WHAT IS CHEMISTRY?

Chapter 2 Section 1 Describing Matter

Matter Properties of Matter Anything that has mass and takes up space Hard, soft, rough, smooth, flammable, hot cold, liquid, solid, gas, etc. The properties of any type of matter depend on its makeup Every form of matter has two kinds of properties: physical and chemical

Physical Properties A property of a substance that can change without involving a chemical change: Density Hardness Texture Color Solid Liquid Gas Flexibility Luster Ability to conduct heat or electricity Magnetism Breaking into pieces Table Talk: How many of these physical properties describe water?

Chemical Properties A characteristic that describes a substance’s ability to change into different substances Examples: – Natural gas can catch fire and burn in air – Iron can combine with oxygen and form rust – Silver will react with sulfur in the air and tarnish – Baking bread (the yeast creates gas which causes bread to rise)

Table Talk: Describe the difference between a physical property and and chemical property; use the picture provided to help you.

Elements What matter is made of The simplest substances An element is a pure substance that cannot be broken down into any other substance Early Greeks believed everything on Earth was composed of 4 “elements”: earth, wind, fire, water We now know that there are slightly more than 100 elements!

Particles of Elements - Atoms Elements are usually represented by one- or two- letter symbols: – H = hydrogen – Z = zinc – He = helium – Al = aluminum, etc. Atoms are the smallest possible pieces of elements Different elements have different properties because their atoms are different Table Talk: How do you think the periodic table might be arranged?

Chemical Bond When atoms combine, this is a force of attraction Many atoms combine to form molecules (groups of 2 or more atoms held together by chemical bonds) Carbon dioxide CO 2 Oxygen O 2 Water H 2 O Table Talk: How many atoms are in each of these molecules?

Compounds Most elements in nature are found combined with other elements A compound = a pure substance made of two or more elements chemically combined in a set ratio A compound is represented by a chemical formula. For example, CO 2 is carbon dioxide. There are 2 oxygen atoms combined with every carbon atom in this compound When elements are combined, they form compounds having properties that are different from the uncombined elements Table Talk: Table sugar C 12 H 22 O 11 is made up of carbon, hydrogen, and oxygen. What is the ratio of elements in this compound?

Mixture Elements and compounds are pure substances Most materials we see are not pure A mixture is two or more substances (elements, compounds or both) that are together in the same place but not chemically combined Table Talk: What materials might you find in a potting soil mixture?

Heterogenous mixtures Homogenous mixtures “hetero” means different In these mixtures, you can see the different parts “homo” means same In these mixtures, you can’t see the different parts A solution is an example of a homogenous mixture Table Talk: When you boil salt water, the water evaporates, leaving salt behind. Is salt water a compound or a mixture? Why? See BrainPop “compounds & Mixtures” end