Presentation on theme: "Atomic Theories Democritus (300 B. C.)"— Presentation transcript:
1 Atomic Theories Democritus (300 B. C.) Matter can be cut into smaller and smaller pieces,but eventually you will end up with tiny particles(called atoms) that are indivisible.
2 1. All matter is made up tiny particles called atoms. Dalton’s Atomic Model (1808)1. All matter is made up tiny particles called atoms.2. Atoms cannot be created, destroyed, or subdivided in chemicalchanges. (Law of Conservation of Mass)3. All the atoms of one element have the same properties,such as mass and size. These properties are different fromthe properties of the atoms of any other element.4. Atoms of different elements combine in specific proportions to form compounds. (Law of Definite Proportions)
3 Electronscathode ray tubeJ. J. Thomsonpaddlewheel+-
10 Quantum Theory of Light Light consists of a stream of energypackets (or quanta) called photons.Fire photon torpedo, Mr. Sulu!
11 Evidence for the Quantum Theory Photoelectric Effect : the release of electrons from a substance dueto light striking the surface of a metalAccording to the classical theory of light, the brightness(intensity) of the light shone on the metal would determine thekinetic energy of the liberated electrons. This prediction was shown to be false. The frequency (colour/energy ) of the light was the most important characteristic of the light producing the effect.
12 Einstein’s Explanation for the Photoelectric Effect (1905) Light is transmitted in the form of energy packets called photons.2. The energy of a photon depends onits frequency.
13 Neils Bohr An electron is so small that it DOESN’T obey the classical (Newtonian) laws of motion.Therefore, an electron does NOT necessarily lose(radiate) energy as it orbits the nucleus.2. An electron can only have certain energies, just as the gearboxin a car can only have certain gears. (Its energy is quantized.)
14 Bohr’s Model of the Hydrogen Atom (1914) electron droppingto a lower orbitorbitselectron in excited statephoton of lightemitted whenelectron drops●electron in ground state
16 The line spectrum of each element is unique, like a fingerprint.
17 Helium was first discovered when scientists looked at the pattern of spectral lines during a solar eclipse.
18 The colours in fireworks are a result of electrons becoming “excited” and then dropping back down to orbits closer tothe nucleus.
19 Problems with Bohr’s Model Although Bohr’s model successfully predicted the line spectrumfor hydrogen, the extension of his model to atoms with two(or more) electrons did not agree with experimental evidence.Gimme a break!!!
20 The Wave Mechanics Model of the Atom (Schrodinger) A model of the atom based on the fact that the electronexhibits properties of a particle AND a wave (but never both simultaneously).
21 The idea that an electron had a dual nature was first proposed by Louis de Broglie in 1923.
22 Particle-Like Properties of Electrons +Electrons are deflectedby magnetic or electric fields.-2. Electrons can makea paddlewheel turn.
23 Wave-Like Properties of Electrons Diffraction of electronsthrough a crystal.diffraction : the spreading out of a wave whenpassing through a small opening
26 Since electrons are “tied down” by the nucleus, they create standing wave patterns like a guitar string called orbitals.Unlike the standing wave on a guitar string, thesestanding electron waves/orbitals occur in 3-D.
27 Heisenberg Uncertainty Principle If the velocity of an electron is known, its position cannot be determined exactly.(i.e.- While measuring the velocity of tiny particles like electrons, you will affect their position.)
28 Electron Cloud: 3-D representation of the probability of finding an electron in an orbital.Where there are large #s of dots,the probability of finding theelectron is high.