Matter

Chapter 2, Section 1 - Classifying Matter                                                                                                                       


Matter - Anything that has mass and takes up space.
  • All matter is either...
    • an element
    • a compound
    • a mixture
Element - A substance that cannot be broken down into simpler substances by chemical means.
  • Any element contains only one type of atom.
  • Elements are represented by chemical symbols.
    • One or two letters - the first is always CAPITALIZED, the second is always lower case.
    • Examples...
      • Hydrogen - H
      • Helium - He
  • Atom - The smallest piece of an element that has all of the element's chemical properties.
    • Atoms join together to make molecules.
    • Molecule - The smallest unit of a substance that behaves like that substance.
  • Some elements can exist as single atoms, some make molecules with more than one atom of the same element.
    • Example:  O2 = Two atoms of oxygen, bonded together.  (Still one element, because they are the same type of atom.)
Compound - A substance made up of atoms of different elements.
  • Compounds contain more than one type of atom.
  • The atoms in a compound always combine in the same proportions.
    • Example: Water always has one oxygen atom and two hydrogen atoms.
  • The properties of a compound are different than the properties of the elements that make it up.
  • Compounds are represented by chemical formulas.
    • Chemical formulas show how many of each kind of atom that are in a molecule.
      • Example:  Water = H2O
    • The small numbers (subscript) in a formula tell how many atoms of the element that comes before it.  In water, the "2" stands for two hydrogen atoms.  If there's no number, than there is one of these atoms.  (One oxygen atom in water.)
Pure Substances - A substance always has the same composition and properties.
  • Examples:
    • Elements
    • Compounds
Mixture - A combination of different substances, which are not chemically combined.

Word Parts

homo-: same
hetero-: different
  • Mixtures can be physically separated into their components.  Pure substances cannot.
  • Mixtures are classified by how well their components mix...
    • Homogeneous Mixtures - The components are evenly spread throughout the mixture.
      • Example - In Kool-Aid, the Kool Aid particles are evenly spread throughout the water.  It looks like one substance.
    • Heterogeneous Mixtures - The components are not evenly  spread throughout the mixture.
      • Example - In a chocolate chip cookie, some parts have chocolate chips, others don't.  You can see the different parts.
      • Note - You can't always see the different parts in a heterogeneous mixture.
  • Miscible - Able to be mixed.  (Like Kool Aid powder and water.)
  • Immiscible - Not able to be mixed.  (Like oil and water.)
  • Gases can mix with liquids - such as the carbon dioxide that makes the bubbles in soda.

Chapter 2, Section 2 - Properties of Matter                                                                                                                    

Physical Properties - Characteristics that can be observed without changing the substance.
  • Examples...
    • Color
    • Shape
    • Size
    • Mass
    • Volume
    • Density
  • Physical properties can be observed and/or measured.
    • Shape, Color, Texture, Odor (Use your senses!)
    • Melting Point - The temperature at which a solid turns into a liquid.
    • Boiling Point - The temperature at which a liquid turns into a gas.
    • Strength
    • Hardness
    • Magnetism
    • Ability to conduct electricity
  • Density - How much matter is in a certain volume of a substance.
    Formula for Density
    • density = mass/volume
    • measured in grams per cubic centimeter (g/cm3)
      • 1cm3 = 1 mL
    • Density, mass, and weight are different things...
      • Mass - The amount of matter in an object.
      • Density - The amount of matter per unit of volume in an object.
      • Weight - The force of gravity pulling on an object's mass.
Chemical Properties - A substance's ability to change into a different substance.  (This is done by either combining with other substances or breaking apart.)
  • Usually not as easy to observe as physical properties.  (The substance has to change for you to see the change; sometimes the change is not noticeable.)
  • Examples...
    • Flammability - The ability to burn.
    • Reactivity - The ability to combine with another substance.
      • Iron combines with oxygen to form rust.  Chrome doesn't rust because chromium doesn't react with oxygen.
Physical vs. Chemical Properties
  • You can observe/measure physical properties without changing the substance.
  • You can only observe/measure chemical properties when the substance changes.

Chapter 2, Section 3 - Changes of Matter                                                                                                                       

Physical Change - A change that affects the physical properties of a substance without changing the chemical properties.  (It remains the same substance.)
  • When you tear a piece of paper in half, it is still paper.  (Physical change.)
  • When you melt an ice cube, it is still H2O.  (Physical change.)
  • When you dissolve sugar in water, it is still sugar.  (Physical change.)
Chemical Change - A change in which one or more substances are changed into entirely new substances with different properties.  (It becomes a different substance.)
  • When an iron tool rusts, a new substance is formed.  (Chemical change.)
  • When fruit ripen and then spoil, new substances are formed.  (Chemical changes.)
Chemical changes are often indicated by...
  • Change in color or temperature.
  • Light, sound, heat, odors.
  • Activity such as fizzing, foaming, popping, etc.
Most chemical changes cannot be reversed.  None of them can be reversed by physical means - some can be reversed by chemical means.

Mixtures can be separated by physical means.
Compounds must be broken down by chemical means.