Compounds A compound is a substance formed when two or more elements combine chemically. The properties of compounds are different from the properties of the elements that make it up. Example: Sodium (Na) is a very reactive metal. Chlorine (Cl) is a green poisonous gas. Together they form salt (Edible Solid).

Chemical bonds When atoms combine to form compounds, they are held together by forces called chemical bonds There are 2 main types:

Ionic Bond Ionic bond– a bond that forms as a result from the attraction between positively and negatively charged atoms (called ions). Electrons are transferred from one atom to the other. Common ionic compounds are formed when metals react with nonmetals . Examples: Sodium chloride, Magnesium Oxide, Potassium dichromate.

Covalent Bonds Covalent Bond– a bond that forms when atoms share electrons. The shared electron moves around the nucleus of each atom. Covalent compounds are usually made of nonmetals. Common covalent compounds are gasoline, sugar , and plastics, and water .

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FORMULAS A chemical formula is a combination of chemical symbols and numbers that indicate which elements and how many atoms of each element are present in a compound. Symbols are used to represent the elements.

Subscripts Numerical subscripts are used to represent the number of each element and are written below and to the right of a symbol. When a symbol has no subscript, then it means only one atom of that element is present. There are no spaces between the different elements in the compound when writing the formula.

Compounds and Molecules

Write ONE sentence to summarize the difference between compounds and molecules

Reminders: Some elements have 1 letter. Others have 2 letters Reminders: Some elements have 1 letter. Others have 2 letters. Do not let this confuse you. All symbols START with a capital letter.