Presentation on theme: "Explain the difference between an element and a compound. Distinguish between a substance and a mixture. Identify the chemical symbols of elements, and."— Presentation transcript:
Explain the difference between an element and a compound. Distinguish between a substance and a mixture. Identify the chemical symbols of elements, and name elements, given their symbols.
Substances can be classified as elements or compounds. An element is the simplest form of matter that has a unique set of properties. Cannot be broken down into simpler substances. EX: H or Ne A compound is a substance that contains two or more elements chemically combined in a fixed proportion. Can be broken down into simpler substances. EX: H₂O, NaCl
Compounds cannot be broken down into simpler substances by physical means. A chemical change is a change that produces matter with a different composition than the original matter.
The properties of compounds are quite different from those of their component elements.
Chemists use chemical symbols to represent elements, and chemical formulas to represent compounds. Chemical symbols are one or two letters. First letter is always capitalized, second letter is always lower case. EX: He, Mg, Mn Some symbols come from the Latin name. EX: Sodium, Na, natrium Gold, Au, aurum Iron, Fe, ferrum Lead, Pb, Plumbum
Formulas have element symbols and numbers Subscripts in chemical formulas are used to indicate the relative proportions of the elements in the compound. EX: H₂O
Describe what happens during a chemical change. Identify four possible clues that a chemical change has taken place. Apply the law of conservation of mass to chemical reactions.
The ability of a substance to undergo a specific chemical change is called a chemical property. Chemical properties can only be observed only when a substance undergoes a chemical change. During a chemical change, the composition of matter always changes. A chemical change is also called a chemical reaction.
One or more substances change into one or more new substances during a chemical reaction. A substance present at the start of the reaction is a reactant. A substance produced in the reaction is a product.
Possible clues to chemical change include a transfer of energy, a change in color, the production of a gas, or the formation of a solid. Sometimes these clues may be the result of a physical change (bubbles forming from water and soap mixing together) A precipitate is a solid that forms and settles out of a liquid mixture.
During any chemical reaction, the mass of the products is always equal to the mass of the reactants. The Law of Conservation of mass states that in any physical change or chemical reaction, mass is conserved. Mass is neither created not destroyed.