Topic 3 - Covalent Compunds And Seperation Teachniques Flashcards
Why does covalent bonding take place?
So both atoms have a full outer shell so atom is more stable, as it takes more force to break the electrons apart
What are covalent bonds?
Sharing a pair of electrons between non-metal atoms. Each bond consists of a shared pair of electrons, and is very strong.
What does each covalent bond do to an atom?
Each covalent bond provides one extra shared electron for each atom
Each atom has to make enough covalent bonds to fill up its outer shell
What happens if an atom makes covalent bonds with one of more other atoms?
They form a molecule
How is a molecule formed in covalent bonding?
What atoms make covalent bonds with one or more other atoms
Simple molecular covalent substance structure
Only contain a few atoms held together by strong covalent bonds.
Example of a single molecular covalent substance
Carbon dioxide, as the molecules contain only one atom of carbon, which is then bonded with two atoms of oxygen.
Properties of simple molecular covalent substances
Low melting and boiling points - because the weak intermolecular forces break down easily
Non-conductive - substances with simple molecular structure do not conduct electricity as they don’t have any free electrons or an overall electric charge
Other examples of simple covalent molecules
Hydrogen, ammonia, methane and water.
- Have very strong bonds between the atoms, but much weaker forces holding the molecules together
What happens when a simple covalent molecule melts or boils?
The weak ‘intermolecular forces’ break.
Simple molecular substances are gases, liquids or solids with low melting and boiling points.
Do giant molecular covalent substances have charged ions?
NO!
Describe a giant molecular covalent substance
- Contains a lot of non-metal ions, each joined to adjacent atoms by covalent bonds
- Usually arranged in giant regular lattices (very strong structures due to the amount of bonds involved)
How are giant molecular covalent substances structured usually?
In giant regular lattices
Properties of giant molecular covalent substances
- Very high boiling points (because a lot of strong covalent bonds must be broken)
- Variable conductivity (diamonds don’t, but graphite does)
Three examples of very weak intermolecular forces
Hydrogen
Oxygen
Water
Substances with covalent bonds often form molecules what kind of melting and boiling points?
Low melting and boiling points
How do non-metals combine together?
They share electrons, as the shared pair of electrons holds the two atoms together. This is called a covalent bond.
The group of atoms bonded together in a covalent bond is called what?
A molecule
Covalent compound properties
Low melting point and low boiling point
Don’t conduct electricity
What temperature (low or high) is needed to separate the molecules when they are melted or boiled?
A LOW temperature
Why don’t covalent compounds conduct electricity
Because they don’t have free electrons
Uses of carbon compound of a diamond
Colourless, transparent, reflects light - jewellery
Hard, high melting point - used for cutting tools
Uses of carbon compound of graphite
Pencil leads - a black, shiny, opaque, slippery metal
Good electrical conductor - the layers are only weakly held together so they can slip over each other
What are the three forms of carbon known as?
Allotropes
How many bonds does carbon form in a diamond?
4 bonds
How many bonds does carbon form in a graphite
3 bonds
What does an immiscible liquid mean? Example
That the liquids don’t dissolve together.
ie water and oil
How to separate immiscible liquids
Use a separating funnel
What are miscible liquids?
When the substance do dissolve into each other
How to separate miscible liquids
Fractional distillation as miscible liquids have different boiling points
How can nitrogen and oxygen be obtained from the air?
Fractional distillation of liquid air
Soluble
Able to dissolve
Insoluble definition
Unable to dissolve
Solvent definition
The liquid in which a solute dissolves
Solubility definition
A measure of how soluble something is
Chromatography definition
A separation technique used to separate mixtures of ink and dyes
Chromatography in the real world
Food industry
Forensics
Conserving artefacts
How does chromatography work
The different coloured compounds have different solubilities
In chromatography, the more soluble the compound is…
The faster it is carried up the paper
Why did Mendeleev leave gaps in the periodic table?
To keep elements with similar properties in the same group/column
What info did Mendeleev use to predict properties of missing elements
He used the properties of other elements in the same group/column
Why does a catalytic converter work better when it’s hot
The rate of reaction is increased because the particles are moving faster, which means more successful collisions occur
