Atomic theory Atoms: The Building Blocks of Matter
First, there was Democritus Democritus was a Greek philosopher “atomos” He came up with the idea of the atom around 400BCE He had no evidence, he just thought that that was just the way the world should work
Aristotle Aristotle is the most famous and most influential of the Greek philosophers He thought Democritus was nuts! Too bad for Democritus And atomic theory
A brief history of the atom… Democritus: “atomos” No experiments…not believed Aristotle: 4 elements make up everything Earth Air Fire Water 4th century BCE Ancient Greece
The word “atom” comes from a Greek word that means “unable to be cut” … and you kept on cutting the leftover piece in half… Imagine you had a piece of gold that you then cut in half… …and then you cut one of these smaller pieces in half… Gold Go ld
The word “atom” comes from a Greek word that means “unable to be cut” …and kept going… Eventually you would have 1 piece of gold left. If you cut it in half, you wouldn’t have gold any more – you’d have something else. This tiny, tiny single piece of gold is called an atom of gold. An atom is the smallest particle of an element that acts like the element. …and kept going… …and kept going… An atom of gold
Hundreds of years later… Law of Conservation of Mass (1789) Mass is neither created nor destroyed during chemical or physical reactions. Antoine Lavoisier Total mass of reactants = Total mass of products
Soon after that… Early 1800’s England John Dalton Atomic Theory All matter is made up of tiny, indivisible particles called atoms. Atoms of the same element are identical – same physical and chemical properties Atoms of different elements are different – different physical and chemical properties Atoms can chemically combine in whole number ratios to form compounds and physically mix to form mixtures. An atom cannot be changed into an atom of a different element by a chemical change – they may be combined, separated, or rearranged, but never created, destroyed, or changed.
A little after that…1897 JJ Thomson Cathode Ray Tube Discovers the electron is negative
And a little after that… Goldstein (1886) Discovers canal rays (proton) Milliken (1909) Oil drop experiment finds the charge on an e-
Rutherford’s Gold Foil Experiment And after all that…1911 Rutherford’s Gold Foil Experiment start experiment DO NOT OPEN RADIOACTIVE MATERIAL INSIDE + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + LOOK INSIDE THE GOLD
And after all that… Ernest Rutherford Gold Foil Experiment Discovers the Nucleus
Models of the Atom Thomson Model Dalton Model Blueberry Muffin e- Solid Sphere Thomson Model Blueberry Muffin blueberries = electrons cake/muffin = positive matter e- Positive material
Models of the atom Rutherford Model Dense, positive nucleus Electrons revolving around nucleus in circular or elliptical orbits Mostly empty space
Models of the atom Bohr Electrons are found in specific energy levels Like planets around the sun
More on Models Electron Cloud or Quantum Mechanical Model Electrons are in continuous motions and are shown as a probability cloud
Orbitals Orbital- the area around the nucleus in which it is most likely to find an electron. The come in a variety of shapes and sizes!!! S P D F Sphere peanut daisy/donut funkadelic
Check out this site for cool pics of orbitals!!!!!!!!!! Orbital Shapes 1 type 3 types 5 types 7 types Check out this site for cool pics of orbitals!!!!!!!!!!
Starting Electron Configurations You have an address, so does an electron. Most general = energy level (1, 2, 3, etc) sub- level (s, p, d, or f) degenerate orbital Most specific = spin
Electron Configuration Rules The Rules Aufbau Principle- electrons fill lowest energy orbitals first. Pauli Exclusion Principle- electrons will spread out into degenerate orbitals before pairing. Hund’s Rule- electrons in the same orbital will have opposite spins (one up and one down)
The Diagonal Rule Tells the order of the energy of the orbitals 7s 7p 7d 7f 6s 6p 6d 6f 5s 5p 5d 5f 4s 4p 4d 4f 3s 3p 3d 2s 2p 1s
Configuration Diagrams An electron is represented by an arrow Only two arrows per box Place all up arrows in first Try to create some Diagrams at this Website http://www.wellesley.edu/Chemistry/chem120/elecconfigdrag.html
Electron Configurations These are the same as the boxes, only they take up less space Large # = energy level Letter = orbital shape superscript = how many electrons Element # 19, Potassium: 1s22s22p63s23p64s1
Noble Gas Notation Look for the noble gas that comes before the element you are trying to describe. Write the noble gas symbol in brackets [ ] Follow the symbol with the remaining orbitals that are necessary to account for all the electrons in the desired element.
The Electromagnetic Spectrum Organizes light waves by energy, wavelength, and frequency
The photoelectric effect Photon a particle of light that contains a specific amount of energy (quantized) The photoelectric effect a photon of light hits and energizes an electron in an atom. This causes the electron to jump to a higher energy level. The electron inevitably falls back down to the lower energy level, and releases light.