Chapter 6 Review

Test: Friday December 09, 2011

Be sure to know the following terms

• Chemical bond• Nonpolar covalent bond• Polar covalent bond• Chemical formula• Unshared (lone) pair• Resonance• Polyatomic ions

What is the most electronegative element on the periodic table? • Fluorine (F)

What is the least electronegative element on the periodic table?• Cesium (Cs)

According to the rules of drawing Lewis structures, which atom is the central atom?• The least

electronegative atom

Use electronegativity differences to determine whether each of the following bonds is nonpolar covalent, polar covalent, or ionic. Determine the

direction of polarity.

H—F Na—Cl4.0 – 2.1 =1.9 3.0 – 0.9 = 2.1

H—O N—N3.5 – 2.1 = 1.4 3.0 – 3.0 = 0

H—C H—N2.5 – 2.1 = 0.4 3.0 – 2.1 = 0.9

Ba—O C—O 3.5 – 0.9 = 2.6 3.5 – 2.5 = 1.0

Define single bond, double bond, and triple bond. List them in order

of increasing bond energy…Increasing bond length.

• Single bond: bond in which one pair of electrons is shared (C--C)• Double bond: bond in which two pairs of electrons are shared (C=C)• Triple bond: bond in which three pairs of electrons are shared • BEsingle > double > triple• BL triple > double > single

Compare and contrast ionic and covalent compounds.

CovalentElectrons are shared

Atoms vibrateSmallest unit called

moleculeLow melting/boiling points

WeakerNonmetal+nonmetal

IonicBond between ionsIons cannot move

Smallest unit called formula unit

High melting/boiling points

Solutions can conduct electricity

StrongerMetal + nonmetal

The manner in which ions lower their potential

energy and stabilizing ionic compounds by

combining in an orderly arrangement is called….• Crystal lattice

What is the octet rule? • Outer energy level with 8 electrons

Name exceptions to the octet rule.• Hydrogen, boron• Oxygen, fluorine, chlorine

What is meant by expanded valence? Which elements can have an expanded valence?

• An outer energy level with more than 8 electrons

• The most electronegative elements Cl, F, O

What is the amount of energy required to separate bonded atoms into neutral

atoms?•Bond energy

What is the amount of energy required to separate an ionic compound into its

constituent ions?•Lattice energy

Metallic Bonding• The highest energy levels of most metal atoms are

occupied by very few electrons. For example s-block metals contain only 1 or 2 electrons and all three p orbitals are empty.

• Within a metal, the vacant orbitals in the atoms’ outer energy levels overlap. This overlapping of orbitals allows the outer electrons of the atoms to roam freely throughout the entire metal the electrons do not belong to any one atom but move freely about the metal’s network of empty atomic orbitals (sea of electrons)

METALLIC BONDING (CONT’D)* The chemical bonding that results from the attraction between metal atoms and the surrounding sea of electronsThe freedom of electrons to move in a network accounts for the properties of metals: electrical and thermal conductivity, absorption/reflection of light, luster, malleability, ductility

Metallic Bonding• Metal atoms in electron

sea• Good conductors• higher melting

point/boiling point• Overall “negative” charge

due to moving electrons• Can be shaped: malleable

and ductile

Ionic Bonding• Cations and anions in

crystal lattice• Solution/molten state

good conductors• Lower melting/boiling

points• Bonded ions form

neutrally charged compound

• Hard and brittle

Enthalpy of vaporization• Enthalpy = heat• Just as lattice energy represents the

strength of an ionic bond, enthalpy of vaporization represents the strength of a metallic bond

*amount of energy (as heat) required to vaporize the metal

Intermolecular Forces(forces of attraction between molecules)

-vary in strength, but generally weaker than covalent, metallic, and ionic bonds1. dipole: created by equal but opposite charges

separated by a short distance-occurs when a slightly negatively charged atom

in a polar bond is attracted to a slightly negatively charged atom in a nearby molecule

