1. Leaving Certificate Chemistry
3 – Chemical Compounds
Leaving Certificate Chemistry

2. Chemical Compounds
Carbon Dioxide (CO2) is an example of a compound

3. Further examples of chemical compounds
Sodium Chloride (NaCl)
Methane (CH4)

4. The Noble Gases
The Noble Gases are very unreactive - They are not found combined with any other element
Helium – a full outer shell of electrons
Argon – a full outer shell of electrons

5. The uses of helium & argon
Helium – used in weather balloons
Argon – used in light bulbs

6. Valence

7. The Octet Rule There are exceptions:
When elements combine they do so to ensure that the outermost electron of each bonding atom has 8 electrons in its outer shell.
There are exceptions:
Hydrogen and lithium look to have a full outer shell of 2 electrons.
Boron (element no.5) forms many compounds with 6 electrons in its outer shell.

8. Using valencies to predict the chemical formula of compounds
What is the chemical formula for hydrogen sulfide?
Hydrogen (H)
Sulfur (S)
Valence 1 2
Chemical Formula is H2S

9. Can you… Give the definition of a chemical compound?
Give some examples of compounds?
Tell some uses of noble gases
Say what the octet rule states and some exceptions
Define vacancy?

10. Some common groups Some common groups Hydroxide (OH)- 1
Complex ion name
Complex ion formula
Valency
Hydroxide
(OH)- 1
Hydrogen carbonate
HCO3-
Nitrate
NO3-
Carbonate
CO3-2 2
Sulfite
SO3 -2
Sulfate
SO4-2

11. Using valencies to predict the chemical formula of compounds
What is the chemical formula for Magnesium Hydroxide?
Magnesium (Mg)
Hydroxide
(OH)-
Valence 2 1
Chemical Formula is Mg (OH)2

12. Practice Questions Write the formula of each of the following:
Aluminium hydroxide
Calcium carbonate
Magnesium nitrate
Sodium hydrogencarbonate
Potassium sulfite
Aluminium sulfate

13. SO4-2 Fill in the gaps... Hydroxide HCO3- 1 Nitrate NO3- Carbonate
Complex ion name
Complex ion formula
Valency
Hydroxide
HCO3- 1
Nitrate
NO3-
Carbonate
SO3 -2 2
Sulfate
(OH)- 1
Hydrogen carbonate
CO3 - 2 2
Sulfite
SO4-2 2

14. Using valencies to predict the chemical formula of compounds
What is the chemical formula for Calcium carbonate?
Calcium (Ca)
Carbonate
(CO3-2)
Valency 2 2
Chemical Formula is Ca CO3

15. Using valencies to predict the chemical formula of compounds
What is the chemical formula for Magnesium Nitrate?
Magnesium (Mg)
Nitrate
(NO3-1)
Valency 2 1
Chemical Formula is Mg(NO3)2

16. Using valencies to predict the chemical formula of compounds
What is the chemical formula for Sodium Hydrogen carbonate?
Sodium (Na)
Hydrogen carbonate
(HCO3-1)
Valency 1 1
Chemical Formula is NaHCO3

17. Using valencies to predict the chemical formula of compounds
What is the chemical formula for Potassium Sulfite?
Sulfite
(SO3-2)
Potassium (K)
Valency 1 2
Chemical Formula is K2SO3

18. Using valencies to predict the chemical formula of compounds
What is the chemical formula for Aluminium sulfate?
Sulfate
(SO4-2)
Aluminium(Al)
Valency 3 2
Chemical Formula is Al2(SO4)3

19. Variable valances
The transition metals can have more than one valency number
Examples : Iron, Copper, Chromium and Manganese

20. Groups 3 -11 The d block metals
Includes the following elements:
Scandium (Sc)
Titanium (Ti)
Vanadium (V)
Chromium (Cr)
Manganese (Mn)
Iron (Fe)
Cobalt (Co)
Nickel (Ni)
Copper (Co)
Zinc (Zn) and others!
First row from scandium to zinc are called the d block elements
A transition element metal is one which forms at least one ion with a partially filled d sublevel
group 12 are not transition metals
They are all metals and are usually brightly coloured and act as catalysts for chemical reactions