chemistry - tro-structure & properties 2e ch.5 - chemical...

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CHEMISTRY - TRO-STRUCTURE & PROPERTIES 2E

CH.5 - CHEMICAL BONDING I

CONCEPT: ATOMIC PROPERTIES AND CHEMICAL BONDS

Before we examine the types of chemical bonding, we should ask why atoms bond at all.

• Generally, the reason is that ionic bonding ____________ the potential energy between positive and negative ions.

• Generally, the reason covalent bonds form is to follow the ____________ rule, in which the element is then

surrounded by 8 valence electrons.

There are three models of chemical bonding:

In ____________________ bonding, metals connect to non-metals.

• __________________ transfers an electron to the ________________ , creating ions with opposite charges that

are attracted to each other.

Li F Li F Li F

In _______________ bonding, non-metals connect to non-metals.

• In it the nonmetals __________________ electron pairs between their nuclei.

ClCl

In _______________ bonding, metal atoms “pool” their valence electrons to form an electron “sea” that holds the metal-ion

together



CONCEPT: CHEMICAL BONDS (PRACTICE)

EXAMPLE: Describe each of the following as either a(n): atomic element, molecular element, molecular compound or ionic compound.

atomic element ––

molecular element ––

molecular compound ––

ionic compound ––

a. Iodine

b. NH3

c. Graphite

d. Na3P

e. Ag2(SO4)2



CONCEPT: THE IONIC-BONDING MODEL

The central idea of ionic bonding is that the metal transfers an electron(s) to a nonmetal.

• The metal then becomes a(n) ____________ (positive ion). and the nonmetal becomes a(n) _____________ (negative ion).

• Their opposite charges cause them to combine into a crystalline solid.

PRACTICE: Determine the molecular formula of the compound formed from each of the following ions.

a. K+ & P3-

b. Sn4+ & O2-

c. Al3+ & CO32-



CONCEPT: DIPOLE ARROWS

Before drawing covalent compounds we first need to understand the idea of polarity and its connection to electronegativity.

• Polarity arises whenever two elements are connected to each other and there is a significant difference in their

electronegativities.

• Generally, electronegativity ________________ going from left to right of a period and ________________ going

down a group.

To show this difference in electronegativity we use a dipole arrow.

The dipole arrow points towards the ________________ electronegative element.

The Effect of Electronegativity Difference on Bond Classification

Electronegativity Difference (ΔEN)

Bond Classification

Example

Zero (0.0)

Pure Covalent

Small (0.1 – 0.4)

Nonpolar Covalent

Intermediate (0.4 – 1.7)

Polar Covalent

Large (Greater than 1.7)

Ionic



PRACTICE: DIPOLE ARROWS

EXAMPLE: Based on each of the given bonds determine the direction of the dipole arrow and the polarity that may arise.

a. H Cl

b. S O

c. Br B Br

PRACTICE 1: Based on the given bond determine the direction of the dipole arrow and the polarity that may arise.

a. H C


a. N F


a. H N H



CONCEPT: CHEMICAL BOND IDENTIFICATION

PRACTICE: Answer each of the following questions dealing with the following compounds.

KBr NH3 F2 CaO NaClO

a. Which of the following compound(s) contains a polar covalent bond?

b. Which of the following compound(s) contains a pure covalent bond?

c. Which of the following compound(s) contains a polar ionic bond?

d. Which of the following compound(s) contains both a polar ionic bond and a polar covalent bond?



CONCEPT: ELECTRON-DOT SYMBOLS

Before we look at the first two bonding models, we have to figure out how to depict the valence electrons of bonding atoms.

• In the _________ electron-dot symbol, the element symbol represents the nucleus and inner electrons, and the

surrounding dots represent the ________________ electrons.

EXAMPLE: Draw the electron-dot symbol for each of the following elements.

1A 2A 3A 4A 5A 6A 7A 8A

Li

Be

B

C

N

O

F

Ne

It’s easy to write the Lewis symbol for any Main-Group element:

1) Remember that Group Number equals Valence Electron Number.

2) Place one dot at a time on the four sides (top, right, bottom, left) of the element symbol.

3) Keep adding dots, pairing them up until you have reach the number of total valence electrons for that element.

PRACTICE 1: Draw the electron-dot symbol for the following ion.

Mg2+


N3-


Cr1+



CONCEPT: CHEMICAL BONDING I

Rules for Drawing

1. Least electronegative element goes into the center. Important Facts to Know:

(a) Electronegativity increases across any Period going from left to right and up any Group going from bottom to top.

(b) Hydrogen and Fluorine ________________ go in the center and they only make _________ BOND.

