In 1803, John Dalton proposed that atoms were solid spheres, and different spheres represented different elements.
By 1897, JJ. THOMSON had discovered ELECTRONS, leading to the "PLUMPUDDINGMODEL", which showed the atom as a sphere of positive charge with electrons embedded within it
ERNEST RUTHERFORD and his student Ernest Marsden conducted the ALPHA PARTICLE SCATTERING experiment, which disproved the Plum Pudding model. They fired alpha particles (particles consisting two protons and two neutrons tightly bound together) at a gold foil, which they assumed was one atom thick.
They observed that most alpha particles passed straight through the gold foil, but some were deflected, Suggesting a small, dense, positively charged nucleus at the centre of the atom.
The PlumPudding model does NOT explain the results because it shows the whole atom as a ball of positive charge with NO EMPTY SPACE.
In 1909, Rutherford's findings led that the atom consists mostly of empty space, with a dense nucleus surrounded by a cloud of electrons.
In 1913, NIELS BOHR introduced that ELECTRONSORBIT the nucleus in fixed SHELLS.
Bohr's model suggested that electrons could only occupy certain orbits or ENERGY LEVELS, at FIXED DISTANCES from the nucleus.
Bohr revealed the nucleus could be SUBDIVIDED into a whole number of smaller particles, each particle having the same amount of POSITIVE charge. These were called PROTONS.
In 1932, JAMES CHADWICK discovered NEUTRONS, neutral particles in the nucleus, solidifying the nuclear model close to what is accepted today.
Electron structure
when ELECTRONS are organised around the nucleus in SHELLS or energy levels to determine the CHEMICALPROPERTIES of an atom.
The shells are filled from the LOWEST to the HIGHEST energy levels.
ELECTRON SHELL RULES:
A) 2
B) 8
C) 8
ELECTRON CONFIGURATIONS
Can be represented by diagrams or as numbers indicating how many electrons are in each shell.
Development of an atom:
A) John Dalton
B) JJ Thomson
C) ernest Rutherford
D) neils bohr
E) james chadwick
most alpha particles passed straight through the gold foil without deflecting meaning that most of the atom is made of empty space and the majority of its mass is in the nucleus.
A small part of alpha particles were deflected meaning that the nucleus has a positive charge that can repel positively charged alpha particles.
Explain why the total positive charge is every atom of an element is always the same.
Positive charge is provided by protons and every atom of the same element contain the same number of protons.
Compare the positions of the subatomic particles in the plum pudding model with the nuclear model.
Plum pudding model has a single ball of positive charge and nuclear model has positive charges in the nucleus.
plum pudding model has electrons in random positions and nuclear model has electrons in fixed positions.
plum pudding model has no nucleus and the nuclear model has a nucleus.
plum pudding model has no neutrons and the nuclear model has neutrons in the nucleus.
Nuclear model is mostlyempty space
Nuclear model's positive charge is in the nucleus.
Plum pudding model's mass is spread out.
In the nuclear model, the electrons are in orbits.
Niels Bohr adapted the nuclear model.
Describe the change the Bohr made to the nuclear model.
electrons orbit the nucleus and electrons are at specific distances from the nucleus.
Most alpha particles pass straight through the gold foil, so most of the atom is empty space.
Some alpha particles were deflected, so the atom has a positively charged nucleus.
Chadwick's experimental work on the atom led to a better understanding of isotopes.
Explain how his work led to this understanding.
Chadwick discovered neutrons, this was necessary because isotopes have the same number of protons, but with different number of neutrons.
inner shell can only have a maximum of 2 electrons and there's too few electrons in the outer shell.