7 - Types of Substance Flashcards
What are the properties of a compound influenced by?
- Atoms
- Type of bonding
What is simple molecular also known as?
Simple covalent
What type of elements are simple molecular compounds made of?
Non metal
What are the physical properties of simple molecular substances?
- LOW melting & boiling points
- Insoluble in water (some are soluble)
- CAN NOT conduct electricity
Why do simple molecular compounds not conduct electricity?
As the small molecules do not have an overall electric charge
Why are some simple molecular compounds soluble in water?
As they can form intermolecular forces with water which are stronger than those between water molecules or their own molecules already
What state are simple molecular substances often at room temperature?
Liquids or gases
Why does the larger simple molecular substances have higher mp &bp?
The intermolecular forces increase with molecular size, hence large molecules have higher melting and boiling points
What are the physical properties of ionic compounds?
- High mp & bp
- CAN conduct electricity as a liquid NOT SOLID
- Soluble
What type of elements are ionic compounds made of?
metal & non metal
Why do ionic compounds have a high mp/bp?
As a lot of energy is required to break the many strong bonds
Why do ionic compounds conduct electricity ONLY when melted/dissolved?
The ions are free to move and carry current
They do not conduct electricity
as solids, because the ions are fixed and are not able to move
What type of structures are ionic compounds usually in?
Giant ionic lattices
What are the physical properties of Giant covalent structures?
- Very high mp
- SOME can conduct electricity
Why can’t most giant covalent structures conduct electricity?
As they do not have free electrons
What type of elements are Giant covalent structures made of?
Non metal
Why do Giant covalent structures have a high mp/bp?
- Strong covalent bonds
- These bonds must be overcome to melt or boil these substances
What are the different forms of carbon?
- Diamond
- Graphite
What are diamond & graphite examples of?
Giant covalent substances
Describe the structure of diamonds?
- Each carbon is joined to 4 other carbons
- Tetrahedron
What is an allotrope?
Different atomic or molecular arrangements of the same element in the same physical state
Why does diamond and graphite have completely different physical properties even though they are made of the same material?
Bc they have different bonding arrangements
Describe the physical properties of diamonds?
- Hard
- Very high mp
- Does NOT conduct electricity
What are the uses of diamonds?
- Jewellery
- Cutting tools
Describe the structure of Graphite?
Each carbon is bonded to 3 other carbons
—> Forms layers of hexagonal rings
—> No covalent bonds between the layers
Why can the layers in Graphite slide over each other?
As no covalent bonds are between the layers (only weak intermolecular forces)
Describe the physical properties of Graphite?
- Soft
- Slippery
- CAN conduct electricity
Why can Graphite conduct electricity?
As ONE electron from each carbon is delocalised & these can move in between the layers
What are the uses of graphite?
- Pencils
- Industrial lubricants
- Inert electrodes (for electrolysis)
What are the physical properties of metals?
- High mp & bp
- CAN conduct heat & electricity
- Insoluble in water (but can react w/ water)
- Malleable
- High density
Why can metals conduct electricity?
Due to the delocalised electrons
Why do metals have a high mp/bp?
Metallic bonds are very strong
—> Result of the attraction between positive metal ions & the negatively charged delocalised electrons
Why are metals malleable?
Layers of atoms in metals can slide over each other
—> Can be hammered and bent into shape
Compare the difference of physical properties between metals & non-metals
What are fullerenes?
A group of carbon allotropes which consist of molecules that form hollow tubes or spheres
What was the first fullerene to be discovered?
Buckminsterfullerene
Describe the structure of buckminsterfullerene?
60 carbon atoms are joined together forming 20 hexagons and 12 pentagons
Describe the structure of graphene?
- Single layer of graphite
- ONE atom thick
What are some physical properties of fullerenes?
- High surface area
- Good lubricants
What are the physical properties of Graphene?
- Extremely strong but also amazingly light
- Conducts heat and electricity
- Transparent
- Flexible
Why can Graphene conduct electricity?
Has free electrons which can move along its surface allowing it to conduct electricity
Why is graphene very strong?
Due to its unbroken pattern and the strong covalent bonds between the carbon atoms
Why is graphene transparent?
Absorbs around 2% of the visible light that hits it
—> Means you can see through it without any glare
What are polymers?
Very large molecules which are built up by linking together 50 or more monomers
What type of bonds are polymers connected to each other by?
Covalent bonds
How is poly(ethene) formed?
From the addition of many ethene monomers together
What are the physical properties of polymers?
- Strong intermolecular forces
- Solid at room temp
What are homopolymers?
Contain just one type of monomer unit
What are copolymers?
Contain two or more different types of monomer units
What are the advantages of dot & cross diagrams?
- Useful for illustrating the transfer of electrons
- Indicates from which atom the bonding electrons come from
What are the disadvantages of dot & cross diagrams?
- Fails to illustrate the 3D arrangements of the atoms and electron shells
- Doesn’t indicate the relative sizes of the atoms
What are the advantages of the ball & stick model?
- Useful for illustrating the arrangement of atoms in 3D space
- Useful for visualizing the shape of a molecule
What are the disadvantages of the ball & stick model?
- Doesn’t indicate the movement of electrons
- Atoms are placed far apart from each other = In reality is not the case as the gaps between atoms are much smaller
What are the advantages of 2D representations of molecules?
- Displayed formulae are 2D representations & are simpler versions of the ball and stick model
- Indicates what atoms are in a molecule and how they are connected
What are the disadvantages of 2D representations of molecules?
- Doesn’t illustrate the relative sizes of the atoms and bonds
- Doesn’t give an idea of the shape of a molecule and what it looks like in 3D space
What are the advantages of 3D representations of ionic solids?
- 3D drawings and models depict the arrangement in space of the ions
- Shows the repeating pattern in giant lattice structures
What are the disadvantages of 3D representations of ionic solids?
- Only illustrates the outermost layer of the compound
- Difficult and time-consuming to draw
