1. Why compounds are formed
20/09/2018
Why compounds are formed

2. Most elements form compounds
20/09/2018
Elements react together to form compounds. Here are some examples:
Sodium chloride (salt)
Sulphuric acid, H2SO4

3. Atoms
20/09/2018
Remember, atoms are the “building blocks” of all matter. They are all made up of protons, neutrons and electrons. They look something like this:
The Nucleus – this contains neutrons and protons
Electrons – these orbit around the nucleus

4. Electron structure 39 K 19 Consider an atom of Potassium:
20/09/2018
Consider an atom of Potassium:
Nucleus K 19 39
Potassium has 19 electrons. These are arranged in shells…
The inner shell has __ electrons
The next shell has __ electrons
The next shell has the remaining __ electron
Electron structure
= 2,8,8,1

5. Why do atoms react together?
20/09/2018
By reacting with each other, atoms can obtain full outer shells and so become stable. A full outer shell makes an atom stable. The noble or inert gases are different from other elements because they are un-reactive or stable as their outer shells are full. He Ne Ar Kr Xe Rn

6. This is called an ion (in this case, a positive hydrogen ion)
Atoms form ions
20/09/2018
Atoms of some elements can obtain full shells by losing or gaining electrons, when they react with other atoms. An ion is formed when an atom gains or loses electrons & becomes charged. + -
The electron is negatively charged
The proton is positively charged + +
If we “take away” the electron we’re left with just a positive charge:
This is called an ion (in this case, a positive hydrogen ion)

7. The electron arrangement of the atoms on the Periodic Table tells you which atoms will form ions. Metals form positive ions and most non-metals form negative ions.
20/09/2018 ) )
Electron transferred
Figure: 02-03a
Title:
The formation of ions and ionic bonds.
Caption:
(a) Sodium has only one electron in its outer electron shell; chlorine has seven.

8. Metals form positive ions
20/09/2018
Consider a sodium atom: +
Loses one of the electrons
Sodium ion
Na+
Now consider a potassium atom: +
Loses one of the electrons
Potassium ion K+
Potassium loses its electron more easily because its further away – potassium is MORE REACTIVE

9. Non-metals form negative ions
20/09/2018
Consider a fluorine atom: -
Gains an electron
Fluoride ion F-
Now consider a chlorine atom: -
Gains an electron
Chloride ion
Cl-
Chlorine doesn’t gain an electron as easily as fluorine so it is LESS REACTIVE

10. Ionic bonding Na Cl Na + Cl -
20/09/2018
When two ions have opposite charges they attract each other. The force of attraction between them is strong and is called an ionic bond. For example, consider sodium and chlorine:
Sodium has 1 electron on its outer shell and chlorine has 7, so if sodium gives its electron to chlorine they both have a ___ outer shell and are ______.
A _______ charged sodium ion
A _________ charged chloride ion
Ionic bonds form strong forces of attraction between different ions due to their opposite ______, causing GIANT IONIC STRUCTURES to form (e.g sodium chloride) with ______ melting and boiling points. Na Cl Na + Cl -

11. Chlorine atom (neutral)
20/09/2018
Sodium atom (neutral)
Chlorine atom (neutral)
Electron transferred
Figure: 02-03a
Title:
The formation of ions and ionic bonds.
Caption:
(a) Sodium has only one electron in its outer electron shell; chlorine has seven.

12. Sodium ion (+) Chlorine ion (–)
20/09/2018
Sodium ion (+)
Chlorine ion (–)
Figure: 02-03b
Title:
The formation of ions and ionic bonds.
Caption:
(b) Sodium can become stable by losing an electron, and chlorine can become stable by gaining an electron. Sodium becomes a positively charged ion and chlorine a negatively charged ion.
Attraction between opposite charges

13. Properties of elements vs compounds
20/09/2018
Properties of elements vs compounds
Properties of the compound can be very different from the properties of the individual elements that form it.
For example, table salt (NaCl), is made up of sodium and chlorine, two dangerous elements on their own!
Na is a silvery, white metal that is explosive when combined with oxygen.
Cl is a poisonous greenish-yellowish gas.
NaCl is a white solid that is great on french fries.
sodium chloride table salt
+ =

14. Some other examples + + Magnesium chloride: Cl Cl Mg Mg Cl Cl MgCl2
20/09/2018 Cl -
Magnesium chloride: Cl Mg 2+ Mg + Cl - Cl
MgCl2
Calcium oxide: O Ca + 2+ 2-
CaO

15. Water, iron oxide or carbon dioxide?
Making compounds
20/09/2018
Compounds are made when two or more elements (or compounds) go through a chemical reaction.
For example:
When carbon reacts with oxygen it usually forms ____ _________
When oxygen reacts with hydrogen it could form ______
When iron reacts with oxygen it could form ______ ______
There are usually “tell-tale” signs to show when a compound is being made, such as bubbling, heat given off, colour changes, fizzing etc.
Water, iron oxide or carbon dioxide?

16. Rule 1 – When two elements join the end is usually _______ide.
Naming compounds
20/09/2018
Rule 1 – When two elements join the end is usually _______ide.
e.g. Magnesium + oxygen magnesium oxide
Sodium + chlorine
Magnesium + fluorine
Lithium + iodine
Chlorine + copper
Oxygen + iron
KBr
LiCl
CaO
MgO2 KF

17. e.g. Copper + sulphur + oxygen Copper sulphate
Naming compounds
20/09/2018
Rule 2 – When three or more elements combine and one of them is oxygen the ending is _____ate
e.g. Copper + sulphur + oxygen Copper sulphate
Calcium + carbon + oxygen
Potassium + carbon + oxygen
Calcium + sulphur + oxygen
Magnesium + chlorine + oxygen
Calcium + oxygen + nitrogen
AgNO3
H2SO4
K2CO3