classification of matter chapter 17 p. 517-541. composition of matter chapter 17 section 1 p....
TRANSCRIPT
Pure Substances
• Have you ever looked at a picture and couldn’t tell whether it was a painting or copy? Did you go up and touch it?
• The properties of materials can be used to classify them into categories.
Pure Substances
• Materials are either pure substances or a mixture of substances.
• Pure substances – AKA substance – are either an element or compound
Pure Substances
• Substances can’t be broken down into simpler substances and still have the same properties
• Ie – what are the properties of a piece of gum?
• If I break it into smaller pieces, does it still have those properties?
• Ie – what are the properties of water?• If I separate a bottle of water into different
glasses, is it still water?
Elements
• Remember:– An atom is the smallest piece of
matter that still retains the properties of the element.
• All substances are made from atoms.
• If all the atoms in a substance are alike, it is called an element.
Elements
• Ie – the graphite in your pencil is an example of an element. – All the atoms in the graphite are carbon atoms
• Ie – the copper covering on your penny is an example of an element.– All the atoms that make up the covering are
copper atoms.
• Ie – the zinc in the middle of your penny is an example of an element. – All the atoms that make up your penny center
are made of the element zinc.
Elements
• There are 90 elements found in nature• Over 20 have been made in laboratories
– These are usually unstable and don’t last long
•Some elements you might recognize in your everyday life.
Copper pot or pan
Compounds
• Two or more elements can combine to form a compound
• These elements combine in a fixed proportion • Ie - water is a compound in which 2 hydrogen
atoms combine with 1 oxygen atom • Can you imagine putting a silvery metal and a
greenish-yellow, poisonous gas on your food??
Compounds
• You may have if you dashed some salt on your food today!
• Salt is a compound made up of the 2 elements sodium and chlorine
• Like salt, compounds usually look different from the elements in them
Mixtures
• Who enjoys eating pizza and pop for lunch?
• If so, then you enjoy 2 foods that are classified as mixtures
• A mixture, such as pizza or pop, is a material made up of two or more substances that can be easily separated by physical means.
Mixtures
• Heterogeneous Mixtures:• Unlike compounds, mixtures aren’t always
made of the same proportions of the substances that make them up.
• Remember that pizza? The chef doesn’t measure out precisely how much of each topping is sprinkled on. Plus, you can easily see most of the toppings on the pizza
• A mixture in which different materials can be distinguished easily is called a heterogeneous mixture
• Other examples: granite, dry soups, concrete
Mixtures
• Homogeneous Mixtures:• Remember that pop? It’s an example of a
homogeneous mixture• A homogeneous mixture contains 2 or more
substances blended evenly throughout• These mixtures are also known as solutions• Solutions remain constantly and uniformly mixed• Other example: Vinegar
Colloids
• A colloid is a type of mixture that never settles
• Its particles are larger than those in solutions but not heavy enough to settle
• Examples: Milk, paint, fog
Colloids• Detecting Colloids:• To tell for certain if a liquid is a colloid, pass a
beam of light through it• A light beam is invisible as it passes through a
solution, but can be seen when passing through a colloid
• This occurs because the particles in a colloid are large enough to scatter light
• The scattering of light by colloidal particles is called the Tyndall effect
• Can you think of any other colloids?
Website
• http://www.brainpop.com/science/matter/compoundsmixtures/index.weml
Physical properties
• Physical properties are observations that you make without changing the identity of the substances that make up the material
• For instance, you can stretch a rubber band or bend a piece of wire
• The ability to stretch or bend are physical properties
• Some other physical properties are color, shape, size, melting point, and boiling point
Physical Properties
• Appearance:
• How would you describe a tennis ball? (shape, color, state of matter)
• How would you describe a soft drink? (color, state of matter, taste)
• You could also measure its volume and temperature—these are all physical properties
Physical Properties• Behavior:• Some physical properties
describe the behavior of a substance
• For instance, objects containing iron (I.e. safety pins) are attracted by a magnet
• Remember that soft drink? If you were to knock it over, it would spread onto the table and floor—the ability to flow is a physical property of liquids
Physical Propertiesto Separate
• Have you ever licked the icing from the middle of a sandwich cookie?
• If so, then you’re using physical properties to identify the icing and separate it from the rest of the cookie
• You can use other physical properties to separate such as using a sifter to separate poppy seeds from sunflower seeds
• Or sand from iron fillings by using a magnet
Physical Change
• If you break a piece of gum, you change some of its physical properties—shape and size
• However, you haven’t changed the identity of the materials that make up the gum
• Each piece still tastes and chews the same
Physical Change
• A physical changephysical change is any change in size, shape, or state of matter
• These changes might involve energy changes, but the kind of substance—the identity of the element or compound—does not change!
Physical Change to Separate
• I some parts of the world, water is very scarce, many such areas lie near the sea
• They obtain their drinking water by using the physical property of boiling point to separate the the salt from the water
• This process is called distillation• In distillation, you use an apparatus to
vaporize and condense liquid, leaving the solid material behind