Composition of Matter Chapter 17 Section 1 p. 518-525
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?
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 Properties to 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 physical changeA physical 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 So, does a change in state mean that a new substance has formed?
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
Chemical Properties Have you ever seen the warning labels on paint thinners and lighter fluids that read “FLAMMABLE” Flammability is a chemical property Burning produces new substances during a chemical change