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Compounds and Elements

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Title: Compounds and Elements


1
Compounds and Elements
  • Breaking it Down

2
Compounds and Elements
  • Compounds are pure substances
  • They are made up of two or more elements
    chemically bound together.
  • So what are elements??

3
The Elements - a brief history
  • For thousands of years people wondered why matter
    behaved the way it did.
  • What is everything made of?
  • Why does water freeze?
  • What am I made of?

4
The Elements - a brief history
I dont want to get my hands dirty!
  • Philosophers spent a lot of time thinking and
    talking about matter but very little time doing
    anything with it.

5
The Elements - a brief history
  • For centuries scientists and philosophers
    believed that all matter was made up of
  • Earth
  • Air
  • Fire
  • Water

6
Earth, Wind and Fire
Not these guys !
When they looked like this.
Ahhh.the 70s
I looked like this.
7
The Elements - a brief history
  • This view of all matter being made up of only
    four elements lasted until the 17th century in
    Europe,

8
Alchemists
  • While philosophers were thinking about matter,
    Alchemists were doing something about it.
  • They believed that one element could be changed
    into another.
  • Part Chemist , Part Magician

Gold
Lead
9
(No Transcript)
10
Alchemists
  • Alchemists did all sorts of hands-on chemistry.
  • They did many experiments and discovered many
    things.
  • They were very secretive and developed a secret
    code to keep track of their experiments.

11
Sir Francis Bacon1561 - 1626
  • In the 17th century Francis Bacon wrote a book
    that changed the way people thought about
    science.
  • Bacon asked people to let go of the old way of
    looking at science
  • He developed the scientific method.
  • Convinced people that science should be based on
    experimental observation, not just thought.

12
Robert Boyle1627-1691
  • First scientist to express public
  • skepticism of the four elements view of
    matter.
  • Called elements unmingled bodies.
  • Recognized that elements could be combined to
    form compounds.

13
Breaking it down
  • In the 17th century scientists got very excited
    about breaking matter apart until it couldnt be
    broken apart anymore.
  • These elemental parts are called elements.
  • They heated, burned, cooled and mixed everything
    they could get their hands on to see how things
    could be broken down.

14
The Mad Scientist Was Born
15
Antoine Lavoisier1743 - 1794
  • Lavoisier was a pioneer in this field.
  • He identified 23 new elements by breaking things
    down into the smallest parts.
  • Realized that measuring the mass of all parts of
    a chemical reaction was essential to making
    inferences about what was happening in chemical
    reactions.

16
Volta!!
  • In the 19th century a new investigative tool was
    invented - the Voltage Pile.
  • Invented by Allesandro Volta
  • Essentially - a battery.

17
Voltage Pile
  • The voltage pile was much like a battery.
  • Delivered a reliable supply of electric current.
  • What did scientists do first?

18
Stick It Up Their Nose?
19
Eat it?
20
Nope! They did something way more cool.
  • They immediately began passing currents through
    water and what do you think happened?

21
Making Gas.
  • They found that
  • hydrogen and oxygen gases were produced.
  • the water level fell slightly

Hmmm..
22
Inferring.
  • They inferred that some of the water had been
    decomposed into hydrogen and oxygen.

23
So if that works.
  • Humphry Davy (1778-1829) wanted to see what else
    could be decomposed using electricity.

24
Using Current
  • Davy found that he had to start with a liquid
    mineral or a solution of a mineral.
  • His assistant, Mike Faraday called this process
    electrolysis.
  • Davy discovered
  • Potassium
  • Sodium
  • Magnesium
  • Calcium
  • Barium
  • Strontium

25
Not this kind of electrolysis
26
This kind
27
Law of Definite Proportions
  • Compounds are pure substances that contain two or
    more elements combined together in fixed or
    definite amounts.
  • So if you have 300 units of water you will have
    200 units of Hydrogen and 100 units of Oxygen.
  • Because of the difference in weight
  • Water 11 Hydrogen 89 Oxygen

28
Law of Definite Proportions
  • Hydrogen peroxide contains H and O but in
    different proportions
  • 6 Hydrogen 94 Oxygen
  • These proportions always hold true.

29
Properties of Compounds
  • Pure substances have constant composition
  • They also tend to have constant properties - they
    tend to always behave the same way.
  • We can use these constant properties to identify
    the element
  • How might you do this?

30
One more thingLaw of Conservation of Mass
  • In a chemical change, the total mass of the new
    substance is always the same as the total mass of
    the original substances.
  • What goes in gotta come out
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