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Explain 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 that "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 hard, 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:

In this diagram, each dot or cross represents an electron. We can also use numbers to show the electron configurations; sodium is 2.8.1 and chlorine is 2.8.7. Sodium has one electron too many, and chlorine has one electron too few. Moving one electron from the sodium atom to the chlorine atom makes 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 over from the sodium to the chlorine is still drawn as a dot, because that shows us where the electron 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.

Fill in the gaps in this paragraph about electron shells. Use these words:

electrons

lose

negative

noble

non-metals

outermost

positive

The electron structure for phosphorus is 2.8.5. What ion will it form?

What ion does oxygen form?

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

Column A

Column B

Group 1
-1
Group 2
+1
Group 6
+2
Group 7
-2
A
B
C

Which of these dot and cross diagrams shows lithium chloride?




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

 




Which of these is the right formula for sodium sulfide?

NaS

Na2S

Na3S

NaS2

Which is the right formula for strontium bromide?

SrBr

Sr2Br

SrBr2

Sr2Br3

Iron is unusual, because it can form two different ions- Fe2+ and Fe3+. Match these ions with the forms of iron oxide they make,

Column A

Column B

FeO
comes from Fe2+
Fe2O3
comes from Fe3+
Fe3O2
is not possible

Which of these compounds will make ionic bonds? Tick all the correct answers.

iron oxide

nickel chloride

carbon chloride

sulfur nitride

zinc bromide

  • Question 1

Fill in the gaps in this paragraph about electron shells. Use these words:

electrons

lose

negative

noble

non-metals

outermost

positive

CORRECT ANSWER
EDDIE SAYS
Noble gases don't need to do anything, because they already have a stable outermost shell.
  • Question 2

The electron structure for phosphorus is 2.8.5. What ion will it form?

CORRECT ANSWER
EDDIE SAYS
The five in 2.8.5 tells us that there are five electrons in the outer shell for an phosphorus atom. To complete that shell means gaining three electrons, leading to a 3- ion.
  • Question 3

What ion does oxygen form?

CORRECT ANSWER
EDDIE SAYS
Oxygen has six electrons in the outer shell. To make that outer shell stable, we need to add two electrons to fill up the outer shell.
  • Question 4

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
-1
Group 7
-2
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 5
A
B
C

Which of these dot and cross diagrams shows lithium chloride?

CORRECT ANSWER
EDDIE SAYS
Lithium loses one electron, and chlorine gains one electron. You need to show the electron in its new place (round the chlorine), but it stays as a dot, to remind us that it was originally attached to the lithium.
  • Question 6

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
Beryllium is in Group 2, so needs to lose 2 electrons, making a +2 ion. Oxygen is in Group 6, so needs to gain 2 electrons, making a -2 ion.
  • Question 7

Which of these is the right formula for sodium sulfide?

CORRECT ANSWER
Na2S
EDDIE SAYS
Sodium forms 1+ ions, and sulfur forms 2- ions. This means that we need two sodiums for each sulfur.
  • Question 8

Which is the right formula for strontium bromide?

CORRECT ANSWER
SrBr2
EDDIE SAYS
Sr is in group 2, so forms 2+ ions. Br is in group 7, so forms 1- ions. That means we needs twice as many bromides as strontiums to balance the electrons.
  • Question 9

Iron is unusual, because it can form two different ions- Fe2+ and Fe3+. Match these ions with the forms of iron oxide they make,

CORRECT ANSWER

Column A

Column B

FeO
comes from Fe2+
Fe2O3
comes from Fe3+
Fe3O2
is not possible
EDDIE SAYS
Oxygen forms 2- ions, so one Fe2+ matches one O2-. If you start with Fe3+, you need one and a half oxide ions. We write this as Fe2O3.
  • Question 10

Which of these compounds will make ionic bonds? Tick all the correct answers.

CORRECT ANSWER
iron oxide
nickel chloride
zinc bromide
EDDIE SAYS
For ionic bonding, we need a metal and a non-metal.
---- OR ----

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