Chm151 exam 4 slides sp10

CHM 151 General Chemistry EXAM 4 SLIDES

Electron Energy LevelsElectrons are arranged inspecific energy levels thatare labeled n = 1, n = 2, n = 3, and so on

increase in energy as n increases

have the electrons with the lowest energy in the first energy level (n = 1) closestto the nucleusEnergy Level ChangesAn electron absorbsenergy to “jump” to a higher energy level.

When an electron falls to a lower energy level, energy is emitted.

In the visible range, the emitted energy appears as a color.In each of the following energy level changes, indicateif energy is 1) absorbed, 2) emitted, or 3) not changed.A. An electron moves from the first energy level (n = 1) to the third energy level (n = 3).B. An electron falls from the third energy level to the second energy level.C. An electron moves within the third energy level.Learning Check

SublevelsSublevelscontain electrons with the same energy

are found within each energy level.

are designated by the letters s, p, d, and f The number of sublevels is equal to the value of the principal quantum number (n).

Energy of SublevelsIn any energy levelthe s sublevel has the lowest energy

the s sublevel is followed by the p, d, and f sublevels (in order of increasing energy)OrbitalsAn orbital is a three-dimensional space around a nucleus where an electron is most likely to be found

has a shape that represents electron density (not a path the electron follows)

contains two electrons that must spin in oppositesOrbitalsAn s orbital has a spherical shape around the nucleus

increases in size around the nucleus as the energy level n value increases

is a single orbital found in each s sublevelp OrbitalsA p orbital has a two-lobed shape

is one of three p orbitals that make up each p sublevel

increases in size as the value of n increasesSublevels and OrbitalsEach sublevel consists of a specific number oforbitals. An s sublevel contains one s orbital.

A p sublevel contains three p orbitals.

A d sublevel contains five d orbitals.

An f sublevel contains seven f orbitals.Electrons in Each Sublevel

An orbital diagram represents each orbital with a box, with orbitals in the same subshell in connected boxes; electrons are shown as arrows in the boxes, pointing up or down to indicate their spins.Two electrons in the same orbital must have opposite spins.Orbital Diagrams

An electron configuration lists the occupied subshells using the usual notation (1s, 2p, etc.). Each subshell is followed by a superscripted number giving the number of electrons present in that subshell.Two electrons in the 2ssubshell would be 2s2 (spoken as “two-ess-two”).Four electrons in the 3psubshell would be 3p4 (“three-pea-four”).Electron Configuration

Electron Configurations of ElementsHydrogen contains one electron in the 1s subshell.1s1Helium has two electrons in the 1s subshell. 1s2

Electron Configurations of ElementsLithium has three electrons.1s2 2s1 Beryllium has four electrons.1s2 2s2Boron has five electrons.1s2 2s2 2p1

Carbon, with six electrons, has the electron configuration of 1s2 2s2 2p2.The lowest energy arrangement of electrons in degenerate (same-energy) orbitals is given by Hund’s rule: one electron occupies each degenerate orbital with the same spin before a second electron is placed in an orbital.Orbital Diagram of Carbon

Other Elements in the Second PeriodN 1s2 2s2 2p3O 1s2 2s2 2p4F 1s2 2s2 2p5Ne 1s2 2s2 2p6

Because their electron configurations can get long, larger atoms can use an abbreviated electron configuration, using a noble gas to represent core electrons.Fe: 1s2 2s2 2p6 3s2 3p6 4s2 3d6-> [Ar] 4s2 3d6ArElectron Configurations of Heavier Atoms

Chapter 8The Periodic Table: Structure and Trends

The 4s orbital is lower in energy than the 3d orbital and fills first, starting the fourth period at potassium.The 3dorbitals fill after the 4s.Similar inversions occur in the remaining periods.Electron Configurations

Electron Configurations of AnionsFor anions, the additional electrons fill orbitals following the same rules that applies to atoms.Cl: [Ne] 3s2 3p5Cl-: [Ne] 3s2 3p6 As: [Ar] 4s2 3d10 4p3 As3-: [Ar] 4s2 3d10 4p6Many stable anions have the same electron configuration as a noble gas atom.

