Unit 7 Changes in matter Chapter 19 Molecules and compounds

Chapter 19.1 Chemical Bonds  Octet rule  Valence shell  Periodic table & octet rule  Types of bonds  Ionic Bonds  Ionization  Covalent Bonds  Electron sharing  What type of bond? When?  Predicting bonds

Octet rule  Valence Electrons Valence Electrons Valence Electrons  Electrons that occupy the outermost energy level, called the valence shell  Electrons involved in chemical bonding  Rule of 8  Stable atoms have 8 electrons in their valence shell  In order to achieve this configuration, atoms will lose, share, or gain electrons

The first energy level is the exception to this rule  The first energy level only contains an “s” orbital  The “s” orbital only contain 2 electrons  All other energy levels  When an energy level’s “s” and “p” orbitals are filled, then they have achieved an octet in their outermost energy level  The noble gasses all have 8 electrons in their outermost energy level, except Helium has only 2

Periodic Table & Octet Rule  Groups (columns going down) are arranged by how many electrons are in their valence shell Groups  Transition metals (d orbital) are funky  The number of electrons in their valance shell DOES NOT follow the groups in the periodic table  the numbers of electrons in their valence shells vary

Chemical Bonds  When chemicals bond (atoms joining together chemically), the molecules formed are very different from the original elements they are made from (ex. table salt)  The octet rule and the valence electrons form the bonds that act as the glue that holds molecules together

Types of Chemical Bonds  Ionic Bonds  Covalent Bonds

Ionic Chemical Bonds  Ionic Bonds occur when atoms lose or gain electrons while bonding  Elements with 1 or 2 electrons in their valence shell will give up those electrons to achieve stability (octet rule)  Groups 1 & 2, “s” orbital electrons  Elements with 5, 6 or 7 electrons in their valence shell tend to take electrons in order to achieve stability (octet rule)  Groups 15, 16 & 17- “p” orbital electrons

Octet rule  Valence Electrons Valence Electrons Valence Electrons  Electrons that occupy the outermost energy level, called the valence shell  Electrons involved in chemical bonding  Rule of 8  Stable atoms have 8 electrons in their valence shell  In order to achieve this configuration, atoms will lose, share, or gain electrons

Ionic Bonds  Ionization  When atoms gain or lose electrons they become IONS  An ion is an atom or particle that has an electric charge.  Atoms tend to be neutral (have no net charge) because they have an equal number of protons and electrons  During ionic bonding atoms gain or lose electrons; thus becoming ions  Opposite ions are attracted to each other

Covalent Chemical Bonds  Covalent Bonding occurs when atoms share electrons while bonding  Covalent bonds usually involve nonmetals  Groups 13-18, “p” orbital electrons not including the metalloids (semi- metals)  They can be between 2 different atoms or atoms of the same kind  Different atoms CO 2, N 2 O 3  Same Kind of atoms O 2, N 2, H 2  Many of the elemental gases in our atmosphere exist in pairs called Diatomic Molecules