Chapter 8 Chemical Bonding

Section 1 Electrons A chemical bond is the joining of atoms to form new substances with new properties –Compounds will not have the same properties as the elements that went into them 1.Electrons are the key as chemical bonding involves the interaction of certain electrons (valence). 2.Atoms are most stable when their outer energy level is full. Which group has elements that already have a full outer energy levels?

Valence Electrons Valence electrons refer to the electrons on the outer-most electron level. These are the only electrons involved in a chemical reaction. Atoms will be most stable if they have a full outer energy level. Some atoms will lose electrons,… Na Sodium 11 protons

Valence Electrons Valence electrons refer to the electrons on the outer-most electron level. These are the only electrons involved in a chemical reaction. Atoms will be most stable if they have a full outer energy level. Some atoms will lose electrons, other will gain electrons S Sulfur 16 protons

3. Only valence electrons are involved in chemical bonding. Valence electrons are the outer-most electrons –There are only 8 electrons that are valence. Group 1 = 1 valence electron Group 2 = 2 valence electrons Group 13 = 3 valence electrons Group 14 = 4 valence electrons Group 15 = 5 valence electrons Group 16 = 6 valence electrons Group 17 = 7 valence electrons Group 18 = 8 valence electrons (full) Group 1 Group 2Group 13 Groups 3-12 Transition Metals Group 14Group 15Group 16Group 17 Group 18 There is no rule for the valence electrons of Transition Metals. Some have one, others two or three.

Electron Dot Diagrams Electron Dot Diagrams can be used to represent how many valence electrons there are for each atom Follow the pattern E

For example…Special Exceptions… B O N He C

Types of Chemical Bonds: 1. Ionic Bonds Ionic bond is the force of attraction between oppositely charged ions –Ions are atoms that have lost or gained electrons in a chemical reaction. –The positive ion and the negative ion form a neutral compound. Examples of ionic bonds –Salt (NaCl) –Plaster (cast) –Seashells (calcium carbonate)

Ions –Through chemical reactions atoms may gain or lose electrons –Ions are charged particles Positive ions have lost one or more electrons Negative ions have gained one or more electrons Lithium ion (Li + ) has lost one electron (should have three) 3 positive protons 2 negative electrons Oxygen ion (O -2 ) has gained two electrons (should have eight) 8 positive protons 10 negative electrons When an alkali metal reacts with a halogen it forms a salt Metals lose electrons Nonmetals gain electrons

Ions are identified by their oxidation numbers For example Li + Ca +2 Al +3 N -3 S -2 Br - Lost one electron Lost two electrons Lost three electrons Gained three electrons Gained two electrons Gained one electron Oxidation numbers represent the number of electrons lost or electrons gained, written above and to the right of the symbol

Positive Ions Group NameValence Electrons Gain/loseOxidation number Group 1Alkali Metal1Lose+1 Group 2Alkaline Earth Metal 2Lose+2 Group 13Boron3Lose+3 Losing Electrons in chemical reactions is Endothermic.

Making Positive Ions Positive ion (metals) –Ions where electrons have been lost –Example Sodium Sodium is an alkali metal, having one valence electron In a chemical reaction it will lose that electron. Sodium becomes a positive ion after a chemical reaction because it has more protons than electrons. Atoms require extra energy to remove electrons (losing electrons is endothermic) P 11+ Na Na + CHEMICAL REACTION Notice: 11 + protons 10 - electrons

Example aluminumAluminum is a group 13 atom, having 3 valence electrons. During a chemical reaction aluminum will lose 3 electrons Aluminum becomes a positive ion because it has more protons than electrons. P 13+ Al CHEMICAL REACTION Al +3 Notice: 13 + protons 10 - electrons

Negative Ions Group NameValence Electrons Gain/loseOxidation number Group 15Nitrogen5Gain-3 Group 16Oxygen6Gain-2 Group 17Halogen7Gain Gaining Electrons in chemical reactions is Exothermic.

Making Negative Ions Negative ions (nonmetals) –Ions where electrons have been gained –Add an “ ide ” ending to show which atoms have gained electrons –Example chlorine Chlorine is a halogen (group 17), having 7 valence electrons. Chlorine, a nonmetal, will gain electrons in a chemical reaction. It will become a negative ion because it has more electrons than protons after a chemical reaction. Gaining electrons releases energy ( gaining electrons is exothermic). P 17+ ClCl - CHEMICAL REACTION Notice: 17 + protons 18 - electrons Chlorine becomes chloride

–Example oxygen Oxygen is a group 16 atom, having 6 valence electrons. Oxygen, a nonmetal, will gain 2 electrons in a chemical reaction. It will become a negative ion because it has more electrons than protons after a chemical reaction. P 8+ OO -2 CHEMICAL REACTION Notice: 8 + protons 10 - electrons Oxygen becomes oxide

Group 1 has 1 valence electron… becomes +1 ions Group 13 has 3 valence electrons… becomes +3 ions Group 2 has 2 valence electrons… becomes +2 ions Metals lose electrons in chemical reactions Metals become positive ions in chemical reactions

Group 15 has 5 valence electrons… becomes -3 ions Group 17 has 7 valence electrons… becomes -1 ions Group 16 has 6 valence electrons… becomes -2 ions Nonmetals gain electrons in chemical reactions Nonmetals become negative ions in chemical reactions Noble gases do not react and do not form ions.

Positive and negative ions will attract each other Ionic bonds have the following properties 1. High melting/boiling points (strong bonds) 2.Form crystal lattices 3.Brittle Na+ Cl-

Covalent Bonds A covalent bond involves the sharing of electrons to form molecules –Electrons are not exchanged (ions are not formed) –Nonmetals –Properties 1.Low melting and boiling points 2.brittle when solid Examples –Water (H 2 O) –Carbon dioxide (CO 2 ) –Sugar (C 6 H 12 O 6 ) –Diatomic molecules Elements that are found in pairs when not part of a compound, never alone There are 8 of them (H 2, N 2, O 2, Group 17)

No, really….. DIATOMIC Hydrogen Nitrogen Oxygen Group 17 –F–Fluorine –C–Chlorine –B–Bromine –I–Iodine –A–Astatine H 2 N 2 O 2 F 2 Cl 2 Br2 I 2 At 2

Diatomic molecules are formed because certain elements react so easily they automatically combine with each other when they are in their gaseous state. H2H2 Cl 2 H + H H H HH H Cl + Cl Cl

Other Covalent Molecules Water (H 2 O) HHHH OOOO H O H - +

Metallic Bonds Metallic bond is the force of attraction between positive metal ions and the loose valence electrons in a metal –Valence electrons can easily travel from one atom to the next because of overlapping electron rings Fe + (Iron ion) Fe + (Iron ion) Fe + (Iron ion)

The properties of metals are explained by metallic bonds –Malleabililty/ductility because the atoms are not locked to one single atom –Conducting heat/electricity because electrons can move freely or can be forced to move in one direction

AuAuAuAuAuAu

Electrons can be made to travel in one direction AuAuAuAuAuAu WIRE