Zusammenfassung der Ressource
Atomic structure
- Plum Pudding model
- It was previously believed
atoms were the smallest
particles that existed
- In 1804 Dalton agreed with
Democritus, that matter was made
up of atoms which couldn't be broken
up but he thought each element was
made of a different type of atom
- In 1897 J.J Thompson discovered tiny,
negatively charged particles(electrons)
and that atoms can give out electrons
so Dalton's theory was slightly wrong
as atoms could be broken up
- Thompson suggested atoms were
spheres of positive charge with tiny
negative electrons stuck in them -
like plums in a plum pudding
- However the 'plum pudding' theory didn't last long as in 1909
Rutherford and Marsden fired a beam of alpha particles at thin gold
foil, a slight deflection of the positive alpha particles was expected
to be caused by the electrons in the 'plum pudding' model
- However - most alpha particles just went straight
through with the odd one coming straight back at
them, which was a bit of a shocker
- Rutherford and Marsden realized this meant most of an
atoms mass was in its centre in a tiny nucleus they also
realized the nucleus must have a large positive charge since
positive alpha particles were repelled at such large angles
- The experiment also
showed that most
of an atom is just
empty space which
was also shocking
as atoms make up
everything
- In short Rutherford
concluded: Most an atom is
empty space, Most of an
atoms mass is compressed
into a tiny central volume
called a nucleus and that an
atoms nucleus has an
overall positive charge
- Rutherford and Marsden came up
with the nuclear model of the atom
- Nucleus is tiny but makes up most the
atoms mass, it contains protons(positive
charge) & neutrons(neutral charge) so
overall positive charge on nucleus
- The rest of the atom is mostly empty space
- Negative electrons whizz round the outside of
the nucleus and give the atom its overall size
- atoms have no overall charge an electrons charge
size is the same as a protons but opposite
- This means the number of protons and electrons
is always equal in a neutral atom
- If electrons are added or removed the atom
becomes a charged particle called an ion