Chapter 22: Chemical Bonding

Section 1– Electrons and Chemical Bonding Chemical bonding – joining of atoms to form new substances Chemical bond – interaction that holds 2 atoms together

Valence Electrons e- in outermost shell Determines an atom’s chemical properties Used to form bonds Within a group, or family, atoms have the same # of valence e- Atoms with fewer than 8 valence e- are more likely to form bonds than an atom with 8 e-

Types of Bonds Ionic, Covalent, Metallic Atoms bond by sharing, gaining or losing e- to have a filled outermost energy level. A full set = 2 e- for a few of the elements A full set = 8 e- for most elements Which ones? Why?

Section 2: Ionic Bonds Bonds form by gaining or losing e-, resulting in charged atoms called ions. Oppositely charged ions are attracted to one another Metal + Nonmetal Positive and negative charges cancel each other out to form an overall neutral compound

Metal Atoms Have few valence electrons Usually lose these valence e- and form positive ions (cations) Some transition metal ions can have multiple charges. For example, iron can have a +2 or a +3 charge. The charge is written as a superscript of the symbol: Ex. K+, Ca2+, Al3+

Nonmetal atoms Have almost full valence shells Tend to gain e- from other atoms and form negative ions (anions) The charge is written as a superscript of the formula: Ex. P3-, S2-, Cl-

Polyatomic Ions Poly = “many” Polyatomic = “many atoms” A group of atoms that behave as a single ion with an overall positive or negative charge Treat the polyatomic ion as a single unit with a single charge.

Writing formulas for ionic compounds The number of positive charges and negative charges must balance in an ionic compound The formula represents this balance Subscripts are used to indicate the ratio of elements in the compound (no “1”)

Writing formulas for ionic compounds Find oxidation number (charge) for both parts For elements in groups 1 and 2, use group #. Boron family is 3+, Carbon family ± 4, Nitrogen family is -3, Oxygen family is -2 and halogens are -1. For cations followed by a roman numeral, the roman numeral is the oxidation # For polyatomic ions check the list. Do not change the subscripts within the polyatomic ion formula. ----- Meeting Notes (2/7/13 10:56) ----- go to periodic table

2. Write symbols. The positive ion first and negative ion second. 3. Put polyatomic ions in parentheses if more than one is needed. 4. Use subscripts to designate the number of each part for the total + and – charges to be = a. Find the least common multiple of both charges b. determine the factor needed to get that charge and use that as the subscript.

Sodium sulfide Potassium iodide Lithium oxide Barium fluoride Iron(III) oxide Copper(II) chloride g. Sodium acetate h. Zinc(II) carbonate i. Chromium(II) sulfate j. Cobalt(III) iodide

Answers Na2S KI Li2O BaF2 Fe2O3 f. CuCl2 g. NaC2H3O2 h. ZnCO3 i. CrSO4 j. CoI3

Writing names for ionic compounds Write the names of the + and - part of the formula The + part is the name of the element or polyatomic ion Check the list of elements to see if it needs a roman numeral. If so, use the negative part of the formula to figure out the positive charge on the metal. To name the second/- part, if it is an element change the ending to “-ide” If it is a polyatomic ion, keep the name as is

Practice LiCl MgCl2 g. (NH4)3PO4 h. ZnCO3 BeO i. Sn(OH)2 CaCl2 HgS SnF2 g. (NH4)3PO4 h. ZnCO3 i. Sn(OH)2 j. Li2SO4 k. KC2H3O2

Answers Lithium chloride Magnesium Chloride Beryllium oxide Calcium Chloride Mercury(II) sulfide Tin(II) fluoride g. Ammonium phosphate h. Zinc(II) carbonate i. Tin(II) hydroxide j. Lithium sulfate k. Potassium acetate



Section 3: Covalent and Metallic Bonds Covalent bonds are formed when atoms share one or more pairs of valence e-. Forms between 2 nonmetals. Covalent bonds result in the formation of molecules. Define molecule

Octet Rule Atoms combine in such a way so as to fill the valence shell (usually that means 8 e- but could be just 2 e-)

How many bonds? The number of e- that an atom needs to fulfill it’s valence is equal to the number of covalent bonds it can form. Ex. N can make 3 covalent bonds because it has 5 e- in its valence shell Ex. H can make 1 covalent bond because it has 1 e- its valence shell.

Diatomic Elements Certain elements exist as pairs in nature because that is how they are most stable. Di = 2 Just remember Professor BrINClHOF (Bromine, Iodine, Nitrogen, Chlorine, Hydrogen, Oxygen and Fluorine) You need to memorize the 7 diatomic elements!!

Practice! Draw a Bohr diagram and Lewis structure for the following: Water (H2O) Diatomic Fluorine (F2) Silicon tetrafluoride (SiF4)

Double Bonds When atoms share 2 pairs of e-, it is a double bond

Triple Bonds When atoms share 3 pairs of e-, it is a triple bond

Naming Covalent Compounds Many compounds have common names such as "methane", "ammonia" and "water” Simple covalent compounds can be named using prefixes to indicate how many atoms of each element are in the formula. The ending of the last (most negative) element is changed to -ide.

Naming Covalent Compounds Prefixes: Mono = 1 Di = 2 Tri = 3 Tetra = 4 Penta = 5 Hexa = 6 *If there is just 1 of the first element no prefix is used

Practice CO2 SiF4 CO NBr3 P2O5 BCl3

Answers CO2 – carbon dioxide SiF4 – silicon tetrafluoride CO – carbon monoxide NBr3 – nitrogen tribromide P2O5 – diphosphorus pentoxide BCl3 - boron trichloride

Practice Carbon tetrabromide Phosphorus triiodide Bromine silicon monoxide Silicon disulfide

Answers CBr4 PI3 Br2 (Bromine is a diatomic molecule!) SiO SiS2

Metallic Bonds A bond formed by the attraction between positively charged metal ions and surrounding e- Think of a metal as being made up of positive ions with electrons “swimming” around keeping the ions together

Properties of Metals Because e- can move freely about, metals have particular propeties.

Conduct electricity well

Metals can be reshaped (ductile, malleable)

Metals can bend without breaking