Test Your SkillWrite the electron configurations of the following ions: (a) N3- (b) Co3+ (c) K+

Test Your SkillWrite the electron configurations of the following ions: (a) N3- (b) Co3+ (c) K+Answers:(a) 1s2 2s2 2p6(b) [Ar] 4s23d4(c) [Ar]

Size Trends for an Isoelectronic Series

Sizes of the Atoms and Their CationsAtoms are always larger than their cations.Sizes of the Atoms and Their CationsIf an atom makes more than one cation, the higher-charged ion has a smaller size.Anions are always larger than their atoms.Atomic and Ionic Radii

Identify the larger species of each pair: (a) Mg or Mg2+ (b) Se or Se2-Test Your Skill

Identify the larger species of each pair: (a) Mg or Mg2+ (b) Se or Se2-Answer: (a) Mg is larger. (b) Se2- is larger.Test Your Skill

Chemical BondsChemical bonds are the forces that hold the atoms together in substances.This chapter discusses two limiting types of bonding.Ionic bondingCovalent bonding

Lewis Electron-dot SymbolsA Lewis electron-dot symbol consists of the symbol for the element surrounded by dots, one for each valence electron.

Cations of most representative elements have no valence shell electrons shown in the Lewis symbol.Na×® Na+ + e-×Ca×® Ca2+ + 2e-Lewis Symbols for Cations

Lewis Symbols for AnionsThe Lewis symbols of most monatomic anions show eight valence electrons.Cl + e--> Cl -Se + 2e- -> Se 2-

Ionic BondingIonic bonding results from the electrostatic attraction between cations and anions. Formation of an ionic bond can be viewed as a transfer of electrons. Na + F -> Na+ + F - (or NaF)

A covalent bond result from the sharing of two electrons between two atoms, as shown here for H2.Covalent Bonding

Two hydrogen atoms become more stable as their orbitals, each containing one electron, overlap.Orbital Overlap

Lewis StructuresBonding PairH ClLone PairLewis structures represent covalent bonding by showing how the valence electrons are present in a molecule.Bonding pairsare shared between two atoms and are represented by lines .Lone pairs are entirely on one atom and are represented by two dots.

The number of Covalent BondsThe number of covalent bonds can be determined fromthe number of electrons needed to complete an octet.

Octet RuleOctet Rule:atoms share electrons until each atom is surrounded by eight.Single Bond- sharing one pair of electrons

Double Bond- sharing two pairs of electrons

Triple Bond- sharing three pairs of electrons1. Write the skeleton structure. 2. Sum the valence electrons.3. Subtract two electrons for each bond in the skeleton structure.4. Count the number of electrons needed to satisfy octet rule for each atom.If the number of electrons needed equals the number remaining, go to 5.If fewer electron remain, add one bond for every twoadditional electrons needed.5. Place remaining electrons as lone pairs to satisfy the octet rule for each atom (not H).Writing Lewis Structures

Writing Lewis StructuresWrite the Lewis structure of fromaldehyde, H2CO. The skeleton structure isOCHH

Writing Lewis StructuresOCHHThe total number of valence electrons is1(C) 1 x 4 = 41(O) 1 x 6 = 62(H) 2 x 1 = 2 12

Writing Lewis Structuresneeds 6e- to complete octetOCneeds 2e- to complete octetHHOCHHRemaining valence electrons = 68 electrons needed to obey the octet ruleAdd one bond because 2 more electrons are needed than are available.

Writing Lewis StructuresOCHHFinish the structure by placing remaining electrons as lone pairs.Check that the final Lewis structure has the correct number of valence electrons (12) and each atom (not H) has 8 electrons.

Test Your SkillWrite the Lewis structure of N2H2. The skeleton structure is:H N N H

Test Your SkillWrite the Lewis structure of N2H2. Answer:H N N H

Polar BondPolar Bond – A covalent bond in which the two atoms do not share the bonding electrons equally. Note: The higher electronegative element takes on a partial negative charge and the lower electronegative element takes on a partial positive charge.d+ d- I—Br (a polar covalent bond)  arrow indicates direction of more electronegative element

In I2 the sharing of the electrons in the covalent bond is equal; in ClF it is not.Dipole moment is a measure of the unequal sharing of electrons.The unequal sharing leads to a polar covalent bond that is indicated with the symbol d followed by a sign to show partial charges. d+ d-Cl-FBond Polarity

Electronegativityis a measure of the ability of an atom to attract the shared electrons in a chemical bond.Electronegativity

Example: ElectronegativitySelect the most polar bond.Cl-F O-F P-F

Formal charge is a charge assigned to atoms in Lewis structures by assuming the shared electrons are divided equally between the bonded atoms.

