History Of an Atom

Question 1

Democritus

Answer 1

He discovered atoms- the smallest unit of matter
Physically, but not geometrically divisible
Billiard ball

Question 2

Dalton (1803)

Answer 2

An element consists of identical atoms

Different elements have different types of atoms

Question 3

Thomson (1897)

Answer 3

Discovered that there is negative charge in an atom- he named them electrons
He formed the plum pudding model- which is a sphere of positive charge with electrons dotted around inside.

Question 4

Rutherford (along with Marsden and Geiger) 1909-1911

Answer 4

Gold foil experiment
Aimed beams of alpha particles (positively-charged particles) at very thin gold foil.
Most of the particles went straight through; some of them deflected off in different directions and few of them shot straight back.
Atoms have a very small, positively charged nucleus with most of the mass
Electrons orbit the nucleus, like planets around a star

Question 5

Neil Bohr (1913)

Answer 5

He used logic to improve the model
He discovered the electron shells
He reasoned that without them, the electrons would spiral into the positively-charged nucleus due to electrostatic attraction.

Question 6

Henry Moseley 1913

Answer 6

Discovered the atomic number of each element using x-rays which led to more accurate organisation of the periodic table.

Question 7

Erwin Shroëdinger 1926

Answer 7

Used mathematical equations to describe the likelihood of finding an electron in a certain position.