Properties of small molecules
Quick Starter
What do these
three substances
have in common?
show hint
show answer
© HarperCollinsPublishers 2016
Properties of small molecules
Quick Starter
What do these
three substances
have in common?
They are all gases
under normal
conditions
show hint
show answer
X
© HarperCollinsPublishers 2016
Properties of small molecules
Quick Starter
What do these
three substances
have in common?
show hint
show answer
© HarperCollinsPublishers 2016
Properties of small molecules
Quick Starter
They are harmful to human health or the climate
(CO and SO2 are toxic; CO2 can cause suffocation)
They all consist of small molecules, with covalent bonds
within the molecules and much weaker intermolecular
forces between molecules
Weak intermolecular forces explains why they are gases
even at low temperatures
back to question
© HarperCollinsPublishers 2016
Learning questions
• What are simple covalent structures?
• What do they have in common?
• Why do they show these properties?
Keywords:
Simple covalent, melting point, boiling point, properties, attraction, intermolecular forces,
weak, conductivity, energy.
© HarperCollinsPublishers 2016
NK
What are simple covalent structures?
• What type of elements are found in covalent
compounds?
• Non-metals only.
• Why are some structures called simple covalent
structures?
• Just a few atoms joined together by sharing
electrons. Not joined to other molecules.
Keywords:
Simple covalent, melting point, boiling point, properties, attraction, intermolecular forces,
weak, conductivity, energy.
© HarperCollinsPublishers 2016
What properties do simple covalent
molecules have?
• Lets see if they can conduct electricity.
• Write down your observations.
• Explain what you noticed and why you think it
happened. Try comparing the simple covalent
molecules to the ionic compounds, what is the
difference?
• Try heating a small amount in a boiling tube. What
do you notice? What does this tell you about their
melting/boiling points?
Keywords:
Simple covalent, melting point, boiling point, properties, attraction, intermolecular forces,
weak, conductivity, energy.
How are the particles arranged in a
solid, liquid and a gas?
• Do a quick diagram to
show them.
• What happens to
particles as they get
heated?
• Why do you think this
happens?
Main properties of simple covalent
molecules
• Don’t conduct electricity.
• Low melting and boiling points.
• Try and explain why this is.
Keywords
Intermolecular forces, charge, weak, attraction, covalent
molecules, electrons,
Extension: Why is it dangerous to take electrical
appliances near a bath as water doesn’t conduct
electricity?
Explaining properties of simple
molecules
Not conducting electricity
• Do they have a charge that can move?
• If not they can’t conduct electricty.
Low melting point
• Whilst they have strong bonds between atoms but
weak attractions between molecules which means
they can be separated easily.
• If the molecules are further aoart how does this
relate to its state? (solid, liquid, gas)
Compare the properties of sodium chloride
and water.
Include: Melting point, conductivity, type of
bonding, type of structure
Keywords:
Simple covalent, melting point, boiling point, properties, attraction, intermolecular forces,
weak, conductivity, energy.
Key points
Sodium chloride
• Giant ionic structure.
• Conducts electricity as
liquid not as solid.
• High melting point
Water
• Simple covalent
structure.
• Doesn’t conduct
electricity.
• Low melting point