C4 Flashcards
What did john Dalton say about atoms in the 19th century?
They were solid spheres and different ones made up elements
What did jj Thompson ten say about atoms in 1897?
That they were not solid spheres. His measurements of charge and mass showed at atom must contain smaller negatively charged particles- electrons
What was the name of the theory that came after the solid sphere idea?
The plum pudding model
What did Rutherford prove wrong?
The plum pudding model
How was the plum pudding model proved wrong./
Rutherford conducted the gold foil experiment where positively charged particles were fired at a very thin sheet of gold. Most of the particles passes straight through and a small number bounced back. This showed the plum model was incorrect as according to that the particles would be defected back.
What was rutherfords idea?
That the nuclear atom. There is a tiny positively charged nucleus at the centre surrounded by a cloud of negative electrons. Most of the atom is empty space
What did bohr add to the atom theory?
The idea that the electrons were not a cloud but in shells. They exist in fixed orbits and each shell has a fixed energy.
Why were ideas of atoms accepted?
Because they fitted the evidence available at the time. As more experiments were carried out the theories of atoms and structure was modified to suit. More scientific knowledge means improved ideas and predictions
What is peer review?
Everyone gets a chance to see new ideas and check them for errors, this helps scientists develop ideas and work
What is the nucleus in an atom/ properties?
It’s in the middle and contains protons and neutrons, it has a positive charge due to the protons. Almost the whole mass of the atoms is concentrated in the nucleus
What are the electrons in an atom/ properties?
Move around the atom in shells. They are negatively charged. They are very tiny but cover a large amount of space. The volume of their orbits determines the size of the atom. The have virtually no mass
What’s a proton/
They are heavy and positively charged
What’s a neutron?
They are heavy and neutral
What’s an electron?
They are tiny and negatively charged
Why do neutral atoms have no charge?
Because they have the same number of protons and neutrons. The charges cancel each other out.
What does the atomic number tell you?
The number of protons ( the bottom number)
What is the mass number?
The total number of protons and neutrons ( the top number)
How can you calculate the number of neutrons?
Subtract the atomic number form the mass number
What is an isotope?
A different form of the same element which has the same number of protons but a different number of neutrons
What does an isotope have the same a different?
Same atomic number but different mass numbers
How can you remember the history of the periodic table?
Dobby likes triangles but newlands came along and rearranged dobby triangle’s into octagon. Mendeleev came along and mended the periodic table and left. He came and left gaps.
What did dobereiner do to the periodic table?
He organised the elements into triads. And groups based on chemical properties. He put them into groups of three. The middle element of each triad had a relative atomic mass that was average of the other two.
what did newlands notice about the elements?
every eights element had similar properties and so he listed the known elements in rows of 7.
why did newlands octaves not work?
the pattern broke down on the third row as transition metals like titanium and iron messed it up and did not fit. he aso lef no gaps so his work wa ignored.
why was newands ideas criticized?
his groups contained elements that did not have similar properties ( carbon and titanium)
he mixed up metals and nonmetals
he did not leave any gaps for new elements
what did dmitri mendeleev do to the perodic table
he organized the known 50 elements into a table with gaps for new ones. he put them in order of atomic mass like newlands but he left gaps to keep elements with similar properties in the same vertical groups.
what are the 3 rules for electron shells?
electrons always occupy shells/ energy levels
lowest energy levels filled first
only a certain number of electrons allowed in each shell
how many electrons are allowed in each shell
1st shel: 2 electrons
2nd shell : 8
3rd shell: 8
define ionic bonding
transferring electrons
in this bonding atoms lose or gain electrons to form charged particles or ions which are then strongly attracted to each other.
if an atom has an outer shell with just one electron what is it keen to do?
get rid of it and lose them so they can have a complete outer shell. they become positive ions
if an atom has a nearly full out shell of 6/7 what is it keen to do/
to gain an extra electron or two to complete their shells . they become negative ions
what kind of structure do ionic bonds have
giant ionic lattices. the ions are closely packed together in a regular lattice arrangement. the ions are not free to move so the compounds do not conduct electricity when slid. they are very strong
what makes magnesium oxide and sodium chloride have high melting and boiling points?
they have very strong attraction forces between oppositely charged ions in the giant lattice structures. to break the bonds you have to overcome these attraction forces and this take allot of energy
when metal form ions they…
lose electrons and form positive ions
when non metals form ions they…
gain electrons and form negative ions
what happens when a metal and a non mental combine.
they form ionic bonds
if a electron is gained will it become negative or positive
negative
if an electron is lost will it become negative or positive
positive
what a covalent bond?
sharing an electron
when are covalent bonds formed/?
when non metals combine they share their electrons to complete both their outer shells
what is the structure in covalent bonds?
simple molecular structures. the atoms within the molecule are held together with very strong covalent bonds but the forces of attraction between molecules are very weak
what are the properties of covalent bonds?
melting and boiling points are low due to weak intermolecular forces as molecules are easily parted form each other.
they are gasses and liquids at room temp
they dont conduct easily as there are no free electrons
what is group one in the periodic table know as?
the alkali metals
what is so special about group one alkali metals?
as you go down they become more reactive
why do alkali metals become more reactive as you go down/
the outer electron is more easily lost because its further away from the nucleus so less energy is needed to remove it ( the atomic radius is larger)
how many electrons do alkali metals have in outer shel?
one. so they are very reactive and always form ioni bonds
what physical properties do alkali metals have ?
low melting and boiling points
low density so can float
very soft. can be cut with a knife
what is oxidation?
the loss of electrons. the more reactive something is the more happier it is to lose ad electron, this is oxidation
what happens to alkali metas when with water?
they move around the surface fizzing and produce hydrogen. the reactivity with water increases as you go Down the group
what happens to the group one metals when the react with water?
they react with water for form a hydroxide of the metal and hydrogen
what does lithium burn?
red flame
what colour does sodium burn?
yellow/orange flame
what colour does potassium burn?
liac flame
what is group 7 known as?
the halogens
how many electrons are in the outer shell of halgens?
