Chem LO 4

JJ Thompson Experiment

Cathode Ray Tube

Select the correct progression for the development of the atomic model: a.) planetary, electron cloud, billiard ball, plum pudding b.)BB, Planet, PP, EC c.) EC, PP, Planet, BB d.) BB, PP, Planet, EC e.) all 4 models existed simultaneously

D

Provide evidence for the existence of atoms, electrons, AND the existence of a small, massive, and positively charged nucleus (for a 4)

Ernest Rutherford's Gold Foil Experiment shows that the atom is mostly empty space with a tiny, dense, positively-charge nucleus. When alpha particles, a relatively heavy particle ( about 4,000 times more mass than an electron) with a positive charge, were directed at a thin gold foil.. 1. most of the particles were detected went straight through the foil 2. The path of some of the particles were significantly bent off course instead of straight through 3. Some of the particles bounced back So.. Evidence 1: The atom must be primarily empty space since a massive particle just passed right through Evidence 2 and 3: The atom contains a small dense concentration of mass, the nucleus, inside the atom with a positive charge. This experiment provided evidence that the positive charge was not uniformly spread out in the atom To account for the electrons discovered with the cathode ray tube, it was proposed that the electrons then circle the nucleus. The Gold Foil experiment did not provide direct evidence for the electrons orbiting Thomson's Plum Pudding Model had negatively-charged electrons within a positively-charged outer. His Cathode Ray Tube experiment. Rays emerge from one metal disc (cathode)and move to the other. The cathode ray was deflected by both electrical and magnetic fields (meaning the cathode ray had a charge). The cathode ray was independent of the metal used for the cathode and bent towards the positive plate of an external electric field meaning that it was negatively charged. So, Evidence: The evidence from the cathode ray tube challenged the first part Dalton's "billiard ball" model. There are particles that can be ejected and therefore no longer "indivisible". The fact that the particles carried a negative charge meant that the atom must also have a positive charge. The adjustment- The atom is still a ball that is now positively charged and amorphous. The negative particles, electrons, are then stuck randomly on the surface of the sphere and therefore can be "plucked" out. This model did not change any of the other postulates of Dalton's theory.

Ernest Rutherford : How experimental evidence contributed to their model of the atom

Evidence 1: The atom must be primarily empty space since a massive particle just passed right through. Evidence 2 and 3: The atom contains a small dense concentration of mass, the nucleus, inside the atom with a positive charge. This experiment provided evidence that the positive charge was not uniformly spread out in the atom. To account for the electrons discovered with the cathode ray tube, it was proposed that the electrons then circle the nucleus. The Gold Foil experiment did not provide direct evidence for the electrons orbiting.

Rutherford (Planetary) Draw a pic of the model and label Provide the experimental evidence (not the experimental set up) that supports that model Provide the reasoning that explains how the evidence supports that model

Evidence: Most alpha particles shot at gold foil go through to the other side. However, a few get deflected or bounce back Reasoning: Because most alpha particles go through, this indicates that most of the atom is empty space. However, those that deflect/bounce back MUST have "hit: something massive (but small) within the atom. This would be the nucleus.

Thomson (Plum Pudding) Draw a pic of the model and label Provide the experimental evidence (not the experimental setup) that supports that model Provide the reasoning that explains how the evidence supports that model

Evidence: Negatively charged "particles" are ejected from electrodes regardless of the metal Reasoning: Previous model (Dalton's) said atoms were indivisible (not made up of smaller parts). However, these particles (electrons) were ejected from all types of metals and therefore must exist within all types of atoms

Ernest Rutherford Experiment

Gold Foil Experiment

Draw AND explain diagrams of the plum pudding, planetary AND electron cloud/quantum models of the atom (for a 4)

Plum Pudding- JJ Thompson. His idea was that the atom is a ball of positively charged, but apparently amorphous, matter with electrons studded here and there, like the raisins in a pudding. Because it contained equal numbers of positive and negative charges, the overall structure was electronically neutral. All electrons are identical, each with the same, very small mass and negative charge. The mass of an electron is less than 1/1000th of the mass of a hydrogen atom. Planetary- Ernest Rutherford. his model postulated a very,very small nucleus where all of the positive charge and nearly all of the mass of the atom was located. This nucleus was encircled by electrons. Rutherford later identified the unit of positive charge and called it a proton. Electron Cloud- Erwin Schrodinger Quantum models-

JJ Thompson Experimental evidence gathered

Rays emerge from one metal disc (cathode) and move to the other. The cathode ray was deflected by both electrical and magnetic fields (meaning the cathode ray had a charge). The cathode ray was independent of the metal used for the cathode and bent towards the positive plate of an external electric field meaning that it was negatively charged.

JJ Thompson: How experimental evidence contributed to their model of the atom

The evidence from the cathode ray tube challenged the first part Dalton's "billiard ball" model. There are particles that can be ejected and therefore no longer "indivisible". The fact that the particles carried a negative charge meant that the atom must also have a positive charge. The adjustment- The atom is still a ball that is now positively charged and amorphous. The negative particles, electrons, are then stuck randomly on the surface of the sphere and therefore can be "plucked" out. This model did not change any of the other postulates of Dalton's theory.

Ernest Rutherford Experimental evidence gathered

When alpha particles, a relatively heavy particle (~4000 times more mass that an electron) with a positive charge, were directed at a thin gold foil most of the particles were detected went straight through the foil The path of some of the particles were significantly bent off course instead of straight through Some of the particles bounced back.