Atomic theory Atoms: The Building Blocks of Matter

First, there was Democritus Democritus is not a foot fungus, he 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

This guy thought he was nuts His name is Aristotle He is the most famous and most influential of the Greek philosophers 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 4 th century BCE Ancient Greece

Gold Gold The word “atom” comes from a Greek word that means “unable to be cut” Imagine you had a piece of gold that you then cut in half… …and then you cut one of these smaller pieces in half… … and you kept on cutting the leftover piece in half…

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. An atom of gold

Law of Conservation of Mass (1789) Hundreds of years later… Law of Conservation of Mass (1789) Total mass of reactants = Total mass of products Antoine Lavoisier Mass is neither created nor destroyed during chemical or physical reactions.

Soon after that… John Dalton Atomic Theory 1. All matter is made up of tiny, indivisible particles called atoms. 2. Atoms of the same element are identical – same physical and chemical properties 3. Atoms of different elements are different – different physical and chemical properties 4. Atoms can chemically combine in whole number ratios to form compounds and physically mix to form mixtures. 5. 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. Early 1800’s England

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

And after all that… Ernest Rutherford Gold Foil Experiment Discovers the Nucleus

Models of the Atom Dalton Model 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

Needless Cartoonage

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 Spherepeanutdaisy/donutfunkadelic

Orbital Shapes Check out this site for cool pics of orbitals!!!!!!!!!! 1 type5 types3 types7 types

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 7s7p7d7f 6s6p6d6f 5s5p5d5f 4s4p4d4f 3s3p3d 2s2p 1s

Configuration Diagrams Place all up arrows in first Try to create some Diagrams at this Website Only two arrows per box An electron is represented by an arrow

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: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1

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.