Atoms Flashcards
all substances are made of…
atoms
the nucleus contains…
proton and neutrons
the nucleus has a radius of…
1x10-14m
what is the relative mass of a proton?
1
what is the relative mass of neutrons?
1
what is the relative mass of electrons?
0
what is the charge of protons?
+1
what is the charge of neutrons?
0
what is the charge of electrons?
-1
what does the atomic number do?
tells you the number of protons
what does the mass number do?
tells you the total number of protons and neutrons in the atom
to get the number of neutrons…
subtract the atomic number from the mass number (top - bottom)
?—>2311Na
mass number
23?–>11Na
atomic number
What is an element?
- substance made up of atoms
- all have same number of protons in thier nucleus
what are isotopes?
- different forms of the same element
- same atomic number
- different mass numbers
how do you work out the relative atomic mass of an element?
sum of (isotope abundance x isotope mass number)
sum of abundance of all isotopes
what are compounds?
- formed from two or more elements
- elements react and atoms combine
a non-metal and metal compound
- consists of ions
- metal atoms lose electrons to form positive ions
- non-metal atoms gain electrons to form negative ions
- ionic bonding
what is ionic bonding?
- oppositely charged ions strongly attracted
- sodium chloride
- magnesium oxide
- calcium oxide
a non-metal compound
- consists of molecules
- each atom shares an electron with another atom
- covalent bonding
- hydrogen
- chloride gas
- carbon monoxide
- water
what is a mixture?
-no chemical bonds between elements, compounds
air is a mixture of gases
- nitrogen
- oxygen
- carbon dioxide
- argon
crude oil is a mixture of…
- different length
- hydrocarbon molecules
what are physical methods to seperate mixtures?
- filtration
- crystallisation
- simple distillation
- fractional distillation
- chromatography
chromatography - seperate dyes in and ink
- draw line near bottom of a sheet of filter paper (pencil insolube wont dissolve in solvent)
- add spot of ink to line and place sheet in beaker of solvent
- make sure ink isnt touching the solvent
- place lid ontop of beaker stop solvent evaporating
- solvent seeps up paper carrying ink
- different dye moves up at different rates seperating out forming spots
- insoluble dyes stay on baseline
- solvent reaches top of paper take out beaker and dry
- result is chromatogram
what methods can you use to seperate soluble solids from solutions?
- evaporation
- crystallisation
evaporation as a seperation technique?
- pour solution into evaporating dish
- slowly heat so solvent will evaporate, solution gets more concentrated
- keep heating until dry crystals are left
when can you not use evaporation?
-soluble solid doesnt decompose when heated
crystallisation as a seperation technique
- pour solution into evaporating dish and gently heat
- once some solvent has evaporated or crystals start to form remove dish from heat and leave to cool
- salt should start to form crystals as it becomes insoluble in cold, highly concentrated solutions
- filter crystals leave them in warm place to dry
what can you use to dry crystals in crystallisation?
- warming oven
- desiccator
how can filtration and crystallisation be used to seperate rock salt?
- grind mixture so salt crystals are small enough to dissolve
- stir mixture in water so salt will dissolve not sand
- filter and there will be residue of sand
- evaporate water from salt to form dry crystals
- remove dish from heat and leave to cool
- salt should start to form crystals as it becomes insoluble in cold, highly concentrated solutions
- filter crystals leave them in warm place to dry
what is simple distillation used for?
-seperate liquid from solution
how to do simple distillation?
- solution is heated so part which has lowest boiling point evaporates first
- vapour cools, condenses and is collected
- rest of solution left in flask
what can you use simple distillation for?
- get pure water from seawater
- water evaporates, condenses and is collected
- salt left in flask
a disadvantage of pure distillation?
- only use to seperate things with very different boiling points
- is temp passes the boiling point of the substance with the highest they’ll mix again
what is fractional distillation used for?
-seperate a mixture of liquids
how to do fractional distillation of crude oil in a lab?
- put mixture into flask and stick fractionating column on top then heat it
- different liquids have different boiling points so they’ll evaporate at different temp
- liquid with lowest boiling point evaporates first as it reaches the top of the column
- liquids with higher boiling points rises but condenses back into the flask as the top is cooler
- when first liquid is collected raise temp until next one reaches top
what did John Dalton describe atoms as?
- start of 19th century
- solid spheres
- made up different elements
how did JJ Thomson prove John Dalton wrong?
- 1897
- ‘plum pudding model’ theory
- measurements of charge and mass
- shows atoms contain electrons
what does the ‘plum pudding model’ show?