7
what makes group 7 so special?
as you go down the group they become less reactive as there is less inclination to gain the extra electron to fill outer shell when its further away form the nucleus
what are the boiling and melting points like in halgens?
as you go down the melting and boiling points increases
what are the properites of halogen at room temperature? chlorine
chlorine is fairly reactive , poisonousm dense green gas with a low boiling point
what are the properites of halogen at room temperature? bromine
bromine is a dense poisonous orange liquid
what are the properites of halogen at room temperature? IODINE
iodine is a dark grey crystalline solid with a high boiling point
what is reduction?
the gain of electrons. halogens are keen to gain an electron, the more reactive it is the happier it is to gain. halogens gain so are reduction
what happens when halogens react with alkali metals?
they form salts called metal halides
eg. sodium+chloride= sodium chloride
what is displacement?
when a more reactive halogen displaces a less reactive one.
chlorine can displace bromine and iodine
bromine can displace iodine
what structure do metals have?
a crystal structure
why do metals have a crystal structure?
metals are held together by a special type of metallic bonding. this allows the outer electrons to move freely. this crates a sea of delocalized electrons throughout the metal
what properties do metals have?
hard dense lustrous strong attraction between delocalized electrons and positive ions- strong metallic bonding high melting and boiling points
what is tensile strength?
metals have a high one. they are strong and hard to break. they are also malleable
why are metals good conductors?
they have a sea of delocalised electrons which can carry an electrical current through the metal and heat energy too
what metal is used for saucepans and why/?
stainless steel
as its a good conductor of heat and it wont rust easily
what metal is sued for electrical wiring and why/
copper
good conductor of electricity. easily bent
what metal is used for airplanes and why?
aluminum
low density. light, strong
doesn’t corrode
what metal is used for bridges and why?
steel
strong
what is electrical resistance?
when electricity flows through a met they eat up and some of the energy is wasted as heat. all metals have this resistance
how can a metal become a super metal?
when some metals become cold enough their electrical resistance disappears and the metals become a superconducor
what does it mean to be a super conductor?
you could start s current flowing thought a superconducting circuit and take out the batter the current would continue flowing forever
what can super conductors be used for?
power cables
strong electromagnets
circuits
whats the problem with super conductors/
it is very expensive to keep the metals at such cold temps -265 degrees Celsius
how are scientists coping with the issue of cold superconductors?
trying to find new metals that conduct as warmer conditions. they have found some that work at -135 but they ideally want one at 20 degrees
whats a transition metal?
the metals in the middle of the periodic table
what are the properties of transition metals?
the same as normal metals.
what are the uses of transition metals?
catalysts
iron= harber process
nickel= hydrogenation of alkenes
what is thermal decomposition?
when a substance breaks down into at least two other substances when heated.
what is a transition metal carbonate?
copper carboate
iron carbonate
zinc carbonate ect
they break down into a metal oxide and carbon dioxide. usually has a colour change too.
what is a precipitation?
a reaction where two solutions react and an insoluble solid forms in the solution. the solid is sad to precipitate out and the solid is also called a precipitate
eg. copper sulfate+sodium hydroxide= copper hydroxide+sodium sulfate
how can precipitations be used ?
to test for transition metals. some insoluble transition metal hydroxides have distinctive colors. we can sue this to test which metal ions a solution contains
what colour is:
coper hydroxide
iron2 hydroxide
iron3 hydroxide
copper= blue solid
iron2=grey/green solid
iron3=orange/brown solid
what do we need water for?
lots of domestic uses
industrially its cheap and used a coolant
in the uk where is water obtained form?
surface water= lakes rivers reservoirs, run dry in sumer months
groundwater= aquifers, rocks that trap water underground.
what are the three stages of water purification?
filtration
sedimentation
chlorination
how is water purified?
put through a wire mesh to remove large things such as twigs.
iron sulfate or aluminum sulfate added to make fine particles clump together and settle to bottom
chrloine gas bubble thought to kill bacteria and microbes
what can pollute our water
nitrate reside form excess fertilizers that run off into rivers and lakes
lead compounds form pipes
persicide reside form spraying to close to lakes and rivers
what is the probem with nitrates in water/
prevent the blood carrying oxygen properly
what is the issue with lead in water supplies?
it is poisonous particularly in children
what does distilling do?
it makes water fresh. it needs lots of energy and its very expensive and not practical for large amounts of water but can be done to sea water.
how can you test water for dissolved ions?
precipitation reaction
how can you test for sulfate ion in water?
use barium chloride. add dilute HCL then barium chloride. if a white precipitate appears there are sulfate ions present
how can you test water for halide ions?
add nitric acid then drops of silver nitrate.
a precipitate will form if halide ions are present
whats a halide ion?
anything form the group 7 halogens
chloride
bromide
iodide
what does a white precipitate show when silver nitrate is added to water?
chloride ions are present
what does a cream precipitate show when silver nitrate is added to water?
bromide ions are present
what does a pale yellow precipitate show when silver nitrate is added to water?
iodide ions are present
