Make sure this is handed in! Based on the 3 groups in early atomic history, pick one of the groups and explain how they progressed the current knowledge of atoms and elements at their time. OR Explain and research why there is such a large gap in this timeline below. /2 for answering the question /1 for complete sentences /3 marks total CE (Common Era)
Atomic Model S1-2-02 Objective: Investigate the historical progression of the atomic model.
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Dalton s Billiard Ball Atomic Model - Early 1800s The father of atomic theory Came up with the billiard ball model explaining atoms All matter is made of indivisible particles called atoms The atoms of different elements are unique Atoms cannot be created or destroyed Anybody heard of these points before?
Thomson s Plum Pudding Atomic Model - 1904 Sometimes referred to as the oatmeal cookie model or the raisin bun model Experimented with electricity flowing through gas filled chambers (sort of like neon lights) Used cathode ray tubes to prove the existence of the first subatomic particle, the electron
Cathode what tubes? A tube that has a piece of metal at each end One end called a cathode (positively charged) Other end called anode (negatively charged) When a power source is connected a beam is seen to travel from the cathode to the anode
Magnets? How do they work? North side of magnet (negative) Beam When the north side of a magnet was placed near the tube the beam was deflected away from it Like charges repel each other so that must mean the beam had a negative charge This means the beam was actually a stream of electrons traveling from the cathode to the anode
Plum Pudding Model The beam is actually made up of electrons These electrons had to have come from the metal electrodes at either end of the tube! Since the type of metal could change this electrons had to exist within the atoms of the metal All atoms must contain electrons! This is what spurred the plum pudding model. The atom itself (the pudding or bun) had an overall positive charge, but the electrons in it (little raisins) had negative charges The overall charge of the atom was neutral
Thomson vs Dalton Who was more right?
Rutherford s Beehive Atomic Model 1911 Expanded on Thomson s model but specifically used radiation and gold foil for his experiment He fired very small particles at a piece of gold foil He hypothesized that these particles would just travel straight through the gold foil
The Gold Foil Experiment The a particles mostly went right through the gold foil but a small amount were deflected off to the side and some bounced right back!
WWRD (What Would Rutherford Do) x1000
Gold Foil Experiment Because of the surprising observations found with the golf foil experiment this led Rutherford to make the following hypothesis Thomson s model is WRONG Atoms are mostly empty small (this allows the small particle to go through 99% of the time) There is a small center of an atom that contains something very dense (this allows the small particle to be bounced off of it or deflected by it) He called the center a nucleus
What about the positive atom? And what happened to the electrons? Thomson didn t lie electrons existed! The particles that Rutherford was shooting were positively charged The nucleus MUST be positively charged filled with a particle called protons (the 2 nd subatomic particle) The electrons must exist on the outside of the nucleus The electrons on the outside and the nucleus (with protons inside of it) all make up an atom electrons
The bee hive model Rutherford s honey
Bohr s Atomic Model 1913 Worked alongside Rutherford as a student Wondered why the electrons (-) weren t attracted to the nucleus (+) Improved the Nuclear Model by placing electrons in specific orbits Called the Planetary Model Placed electrons in orbits around the nucleus travelling in circular paths (like the planets and the sun!) Discovered the 3 rd subatomic particle and called it the neutron (located in the nucleus with the protons) Neutrons are neutral in charge (they have no charge!)
Planetary Model Bohr continued and proposed the following Each electron in a specific orbit has a specific amount of energy. Electrons can only exist in these orbits, not in-between Scientists thought this was the perfect atomic model. It explained Thomson s and Rutherford s experiments but also improved the atomic model
From Dalton to Thomson to Rutherford to Bohr
The Atom How big is it?
The Atom To summarize some of the important part of the atom make sure you know this list! Subatomic Particle Symbol and Charge Mass Location Proton p + 1 amu Nucleus Neutron n 0 1 amu Nucleus Electron e - 2000 times lighter than a proton & neutron! Electron orbitals (outside the nucleus) AMU = Atomic mass unit = 1.66 x 10-27 kg
One More Model! Quantum Model Various scientists were responsible for this model and it is one of the current models we hold today Bohr s was good but incomplete when trying to explain large and complex atoms Sometimes, particles act like solid forms of mass, but other times they act like waves. This is called the wave particle duality the basis of quantum mechanics
Quantum Model cont Using this knowledge, the Quantum model proposes the following Electrons do not move around the nucleus in a definite path Its impossible to determine the exact location of an electron, rather you only know the probabilities of where it could be Electrons move randomly in electron clouds called orbitals No longer just travel around in circles like Bohr s model
Our Objective: Definitions 6-22 can be filled out Investigate the historical progression of the atomic model. Reflect on the different models we have discussed today Early and Modern Chemists Atomic Models Outcome Questions Can be completed! The video provides a good overview of what was covered!