Developing Ideas about Matter Section A1.3

Objectives describe examples of practical applications of chemistry in food storage identify and explain early forms of chemistry outline the development of our understanding of the atomic model as consisting of protons, neutrons and electrons give examples of chemistry based careers in the community

Review Last class: Physical and chemical properties (what is the difference? Examples?) What is the difference between a pure substance and a mixture? What are signs of a chemical reaction? Which ones did we see in the lab?

Back in the day… People have been using chemical properties of substances for centuries First Nations people had extensive knowledge of plant use Our ancestors began to understand relationship between temperature and states of matter

Food Chemistry How do physical changes apply to food? Chemical changes? Examples? Physical changes: freezing (chemical components stay the same) Chemical changes: baking (formation of new substance)

Food Chem: Heating and Freezing Heating- temporary sterilization Kills micro-organisms Canning- heat sterilization Freezing- preserve almost indefinitely Prevents growth of micro-organisms

Salting Way to preserve meat and fish Method of drying Draws water out of meat and bacteria Used by sailors

Fermentation Biochemical preservation technique Bacteria convert starches and sugars into alcohol & carbon dioxide; others into acids Prevents growth of bacteria More digestible and higher vitamin content Helpful in preventing scurvy

More Early Chemistry Metallurgy Producing and using metals Early peoples used gold, copper, silver, lead, and iron Used copper for weapons by hammering it into shapes Annealing- heating copper so not brittle when hammered

Metallurgy continued… Smelting- separating metal from other elements in a compound Way to get copper Done in Egypt by 4000 B.C. Alloy- mixture of metals What is bronze an alloy of? Tin and copper Steel? Iron and carbon

Aristotle and Matter Aristotle thought matter composed of combinations of fire, earth, water, and air Continuous (no such thing as a smaller piece) Democritus- proposed tiny particles (atomos) Didn’t test their ideas

Alchemy Science and magic Experiments to turn cheap metals into gold Many important scientific discoveries made Mercury, procedures for making acids, developed lab equipment

Atomic Theory Theory: a major idea that explains a large amount of data; based on many experiments; may be changed when new data is collected Atomic Theory: explains what the structure of the atom is like

Developing Theories about Matter Four classic models of atoms Examples of the scientific process Founded on experiments Dalton, Thomson, Rutherford and Bohr Modern model of the atom: based on quantum mechanics

Atomic Models Activity: Jigsaw In groups of 5, you will become “experts” on a particular model of the atom You must teach the concept in a way to answer the questions on the worksheet and be useful to your fellow classmates You will teach your classmates about the topic so be comfortable with it!

Atomic Models Activity: Summary Chart The Atom Chart While groups present fill in the chart

Dalton Described atoms as small spheres, different in size, mass, and color depending on type

Thomson Discovered the electron Experimented with beams of particles in a vacuum tube Found that all elements produced the same type of beam made of negative charges Atoms made of smaller subatomic particles in different combinations Electrons imbedded in positive sphere

Rutherford Discovered the nucleus Gold foil experiment Shot positively charged particles at a thin piece of gold foil Expected all particles to go right through, though some deflected and some reflected right back Unexpected result: like firing a cannon ball at tissue paper and having it bounce back! What does this mean? http://www.youtube.com/watch?v=Q8RuO2ekNGw http://www.youtube.com/watch?v=5pZj0u_XMbc&saf ety_mode=true&persist_safety_mode=1&safe=active

Rutherford continued… What this means: There is a strong, dense positively charged core Called the nucleus Most of the atom empty space Nucleus very small (1/10 000 size of atom)

Bohr Proposed that electrons surrounded nucleus in specific energy levels Found evidence based on light released by hydrogen atoms (gaps between energy levels) Falling from higher to lower energy levels releases particular color of light

Bohr continued…

Bohr continued … Discovered every element has its own unique pattern, and thus unique atomic structure http://jersey.uoregon.edu/vlab/elements/El ements.html

Quantum Mechanical Model of the Atom Electron cloud around nucleus Occupy whole space all at once at different energy levels Nucleus contains nucleons Protons- positively charged Neutrons-no electrical charge