Leaving Certificate Chemistry 3 – Chemical Compounds Leaving Certificate Chemistry

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

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

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

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

Valence

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.

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

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?

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

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

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

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

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

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

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

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

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

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

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