Development of atomic theories

Question 1

observations and theories of Thompson

Answer 1

• provided evidence for the existence of the electron
• experimented by applying electrical currents through the gases
• the ray produced started from the negative electrode (aka cathode), as a result, cathode rays were made up of tiny negatively charged particles- ELECTRONS

Question 2

Explain Joseph Thompson’s plum pudding model

Answer 2

After providing evidence for electrons, he determined that all atoms contain electrons, but since atoms are electrically neutral he reasons that a positive charge must also be present

Question 3

observations and theories of Rutherford

Answer 3

• blasted a thin foil of gold with a beam of alpha particles (positively charged) and then onto a fluorescent screen
• to explain back scattering he proposed the atoms core is positively charged
• proposed that the atoms positive charge, together with most of its mass, is concentrated in the centre
• alpha particles which travel close to the nucleus are strongly deflected, the degrees depends on how close it approaches

Question 4

Problems with Ruhterfords theories

Answer 4

• • contradicted laws of physics: he proposed that e- orbit the nucleus like planets orbit the sun but e- lose energy while moving in circles
• nuclear atom problem, would collapse into the nucleus
• could not explain mass of an atom

Question 5

observations and theories of Bohr

Answer 5

-proposed restrictions on the movements of e-
- specific energy levels (circular orbits around nucleus
- atom has “stationary” states and chnages between these by emitting or absorbing a specifc quantity of energy (a quantum amount)
- explained line specturm for hydrogen: e- absorbs photons and moves to further energy level (atom in excited state), excited e- drops to a lower energy level giving off light, this wavelength emitted depends on energy level transition for the e-

Question 6

Limitations to Bohrs theory

Answer 6

• could not explain spectra of atoms with two or more e-
• did not account for energy differences between e- in the same orbit (sublevels)
• could not explain the shape and characteristics of molecules
• could not describe or make predictions for multi-electron atoms

Question 7

what is the equation for the specific quantity of energy for an orbit

Answer 7

E= (-13.6/ n^2) eV
eV= 1.602 x10^-19 j

Question 8

Heinsenbergs uncertanty principle

Answer 8

it is impossible to know precisely both the position and velocity of an object
-disproved bohrs idea of a definite path

Question 9

Erin Schrodinger

Answer 9

• used mathematics and stats to define the probability of finding e- in a certain region around the nucleus
• this wave function gives information about the energy and location of an e- (orbitals)
• orbitals indicate where there is a high possibility of finding e-
• The densest part of the cloud is where the probability of finding e- is the greatest