Atomic Theory History

Question 1

Timeline of the atomic theory:
(we don’t have to know the years)

Answer 1

• John Dalton (oldest)
• J.J. Thomson
• Ernest Rutherford
• Neils Bohr
• Erwin Schrodinger (newest)

Question 2

John Dalton: his model, how he discovered it, and notes

Answer 2

Model: solid sphere model

Discovery: investigated pressure of gases to discover the atom

• formulated the idea of the atomic theory of matter, “energy cannot be created nor destroyed”, atoms of the same element have identical size, mass, and other properties

Question 3

J.J. Thomson: his model, how he discovered it, and notes

Answer 3

Model: Plum Pudding model

Discovery: discovered the electron using a cathode ray tube
(electrons shot out producing a ray that were attracted to the positive end of the tube, hence its negatively charged)

• thomson knew atoms were neutral, and discovered the e-, so he knew there had to be a positive charge to balance it out (did not theorize for the positive charges to be particles, but rather an overall)

Question 4

what is radioactivity

Answer 4

spontaneous decay of nucleus

Question 5

Ernest Rutherford: his model, how he discovered it, and notes

Answer 5

Model: Nuclear Model

Discovery: Rutherford fired alpha particles (positively charged helium nucleus) at a gold foil sheet that would be detected on a screen
- most passed straight through (showed atoms had empty space)
- some were deflected an angles
- some reflected back
- therefore, the positive charge had to be in the centre

• Ernest was the first person to design an experiment to look at atomic components

Question 6

Neils Bohr: his model, how he discovered it, and notes

Answer 6

Model: Planetary Model

Discovery: Experimented with samples of hydrogen gas spectrum were composed up of discrete colours (spectroscopy), said that the lines were different amounts of energy (shorter wavelength=higher energy, and longer wavelength=lower energy)

• Bohr model assumed that the electrons can orbit the nucleus only at fixed distances
• energy level of an electron depends on its distance from the nucleus, closer it is=less energy, farther=more
• electrons jump from one energy level to another, each package of energy is a quanta/photon (Plancks constant)

Question 7

Erwin S….(can’t spell name; too long :)) : his model, how he discovered it, and notes

Answer 7

Model: Quantum Model (current)

Discovery: combined wave equations to come up with a mathematical formula for electron distribution in an atom

• rejected bohrs ideas and introduced the idea of orbitals….
  ORBITAL: a wave function that describes the location and wave behaviour of an electron…AREA USED TO CALC PROBABILITY OF FINDING ANY ELECTRON (95% chance)

Question 8

alpha particle

Answer 8

helium nucleus, 2 p+, 2 neutrons
*small and positively charged, which is why they were used

Question 9

isotopes

Answer 9

atoms with the same number of protons but different number of neutrons

atoms of the same isotope have identical chemical properties

Question 10

radioisotopes

Answer 10

isotope that emits radioactive gamma rays and/or subatomic particles (alpha or beta for ex)

Question 11

classical theory of light

Answer 11

light: electromagnetic wave composed of various wavelengths to form a spectrum

photoelectric effect: electrons are emitted by matter that absorb energy from shortwave electromagnetic radiation (REQUIRES A SPECIFIC AMOUNT OF ENERGY/FREQUENCY OF LIGHT)

Question 12

ground and excited states of electrons

Answer 12

basis:

• electrons are attracted to nucleus
• outer electrons have more energy than inner electrons (because inner electrons are held more in-tact to the nucleus, less ecstatic)
• when an outer electron falls into an empty spot, energy is released (the energy released is the difference between inner electron energy and outer electron energy) as light

Question 13

wave particle duality

Answer 13

idea introduced by Einstein, light acts as both a particle AND a wave

Question 14

what did Planck suggest about the photoelectric effect

Answer 14

the emission and absorption of energy can only occur in discrete packets (E=hv)

E=energy
h=planck constant
v=frequency

Question 15

Problems with John Daltons model

Answer 15

if dalton said all atoms are made of the same particles, then why are there diff chemical properties for them?

and also what abt isotopes?

(in reality, electron number and arrangement determine the properties of atoms)

Question 16

Problems with J.J. Thomsons model

Answer 16

• If there was an overall positive charge in an atom to balance out negatives, then why did most atoms pass through the gold foil signifying empty space?
• Failed to explain how positive charge holds on electrons

Question 17

Problems with E.R model

Answer 17

• Didn’t explain why the negatively charged electron wasn’t pulled directly into the positively charged nucleus (like a black hole-ish)
• a travelling electron SHOULD emit radiation as it accelerates, it will not self-destruct. It’s stable.

Rutherford proposed that the electrons revolve around the nucleus in fixed paths called orbits

Question 18

Problems with N.B. model

Answer 18

• ideas only work well for small atoms (He and H) BUT doesn’t help explain larger atoms (since it states that the orbit of e- and radius is known)
• doesn’t explain effect of magnetic field on atom spectra

Question 19

Bohrs contributions (further), (extra)

Answer 19

SUMMARY:

• developed spectroscopy, each atom has a specific spectra that defines properties and measures intensity of light at diff wavelengths
• developed quantum number “n” angular momentum whole number
• electron has to be in a discrete set of orbits

DETAILED:
- applied quantum mechanics: an electron can only be in a discrete set of orbits
orbits have to be an angular momentum whole number (quantum number: n)

newtons laws of motion (:/) apply to electrons orbiting the nucleus,
the force on the electron is the electrostatic attraction btwn positively charged nucleus and negative electron

• helped develop spectroscopy (each atom has a defining set of lights, each spectra defines properties of the source and it measures the intensity of light at different wavelengths)

Question 20

BOHRS CONTRIBUTIONS 3 (GROUND STATE AND EXCITED STATE)

Answer 20

• electron absorbs energy (moves up energy levels, ground to excited)
• electron loses energy, returns to og orbit and releases energy as light (moves down energy levels, excited to ground)

Question 21

How did Rutherford know that the nucleus was positively charged?

Answer 21

the alpha particles (positive helium nucleus) he used in his gold foil experiment were positively charged