

Chemical symbols and formulae

Complete each item using the element names and symbols you know. Remember that a symbol may have one or two letters, and only the first letter is capitalised. For formula questions, count the atoms represented by the formula.

1. Write the chemical symbol for sodium.

2. Write the chemical symbol for iron.

3. Name the element represented by the symbol Cl.

4. How many oxygen atoms are shown in CO₂?

5. How many different elements are present in H₂O?

Explore the periodic table

Use the element data supplied in the table. A period is a horizontal row and a group is a vertical column. Answer each question from the table, then use your knowledge of the periodic table for the final question.

Element	Symbol	Group	Period
Hydrogen	H	1	1
Carbon	C	14	2
Oxygen	O	16	2
Sodium	Na	1	3
Chlorine	Cl	17	3
Argon	Ar	18	3

1. Which listed element is in Group 17?

2. Which two listed elements are in Period 3 and Group 1 or Group 17?

3. What is the symbol for the element in Group 18, Period 3?

4. Which listed element is in Period 2 and has the greatest group number?

Apply your understanding

Choose the best answer for each question. Read every option carefully; some substances that look similar may be classified differently because of how their particles are joined.

1. Which statement describes an element?

2. Which formula represents a compound?

3. In a mixture, the different substances are usually…

4. Which pair contains two elements?

Answer Key

Activity 1: Element ; Compound ; Mixture ; Compound ; Element

Activity 2: Element — only oxygen atoms are present ; Compound — carbon and oxygen atoms are chemically joined ; Mixture — helium and oxygen particles are present without being chemically joined ; Compound — hydrogen and oxygen atoms are chemically joined

Activity 3: Na ; Fe ; Chlorine ; 2 ; 2

Activity 4: Chlorine ; Sodium and chlorine ; Ar ; Oxygen

Activity 5: A substance made from one type of atom ; CO₂ ; not chemically joined to each other ; Copper and oxygen