Classifying Matter

Let’s start small and work up from there. Atom – the smallest unit of an element that maintains the properties of the element The can be physically mixed or chemically joined to make up other forms of matter

Pure Substance A sample of matter, either a single element or a single compound, that has definite chemical and physical properties Figure 14, Page 22

Physical Properties Characteristic of a substance that does not involve a chemical change Examples: Density, color, hardness Does this test change the chemical make-up of the material? No

Chemical Property Characteristic of matter that describes a substance’s ability to participate in chemical reactions Example: Oxidation, flammability, and combustion Does this test change the chemical make-up of the material? Yes

Figure 12, page 19

Elements A pure substance that contains only one kind of atom It cannot be separated or broken down into simpler substances by chemical means. All atoms of the same element have the same atomic number Elements may bond in different ratios with itself. These are called allotropes.

Compounds A pure substance that is made up of two or more different elements joined by chemical bonds. They are represented by formulas

Molecules The smallest unit of a substance that keeps all of the physical and chemical properties of that substance. It can consist of one atom or two or more atoms bonded together In other words, molecules can be of the same element or of the same compound only

All of the following are molecules, but are they compounds or elements? Br2 H2O O2 O3 C12H22O12 Compound Element Element Compound

Mixtures A combination of two or more substances that are not chemically combined. Examples are air, ice tea, and even cake batter The proportions of the substances can vary

Mixtures can be homogeneous or heterogeneous Homogeneous mixtures have a uniform structure or composition throughout Because of the even distribution, any two samples taken from the same homogenous mixture will have the same proportions of ingredients Examples: Gasoline, air, and syrup

Mixtures can be homogeneous or heterogeneous Heterogeneous mixtures are not evenly mixed. Different regions of the same heterogeneous mixture will have different proportions Examples: Pulpy Orange Juice, chocolate chip cookie dough, and granite.

Visuals of Homogeneous and Heterogeneous Mixtures Figure 19, Page 26

Mixtures verses Compounds, How can you tell which is which? Compounds are two or more elements that are chemically bonded together. Mixtures are two or more substances physically mixed together, but not chemically joined

Therefore Properties of a mixture reflect the properties of the substances mixed in it; compounds have new properties of their own. Compounds have definite composition; mixtures composition can vary from mixture to mixture of the same substances

In other words, You can have a mixture of hydrogen gas and oxygen gas in various concentrations, but the compound water, H2O, will always have 2 hydrogen atoms bonded to one oxygen atom.

Figure 20, Page 28

Classify each of the following as an element, compound, homogeneous mixture, or a heterogeneous mixture Iron (III) Oxide (Fe2O3) 24 Karat gold Sugar Water Ozone Fizzy Soda Flat Soda Compound Element Homogeneous Mix Element Heterogeneous Mix Homogeneous Mix

Since mixtures are just physically combined, they can be separated. Separating Mixtures Since mixtures are just physically combined, they can be separated.

Separating Mixtures Some Methods include: Filtering – separation of a mixture’s components through differences in particle size Decanting – a fancy term for separating two components by pouring Distillation – used to separate two liquids based on their differences in boiling points Magnetism – used to separate magnetic substances Evaporation – removing a liquid to leave a solid behind Centrifuge – separates substances of different densities using a fast rotational motion Chromatography – Separates two substances by using a mobile phase and a stationary phase