development of the model of atom

radius of atom

1×10 -10 meters

radius of nucleus

1×10-14 meters or 1/10000 of radius of atom

where is most mass concentrated in atom

nucleus

basic structure of atom

positively charged nucleus composed of protons and neutrons surrounded by negatively charged electrons.

how do electron arrangement change

-absorption of electromagnetic radiation

-emission of electromagnetic radiation

absorption of electromagnetic radiation

electrons will move further away from nucleus; a higher energy level

emission of electromagnetic radiation

electrons will move closer to nucleus; a lower energy level

why don’t atoms have no overall electrical charge

in an atom, number of electrons is equal to number of protons in the nucleus.

atomic theory before discovery of electron

atoms were thought to be tiny spheres that could not be divided

What did John dalton say about atoms

Solid spheres and that different elements are made of different types of spheres.

What did the discovery of electron lead to

Plum puddling model suggesting that atom is a ball of positive charge with negatively charged electrons embedded

What happened in alpha particle scattering experiment

Took positively charged alpha particles and they fired it through a thin sheet of gold

What was prediction of alpha experiment

If positive charge in gold atoms was generally spread out as plum pudding proposed then alpha particles should pass through thin sheet of gold because the weak positive charge wouldn’t be strong enough to affect them

Why was gold used for alpha scattering experiment

Hammer gold into very thin foil with just a few atoms thick

Observations from alpha scattering experiment

-most of alpha particles passed straight through gold foil without change in direction

-some alpha particles were deflected(changed direction as it passed gold foil)

-some alpha particles bounced straight back off the gold foi

Explanations for the observations from alpha scattering experiment

—most of alpha particles went straight through gold foil therefore atoms are mainly empty space

-some of alpha particles were deflected therefore centre of atom has positive charge and that repelled the alpha particles

-sometimes an alpha particle would bounce straight back meaning mass was concentrated in the centre.

what was the plum pudding model replaced by

nuclear model- atom mostly empty space with a positive nucleus in the centre with containing most of mass and surrounded by negative electrons

what did Niels Bohr propose

electrons orbit the nucleus at specific distances

why was Bohr’s work accepted

agreed with the results of experiments by other scientists

several years later, what did scientists found about positive charge in nucleus

due to positive charge called protons

what did James Chadwick discover

nucleus contains neutrons and they have no charge and are neutral