CC3 - atomic structure Flashcards
what are atoms
miniscule particles of matter that make up everything in the universe
John Dalton
- early 19th century
- described atoms as solid spheres
- atoms cant be broken down into anything simpler
- atoms of same element are identical
why did Daltons idea about atoms change
discovery of subatomic particles disproved his idea
what are the subatomic particles
- protons
- neutrons
- electrons
nucleus of an atom
- found in the centre of the atom
- contains protons and neutrons
- positivley charged (because protons)
electrons
- orbit the nucleus in electron shells
- negativley charged
- size of shells determines size of atom
how are atoms of different elements different
- all atoms of the same element have a unique atomic number (no. protons)
- no two elements have the same atomic number
charges of subatomic particles
proton: +1
neutron: 0
electron: -1
relative mass of subatomic particles
proton: 1
neutron: 1
electron: negligable (almost 0)
why do atoms have no overall charge
- have the same no. protons as electrons
- opposite charges cancel out
size of atom compared to nucleus
compared to atom, nucleus is tiny, most size comes fromo electron shells
where is most of the mass of an atom concentrated
in nucleus
atomic number
- smaller number of the nuclear symbol
- shows how many protons an element has (every atom of element will ahve same)
mass number
- larger number on nuclear symbol
- total number of protons and neutrons together
how can number of neutrons be found
mass number - atomic number
how can number electrons be found
- neutral electron there is same number of protons and electrons so…
- electrons = atomic number
what is an iscotope
- atoms of an element that have the same number of protons, but different numbers of neutrons
- (same atomic no. diff mass no.)
what is relative atomic mass
- weighted average of the relative atomic masses of the isotopes in the element
- have the symbol Ar
relative atomic mass vs mass number
- mass numbers always whole numbers (not possible to have part of a proton or neutron)
- relative atomic masses are often rounded to the nearest whole number, but arent actually whole numbers
element with only 1 iscotop
realtive atomic mass will be same as mass number
how to calculate relative atomic mass from iscotopes
[(% of isotope 1 x mass of isotope 1) + (% of isotope 2 x mass of isotope 2)]
/ 100
Mendeleev (3)
- sorted elements in order of increasing relative atomic mass
- noticed a pattern in chemical properties
- arranged the elements by putting those with similar properties in groups (columns)
what did mendeleev predict
- where missing elements could go and their properties
why did mendeleev switch Iodine and Tellurium
were in the wrong group for their behaviour
switched order of a few elements to keep groups consistant
what are elements of the periodic table ordered by today
atomic number
what do groups show
(columns) number of electron in outer shell
eg. group 1, 1 electron in outer shell
exeption to groups and outer shells
group 0, have a full outer shell
what do periods show (rows)
number of shells an element has
eg. lithium is in 2nd period, has 2 shells
where are metals found on periodic table
left hand side
where are non-metals found on periodic table
right hand side in a zig-zag line under boron, around aluminium
