1. Developing Ideas about Matter
Section A1.3

2. 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

3. Review Last class: Hand in: MSDS worksheet
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 demo?
Hand in: MSDS worksheet

4. 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

5. 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)

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

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

8. 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

9. 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

10. 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

11. 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

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

13. 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

14. 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

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

16. 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

17. 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?
ety_mode=true&persist_safety_mode=1&safe=active

18. 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/ size of atom)

19. 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

20. Bohr continued…

21. Bohr continued …
Discovered every element has its own unique pattern, and thus unique atomic structure
ements.html

22. 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

23. Atomic Models Activity: Summary Chart
Using your textbook, complete a chart with the following headings for the 5 models discussed

24. Atomic Models Activity: Jigsaw
In groups of 5, you will become “experts” on a particular model of the atom
In your group, make a poster which explains the particular model you are given
Poster must teach 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!