Ionic bonding

Atoms are only "happy" when their outside layers are either completely full or completely empty. The atom on the left had 2 atoms on its outside layer.
To get a completely empty layer, it loses two electrons. Taking away 2 negative electrons makes it doubly positive (2+).

The atom on the right had only 6 electrons on its outside layer. It needs 8 to have a full layer so it gains two electrons. Gaining 2 negative electrons makes it doubly negative (2-).

Opposites attract so the (2+) and the (2-) stay together. This is an ionic bond. The bonds are very strong so ionic compounds have very high melting and boiling points.

How to work out where to put electrons

To work out where to put the electrons, start by looking at the Periodic Table. You need the bottom number to give you the number of electrons.

Let's start with ALUMINIUM. It has 13 electrons because the bottom number is 13.

We get the 13 like this:

• The first 2 go on the inside layer.
• The next 8 go on the second layer out.
• 2 and 8 make 10. That means there are 3 left for the outside layer.

Oxygen is the next example. It's bottom number on the Periodic Table is 8.

• 2 on the inside layer.
• That means that there are 6 left to go on the second layer. (It can have up to 8)
  
  
  

Final example is lithium. It's bottom number is 3.

• 2 on the inside layer.
• That leaves 1 on the second layer this time.
  
  

Electrolysis

Electolysis is where we use an electric current to split up an ionic compound that has been dissolved in water.

Our example was sodium chloride solution (salt water)

It contains H+ and OH- ions from the water.
It contains Na+ and Cl- ions from the chlorine.

Two Cl- ions lose 2 electrons at the positive electrode and turn into chlorine gas. It bleached blue litmus paper, turning it white.

The two electrons join up with two H+ ions at the negative electrode to make hydrogen gas.

Na+ and OH- are left behind. This makes sodium hydroxide which is an alkali and turns the universal indicator purple.

Re-sit papers

If you are re-sitting the year 10 modules on Monday 23 June, here's a link to get you the past papers that you need. There are mark schemes too.

http://www.aqa.org.uk/qual/gcse/newscience/extassessover.php

Star formation

Satellites

A geostationary orbit is one above the equator. It takes the satellite 24 hours to go round once. This means that satellite Y is always above town A. (Note that the satellite doesn't stay still. It does move but so does town A. They stay fixed relative to each other.)

• Used for communications eg phone and TV
• Because the satellite is in a fixed position relative to the Earth so dishes can always point in the same direction.
• GPS satellites are geostationary too.
• You SatNav constantly checks where it is in relation to these satellites.

Polar orbit goes over the poles and covers a lot of territory.

• Many countries visited so good for spying.
• Close to the ground so better photos (GoogleEarth)
• Weather photos

Ultrasound

Think about what happens when light hits a window. Some of it goes through and some is reflected. You can choose to focus on what is reflected or on what is on the other side of the window. We call this partial reflection.

In the same way, ultrasound is partially reflected when it goes from one medium into another medium. The ultrasound changes speed when it goes from one medium to another. The bigger the change in speed, the more is reflected. It is the reflection that allows us to make up a picture using ultrasound scanning for eg foetuses.

There is a big change in speed between air and muscle, so if you fire ultrasound towards a woman's stomach, it would mostly reflect and not get into her. For this reason, they smear saline gel on first because there is less of a reflection between saline gel and muscle.