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Understand Ionic Bonding

Worksheet Overview

QUESTION 1 of 10

A single atom is tiny, so to make anything interesting, we need to join atoms together. Chemists call this "making bonds between atoms". There are three ways of making bonds that you need to know; this activity will help you to learn about the first of them, which is called ionic bonding.

The first thing to remember is that all atoms are more stable if they have a stable outermost electron shell. Noble gases have this already, but most elements need to gain or lose electrons to become stable. Elements which need to lose electrons are called metals, and elements which need to gain electrons are called non-metals.

If you react a metal with a non-metal, the metal can lose its unwanted electrons, and the non-metal can take those electrons to get the extra electrons it needs. If you can imagine atoms being happy, both atoms would be happy. Because electrons have moved around, both atoms will become ions. Ions are charged atoms, where the number of protons isn't the same as the number of electrons. The metal will have fewer electrons than before, so it will be a positively charged ion. The non-metal will have more electrons than before, so will be a negatively charged ion.

The Periodic Table Group tells you which ion will form:

Group Ion charge
1 +1
2 +2
6 -2
7 -1
0 0

This seems difficult, but makes more sense with a real example. Sodium and chlorine react to make sodium chloride, which is the salt people put on food. Let's start with the electron structures of the atoms before the reaction:

Sodium is atomic number 11, so its electron structure is 2.8.1; chlorine is atomic number 17, so its electron structure is 2.8.7. We use different symbols for the electrons around each atom; I've used dots around the sodium and crosses around the chlorine. It doesn't matter where you use dots and where you use crosses, but they need to be distinct.

In this picture, each dot or cross represents a single electron. Sodium has one electron too many, and chlorine has one electron too few. Moving one electron from the sodium atom to the chlorine atom turns both atoms into stable ions. The sodium has +1 charge (it's lost one negatively charged electron), and the chlorine has -1 charge (it's gained one negatively charged electron). The chlorine atom gets a new name; we call it a chloride ion. The electron which moved from the sodium to the chlorine is drawn as a dot, to show where it came from.

Because the ions have opposite charges, they will be attracted to each other by electrostatic forces. That's why we talk about ionic bonding- the bond is an electrical force between different ions. Each positive ion attracts negative ions in all directions, so you get a repeating pattern which only stops when you run out of atoms.

The dot and cross diagram works a bit differently for different compounds. To see this, let's think about magnesium and chlorine reacting to make magnesium chloride.

Step 1: Draw the electron structure for the two elements you are reacting.

Magnesium has two electrons in its outermost shell, which it needs to lose. Chlorine has one empty slot in its outermost shell, which it needs to fill.

Step 2: Decide how many atoms you need of each element.

If each magnesium is losing two electrons, and each chlorine will only take one more, we need two chorines for each magnesium. 

Step 3: Redraw the electron structures, showing the transferred electrons.

Don't try and edit your initial diagrams; you will end up with a confusing mess.

Step 4: Put square brackets round the ions, and record their charges.

The magnesium is Mg2+ (it's lost two electrons) and each chlorine is Cl- (each chlorine gains one electron).

And that's it! Remember that ionic bonding happens between metals and non-metals, and works because the metal loses electrons, the non-metal gains electrons, and both atoms are more stable that way.

What do all atoms "want" to do?

Gain electrons

Get a stable outermost electron shell

Lose electrons

Match the types of element with the way they stabilise their outermost shell.

Column A

Column B

Metals
Lose electrons
Non-metals
Gain electrons
Noble gases
Do nothing

The electron structure for aluminium is 2.8.3. What has to happen for it to have a stable outer shell of electrons?

Gain three electrons

Gain one electron

Lose one electron

Lose three electrons

What ion does aluminium form?

Al+

Al3+

Al-

Al3-

The electron structure for oxygen is 2.6. What has to happen for it to have a stable outer shell of electrons?

