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Define Atoms, Elements, Compounds and Mixtures

In this worksheet, students will learn about atoms and the different ways of mixing and combining atoms to make substances.

Worksheet Overview

QUESTION 1 of 10

How can we work out what things are made of? Imagine cutting something (like a cake) into smaller and smaller pieces. First, we have slices, then crumbs, then little crumbs, until we have pieces so small that they can't be cut any more; even with a magic microscopic knife. The smallest possible pieces are called atoms, and everything is made of atoms.

There are about 120 different types of atom, but that's enough to make everything around us. Atoms are a lot like toy blocks. You can use a few types of block to make all sorts of things, depending on how you join them together. In the same way, different things are made of different atoms combined in different patterns.

 

Each atom has a name and a symbol. You need to know the names and symbols for the first twenty. This looks scary, but if you test yourself on a few at a time, you will soon know them all by heart.

Below are the names and symbols for the first twenty atoms.

 

Hydrogen H Carbon C Sodium Na Sulfur S
Helium He Nitrogen N Magnesium Mg Chlorine Cl
Lithium Li Oxygen O Aluminium Al Argon Ar
Beryllium Be Fluorine F Silicon Si Potassium K
Boron B Neon Ne Phosphorus P Calcium Ca

 

The symbols are always either a capital letter or a capital letter followed by a lower case letter. Most of the symbols start with the same letter as the atom's name, but not all- can you see which atoms have symbols which don't match their name?

Because atoms are so small, we need to think about how to combine them to make things. There are three main ways of doing this:

In an element, all the atoms are the same type. In pure gold bars, all the atoms are gold atoms. When a scientist draws a picture of the atoms in a gold bar, all the atoms look the same.


Gold BarsAtomic structure of gold

 

In a compound, different atoms are joined together (chemists say "bonded"), but in fixed patterns. Water is a compound of hydrogen and oxygen, with two hydrogen atoms for each oxygen atom. In the atomic picture, the two white balls are hydrogen atoms, and the red ball is an oxygen atom.


Glass of water Atomic structure of water


Table salt is a compound of sodium and chlorine, with one sodium atom for each chlorine atom. In this atomic picture, purple means sodium and green means chlorine.


Atomic structure of sodium chloride

 

In a mixture, different elements or compounds are in the same container, but they are not bonded, and they have no pattern. Seawater contains water and dissolved salt, but they don't make a new compound, they are still water and salt.
 

If you have a mixture, you can usually separate it back into different pure elements and compounds. Some ways of separating a mixture are:

 

Filtration, using a sieve or filter paper.


 

Crystallisation, where we remove the liquid by heating it so that it evaporates; the solid gets left behind.

Simple distillation, where we heat a liquid so that it evaporates. We collect the vapour and cool it back down to collect a pure liquid.


 

Fractional distillation, which is like simple distillation, except that we carefully collect different liquids which condense at different temperatures.

Chromatography separates different substances dissolved in a solution, for example, different colours mixed together to make ink.

You will learn a lot more about these methods in another activity. For now, the important thing to remember is that mixtures are fairly easy to separate into pure elements or pure compounds.

Which of these phrases describes an atom best?

Atoms are things we can see

They are tiny particles which everything is made of

There are about 120 types of atom

All atoms are the same

Which of these phrases explains how atoms are like toy blocks?

Atoms have different colours and shapes

Atoms are about as big as toy blocks

Atoms are lumpy when we touch them

We can make many different things by combining blocks in different patterns

Match these element names with their symbols.

Column A

Column B

Hydrogen
C
Oxygen
O
Carbon
Mg
Nitrogen
H
Magnesium
N

Which of these is the right way to write the symbol for helium?

HE

He

he

Match these element names up with their symbols.

Column A

Column B

Helium
K
Lithium
Cl
Sodium
Li
Chlorine
Na
Potassium
He

Match these words up with their meanings:

Column A

Column B

Pure element
mixed up pieces of element or compound
Pure compound
different atoms bonded in a pattern
Mixture
all the atoms are the same type

Does this picture show an element, a compound or a mixture?

