Bonding Unit III

Transcription

1 Bonding Unit III I. Bond A. What is a bond? Attraction of an electron by two nuclei B. What electrons are involved in bonding Valence electrons Electrons in the outermost energy level Represented by an electron-dot diagram example N valence electrons C. Why do atoms bond? Atoms will form bonds to achieve 8 valence electrons o Octet Rule 8 is GREAT o Stable configuration Noble gas configuration (Group 18) Compound has lower potential energy than the un-bonded atoms D. Energy Terms 1. Ionization Energy Amount of energy needed to remove an electron o Compare Na Cl Ar Ionization Energy 496 kj 1251 kj 1521kJ Why? Electronegativity Attraction for electrons o Compare Na Cl Ar Electronegativity Why? E. Types of Bonds 1. Atomic Bonds Holds atoms together to make a molecule 2. Molecular Bonds Holds molecules together to make a solid or liquid

2 II. Atomic Bonds A. Ionic Bond Transfer of electrons from metals to nonmetals o Metals lose electrons Become positive o Decreases in size o Nonmetals gains electrons Become negative o Increases in size 1. Properties High melting points Hard Poor conductor as solid Good conductor in liquid or aqueous states 2. Bond Diagram Write electron dot diagram for each element Transfer electrons from metal to nonmetal until all single electrons are paired up

3 B. Covalent Bond Sharing of electrons between two nonmetals 1. Types Nonpolar Covalent Equal sharing of electrons Atoms have the same electronegativities Usually the same element [diatomic elements] Polar Covalent unequal sharing of electrons Atoms have the different electronegativities Different elements Higher electronegative element is the negative end of the molecule 2. Properties Low melting points Soft Poor conductor 3. Bond Diagram Write electron dot diagram for each element Share electrons of any all single electrons Each loop is a bond example of a nonpolar covalent bonds: Diatomic molecules (H O F Br I N Cl) example of a polar covalent bond

4 C. Network Solid Giant covalent bonds sharing of electrons occurs in the entire crystal 1. Examples C (diamond) C (graphite), SiO 2 (silicon dioxide) SiC (silicon carbide) asbestos 2. Properties Hardest solids Highest melting points Poor conductor D. Metallic Bonding Metals do not have enough valence electrons to stabilize the structure Delocalize electrons Allow them to move anywhere in the structure Positive ions immersed in a sea of mobile electrons 1. Properties Hard High melting points Good conductor in the solid state III. Nomenclature A. Naming Compounds 1. Binary Compounds Compounds that contain two elements Name the first element Name the second element using an ide ending Check the oxidation number of the first element If it has more than one positive value, use a Roman numeral to indicate the number that was used CaCl 2 Calcium chloride Ca is +2 only No Roman numeral needed Calcium chloride CCl 4 Carbon chloride C is -4, +2 and +4 Since there are two positive choices, use a Roman numeral Carbon IV chloride

5 2. Ternary Compounds Compounds that contain more than two elements Polyatomic ion is present Found on Table E Identify the polyatomic used Name the first substance Name the second substance Check the oxidation number of the first element If it has more than one positive value, use a Roman numeral to indicate the number that was used K 2 SO 4 Potassium sulfate Potassium is +1 only No Roman numeral is needed Potassium sulfate Cu(NO 3 ) 2 Copper nitrate Copper can be +1 or +2 Needs a Roman numeral Copper II nitrate FeSO 4 Iron sulfate Iron can be +2 or +3 Needs a Roman numeral Iron II sulfate NH 4 Cl Ammonium Ammonium chloride Ammonium ion is +1 No choice means no Roman numeral needed Ammonium chloride

6 B. Writing Formulas Use ending to tell if compound is binary or ternary Binary usually ends in ide [except hydroxide and cyanide] Ternary usually ends in ate or ite Write the symbols Assign oxidation numbers Positive atom on left, negative on right Reduce if possible and criss-cross These numbers become the subscripts of the formula Strontium phosphide ide means binary Strontium (Sr) Phosphide is phosphorus (P) Sr +2 P -3 criss-cross numbers NOT signs Sr 3 P 2 Iron II Oxide ide means binary Iron (Fe) Oxide is oxygen (O) Fe +2 O -2 Fe 2 O 2 FeO criss-cross numbers NOT signs reduce Manganese IV Carbonate ate means ternary Manganese (Mn) Carbonate is a polyatomic ion (CO -2 3 ) Mn +4-2 CO 3 Mn 2 (CO 3 ) 4 Mn (CO 3 ) 2 criss-cross numbers NOT signs reduce