Chemistry Additional Flashcards
What does the atomic number tell you?
How many protons are there
What 3 types of particle do atoms contain?
Protons
Neutrons
Electrons
What does the mass number tell you
Total number of protons and neutrons
How can you get the number of neutrons?
Subtract the atomic number from the mass number
How are compounds formed
When atoms of two or more elements are chemically combined together
What is the isotope definition
Different atomic forms of the same element which have the same number of protons but a different number of neutrons
Isotopes must have the same atomic number but….
Different mass number
Name two popular pairs of isotopes?
Carbon-12
Carbon-14
Name one of the ways atoms can form compounds
Ionic bonding
What happens in ionic bonding?
Atoms lose or gain electrons to form charged particles (ions)
Which are then strongly attracted to one another
(Because of the attraction of opposite charges)
All atoms over at the left hand side of the periodic table ( sodium potassium calcium )
Have just one or two electrons in their outer shell
Blabla info
Keep going u will get an A*
Why are atoms on the left hand side of the periodic table keel to get rid of their electrons?
Because then they will only have full shells left
Because they try to have the same electronic structure as a noble gas
What happens when an atom on the left hand side of the periodic table gets rid of the atom to get a full shell
The atom is leaved as an ion instead
Who have outher shells which are nearly full?
Group 6/7
Such as oxygen and chlorine
What 4 things do ionic compounds have?
1 giant ionic lattices
2 very strong electrostatic forces of attraction between the opposite charged ions in all directions
3 ions form a closely packed regular lattice
4 a single crystal of sodium chloride is one giant ionic lattice ( which is why salt crystals have cuboid shape
Two properties of ionic compounds?
1 all have high melting points and high boiling points because of the strong attraction between the ions.
It takes large amount of energy to overcome this attraction
When ionic compounds melt the ions are free to move and they will carry electric current
2 they do dissolve easily in water
The ions seperate are free to move in the solution so they carry electric current
How can you get ionic compounds to conduct electricity ?
By melting them
Or dissolving them in water
Dissolving them is easier because it takes a lot of energy to melt an ionic compound
What are ions again?
Atoms that have lost or gained an electron or electrons
What electronic structures do ions have?
Of a noble gas
The elements that most readily form ions are ?
Groups 1.2.6.7
What are group 1/2 elements and what do they form
They are metals and they lose electrons to form positive ions
What are group 6/7 elements and what do they form
They are non metals they gain electrons to form negative ions
Any of the positive ions can combine with any of the negative ions to form an ionic compound
Blabla info
Keep going baby
Only elements at the opposite sides of the periodic table will form ionic compounds
( positive +negative )
Blabla infoooo
What is the overall charge of any compound?
Zero
so all negative charges in the compound must balance all the positive charges
Ionic compound blabla info
Chemical formula for sodium chloride
NaCl
Chemical formula magnesium chloride
MgCl2
What does covalent bonds include
Sharing electrons
Covalent bonds only share electrons in their outer shells ( highest energy levels )
Blablablaaa
covalent bonds is a shared pair of electrons
Belehelhele
Learn 7 covalent bonds examples
1 hydrogen H2
They just have one electron and they only need one more to complete the first shell
2 chlorine Cl2
Chlorine atoms also need only one more electron
Often form single covalent bonds
3 methane CH4
Carbon has 4 outer electrons which is half full shell
So it forms four covalent bonds to make up its outer shell
4 hydrogen chloride HCl
This is very similar to H2 and Cl2
Both atoms needs one more electron to complete their outer shells
5 ammonia NH3
Nitrogen has 5 outer electrons so it needs to form 3 covalent bonds to make up the extra 3 electrons needed
6 water H2O
Oxygen have 6 outer electrons
Sometimes form ionic bonds by taking 2 electrons to complete outer shell
They also form covalent bonds and share 2 electrons instead
In water molecules the oxygen shares electrons with 2 H atoms
7 oxygen O2
In oxygen gas oxygen shares 2 electrons with another oxygen atom to get full outer shell
A double covalent bond is formed
What can substances with covalent bonds form?
Simple molecules
What is the result of intermolecular forces ?
That the melting and boiling points are very low because the molecules are easily parted from eachother.
Its the intermolecular forces thar get broken when simple molecular substances melt or boil ( not much stronger covalent bonds )
Most molecular substances are?
Gases or liquids at room temp
But they can be solids
do molecular substances conduct electricity and why?
they dont conduct electricity because there are no ions so there is no electrical charge
What else could covalent bonds form substances from?
Giant covalent structures
What are giant covalent structures?
Macromolecules
What are giant covalent structures similar to and what is the difference?
Similar to giant ionic structures (lattices) except that there are no charged ions
How are atoms bonded together in giant covalent structures?
Bonded to eachother by strong covalent bonds
do giant covalent structures have high or low melting/boiling points?
VERY high
Do giant covalent structures conduct electricity?
No not even when molten
except graphite
What are the 3 examples for giant covalent structures?
Diamond
Graphite
Silicon dioxide
3 properties of the diamond?
- Each carbon atom forms 4 covalent bonds in a very rigid giant covalent structure.
