Atomic Theories Flashcards
(20 cards)
Scientific notation:
- 2 X 10^4
- 2 X 10^-4
62000
0.00062
What is an atom?
Smallest Particle of Matter
Cannot be divided chemically
Why do scientist create atomic models
To be able to study the atom (too small)
Democritus Discontinuous model
First use of word «atom»
Small invisible particles called atoms
Space between atoms
“Like sand on a beach”
Aristotle Continuous model
Matter is infinitely divisible
Solid with no space in between
John Dalton’s Atomic theory
1) all matter is composed of tiny indivisible particles called atoms (this was proven false as atoms are divisive into protons neutrons and electrons)
2) all atoms of same element are identical
3) different elements are composed of different size atoms which have their own properties
4) atoms combine to make molecules
JJ Thomson discovery
Cathode Rays (composed of electrons)
JJ Thomson experiment (setup)
Thomson used a cottage ray tube connected to a power supply. On one end was a cathode (negative) and an anode (positive).
JJ Thomson Experiment (result)
When connected to a power supply a beam appeared. This beam was either particles or light. When he put a propeller in, it started moving (it was particles). When Thomson out positively charged plates outside the tube, the rays would be attracted to them.
JJ Thomson experiment (conclusion)
There are negatively charged particles in an atom called electrons
Thompson’s model
Raisin Bun or Plum Pudding
Atom is divisible
Big positive with electrons in the middle
Alpha Particles
Beta Particles
Gamma Rays
Alpha=Positive
Beta= negative
Gamma Rays: No charge
Rutherford experiment
Aimed alpha particles (positive) at a price of gold with a detecting screen around.
Rutherford Experiemnt (results)
Most particles went straight through
Some were deflected
Very few bounced right back
Rutherford experiment (conclusions)
Atom is mostly empty space
Contains very dense and small numcleus
Nucleus is positively charged
Properties of protons (3)
Positive
Large mass
Found in nucleus (middle)
Properties of electrons (3)
Negative charge
Small mass
Found on outside of nucleus
Neils Bohr’s observation
Bohr studied the light emitted by elements when hot. He saw different colours. He figured out that electrons were not randomly distributed but they were put on different orbits of energy. When the electrons are heated, they jump to another level of energy. When they come back down, they emit light.
Rutherford Bohr atomic model
Number of protons in middle (nucleus)
Number of electron shells surrounding nucleus
Number of electrons placed on shells
James Chadwick doscivery
He discovered the neutron.
Neutron held the protons from repelling from each other.
