Pure Substances A sample of matter that has definite chemical and physical properties.
Elements pure substance that cannot be separated into simpler substance by physical or chemical means.
Elements In 1813, a system of representing elements with symbols was introduced. Each symbol consists of one or two letters. Two letters are needed for a chemical symbol when the first letter of that element’s name has already been used.
Common Elements AluminumAl BromineBr CalciumCa CarbonC GoldAu HeliumHe HydrogenH NitrogenN
Compounds Pure substance composed of two or more different elements joined by chemical bonds. Made of elements in a specific ratio that is always the same Has a chemical formula Can only be separated by chemical means, not physically
Compounds Compounds are also pure substances. Water is a compound. Water can be broken down into simpler substances – hydrogen and oxygen.
Mixtures A combination of two or more pure substances that are not chemically combined. substances held together by physical forces, not chemical No chemical change takes place Each item retains its properties in the mixture They can be separated physically Chem4kids.com
Is it uniform throughout? If the answer is yes, the matter is homogeneous (looks the same throughout). That leads us to another question.
Homogeneous Mixtures A mixture that appears to be the same throughout. It is “well mixed.” The particles that make up the mixture are very small and not easily recognizable.
Examples of homogeneous mixtures Milk, toothpaste, and mayonnaise are homogeneous mixtures.
Solutions A solution is a type of homogeneous mixture formed when one substance dissolves in another. It is the best mixed of all mixtures. A solution always has a substance that is dissolved and a substance that does the dissolving. The substance that is dissolved is the solute and the substance that does the dissolving is the solvent.
SOLUTIONS HAVE 2 PARTS SOLUTE – The substance being dissolved SOLVENT- The substance doing the dissolving sugar=solute Water = solvent
Types of solutionsGasGas Air (oxygen in nitrogen) GasLiquid Soda water (carbon dioxide in water) SolidLiquid Ocean water (salt in water) SoluteSolventExampleSolidSolid Gold jewelry (copper in gold) Metals dissolved in metals are called alloys.
Alloys Brass is an alloy of copper and zinc. Stainless steel is a mixture of iron and chromium.
Is it uniform throughout? If the answer is no, the matter is a heterogeneous mixture. Considered the “least mixed.” Does not appear to be the same throughout. Particles are large enough to be seen and to be separated from the mixture.
Examples of heterogeneous mixtures Sand and pebbles Oil and water Powdered iron and powdered sulfur
Examples of homogeneous mixtures Milk, toothpaste, and mayonnaise are homogeneous mixtures. THESE ARE EXAMPLES OF COLLOIDS
Mixtures vs. Compounds http://www.bbc.co.uk/schools/ks3bitesize/science/chemistry/elements_com_mix_6.shtml
Can you identify the following? You will be shown a series of photos. Tell if each photo represents an item composed of an element, compound, or mixture. Review: An element contains just one type of atom. A compound contains two or more different atoms joined together. A mixture contains two or more different substances that are only physically joined together, not chemically. A mixture can contain both elements and compounds.