Chapter Sixteen: Compounds  16.1 Chemical Bonds and Electrons  16.2 Chemical Formulas  16.3 Molecules and Carbon Compounds

CHEMICAL BONDING  A chemical bond is an attractive force between 2 or more atoms, making a compound.  Can be from the same element (O 2 ) or different elements (NaCl)  Atoms combine so that they each have a total of 8 valence electrons (full octet)

16.1 Valence electrons  Chemical bonds are formed only between the electrons in the highest unfilled energy level.  These electrons are called valence electrons.

16.1 Valence electrons and the periodic table  Going from left to right across a period each new element has one more valence electron than the one before it. How many valence electrons does nitrogen have?

Group 1  Alkali MetalsGroup 1  Alkali Metals –1 valence e - Group 2  Alkaline-Earth MetalsGroup 2  Alkaline-Earth Metals –2 valence e - Groups 3-12  Transition MetalsGroups 3-12  Transition Metals –Variable valence e - Group 13  Boron GroupGroup 13  Boron Group –3 valence e - Group 14  Carbon GroupGroup 14  Carbon Group –4 valence e - Group 15  Nitrogen Group 5 valence e - Group 16  Oxygen Group 6 valence e - Group 17  Halogens 7 valence e - Group 18  Noble Gases 8 valence e - THIS IS A FULL VALENCE SHELL Exception is Helium, which only has 2, but is still full

16.1 Lewis dot diagrams  A clever way to keep track of valence electrons is to draw Lewis dot diagrams.  A dot diagram shows the element symbol surrounded by one to eight dots representing the valence electrons. What is the dot structure for nitrogen?

Chemical Bonding (cont.)  2 types of Chemical Bonds:  Ionic Bonds  Covalent Bonds

Ionic Bonds  Occur when atoms gain or lose electrons to form ions  Oppositely charged ions are attracted to each other and form a bond  Occur only between metals and nonmetals

Ionic Bonds (cont.)  Metals form Positive (+) ions because they give away electrons  Nonmetals form Negative (-) ions because they gain electrons  Opposites Attract: Na +  Cl - forms NaCl

Covalent Bonds  Occur when atoms share electrons  Rather than lose or gain electrons atoms share their electrons to make a full octet.  Only occur between nonmetals.  Ex: CO 2, H 2 O

16.1 Chemical formulas  A molecule’s chemical formula tells you the ratio of atoms of each element in the compound.

16.1 Reactivity  In chemistry, reactive means an element readily forms chemical bonds, often releasing energy.  Some elements are more reactive than others.  The closer an element is to having the same number of electrons as a noble gas, the more reactive the element is.

16.1 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.

16.1 Valence electrons and the periodic table  Oxygen combines with one beryllium atom because beryllium can supply two valence electrons to give oxygen its preferred number of 8.

16.1 Valence electrons and the periodic table  Carbon has four valence electrons.  Two oxygen atoms can bond with a single carbon atom, each oxygen sharing two of carbon’s four valence electrons.  The bonds in carbon dioxide (CO 2 ) are double bonds because each bond involves 2 electrons.