Equation for Formal Charge:(number of valence electrons in atom) – (number of lone pair electrons) – ½ (number of shared electrons)Formal Charges

Formal Charges# Bonds# Bonds# Bonds-10+1Atom__:______N234NNN::__::_____3O21OOO::::______34CCC:_

Formal ChargesAdd formal charges to the Lewis structure of HNO3 shown below.HON O O

Formal ChargesHON OOThe nitrogen atom has 4 bonds giving it a +1 formal charge.The oxygen atom on the bottom left only has 1 bond giving it a -1 formal charge.The sum of formal charges equals the charge of the species.

Test Your SkillAdd formal charges to the Lewis structure of HNO3 shown below.HON OO

Test Your SkillHON OOAnswer:

Lewis structures that show the smallest formal charges are favored.Lewis structures that have adjacent atoms with formal charges of the same sign are much less favorable.Lewis structures that place negative formal charges on the more electronegative atoms are favored.Formal charges of opposite sign are usually on adjacent atoms.Fewer formal charges overall.Structure Stability (which structure is more favored)

Test Your SkillOf the two structures shown for HNO3, use the stability rules to predict which will be more favored.HHOON ON OOO

Test Your SkillHOHON ON OOOAnswer:The structure on the left is favored because it has fewer formal charges.it does not have adjacent atoms with the same formal charge.

Resonance in Lewis StructuresResonance structures differ only in the distribution of the valence electrons. All resonance structures follow the rules for writing Lewis structures.Resonance structures are indicated by a double headed arrow.HOHON ON OO↔O

Drawing Resonance Structures HOHON ON OO↔ODraw the third possible resonance structure for HNO3, the first two are below.

HOHON ON OO↔OHON OODrawing Resonance Structures First two:

In the third, add the double bond between the nitrogen and the oxygen to the bottom left. Complete the octets with the remaining electrons and add formal charges.HNO3 Resonance FormsA total of three resonance forms can be written for HNO3.The first and last structures are equally favored because of fewer formal charges; the middle structure less favored.↔↔HOHON ON OOOHON OO

Test Your SkillWrite all resonance structures, including formal charges, for O3, O-O-O skeleton structure.

Test Your SkillWrite all resonance structures, including formal charges, for O3, O-O-O skeleton structure.Answer: O OO ↔OOO

No resonance structure is correct by itself; the correct structure is an average of all resonance structures.Average Structure

Equivalent resonance structures, such as the two for O3, contributeequally to the average structure. Bond order in O3 is the average of a double bond and a single bond = 1.5.OOO ↔ OOOContribution of Resonance Structures

Test Your SkillDraw the Lewis structure of IF3.Answer:F IFF

Chapter 10 Molecular Structure and Bonding Theories

Valence-Shell Electron-Pair Repulsion Model (VSEPR) predicts shape from Lewis Structures.VSEPR Rule 1: A molecule has a shape that minimizes electrostatic repulsions between valence-shell electron pairs. Minimum repulsion results when the electron pairs are as far apart as possible.VSEPR

Steric number = (number of lone pairs on central atom) + (number of atoms bonded to central atom)The steric number is determined from the Lewis structure.Stericnumber determines the bonded-atom lone-pair arrangement, the shape that maximizes the distances between the valence-shell electron pairs.Steric Number

In the Lewis structure of BeCl2, beryllium has two bonded atoms and no lone pairs, stericnumber = 2.Alinear geometry places the two pairs of electrons on the central beryllium atom as far apart as possible.Steric Number = 2

The Lewis structure of HCN (H-Cº N:) shows that the carbon atom is bonded to two atoms and has no lone pairs, steric number = 2.The bonded-atom lone-pair arrangement is linear. The number of bonded atoms, not the number of bonds, determines the steric number.Molecules with Multiple Bonds

The Lewis structure of BF3shows the boron atom has a steric number = 3; the bonded-atom lone-pair arrangement is trigonal planar.Steric Number = 3

The Lewis structure of CH4 shows the carbon atom has a steric number = 4; the bonded-atom lone-pair arrangement is tetrahedral.Steric Number = 4

The phosphorus atom in PF5 has a steric number = 5; the bonded-atom lone-pair arrangement is trigonal bipyramidal.Steric Number = 5

The sulfur atom in SF6 has a steric number = 6; the bonded-atom lone-pair arrangement is octahedral.Steric Number = 6

Central Atoms with Lone PairsOHHThe Lewis structure of H2O isStericnumber = 4, 2 bonded atoms and 2 lone pairs.The bonded-atom lone-pair arrangement is tetrahedral.

