Molecular Compounds: Are made of nonmetals

Transcription

1 UNIT 17 Review, Part IV Lewis, IMF, Bonding, Acid-Base, Solutions Molecular Compounds: Are made of nonmetals Nonmetals have high electronegativity, so they do NOT release their electrons. Two nonmetals share some of their valence electrons (in bonds) to Shared Valence achieve full octets. The atoms are CO-valent-ly bonded! 1

2 Molecular Geometry Geometry = shapes VSEPR Theory Valence Shell Electron Pair Repulsion AKA: electrons hate each other VSEPR Theory The electrons interacting in molecules (valence shell electron pairs) Are REPULSED by each other. The electron pairs around the central atom orient themselves as far apart as possible in order to minimize their mutual repulsion. 2

3 I. Lewis Dot Structures 2 O N 3 C 4 CO 2 O N C O C O polar + Cl - 3

4 Assume ALL bonds are polar unless the same element is on both ends! N 2, O 2, & F 2 are made of nonpolar bonds. So are N 3 & O 3 + Cl - I. Lewis Dot Structures 2 O N 3 C 4 CO 2 O N C O C O All of these bonds are polar. 4

5 I. Lewis Dot Structures 2 N 3 Cl 2 O 2 N N N Cl Cl O O All of these bonds are nonpolar. The bonds are all polar. Is the MOLECULE Polar? 2 O N 3 C 4 CO 2 O POLAR N POLAR C NONPOLAR O C O NONPOLAR 5

6 This ATTRACTION between the molecules is the IMF. The three IMFS: o London Dispersion o Dipole-Dipole o ydrogen Bonding weak STRONG 6

7 Instantaneous attraction between temporary dipoles due to uneven e - dispersion All atoms & molecules Weakest strength Stronger for molecules with greater masses. Charge attraction between permanent dipoles All polar molecules Medium strength It is stronger when the molecules are closer. 7

8 I. Lewis Dot Structures 2 O N 3 IGER melting points and O boiling N POLAR points (dipole-dipole) POLAR C 4 CO 2 LOWER melting points C O C O and boiling points NONPOLAR NONPOLAR (no dipole-dipole) Extreme attraction between molecules with N-, O-, or F- bonds. Molecules with bound directly to N, O, F Greatest strength Sometimes called a pseudo bond, but it is NOT chemical bonding. 8

9 Which ones exhibit hydrogen bonding? 2 O N 3 C 4 CO 2 O -Bonding! N -Bonding! C Nope O C O Nope 9

10 10

11 To get to the valence electron on the other side! stable (full octet!) 11

12 12

13 Nonmetals share because their electronegativities are too high to let any electrons go. 13

14 Nonmetals share because their electronegativities are too high to let any electrons go. POLAR molecules are soluble in (polar) water. NON-polar molecules are insoluble. 14

15 Metals release their valence electrons because their electronegativities are too low to hold on. Metals release their valence electrons because their electronegativities are too low to hold on. 15

16 Metals release their valence electrons because their electronegativities are too low to hold on to them. STRONGEST WEAKEST 16

17 ACID-BASE electrolytes sour taste turn litmus red react with metals to form 2 gas vinegar, milk, soda, apples, citrus fruits electrolytes bitter taste turn litmus blue slippery to touch ammonia, lye, antacid, baking soda C. Johannesson ChemASAP ACID-BASE igh + ( 3 O + ) conc. igh O - conc. Low p (<7) igh p (>7) turn litmus red turn litmus blue Formula: Formula (usually): begins with begins with a M ends with a NM Ends with O C. Johannesson ChemASAP 17

18 B. Definitions Acids release hydrogen ions ( + ) Acids create hydronium ions ( 3 O + ) Cl + O O Cl acid hydronium C. Johannesson B. Definitions Bases form hydroxide ions (O - ) + N O N O base hydroxide C. Johannesson 18

19 B. p Calculations [ + ] ( 3 O + ) K w = [ 3 O + ][O - ] [O - ] -log[ 3 O + ] 10^( p) -log[o - ] 10^( po) p 14 = p + po po LPChem:Wz B. p Scale What is the p of M NO 3? p = -log[ 3 O + ] strong acid p = -log[0.010] _ 2 sig figs p = sig figs after the decimal Acidic or basic? Acidic p < 7 C. Johannesson 19

20 B. p Scale What is the [ 3 O + ] of a solution with p = 7.45? p = -log[ 3 O + ] Therefore 10^ -p = [ 3 O + ] 10^ = [ 3 O + ] = 3.6 x 10-8 M LPChem:Wz A. Neutralization Chemical reaction between an acid and a base. LPChem:Wz 20

21 A. Neutralization Chemical reaction between an acid and a base. Products are a salt (ionic compound) and water. LPChem:Wz A. Neutralization ACID + BASE SALT + WATER Cl + NaO NaCl + 2 O Acid + Base = Salt + Water is a neutralization reaction. Titration is used to solve for an unknown concentration in acid-base neutralizations. 21

22 B. Titration moles 3 O + = moles O - MVn = MVn M: Molarity V: volume n: # of + ions in the acid or O - ions in the base C. Johannesson B. Titration 10.0 ml of 2.3M LiO are required to neutralize 20.0 ml of NO 2. Find the molarity of NO 2. O - M = 2.3M V = 10.0 ml n = 1 3 O + M =? V = 20.0 ml n = 1 MV# = MV# (2.3M)(10.0mL)(1) = M(20.0mL)(1) M = 1.15M NO 2 LPChem:Wz 22

23 A. Definitions Solution - homogeneous mixture Solute - substance being dissolved Solvent the dissolver (present in greater amount) C. Johannesson B. Solvation Non- Electrolyte Molecular substances Weak Electrolyte Weak acids & Weak bases i= 1 1 i= < i < 2 Strong Electrolyte Ionic compounds, Strong acids, Strong bases i = 2 or more LPChem:Wz 23

24 B. Solvation NONPOLAR Like Dissolves Like POLAR NONPOLAR POLAR C. Johannesson C. Solubility UNSATURATED SOLUTION more solute can dissolve SATURATED SOLUTION no more solute can dissolve SUPERSATURATED SOLUTION Unstable. crystals form if solute is added concentration C. Johannesson 24

25 A. Definition Colligative Property property that depends on the concentration of solute particles, not their identity C. Johannesson B. Types Freezing Point Depression (T f ) f.p. of a solution is lower than f.p. of the pure solvent T f(normal) - T f = T f(depressed) Boiling Point Elevation (T b ) b.p. of a solution is higher than b.p. of the pure solvent T b(normal) + T b = T b(elevated) LPChem:Wz 25

26 C. Calculations T = K m i T: change in temperature ( C) K: constant based on the solvent ( C kg/mol) m: molality (m) i: ion number (# of particles) C. Johannesson 26