Atoms, Elements, and Compounds

Chapter Fifteen: Molecules and Compounds

• 15.1 Compounds and Chemical Bonds

• 15.2 Electrons and Chemical Bonds

Investigation 15A

• How do atoms form chemical bonds with other atoms?

Chemical Bonds

15.1 Compounds and chemical bonds

• A compound contains two or more different elements that are chemically bonded together.

15.1 Compounds and chemical bonds

• A mixture contains two or more elements and/or compounds that are not chemically bonded together.

15.1 Molecules and covalent bonds

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

• A covalent bond is formed when atoms share electrons.

15.1 Chemical formulas and diagrams

• Molecules are represented by a chemical formula.

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

15.1 Structure and function• The properties of a compound depend MUCH more on the

exact composition and structure (shape) of its molecule than on the elements of which it is made.

15.1 Ionic bonds• Ionic bonds are bonds in which

electrons are transferred from one atom to another.

• Sodium and chlorine form an ionic bond because the positive sodium ion is attracted to the negative chloride ion.

15.1 Why chemical bonds form

• It takes energy to separate atoms that are bonded together.

• The same energy is released when chemical bonds form.

• Atoms form bonds to reach a lower energy state.