Molecular shapeis the arrangement of the atoms in a species.The bonded-atom lone-pair arrangement of H2O is tetrahedral (top); the molecular shape is bent or V-shaped (bottom).Molecular Shape of H2O

What is the electron pair geometry and molecular shape of NH3?Molecular Shape of NH3

Molecular Shape of NH3NHHHFirst, draw the Lewis structure.The nitrogen has 3 bonded atoms and 1 lone pair; the steric number = 4 and the bonded-atom lone-pair arrangement is tetrahedral.

The bonded-atom lone-pair arrangement of NH3 is tetrahedral (top), molecular shape is a trigonal pyramidal (bottom).Molecular Shape of NH3

The measured bond angle in H2O (104.5o) is smaller than the predicted angle (109.5o)Explanation (VESPR Rule #2) Forces between electron pairs vary as: lone pair-lone pair replusion> lone pair-bonding pair replusion> bonding pair-bonding pair repulsionElectron Pair Repulsions

What is the steric number, the bonded-atom lone-pair arrangement, and the molecular shape of ClF3?Test Your Skill

Answer: The steric number is 5, the bonded-atom lone-pair arrangement is trigonal bipyramidal and the molecule is “T” shaped with the two lone pairs in equatorial positions.Test Your Skill

The geometry of each central atom is determined separately.The CH3 carbon in CH3CN has tetrahedral geometry and the other carbon has linear geometry.Multiple Central Atoms

HHN SHShapes of MoleculesWhat are the bonded-atom lone-pairarrangements and the shapes about each central atom in NH2SH?

The bonded-atom lone-pairarrangements of both are tetrahedral, the nitrogen shape is trigonal pyramidal and sulfur is “V” shaped.Polar BondPolar Bond – A covalent bond in which the two atoms do not share the bonding electrons equally. Note: The higher electronegative element takes on a partial negative charge and the lower electronegative element takes on a partial positive charge.d+ d- I—Br (a polar covalent bond)  arrow indicates direction of more electronegative element

In I2 the sharing of the electrons in the covalent bond is equal; in ClF it is not.Dipole moment is a measure of the unequal sharing of electrons.Equals the magnitude of the separated charges X the distance between themThe unequal sharing leads to a polar covalent bond that is indicated with the symbol d followed by a sign to show partial charges. d+ d-Cl-FBond Polarity

The bond dipoles in CO2 cancel because the linear shape orients the equal magnitude bond dipoles in exactly opposite directions. Bond dipole determined by difference in electronegativities of bonded atoms. Polarity of Molecules

The bond dipoles do not cancel in COSe; they are oriented in the same direction and are of unequal length. They do not cancel in OF2 because the V-shape of the molecule does not orient them in opposite directions.Polarity of Molecules

The bond dipoles in BCl3 and CCl4 cancel because of the regular shape and equal magnitude.Polarity of Molecules

The bond dipoles in BCl2F and CHCl3 do not cancel because they are not of the same magnitude.Polarity of Molecules

Test Your SkillAre the following molecules polar or nonpolar: H2S, SiF4, CH2Cl2?Are the following molecules polar or nonpolar: H2S, SiF4, CH2Cl2?Answer: H2S and CH2Cl2 are polar, SiF4 is nonpolar.Test Your Skill

Hybrid orbitalsare:Orbitalsobtained by mixing two or more atomic orbitals on the same central atom.Hybrid Orbitals

The bonds in BeCl2 arise from the overlap of two sp hybrid orbitals on the beryllium atom with the 3p orbitals on the two chlorine atoms.Bonding in BeCl2

The bonds in BF3 arise from the overlap of three sp2 hybrid orbitals on the boron atom with 2p orbitals on the three fluorine atoms.Bonding in BF3

