OCR A 2.1.1 Atomic Structure and Isotopes

history of atom

1803: John Dalton

1897: JJ Thompson

1909: Ernest Rutherford

1913: Neils Bohr

Dalton

1803

atoms are seperate

each element made from dif spheres

Thomson

-1897

-discovered electron

-atom not solid

-made up of other particles

-plum pudding model

Rutherford

-1909

-discovered nucleus

-nucleus is small and +ve charged

-atoms mainly empty space

-and made up negative cloud

-gold leaf experiment

gold leaf experiment

-+ve alpha particles fired at thin gold leaf

-most went thru (empty space)

-some deflected back (hit nucleus)

Niels Bohr

-1913

-electrons in fixed energy shells

-problem w/ Rutherford; e collapse into +ve nucleus

proof:

-when EM radiation absorbed, e move between shells

-emit radiation when move to lower energy shells

relative atomic mass

The weighted mean mass of an atom of an element, compared to 1/12th of the mass of an atoms of carbon-12

relative isotopic mass

The mass of an atom of an isotope compared to 1/12th of the mass of an atom of carbon-12

m/z of mass spectra graph

-mass of isotope/ charge

-most of the time same as isotopic mass; as charge = 1

abundance on mas spectra graph

-percentage of isotopes

-adds up to 100%

relative atomic mass

State two differences between isotopes of the same element

Different numbers of neutrons

Different (atomic) masses/mass numbers

Different physical properties

isotopes

atoms of an element with different numbers of neutrons and different masses

why different isotopes have the same chemical properties

same number of electrons in outer shell