Download Developing Ideas about Matter

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