C2a Flashcards
What is an isotope?
Isotopes are different atomic forms of the same element, which have the same number of protons but different numbers of neutrons
What are compounds?
Compounds are atoms of two or more elements chemically bonded together. It is difficult to separate the elements
What is ionic bonding?
Atoms lose or gain electrons to form ions which are strongly attracted to one another
Why do atoms react?
To get a full outer shell
Describe the structure of a giant ionic lattice
1) Ions closely packed together
2) In a regular arrangement
3) With strong ionic bonds in all directions
Why do giant ionic lattices have a high mpt?
Strong electrostatic forces of attraction in all directions. A lot of (heat) energy is needed to break these bonds
Why are giant ionic lattices brittle?
When layers are hit, they move and similar charges are next to each other. These repel so the substance breaks apart
Do giant ionic lattices conduct electricity?
Only when molten or dissolved as ions are free to move
What is covalent bonding?
Bonding between two or more non-metals, in which they share electrons so they both have a full outer shell
Which atoms form diatomic molecules?
All group 7, H, N and O
Describe the structure of simple molecular substances
1) Strong covalent bonds (intramolecular forces)
2) Weak intermolecular forces
3) No ions
Why are simple molecular substances liquids or gases at room temperature?
Weak intermolecular forces so not much (heat) energy is needed to separate them
Do simple molecular substances conduct electricity?
No as no ions
What is another name for giant covalent structures? Give 3 examples
Macromolecules
Diamond, Silicon dioxide, Graphite
Describe the structure of diamond
1) Each carbon atom forms 4 covalent bonds
2) Rigid structure (hardest natural substance)
Describe the structure of silica
1) Strong covalent bonds
2) Makes sand
Can diamond and silica conduct electricity?
Not even when molten or dissolved as no free ions or electrons
Describe the structure of graphite
1) Each carbon atom forms 3 covalent bonds
2) Arranged in layers
Why is graphite soft and slippery?
It is made up of layers that can slide over each other
Can graphite conduct electricity?
Yes because each carbon atom leaves one delocalised electron
Why do giant covalent substances have high mpts?
Strong covalent bonds so a lot of (heat) energy is needed to break the bonds
Describe the structure of a metal
1) Positive ions in regular arrangement
2) In a sea of free electrons
3) Opposite forces hold it together
Why are metals malleable?
Layers can slide over each other without breaking
Do metals conduct electricity?
Yes because delocalised electrons
Why are alloys harder than pure metals?
Different sized atoms disrupt the regular arrangement so layers can’t slide over each other
Give an example of a smart material and what it is used for
Nitol (nickle + titanium) - shape memory
When cool it can bend, when heated it goes to remembered shape - used in glasses and braces
What are fullerenes?
Carbon nanoparticles
Strong covalent bonds hold it together in balls/ tubes made from hexagonal rings
Used to reinforce graphite in tennis rackets
Why can nanotubes be used as lubricants?
Tubes can roll over each other as there are no bonds between tubes. Lubricant coatings reduce friction in artificial joints/ gears
What can nanoparticles be used for?
Catalysts - high SA:volume Highly specific sensors e.g. water purification Cosmetics - no white mark deodorant Deliver drugs in body Tiny electric circuits
What is the structure of thermosoftening polymers?
Strong covalent bonds to make chains
Weak intermolecular forces - chains free to slide
What are the qualities of thermosoftening polymers?
Low mpt
Easily remoulded
Soft + felxible
How are low density polymers made?
E.g. bags + bottles
High temp (200)
High pressure
What is the structure of thermosetting polymers?
Strong covalent bonds
Crosslinks provide stronger intermolecular forces
What are the qualities of thermosetting polymers?
High mpt
Can’t be remoulded
Hard + rigid
How are high density polymers made?
E.g. drainpipes
Low temp + pressure
Catalyst
What is Ar?
Relative atomic mass - how heavy atoms are compared to C12 (top number)
What is Mr?
Relative formula mass - all Ars of a compound added together
What is a mole?
The Mr of a substance in grams
What is the equation for finding moles?
Moles = mass/Mr
How do you find experimental masses?
1) Balance equation
2) Work out moles
3) Ratio using balanced equation
4) Moles * Mr
What is the empirical formula?
The experimentally derived ratio of the amount of atoms in a compund
How do you find the empirical formula?
1) Write down element and data
2) Divide data by Ar
3) Divide by smallest
4) Make into a whole number
What is the equation for % yield?
% yield = actual/ theoretical * 100
Why is a high % yield important?
Save resources, money, time, energy
Why is % yield never 100%?
1) Products remain on filter paper / glassware
2) Unexpected reactions - useless products
3) Reversible reactions - reaction where the products can themselves react to become the original reactants
In reversible reactions, what is the heat transfer?
Exothermic one way means endothermic the other
What is paper chromatography?
A method of chemical analysis used to separate substances e.g. dyes
How is paper chromatography used?
Pencil (insoluble) baseline on filter paper
Shallow solvent in beaker
Paper just in solvent
What is the Rf value?
Distance travelled by a dye
Why are machines often used in chemical analysis?
Faster, more accurate, more sensitive
How does gas chromatography work?
Gas carries substance through column
Different masses so different speeds so substance separates
What is retention time?
The time of a substance taken to reach the detector
How can you tell the number of compounds in a substance?
Number of peaks
What does a mass spectrometer do?
Work out the Mr of a compound (molecular ion peak)