Intermolecular Forces (cont’d)2. Hydrogen bonding: intermolecular force in which a hydrogen atom that is bonded to a highly electronegative atom is attracted to an unshared pair of electrons of an electronegative atom in a nearby molecule

Intermolecular Forces (cont’d)

3. London dispersion forces: intermolecular attractions resulting from the constant motion of electrons and the creation of instantaneous dipoles*act between ALL molecules and atoms*ONLY intermolecular forces acting among noble gases and nonpolar molecules* Strength of LDFs increasing with increasing atomic or molar mass (more specifically—increasing # of electrons)

Arrange the following attractions in order of increasing strength: covalent, ionic,

metallic, dipole-dipole, hydrogen bonding, London dispersion

1. London dispersion2. Dipole-dipole3. Hydrogen bonding4. Nonpolar covalent5. Polar covalent6. Ionic7. Metallic

Symbol Ion Commonly Formed

Number of Electrons in Ion Z

Te 54In 49Sr Sr2+

Mg2+ 12ClF 9

Be2+ 2Br 36Al 13O

Chemical Symbol

Main Group Number

Group Name

Metal or Nonmetal

Charge of ion formed

K metal

Br halogens

Sr 2+

He 8A

Na Alkali metals

Cl 7A

Mg metal

Xe N/A

O chalcogens

Rb 1+

Which of the following pairs of elements do you expect to be most

similar? Why?(a) Ti and Ga(b) N and O(c) Li and Na(d) Ar and Br(e) Ge and Ga

Predict the ion formed by each of the following. How many electrons

will be gained OR lost?• Rb• K• Al• O• F• N• Mg• C• B

electron

neutron

proton

Classify the following elements as atomic or molecular.

• Xenon• Iodine• Oxygen• Nickel

Classify each of the following compounds as ionic or molecular.

CS2 CuOKI PCl3PtO2 COSO3 H2O

What are the basic units—atoms, molecules, or formula units—that

compose each of the following substances?

BaBr2 Rb2O NONe CF4 N2

I2 N2F4 O3

CO NaCl HBr

Use electron-dot notation to illustrate the number of valence electrons present in one atom of each of the following elements.

Rb C OP B ClLi N TeAr Ca AsGa Ge At

In writing Lewis structures, how is the need for multiple bonds

generally determined?• The need for a multiple bond becomes obvious if there are not enough valence electrons to complete octets by adding unshared pairs.•Multiple bonds are possible in Lewis structures containing C, N, or O.

What is a formula unit? What are the

components of one formula unit of CaF2?

• Smallest whole unit of an ionic compound

• Ca2+ and 2 F-

What type of energy best represents the strength of an ionic bond?

What type of bonding holds a polyatomic ion together?

How does bond length relate to bond energy?

What is the relationship of heat of vaporization of a metal and the strength of the bonds that hold the metal together?

A chemical bond between atoms results from the attraction between the valence electrons of one atom and the ________ in the _________ of another atoms.• Protons; nucleusAtoms with a strong attraction for electrons they share with another atom exhibit ________.• High electronegativityBonds that possess between 5% and 50% ionic character are considered to be _________.• Polar covalentThe greater the electronegativity difference between two atoms bonded together, the greater the bond’s percentage of _________.• Ionic character

The electrons involved in the formation of a chemical bond are called ____________.

If a bond’s character is more than 50% ionic, then the bond is called a(n) ________________.

How can electronegativity be used to distinguish between an ionic and covalent bond?

In a crystal of an ionic compound, each cation is surrounded by a number of _________.

Compared with the neutral atoms involved in the formation of an ionic compound, the crystal lattice that results is _________ in potential energy.

VSEPR valence shell electron-pair repulsion

Identify the major assumption of the VSEPR theory that is used to predict the shape of atoms.• Electrons are located as far apart as possible

because of electron-electron repulsion

In the VSEPR theory, double and triple bonds are treated the same as single bonds.

AB2

AB3

AB4

AB2E

AB3E

AB2E2

BeF2

BF3

ONFCH4

NH3

H2O