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Compounds

In this worksheet, students will explore compounds. The Periodic Table lists all the elements that have been discovered so far, but what is created when these atoms combine?

'Compounds' worksheet

Key stage:  KS 3

Curriculum topic:  Chemistry: Atoms, Elements and Compounds

Curriculum subtopic:  Atoms, Elements and Compounds

Difficulty level:  

Worksheet Overview

QUESTION 1 of 10

The alphabet contains 26 letters, but how many words can you think of... thousands, hundreds of thousands, millions? Combining the letters of the alphabet allows us to create lots and lots of words.

 

This is similar to chemistry. The Periodic Table is composed of over a hundred elements and when these elements combine they form compounds. This means that there are billions of possible compounds in existence. 

 

A compound is made of two or more elements chemically joined together.

 

Elements can combine during chemical reactions to form new compounds. For example:

 

Magnesium + Oxygen Magnesium Oxide
ELEMENT   ELEMENT   COMPOUND

 

Compounds are usually completely different from the elements that formed them. Magnesium is a silver shiny highly flammable metal. Oxygen is a colourless gas. Magnesium oxide however, is a white powder.

 

A molecule is formed when a small group of atoms are joined together.

 

These atoms may all be the same such as in hydrogen (H2) which is a molecule of an element or different, such as water (H2O) which is a molecule of a compound.

 

Hydrogen molecule Water molecule
Hydrogen Molecule Water Module

Which of the following is a compound?

oxygen

magnesium

water

carbon

silver

Which of the following is an element?

water

carbon dioxide

hydrogen

hydrogen fluoride

sodium oxide

Which of the following could be the correct formula of the molecule shown below?

 

Molecule of 3 different atoms

C2H5OH

H2O

CH4

Match the chemical names on the left to the correct descriptions on the right.

Column A

Column B

magnesium oxide
element
carbon dioxide
compound
silicon
element
methane
compound
nitrogen
element
oxygen
compound

The metal sodium reacts with water in a very exothermic reaction. Which of the following compounds could be the product of this reaction?

potassium hydroxide

sodium hydroxide

calcium carbonate

sodium carbonate

calcium hydroxide

Which is the correct equation for the reaction which forms the compound potassium oxide?

 

A) potassium + potassum oxide  oxygen

B) potassium oxide + oxygen potassium oxide

C) potassium + oxygen potassium oxide

A

B

C

A molecule of sulfur dioxide contains sulfur and oxygen atoms. For every sulfur atom the molecule contains two oxygen atoms.

Which of the following is the correct formula of sulfur oxide?

S2O

SO2

SO

Hydrogen is a very flammable gas. When it burns lots of energy is released and water is produced. 

 

Use this information to match each of the terms reactant or product to the chemicals shown below.

Column A

Column B

hydrogen
product
water
reactant
oxygen
reactant

Carbon reacts with hydrogen to form methane gas, which is the main constituent of natural gas. 

 

Use this information to match each of the terms reactant or product to the chemicals shown below.

Column A

Column B

carbon
reactant
hydrogen
reactant
methane
product
  • Question 1

Which of the following is a compound?

CORRECT ANSWER
water
EDDIE SAYS
Water is a compound composed of hydrogen and oxygen atoms: two hydrogen atoms to one oxygen atom, i.e. H20.
  • Question 2

Which of the following is an element?

CORRECT ANSWER
hydrogen
EDDIE SAYS
All the known elements are in the Periodic Table. If it is not listed in the Periodic Table then it is not an element! Sometimes, having two words (like 'carbon dioxide') is a clue that it's not an element, but that doesn't always work (e.g. 'water'). Hydrogen is made ONLY of hydrogen atoms, so it's an element.
  • Question 3

Which of the following could be the correct formula of the molecule shown below?

 

Molecule of 3 different atoms

CORRECT ANSWER
C2H5OH
EDDIE SAYS
Look closely at the molecule. It has 2 grey atoms (carbon), 6 blue atoms (hydrogen) and 1 red atom (oxygen). It has three elements combined to form the compound so it can't be H2O or CH4. The molecule shown is ethanol which is better know as alcohol.
  • Question 4

Match the chemical names on the left to the correct descriptions on the right.

CORRECT ANSWER

Column A

Column B

magnesium oxide
compound
carbon dioxide
compound
silicon
element
methane
compound
nitrogen
element
oxygen
element
EDDIE SAYS
Most compounds are usually easily identified by their name, but some can have other names. For example, the correct chemical name of methane is carbon hydride (CH4).
  • Question 5

The metal sodium reacts with water in a very exothermic reaction. Which of the following compounds could be the product of this reaction?

CORRECT ANSWER
sodium hydroxide
EDDIE SAYS
When sodium reacts with water, sodium hydroxide and hydrogen are produced. The other options contain elements that were not part of the reaction and therefore cannot be part of the product, such as calcium, potassium and carbon. Look at it this way: if you mix together flour, eggs, butter and sugar and pop it into the oven and, an hour later, take it out of the oven, what's the chance that you're looking at a roast chicken?! If you started off with sodium and water (H20 ), there's no way you can end up with some calcium, potassium or whatever atoms: only SODIUM, OXYGEN AND HYDROGEN. That's it!
  • Question 6

Which is the correct equation for the reaction which forms the compound potassium oxide?

 

A) potassium + potassum oxide  oxygen

B) potassium oxide + oxygen potassium oxide

C) potassium + oxygen potassium oxide

CORRECT ANSWER
C
EDDIE SAYS
The reactants - potassium and oxygen - must be on the left of the arrow as the product is on the right.
  • Question 7

A molecule of sulfur dioxide contains sulfur and oxygen atoms. For every sulfur atom the molecule contains two oxygen atoms.

Which of the following is the correct formula of sulfur oxide?

CORRECT ANSWER
SO2
EDDIE SAYS
Read the text carefully 'For every sulphur atom the molecule contains two oxygen atoms.' This statement tells you the formula. There is one sulfur atom for two oxygen atoms so the formula is SO2.
  • Question 8

Hydrogen is a very flammable gas. When it burns lots of energy is released and water is produced. 

 

Use this information to match each of the terms reactant or product to the chemicals shown below.

CORRECT ANSWER

Column A

Column B

hydrogen
reactant
water
product
oxygen
reactant
EDDIE SAYS
So, that's: HYDROGEN + OXYGEN → HYDROGEN OXIDE (WATER) All combustion reactions involve oxygen. So when hydrogen burns only water is produced. This is why some scientists believe that hydrogen maybe the fuel of the future.
  • Question 9

Carbon reacts with hydrogen to form methane gas, which is the main constituent of natural gas. 

 

Use this information to match each of the terms reactant or product to the chemicals shown below.

CORRECT ANSWER

Column A

Column B

carbon
reactant
hydrogen
reactant
methane
product
EDDIE SAYS
So, that's: CARBON + HYDROGEN → METHANE Methane has the formula CH4. This means that each molecule of methane has one carbon atom and four hydrogen atoms.
---- OR ----

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