Developing Ideas about MatterSection A1.3

Objectivesdescribe 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

ReviewLast 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 demo?

Hand in: MSDS worksheet

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 FreezingHeating- temporary sterilization

◦Kills micro-organisms◦Canning- heat sterilization

Freezing- preserve almost indefinitely◦Prevents growth of micro-organisms

SaltingWay to preserve meat and fishMethod of dryingDraws water out of meat and

bacteriaUsed by sailors

FermentationBiochemical preservation

techniqueBacteria 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 ChemistryMetallurgy

◦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 MatterAristotle 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

AlchemyScience and magicExperiments to turn cheap

metals into goldMany important scientific

discoveries made◦Mercury, procedures for making

acids, developed lab equipment

Atomic TheoryTheory: 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 MatterFour classic models of atoms Examples of the scientific

processFounded on experimentsDalton, Thomson, Rutherford and

BohrModern model of the atom:

based on quantum mechanics

DaltonDescribed atoms as small

spheres, different in size, mass, and color depending on type

ThomsonDiscovered the electronExperimented with beams of

particles in a vacuum tubeFound 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

RutherfordDiscovered the nucleusGold 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=Q8RuO2ekN

Gw◦ http://www.youtube.com/watch?v=5pZj0u_XMb

c&safety_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)

BohrProposed 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/Elements.html

Quantum Mechanical Model of the AtomElectron cloud around nucleusOccupy whole space all at once

at different energy levelsNucleus contains nucleons

◦Protons- positively charged◦Neutrons-no electrical charge

Atomic Models Activity: Summary Chart

Using your textbook, complete a chart with the following headings for the 5 models discussed

Atomic Models Activity: JigsawIn 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!