Element

Compound

Mixture

We can't be sure

Does this picture show an element, compound or mixture?

Element

Compound

Mixture

We can't be sure

How do you separate sand from water?

Simple distillation

Chromatography

Filtration

Evaporation

How do we separate different colours in ink?

Filtration

Evaporation

Distillation

Chromatography

  • Question 1

Which of these phrases describes an atom best?

CORRECT ANSWER
They are tiny particles which everything is made of
EDDIE SAYS
If a question asks you to choose the best option, be very careful! There could be some answers which are sort-of true, but aren't as good as the right answer. There are about 120 types of atom but that doesn't describe what atoms are really like. There are different types of atom, but they are all too small to be visible.
  • Question 2

Which of these phrases explains how atoms are like toy blocks?

CORRECT ANSWER
We can make many different things by combining blocks in different patterns
EDDIE SAYS
Thinking about atoms as like toy blocks helps us to understand how a small number of atoms can make so many different things, but atoms don't really look like that. They are much, much smaller, so small that they don't really have shape or colour at all. We pretend they do so that we can see pictures of them in our mind.
  • Question 3

Match these element names with their symbols.

CORRECT ANSWER

Column A

Column B

Hydrogen
H
Oxygen
O
Carbon
C
Nitrogen
N
Magnesium
Mg
EDDIE SAYS
Once you've got these right, you know a quarter of the names and symbols you need. That's a good start! Don't worry if it takes a few attempts, keep coming back to this question until you memorise the element names above and their corresponding symbol.
  • Question 4

Which of these is the right way to write the symbol for helium?

CORRECT ANSWER
He
EDDIE SAYS
It seems picky, but the capital letter rule is really important and useful. For compounds, you need to write the element symbols one after another, so sodium chloride is NaCl. When you've read this, the capital letters tell you that a new element is beginning; it's a bit like a full stop and a capital letter between sentences.
  • Question 5

Match these element names up with their symbols.

CORRECT ANSWER

Column A

Column B

Helium
He
Lithium
Li
Sodium
Na
Chlorine
Cl
Potassium
K
EDDIE SAYS
Once you can get Q3 and Q5 right every time, without looking, you know half of the chemical symbols you need to know. Keep practising them, and soon you'll know them by heart. This set is a bit trickier than the first set. Remember that sodium and potassium don't have obvious symbols. Na comes from the Latin word "natrium", and K comes from the latin word "kalium", but you don't need to remember that!
  • Question 6

Match these words up with their meanings:

CORRECT ANSWER

Column A

Column B

Pure element
all the atoms are the same type
Pure compound
different atoms bonded in a patte...
Mixture
mixed up pieces of element or com...
EDDIE SAYS
Remember that both elements and compounds are pure. Once different atoms are bonded together as a compound they count as a pure substance.
  • Question 7

Does this picture show an element, a compound or a mixture?

CORRECT ANSWER
Compound
EDDIE SAYS
This picture is a compound, because there are two different types of atom. It's actually ice, the red balls are oxygen and the white ones are hydrogen.
  • Question 8

Does this picture show an element, compound or mixture?

CORRECT ANSWER
Element
EDDIE SAYS
This picture is a pure element because all the atoms are the same. They are all carbon atoms, and this picture shows the structure of diamond.
  • Question 9

How do you separate sand from water?

CORRECT ANSWER
Filtration
EDDIE SAYS
Filtration works because sand is solid, so it will get trapped in the filter. A sieve would work if the holes were smaller than the sand grains.
  • Question 10

How do we separate different colours in ink?

CORRECT ANSWER
Chromatography
EDDIE SAYS
Chromatography is useful when we have different substances dissolved in water or another solvent. We can also use it to test chemicals in food or looking for poisons dissolved in the blood. Great focus, that's another activity completed!
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