- this structure makes diamond the hardest natural substance, so it is used for drill tips
- pretty/sparkly
3 properties of graphite?
- Each carbon atom only has 3 covalent bonds.
This creates layers which are free to slide over eachother so graphite is soft and slippery. - The layers are held together loosely so that they can be rubbed off onto paper, thats how pencil works.
This is because there are weak intermolecular forces between layers.
3.graphite is the only non metal.
Which is good conductor of electricity
each carbon atom has delocalised (free) elexreon and its these free electrons that conduct electricity.
2 properties of silicon dioxide (silica)
- Sometimes called silica this is what sand is made of
2. Each grain of sand is one giant structure of silicon and oxygen.
What do metals consist of ?
Giant structure
What do metallic bonds involve?
The free electrons which produce all the properties of metals
These delocalised (free) electrons come from the outer shell of every metal atom in the structure
Why are metals good conductors of heat and electricity?
Because their electrons are free to move through the whole structure.
In What structure do electrons in metalic bonds hold the atoms together?
In a regular structure
There are strong forces of electrostatic attraction between the positive metal ions and the negative electrons
What else does the regular structure of metals allow?
They allow the layers of atoms to slide over each other allowing metals to be bent and shaped
Why do scientists mix 2 or more metals together and what does it create
1.Creates an alloy with the properties they want
2.Different elements have different sized atoms
so when another metal is mixed with a pure metal the new metal atoms will distort the layers of metal atoms making it more difficult for them to slide over eachother .. So alloys are harder
Name the 4 structures again
Giant ionic
Simple molecular
Giant covalent
Giant metallic
In the exam they might test the 4 structures by describing the physical properties of a substance and asking you to decide which type of structure it is
Blabla
Name two groups of materials we really need to know about?
Smart materials
Nanoparticles
What is nitinol and its property
A shaped memory alloy
Its a metal alloy but when its cool you can bend it and twist it like rubber
Bend it too fad though and its stays bent
If u heat it above a certain temp it goes back to it remember shape
It is really handy for glasses frames
If you accidentally bend them you can just pop them into a bowl of hot water and they will jump back into shape
Nitinol is also used for dental braces in the mouth it warms and tries to return to a remembered shape and so it fently pulls the teeth with it
How big is one nanoparticles
1 nano particle = 0.000000001 m
How many atoms does a nano particle roughly contain
A few hundred atoms
What do nanoparticles include and what are they
Fullerenes
These are molecules of carbon shaped like hollow balls or closed tubes
The carbon atoms are arranged in hexagonal rings
A nanoparticle has very different properties from the bulk chemical that its made from
eg; fullerenes have different properties from big lumps of carbon
Bladie bladie bladie
Two properties of fullerenes
1 can be joined together to form nanotubes
Tiny hollow carbon tubes a few nanometres across
2 all those covalent bonds make carbon nanotubes very strong
They can be used to reinforce graphite in tennis rackets
What are the 7 reasons nanomaterials are becomming more and more widely used?
1.huge surface area to volume ratio
So could help make new industrial catalysts
2.you can use nanoparticles to make sensors to detect one type of molecule and nothing else, these highly specific sensors are already being used to test water purity.
3.nanotubes can be used to make stronger,lighter building materials
4.new cosmetics (Example; sun tan cream, deodorant) have been made using nanoparticles
These particles do their job but dont leave white marks on skin.
5.nanomedicine is a hot topic
The idea is that tiny fullerenes are absorbed more easily by the body than most particles.
This means they could deliver drugs right into the cells where they are needed.
6.new lubricant coatings are being developed using fullerenes
These coatings reduce friction a bit like the ball bearings and could be used in all sorts of places from artificial joints to gears
7.nanotubes conduct electricity so they can be used in tiny electric circuits for computer chips.
What are plastics made up of
Lots if molecules joined together in long chains
What determines the properties of plastics
Forces between molecules
Individual tangled chains of polymers held together by weak intermolecular forces are free to slide over eachother
Blablablablaa
4 properties of thermosoftening polymers
1 dont have cross link between chains
2 forces between the chains are really easy to overcome so its easy to melt plastic
3 when it cools the polymer hardens into a new shaper
4 you can melt these plastics and remould them as many times as you like
Some plastics have stronger intermolecular forces between the polymer chains called cross links that hold the chains firmly together
Blabla info
4 properties of thermosetting polymers
1 thermosetting polymers have crosslinks
2 these hold the chains together in a solid structure
3 the polymer doesnt soften when its heated
4 thermosetting polymers are strong hard and rigid
What 2 things will both affect the properties of a polymer
The starting materials
Reaction conditions
What are the 2 types of polythene ?
Low density polythene is made by heating ethene to about 200 degrees under the high pressure
Its flexible and is used for bags and bottles
High density polythene is made at lower temp and pressure (with catalyst)
Its more rigid and used for water tanks and drainpipes
How to calculate relative atomic masses
add for example mgcl2
24(mg) + 35.5(cl) x 2 = 95
Equation of moles
Number of moles = mass in g (of element or compound) / Mr of element or compound
