Table of Contents (UPDATE) Topic Date Page Numbers Unit 1 Study Guide 9/18-19/2014 23 Unit 1 Mastery Tracker 9/22-23/2014 24 History of the Atomic Theory 25-28 Structure of the Atom 9/24-25/2014 29-32

The History of the Atomic Theory

GUIDED NOTES The guided notes you have been given have less information filled provided for you. It is up to you as the student to take accurate notes during todays class. If you miss something in the presentation you can always go to the class website to complete taking your notes.

Theory v. Law Scientific Theory Summarizes a hypothesis or group of hypotheses that have been supported with repeated testing If enough evidence exists, it becomes accepted as a valid explanation of a phenomenon. Theories are foundations for furthering scientific knowledge and for putting the information gathered to practical use. Scientists use theories to develop inventions or find a cure for a disease.

Theory v. Law Scientific Law Is a description of an observed phenomenon, not an explanation for what was observed. For example, Kepler's Laws of Planetary Motion, describe the motions of planets but do not provide an explanation for their movements. In chemistry, laws are often expressed only as an equation. Laws are usually proven, but can be refuted (rarely).

“Atomos” Atom – smallest particle that retains the properties of an element. Atom – comes from the Greek word “atomos” meaning “no cut” or “indivisible.” Throughout the years, scientists have drastically changed what they think an atom look like.

The Earliest Theory of the Atom 5th Century BC Leucippus and Democritus – develop the belief that everything is made up of tiny parts called atoms. The Earliest Model

…and people actually believed him… [straight face] But… Aristotle disagreed with Leu and Demo, the idea of the atom disappeared for the next 2000 years. …and people actually believed him… [straight face] I hereby solemnly decree the atoms do not exist in this world -Aristotle

John Dalton What: Created the atomic theory defining what an atom looks like. When: 1803 Key Points Dalton is called the “father of the modern atomic theory” John Dalton performs experiments which show elements do consist of tiny atoms

Dalton’s Postulates (Theories) Elements are made of tiny particles called atoms. All atoms are identical in composition The atoms of a specific element are different from those of any other element. Atoms can combine to make compounds Atoms cannot be created or destroyed.

J. J. Thompson What: Discovered the electron and charge When: 1897 Key Points Discovered the electron using a cathode ray tube experiment Developed the plum pudding model

Let’s All Go to the Movies… Now, let’s take a look at what J.J Thompson was trying to describe 

Ernest Rutherford What: Discovery of the Nucleus When: 1911 Key Points Gold Foil Experiment Shot radioactive alpha particles at a sheet of gold foil, expected them to go through the foil Some particles went through, some shot off at angles and some came straight back Experiment made him predict a positively charged nucleus off which the particles deflected

Gold Foil Experiment

Expected Results Actual Results

Niels Bohr What: Electron Orbits and Bohr Model When: 1922 Key Points Electrons move around the nucleus in certain paths or energy levels Each distance corresponds to a certain quantity of energy that an electron can have.

Electron Orbits Models:

Shrodinger What: Discovered the Quantum Model When: 1930 Key Points Model shows that electrons do not have a planetary orbit they exist in an electron cloud. Electrons can be thought of as waves instead of particles

Current Atomic Theory Currently the theory tells us that: Atoms are made of smaller particles called protons, neutrons and electrons (and these are made of even smaller particles – quarks!) Electrons don’t travel in definite paths The exact path of electron cannot be predicted. Orbitals are regions where electrons are likely to be found. They are also known as electron clouds.

Let’s Sum it All Up Categories Indivisible Electron Nucleus Orbit Electron Cloud Greek X Dalton Thomson Rutherford Bohr Current Atomic Theory

Independent Practice Page 27 Work on the Worksheet you have been given by your teacher. ASK 3 BEFORE ME RULE IS IN EFFECT

Timeline Project Document Home Learning (Poster Board) A-Day Due: September 26th B-Day Due: September 29th Create a timeline of atomic theory beginning with Leucippus and Democritus and ending with our current model. Use you’re the internet, text books and notes to add details to each contribution. Each contribution should have: Date or time period 2-3 facts Picture of important figure (scientist) or model Timeline Project Document

Structure of the Atom

WHAT IS AN ATOM MADE OF? An atom is the smallest particle of matter. It cannot be created or destroyed by chemical means. Subatomic Particles Protons Neutrons Electrons

Subatomic Particles Proton (p+) Subatomic particles present in the nucleus with positive charge Electron (e-) The negatively charged particles with revolves around the nucleus Neutron (n0) A particle with no charge (neither positive nor negative) that is present in the nucleus. It appears in the nucleus of all atoms except hydrogen

Element Anatomy

Subatomic Particles Information Charge Mass # Location Electron -1 Electron cloud Proton +1 1 Nucleus Neutron

Atomic Number Atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element. Element # of protons Atomic # (Z) Carbon 6 Phosphorus 15 Gold 79

Mass Number Mass # = p+ + n0 Mass number is the number of protons and neutrons in the nucleus of an isotope. Mass # = p+ + n0 p+ n0 e- Mass # Oxygen - 10 - 33 42 - 31 15 18 8 8 18 Arsenic 75 33 75 Phosphorus 16 15 31

Isotopes atoms of the same element having different masses due to varying numbers of neutrons. Isotope Protons Electrons Neutrons Nucleus Hydrogen–1 (protium) 1 Hydrogen-2 (deuterium) Hydrogen-3 (tritium) 2

Composition of the nucleus Atomic Masses Atomic mass is the average of all the naturally occurring isotopes of that element. Isotope Symbol Composition of the nucleus % in nature Carbon-12 12C 6 protons 6 neutrons 98.89% Carbon-13 13C 7 neutrons 1.11% Carbon-14 14C 8 neutrons <0.01% Carbon = 12.011

Independent Practice