- atom as ball of positive charge
- with electrons stuck in it
how did Rutherford show that the ‘plum pudding model’ was wrong?
- 1909 alpha particle scattering experiments
- fired positively charged alpha particles at thin sheet of gold
- expected particles pass straight through or defect slightly
- positive charge of each atom thought to be very spread out through ‘pudding’ of atom
- some went straight through or deflected more than expected or deflected backwards
Rutherford came up with the nuclear model of the atom
- tiny, positively-charged nucleus at centre
- most mass concentrated
- ‘cloud’ of negative electrons surrounds nucleus
- most atom empty space
- alpha particles deflect when near concentrated, positive charge of nucleus
- otherwise pass through empty space
Bohr’s nuclear model
- electrons orbit nucleus in fixed shells
- with fixed distance from nucleus
how did Rutherford show the existence of protons?
- nucleus can divide into smaller particles
- each have same charge as hydrogen nucleus
- protons
who discovered the existence of neutrons?
-James Chadwick
how were elements first organised?
-in order of relative atomic mass
Mendeleev developed the first modern periodic table
- organised elements in increasing atomic mass
- switch order of specific elements fit pattern of others in same group
- predicted properties of undiscovered elements based on those in same group
- left gaps for these elements
how is the modern periodic table laid out?
-in order of increasing atomic number
what are the group 1 (alkaline) metals?
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lithium
sodium
potassium
rubidium
caesium
francium
group 1 metals have one electron in their outer shell
- very reactive
- soft
- low density
what are the trends of the alkaline metals as you go down Group 1?
- increasing reactivity
- lower melting/boiling points
- higher relative atomic mass
why does reactivity increase as you go down Group 1?
- outer electron more easily lost
- attraction between nucleus and electrons decreases
electron gets further away from the nucleus
how do Group 1 metals react with water?
- react vigorously
- produce hydrogen and metal hydroxides
- more reactive lower down the group
- amount of energy increases down the group
how do Group 1 metals react with chlorine?
- react vigorously
- forms white metal chloride salt
- as you go down the group reaction gets more vigorous
how do Group 1 metals react with oxygen?
- lithium = lithium oxide
- sodium = sodium oxide and sodium peroxide
- potassium = potassium peroxide and potassium superoxide
how do Group 1 metals have different properties to transition metals?
- much more reactive
- less dense
- less strong
- less hard
- lower melting points
what are the Group 7 (halogen) elements?
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- fluorine
- chlorine
- bromine
- iodine
- astatine
what coloured vapour is fluorine?
- very reactive
- poisonous
- yellow gas
what coloured vapour is chlorine?
- fairly reactive
- poisonous
- dense
- green gas
what coloured liquid is bromine?
- dense
- poisonous
- red-brown
- volatile liquid
what coloured vapour is iodine?
- dark grey
- crystalline
- solid
- or purple vapour
what are the trends of the halogens as you go down Group 7?
- less reactive
- higher melting/boiling points
- higher relative atomic masses
how can halogens achieve a full outer-shell?
- share electrons via covalent bonding
- with other non-metals
how do halogens form halides?
- form negative ions
- when ionic bond with metal
what are the Group 0 (noble gases)?
- helium
- neon
- argon
- krypton
- xenon
- radon
noble gases have 8 electrons in their outer-shell apart from helium with 2
- don’t need to give up/gain electrons
- not reactive
why are group 0 elements called monatomic gases?
- single atoms
- not bonded to eachother
what are the properties of Group 0 (noble gases)?
- colourless gases at room temp
- non-flammable
what is the trend of the noble gases?
- boiling point increases as you go down the group
- due to increase in no. of electrons in each atom
- leading to greater intermolecular forces between them
how does lithium react with oxygen?
- burns
- strongly-red flame
- produces white solid
how does sodium react with oxygen?
- strong orange flame
- white solid
how does potassium react with oxygen?
- large pieces produce lilac flame
- small make solids
how does lithium react with water?
- fizzes steadily
- floats
- gradually disappears
how does sodium react with water?
- fizzes rapidly
- melts into ball, moves around surface
- dissolves quickly
how does potassium react with water?
- metal melts on surface
- moves quickly
- hydrogen ignites sparks
- lilac flame
- disappears very quickly
how does lithium react with chlorine?
- white metal chloride salt
- settles at sides of container
how does sodium react with chlorine?
- burns bright yellow flame
- clouds of white metal chloride salt
- settles at sides of container
how does potassium react with chlorine?
-reaction more vigorous than sodium