The bonds in CH4 arise from the overlap of four sp3 hybrid orbitals on the carbon atom with 1s orbitals on the four hydrogen atoms.Bonding in CH4

Hybrid orbitals can hold lone pairs as well as make bonds.Lone Pairs and Hybrid Orbitals

Test Your SkillIdentify the hybrid orbitals on the central atoms in SiH4 and HCN.Identify the hybrid orbitals on the central atoms in SiH4 and HCN.Answer: sp3hybrid orbitals on silicon; sp hybrid orbitals on carbon.Test Your Skill

Sigma bonds (s): the shared pair of electrons is symmetric about the line joining the two nuclei of the bonded atoms.Types of Bonds: Sigma Bonds

The C-C sigma bond in C2H4 arises from overlap of sp2 hybrid orbitals and the four C-H sigma bonds from overlap sp2 hybrid orbitals on C with 1s orbitals on H.The second C-C bond forms from sideways overlap of p orbitals.Bonding in C2H4

Pi bonds (p) places electron density above and below the line joining the bonded atoms – they form by sideways overlap of p orbitals.Types of Bonds: Pi Bonds

The double bond in C2H4 is one sigma bond and one pi bond – each bond is of similar strength.Bonding in C2H4

Test Your SkillDescribe the bonds made by the carbon atom in HCN.Describe the bonds made by the carbon atom in HCN.Answer: The carbon is sp hybridized. C sp hybrid forms s bond with H 1s.C sp hybrid forms s bond. N has s, p (along bonding direction) or sp hybrid of the two available for this s bond. Two pi bonds form by sideways overlap of two p orbitals on both C and N.Test Your Skill

Characteristic Properties of Gases, Liquids, and SolidsIntermolecular forces are the attractions that hold molecules together in the liquid and solid states.

Physical State and Energy of Attraction

Boiling PointThe boiling point of a liquid is the temperature at which the vapor pressure is equal to the external pressure.The normal boiling point of a liquid is the temperature at which its equilibrium vapor pressure is equal to 1 atmosphere.At the boiling point, bubbles filled with vapor form below the surface of the liquid.

Electrostatic forces account for all types of intermolecular attractions. There are three types of attractions:Dipole-dipole attractionsLondon dispersion forcesHydrogen bondingIntermolecular Attractions

Dipole-dipole attractions result from electronic forces between molecular dipoles:Dipole-Dipole Attractions

London dispersion forces arise from the attractions between instantaneous dipoles and induced dipoles.London Dispersion Forces

Dispersion Forces and Periodic TrendsPolarizability is the ease with which a charge distorts the electron cloud in a molecule.Polarizability generally increases with the number of electrons in the molecule.For related series of molecules, London dispersion forces increase going down any group in the periodic table.

Hydrogen bonding occurs between a hydrogen atom bonded to N, O, or F, and a lone pair of electrons on a second N, O, or F.Hydrogen bonds are sometimes shown as dotted lines.Hydrogen Bonding

Hydrogen bonding causes ice to have a lower density than liquid water.Structure of Solid Water

Identify the kind of intermolecular forces:(a) BF3, BBr3 (b) C2H5OH, C2H5ClExample: Intermolecular Forces

Answers London dispersion forces for both.C2H5OH is Hydrogen Bonding C2H5Cl is Dipole-Dipole

Capillary action causes water to rise in a small diameter glass tube.Capillary action is the result of a competition between:cohesion: the attraction of molecules for other molecules of the same substance.adhesion: the attraction of molecules for other molecules of a different substance.Liquids: Capillary Action

Water rises because adhesion is stronger than cohesion.

Mercury is lowered because cohesion is stronger than adhesion.Capillary Action

Viscosity is the resistance of a fluid to flow.The stronger the intermolecular forces of attraction, the greater the viscosity.Other factors contribute to viscosity as well, like structure, size, and shape of molecules.Liquids: Viscosity

There are a number of ways to express concentration:Molaritymass percentageppm and ppbmolalitySolution Concentration

All concentration units are fractions.The numerator contains the quantity of solute.The denominator is the quantity of either solution or solvent.They differ in the units used to express these two quantities.Solution Concentration

Units of Concentration Used Earlier

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