Chapter 4

Elements, Compounds & Mixtures Section II

Section 2 - Compounds

II. COMPOUNDS (p.86-89)- a compound is a pure substance composed of elements that are chemically combined. In order to combine chemically they must react or undergo a chemical change. What are the clues to a reaction?

An example of a reaction or chemical changeFireWorks Video 5/18/02   800kb

FireWorks_320x240.avilidmanmusic.com/sled/

SALT Sodium (Na) combines with Chlorine (Cl)

Section 2 - Compounds

A. Elements combine in a definite ratio to form a compound-

A ratio is a comparison of two numbers. It usually looks like a fraction or a time

1/6 or 1:6 or 1 to 6

http://www.windows.ucar.edu/earth/geology/images/water_molecules_sm.gif

Note to martin- add atom ratio and a second example c6h12o6

Ex.) The mass of hydrogen to the mass of oxygen in water is always 1 gram of hydrogen for every 8 grams of oxygen. If the ratio is different, it is not water.What does an atom of oxygen weigh?

16 amuWhat does an atom of hydrogen weigh ?

1 amuHow many atoms of hydrogen in water?2What is the mass ratio ?2:16 which reduces to 1:6

Section 2 - CompoundsB. Every compound has a unique set of properties-

1. Like elements, compounds have their own sets of

chemical properties like boiling point, density and

color.

2. A compound has different properties than the elements that

form it. (Ex.Sodium chloride)www.powerlabs.org/ chemlabs/sodium.htm

http://www.vanderkrogt.net/elements/images/sodium.jpghttp://www.webelements.com/webelements/elements/media/element-pics/Cl.jpg

resourcescommittee.house.gov/.../ photogallery/

Click pic for video

Na

NaCl

Section 2 - Compounds

C. Compounds can be broken down into element or simpler compounds through chemical changes.

http://www.bytocom.com/Gallery/images/electrolysis.gif

1. These chemical changes can be brought about by running electricity though the substance (water and melted sodium chloride) heating the substance (Mercury (II) oxide) or sometimes even exposure to sunlight (hydrogen peroxide).

Section 2 - Compounds

2. Compounds cannot be broken down by

physical changes.

a. Physical changes include filtration, and

grinding the substance into a powder. (Boiling and melting are also physical changes)

Compound review video

Section 2 – CompoundsD. Compounds in your world. 1. Compounds in nature a. Nitrogen is a key element needed to make proteins. Those proteins can only be made by nitrogen compounds. Bacteria in the soil make those nitrogen compounds. http://www.beefretail.org/uDocs/1133Shoulder%20Steak.JPG

anka.livstek.lth.se:2080/ rootnodules.htm

Section 2 - Compounds

b. Another important compound is carbon dioxide.

Carbon dioxide is exhaled by animals and

people and used by plants. Plants then use the

carbon dioxide to make other compounds like

sugar.

Section 2 - Compounds

E. Compounds in industry a. Nitrogen is combined with the element hydrogen to form a compound called ammonia that is manufactured for fertilizers. There are many other compounds manufactured in

industry.

http://www.uyseg.org/greener_industry/pages/ammonia/images/ammonia.gif

Section 2 - Compounds

b. The compounds found in nature are often not the materials needed for industry. Often the compounds need to be broken down to provide elements used for raw materials. For example, aluminum that is used in cans and airplanes is not

found alone in nature. Breaking down the compound aluminum oxide produces it.

http://mineral.galleries.com/minerals/oxides/spinel/spinel.jpg http://www.leeric.lsu.edu/energy/rrr/aluminum2.gif

Fun little clip on this topic