Gain three electrons

Gain two electrons

Lose one electron

Lose two electrons

What ion does oxygen form?

O+

O2+

O-

O2-

Look at this dot and cross diagram.

 

Mark this description of the diagram- tick each correct sentence.

Oxygen has gained two electrons

Each lithium has lost two electrons

The lithium ions are positive

The oxygen ions are positive

Match these groups in the Periodic Table with the ions they form.

Column A

Column B

Group 1
-3
Group 2
+2
Group 6
+1
Group 7
-2

Which of these dot and cross diagrams shows lithium chloride?

A
B
C

 




Draw the dot and cross diagram for magnesium sulfide. Once you've tried drawing this for yourself, choose one of the options below.

A
B
C

 




  • Question 1

What do all atoms "want" to do?

CORRECT ANSWER
Get a stable outermost electron shell
EDDIE SAYS
There are different ways of getting to a stable outermost electron shell, which is important for thinking about how bonding happens. The next question will help you think about this some more.
  • Question 2

Match the types of element with the way they stabilise their outermost shell.

CORRECT ANSWER

Column A

Column B

Metals
Lose electrons
Non-metals
Gain electrons
Noble gases
Do nothing
EDDIE SAYS
Noble gases don't need to do anything, because they already have a stable outermost shell.
  • Question 3

The electron structure for aluminium is 2.8.3. What has to happen for it to have a stable outer shell of electrons?

CORRECT ANSWER
Lose three electrons
EDDIE SAYS
The three in 2.8.3 tells us that there are three electrons in the outer shell for an aluminium atom. To get rid of that shell- and make the stable second shell the outermost one- means losing all three electrons.
  • Question 4

What ion does aluminium form?

CORRECT ANSWER
Al3+
EDDIE SAYS
Aluminium needs to lose three electrons to make a stable ion. Because three negatively charged particles have gone, the ion that's left is positively charged.
  • Question 5

The electron structure for oxygen is 2.6. What has to happen for it to have a stable outer shell of electrons?

CORRECT ANSWER
Gain two electrons
EDDIE SAYS
The six in 2.6 tells us that there are six electrons in the outer shell for an oxygen atom. To make that outer shell stable, we need to add two electrons to fill up the outer shell.
  • Question 6

What ion does oxygen form?

CORRECT ANSWER
O2-
EDDIE SAYS
Oxygen needs to lose two electrons to make a stable ion. Because two negatively charged particles have been added, the ion that's formed is negatively charged.
  • Question 7

Look at this dot and cross diagram.

 

Mark this description of the diagram- tick each correct sentence.

CORRECT ANSWER
Oxygen has gained two electrons
The lithium ions are positive
EDDIE SAYS
The oxygen has gained two electrons, so each lithium has lost one. Ionic bonding doesn't make or destroy electrons, it just moves them around. The oxygen ion has more electrons than before, so it's now negatively charged.
  • Question 8

Match these groups in the Periodic Table with the ions they form.

CORRECT ANSWER

Column A

Column B

Group 1
+1
Group 2
+2
Group 6
-2
Group 7
-3
EDDIE SAYS
The link between the Groups and ions is the number of electrons in the outermost shell. All the elements in Group 1 have 1 outermost electron, which they lose to form a stable (positive) ion.
  • Question 9

Which of these dot and cross diagrams shows lithium chloride?

A
B
C

 

CORRECT ANSWER
EDDIE SAYS
Lithium starts with one electron in its second shell, which then moves over to the chlorine. We have to draw where the electrons are after this transfer; it's not enough just to mark it with an arrow.
  • Question 10

Draw the dot and cross diagram for magnesium sulfide. Once you've tried drawing this for yourself, choose one of the options below.

A
B
C

 

CORRECT ANSWER
EDDIE SAYS
Magnesium is in Group 2, so needs to lose 2 electrons. Sulfur is in Group 6, so needs to gain 2 electrons.
---- OR ----

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