Chapter 2

Objectives  > Explain the relationship between matter, atoms, and elements.  > Distinguish between elements and compounds.  > Describe molecules, and explain how they are formed.  > Interpret and write some common chemical formulas.  > Categorize materials as pure substances or mixtures.

Matter  Composed of mass  Takes up space  Everything is made of matter  Pie charts in book

 A classification scheme for matter.

Classifying matter  Pure substance Elements Compounds  Mixtures Homogeneous Heterogeneous

Pure substances  Definite chemical composition- ratio does not change  Can not be seperated

Elements  Makes up Matter  Substances that cannot be broken down into simpler substances

Atoms  Smallest unit of an element that has the properties of an element  Smallest particle of element  Atomos=no division

Molecule  The joining of atoms to form the smallest unit of a substance that has all the properties of that substance  Acts as a unit

Compound  Atoms of 2 or more elements that chemically combine to form new substances  Has different properties than the elements in it

Compound cont’d  When elements combine or come together to form a specific compound like H 2 O they always combine in the same proportions 2 Hydrogen's for 1 Oxygen

Diatomic elements  Atoms of the same element that combine to form a molecule because they are unable to stand alone  Ex. O, H, Cl, P

Chemical Formulas  Represent compounds and formulas in a short hand way.  All chemicals have a symbol it is 1 or 2 letters

Chem. form. Con’t  The first letter in a symbol is always capitalized and the second, if needed, is always in lowercase.  Formulas show how many atoms of each chemical is used

Chem. form. Cont’d  This number is called a subscript and is smaller and located to the right of the chemical symbol it goes with, ie H 2 O- the 2 is the subscript for 2 hydrogens.

Chemical formulas  1C 16 H 10 N 2 O 2  One molecule of indigo ink contain 16 carbon, 10 hydrogen, 2 nitrogen and 2 oxygen

Mixtures  Combination of pure substances that are not chemically combined

Mixtures  There are 2 types of mixtures Homogeneous Heterogeneous

Homogeneous  Mixture is the same throughout example- Ketchup  Solutions are homogeneous

Heterogeneous  Not mixed evenly example chocolate chip cookies  Homo and Hetero Video Clip Homo and Hetero Video Clip Homo and Hetero Video Clip

 Miscibility- some liquids can dissolve in others like gasoline- they are miscible  Liquids that don’t dissolve are immiscible oil and water

 Gases can dissolve in liquids example –soda and meringue The meringue in this pie is a mixture of air and liquid egg white that has been beaten and then heated to form a solid foam.