Chemistry 5 Flashcards
How are compounds formed ?
When two or more elements are chemically combined. It is difficult to separate this into the original elements
How do you work out the amount of neutrons an element has ?
Mass number - atomic number
What is an isotope ?
Different atomic forms of the same element, which have the SAME number of PROTONS but a DIFFERENT number of NEUTRONS
Why do isotopes have to have the same number of protons ?
Because otherwise they are different elements altogether
Name 2 examples of popular isotopes
Carbon-12 and Carbon-14
What is the difference between carbon-12 and Carbon-14 ?
Carbon-14 has two more neutrons
a mass number of 14
Describe ionic bonding
When atoms lose or gain electrons to form charged particles called ions. They are strongly attracted to each other because opposite charges attract
When elements lose their electrons they become ions, which means …
They react easily and quickly with an ion that has an opposite charge
What structure do ionic compounds have ?
Regular lattice structures
Describe an ionic compounds structure
It is a closely packed regular lattice arrangement. There are very strong forces of electrostatic attraction caused by the opposite charges attracting
Why do ionic compounds have high melting and boiling points ?
A large amount of energy is needed to overcome the high attraction
When ionic compounds melt, what can they do ?
Carry electric current
What happens when ions are added to water ?
They dissolve and the ions separate leaving them free to move
What groups of the periodic table are most likely to form ions ?
1&2 and 6&7
What do ionic compounds contain ?
A positively charged part and a negatively charged point
What is the overall charge of every compound ?
Zero
How can you work out the formula of an ionic compound ?
Look at the charges of each components and remember that when added together they must equal 0
What is covalent bonding ? Why is it done ?
When atoms share electrons in their outer shells. It means both atoms have full outer shells
Substances with covalent bonds can either be …..
Simple molecules or giant covalent structures
Describe simple molecules
- form very strong covalent bonds
* the forces of attraction between molecules are weak (intermolecular)
Why are simple molecular substances easy to break down ?
Their weak intermolecular forces can be broken down easily
Give three examples of simple molecular substances
- Chlorine
- Oxygen
- Water
Give three examples of giant covalent structures
- Diamond
- silicon dioxide (silica)
- Graphite
Are giant covalent structures similar to giant ionic structures ?
Yes, except there are no charge ions. The atoms are bonded by very strong covalent bonds
Do giant covalent structures conduct electricity ?
No, not even when molten. However graphite is an exception to the rule
Describe a diamonds formation and features
Each carbon atom has four covalent bonds forming a very rigid structure. It makes it the hardest natural substance
What is silica comprised of ?
Silicon and oxygen, this is what sand is made of
How does a pencil work ?
Each carbon atom in graphite only forms three covalent bonds. The layers of graphite can slide over each other and therefore rubbed onto paper
Why is graphite the only non-metal to conduct heat and electricity ?
Each carbon atom has a delocalised free electron which carries the heat or electricity through the material
What are free electrons ?
They come from the outer shell of every metal atom. They are free o move throughout the structure.
Why are metals relatively strong ?
They have strong electrostatic attraction between the positive metal ions and the negative free electrons
Why can metals be bent and shaped ?
Their regular structure means layers can slide over each other
What is an alloy ?
A mixture of two or more metals
Why are alloys harder ?
Different elements have different sized atoms, so when mixed the levels are distorted and they cannot be slid over each other
What is an example of a good new material ?
Nitinol - A shape memory alloy
What is nitinol ?
It is an alloy of nickel and titanium that can be bent like rubber when cool. When twisted too much it stays bent, however when heated it returns to a remembered shape
Give 2 uses for shape memory alloys an explain them
- Glasses Frames - if accidentally bent thy can be popped back into shape with hot water
- Dental Braces - when the mouth warms it tries to return to a remembered shape, pulling the teeth in
1nm = how many m
1nm = 0.000,000,001m
How small is a nanoparticle ?
1-100 nanometers across
How many atoms does a nano particle contain ?
Roughly a few hundred
What is a fullerene ?
Molecules of carbon shaped like hollow balls or closed tubes. The carbon atoms are arrange in hexagonal rings
Fullerenes form nanotubes which are tiny hollow carbon tubes. Give an example how this can be used
They can be used to reinforce tennis racket strings as their covalent bonds are very strong
What determines the properties of plastics ?
Forces between molecules
Describe weak forces between molecules
Individual tangled chains of polymers held together by weak intermolecular forces, free to slide over each other
Describe strong forces between molecules
They have strong intermolecular forces, with cross links that hold the chains firmly together
What are termosoftening plastics ?
Polymers that don’t have cross links which can easily be overcome and therefore melted. They can be melted and reshaped as many times as you want
What are thermosetting plastics ?
They have cross links which form a solid structure that won’t soften when heated
What plastic is used for bags and bottles ?
Low density polymers
What plastic is used for drainpipes and water tanks ?
High density polymers
What does Ar stand for ?
Relative atomic mass
What is relative atomic mass ?
A way of saying how heavy different atoms are
Where do you find an elements relative atomic mass ?
The top number for each element on the periodic table
What does Mr stand for ?
Relative formula mass
What does relative formula mass tell you ?
The mass of the whole compound
How do you calculate Mr ?
Add up all of the atomic masses in the formula
One mole of a substance =
It’s Mr in grams
What is the formula for number of moles ?
No. of moles =
Mass in grams divided by Mr
What does the empirical formula do ?
To find the formula of a compound in its simplest form
There are three important steps to calculating masses in reactions, what are they ?
- Write out the balanced equation
- Work out Mr for the bits you need
- Divide by the two you know and then multiply by the other
What does percentage yield compare ?
Actual yield and predicted yield
What does percentage yield tell us ?
How successful the experiment was by comparing how much you actually made compared to what you predicted
What is the formula for percentage yield ?
Percentage yield =
Actual yield divided by predicted yield multiplied by 100
True or False - yields are always less than 100%
True
Why do we find percentage yield ?
It is done to find the most sustainable ways to get as much yield as possible
What is paper chromatography ?
A way of separating artificial colours using paper
Why are machines better than chromatography ?
Very sensitive, very fast, very accurate
How can gas chromatography identify substances ?
The gas is sent through a column at different speeds which separates them, a detector measures their ‘retention time’ (time to exit column) and measures it on a graph
