Notes 2-1 DESCRIBING MATTER

Matter Anything that has mass and takes up space Substance- single kind of matter that has a specific make-up and specific properties -Example: Salt or sugar -Non-Example: Muffin batter (the ingredients can vary)

Physical Properties of Matter Can be observed without changing into another substance Examples: Freezing point, melting point, density, texture, color, flexibility, solubility in water

Chemical Properties of Matter Ability to change into a different substance Examples: flammability, rusting, tarnishing, rising of bread in baking process

Elements Pure substances that cannot be broken down into any other substance Simplest substances Is identified by its specific physical and chemical properties Examples: Carbon, Oxygen, Gold, Silver, Aluminum

Atoms Basic particle that makes up all elements Having different atoms gives elements their unique properties Atoms have a nucleus made up of positively charged protons and neutrally charged neutrons, and they are surrounded by a cloud of negatively charged electrons

Modeling an Atom Pencil “lead” is made of mostly graphite, a form of carbon. Two ways to model atoms used in this presentation are shown here for carbon.

Chemical Bonds Atoms combine by chemical bonds (a force of attraction between the electrons of 2 or more atoms) Often form molecules- groups of 2 or more atoms held together by chemical bonds Examples: H2O, O2, CO2

Modeling Molecules How many atoms are in each of these molecules?

Compounds Pure substance made up of 2 or more elements chemically combined in a set ratio Represented by a chemical formula which shows the elements in the compound and the ratio of atoms When elements combine to form compounds, they have unique properties from those of the uncombined elements -Example: Hydrogen alone is a very combustible gas, Oxygen alone is a major supporter of combustibility, but when combined in the set 2:1 ratio H2O, they put out fires!

Ratios A ratio compares two numbers. It tells you how much you have of one item compared to how much you have of another. For example, a cookie recipe calls for 2 cups of flour to every 1 cup of sugar. You can write the ratio of flour to sugar as 2 to 1, or 2:1. The chemical formula for rust, a compound made from the elements iron (Fe) and oxygen (O), may be written as Fe2O3. In this compound, the ratio of iron atoms to oxygen atoms is 2:3. This compound is different from FeO, a compound in which the ratio of iron atoms to oxygen atoms is 1:1.

Ratios Practice Problem What is the ratio of nitrogen atoms (N) to oxygen atoms (O) in a compound with the formula N2O5? Is it the same as the compound NO2? Explain. N2O5 contains two nitrogen atoms for every five oxygen atoms. Both N2O5 and NO2 are made up of only nitrogen atoms and oxygen atoms. However, the two compounds are different because NO2 contains one nitrogen atom for every two oxygen atoms.

Mixtures Made up of 2 or more substances that are not chemically combined Differ from compounds because they do not have to have a set ratio, and each substance in mixture keeps its individual properties Examples: Air, Soil, Salt water

Heterogeneous Mixtures Hetero = different Can see different parts of mixture Examples: Soil, Salad Who can think of other examples?

Homogeneous Mixtures Who can think of other examples? Homo = same Can’t see different parts of mixture, evenly mixed Examples: Sugar/water solution, Air Who can think of other examples?

Separating Mixtures Compounds are hard to separate Mixtures are easy to separate since each component keeps its own properties Look at figure 10 on page 66, it shows different ways to separate a mixture including using a magnet, filtering, distilling, and evaporating

LET’S REVIEW!! What are some examples of chemical properties of matter? What are some examples of physical properties of matter? Density, melting, freezing, color, flexibility, hardness Rusting, flammability, bread baking

LET’S REVIEW!! What 2 things does a chemical formula show? Give an example of an element. Carbon, Oxygen, Nitrogen, Gold, Silver, etc. The elements present and the ratio of atoms