Unit 7: Compounds and Chemical Reactions

Unit 7: Compounds and Chemical Reactions

Section 7.1 - Compounds and Chemical Bonds

March 9, 2011

Page 175/177

•  An element is a substance made up of one kind of atom

•  Gold (Au) and Silver (Ag) are elements

•  Some elements are made up of molecules with more than one atom – for example, Hydrogen Gas (H2) and Oxygen Gas (O2) are both elements.

•  A chemical bond forms when atoms transfer or share electrons.

•  There are two kinds – ionic (giving/taking electrons) and covalent (sharing electrons)

•  A compound is formed when two or more elements form a chemical bond.

•  Water (H2O) is a compound, and so is salt (NaCl).

•  Compounds have different properties than the elements that make them!!!!!!!!!!

•  If two or more elements or compounds are put together but don’t bond (exchange or share electrons), they make a mixture

•  Mixtures keep the properties of the substances that make them up

•  Salt water is a mixture – it’s still got the properties of both salt and water!

•  Molecules are represented by a chemical formula.

•  The chemical formula tells you the number of each kind of atom in the molecule.

•  The number next to each element’s symbol is the subscript.

•  The properties of a compound depend MUCH more on the shape of its molecule than on the elements of which it is made.

•  Chemical bonds are formed only between the electrons in the highest unfilled energy level.

•  These electrons are called valence electrons.

•  To figure out how many valence electrons an atom has, count right (but skip the transitional metals)

•  Atoms want to have full electron shells (8, or 2 in the case of atoms from H to C)

•  Noble gases have full electron shells, so they don’t form molecules

•  Other non-metals can get full shells easier by getting electrons.

•  Metals can get full shells easier by giving away electrons

•  Metalloids can give or get depending on what they bond with