Title: Compounds and Elements
1Compounds and Elements
2Compounds and Elements
- Compounds are pure substances
- They are made up of two or more elements
chemically bound together. - So what are elements??
3The 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?
4The 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.
5The Elements - a brief history
- For centuries scientists and philosophers
believed that all matter was made up of - Earth
- Air
- Fire
- Water
6Earth, Wind and Fire
Not these guys !
When they looked like this.
Ahhh.the 70s
I looked like this.
7The Elements - a brief history
- This view of all matter being made up of only
four elements lasted until the 17th century in
Europe,
8Alchemists
- 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)
10Alchemists
- 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.
11Sir 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.
12Robert 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.
13Breaking 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.
14The Mad Scientist Was Born
15Antoine 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.
16Volta!!
- In the 19th century a new investigative tool was
invented - the Voltage Pile. - Invented by Allesandro Volta
- Essentially - a battery.
17Voltage Pile
- The voltage pile was much like a battery.
- Delivered a reliable supply of electric current.
- What did scientists do first?
18Stick It Up Their Nose?
19Eat it?
20Nope! They did something way more cool.
- They immediately began passing currents through
water and what do you think happened?
21Making Gas.
- They found that
- hydrogen and oxygen gases were produced.
- the water level fell slightly
Hmmm..
22Inferring.
- They inferred that some of the water had been
decomposed into hydrogen and oxygen.
23So if that works.
- Humphry Davy (1778-1829) wanted to see what else
could be decomposed using electricity.
24Using 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
25Not this kind of electrolysis
26This kind
27Law 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
28Law of Definite Proportions
- Hydrogen peroxide contains H and O but in
different proportions - 6 Hydrogen 94 Oxygen
- These proportions always hold true.
29Properties 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?
30One 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