Chemistry ( atomic structure)

pure substances

elements + atoms

elements

forms of matter than contain only one type of atom

cannot not be broken down into simpler forms by means of ordinary

atoms

smallest unit of an element that has all the properties of that element

1897

JJ thompson 

Electrons 

1904

JJT

plum pudding model

electrons embedded in positively charged sphere

1911

Ernest Rutherford

proposed model with positive nucleus at center

electrons spiral around it and loose energy

electrons 

tiny and negatively charged 

cover a lot of space 

occupy shells or energy levels

what determines the size of an atom

volume orbits occupy

Shells / Energy level

lowest energy levels are filled first

only a certain number of electrons

are allowed in each shell

2

8

8

atomic number

number protons

atomic mass number

protons and neutrons

neutrons 

mass - atomic number 

the mass number 

is about 2 times atomic number