2. Number of valence electrons equals group number.

3. Carbon must make _____ bonds, except in rare occasions when it makes _____ bonds.

• If the carbon atom were positive or negative then it would make _____ bonds

4. Nitrogen likes to make _____ bonds.

5. Oxygen likes to make _____ bonds.

6. Halogens (Group 7A), when not in the center, make _____ bond.

7. Expanded Valence Shell Theory: Nonmetals starting from Period _____ to _____ can have more than 8 valence

electrons around them when in the center.



CONCEPT: INCOMPLETE OCTETS

Nonmetals form covalent bonds to generally follow the ___________ rule, in which the element is surrounded by 8 valence

electrons.

• Sometimes elements form compounds in which they have ____________________ 8 valence electrons.

• These elements are said to have an incomplete octet or to be ________________________________________ .

EXAMPLE: Draw the following molecular compound.

BH3

PRACTICE: Draw the following molecular compound.

BeCl2



CONCEPT: EXPANDED OCTETS

Expanded Valence Shell Theory: Nonmetals starting from Period _____ to _____ can have more than 8 valence

electrons around them when in the center.

EXAMPLE: Draw each of the following molecular compounds.

IF3 KrF5+

PRACTICE 1: Draw the following molecular compound.

SBr4


I3–



CONCEPT: POLYATOMIC IONS

Shortcut: If you have _____, _____, _____, _____, __________________ or __________________ connected to oxygen

then the negative charge tells us how many oxygens are single bonded.

• The remaining oxygens are _______________________ bonded to the central element.

EXAMPLE: Draw each of the following molecular compounds.

SO42-

PO43- H2SO4


SeO42-


XeO64-



CONCEPT: FORMAL CHARGE

Structures and polyatomic ions that break the octet rule often have ________________ Lewis Structures.

• The purpose of using the formal charge formula is to determine which Lewis structure is the best answer.

Formal Charge =

a) Use formal charge formula to check to see if you drew your compound correctly.

b) Formal charges must be either _____, ______, ______.

c) If you add up all the formula charges in your compound that will equal the overall charge of the compound.

EXAMPLE: Calculate the formal charge for each of the following element designated for each of the following.

a. The carbon atom in

b. The sulfur atom in

PRACTICE: Calculate the formal charge for each of the following element designated in the following compound.

a. Both oxygen atoms in:

!A B



CONCEPT: RESONANCE STRUCTURES

Resonance structures are used to represent bonding in a molecule or ion when a single Lewis structure cannot correctly

describe the Lewis structure.

EXAMPLE: Determine all the possible Lewis structures possible for NO2–. Determine its resonance hybrid.

EXAMPLE: Determine the remaining resonance structures possible for the following compound, CO32-.

O

C OO



CONCEPT: ELECTRONIC GEOMETRY

When drawing a compound you have to take into account two different systems of geometrical shape.

• The simpler system known as electronic geometry or __________ shape treats lone pairs (nonbonding electrons)

and surrounding elements as the same.

Key: A = Central Element

X = Lone Pairs and Surrounding Elements

O C O H C N

AX2 = Linear (2 Groups)

AX3 = Trigonal Planar (3 Groups)

F

BF F

SnF F

AX4 = Tetrahedral (4 Groups)

NH

HH C

Cl

ClCl

Cl

Cl

PCl

ClCl

Cl

AX5 = Trigonal Bipyramidal (5 Groups)

Xe FF

Cl

SCl Cl

Cl Cl

AX6 = Octahedral (6 Groups)

Cl

XeH

H

H

H

!

AX

XX

!



PRACTICE: ELECTRONIC GEOMETRY

EXAMPLE: Draw each of the following compounds and determine their electronic geometries.

PH3 BeCl2

PRACTICE 1: Draw the following compound and determine its electronic geometry.

SBr4


IF3


H2S


PO43-



CONCEPT: MOLECULAR GEOMETRY

When drawing a compound you have to take into account two different systems of geometrical shape.

• With the molecular geometry you treat lone pairs (nonbonding electrons) and

surrounding elements as different.

Key: A = Central Element X = Surrounding Element E = Lone Pair

O C O H C N

3 Groups2 Groups F

BF F

SnF F

AX3 - Trigonal Planar AX2E1 - Bent, Angular or V-ShapedAX2 - Linear

4 Groups NH

HHC

Cl

ClClCl H

OH

AX4 - Tetrahedral AX2E2 - Bent, Angular or V-ShapedAX3E1 - Trigonal Pyramidal

5 Groups

Xe FF

AX5 - Trigonal Bipyramidal

ClP

ClCl

Cl Cl

F Cl F

FAX4E1 - Seesaw AX2E3 - Linear

FS FF

F

AX3E2 - T-Shaped

6 Groups ClSCl Cl

Cl ClClXe

H

H

H

HAX6 - Octahedral AX4E2 - Square Planar

F

SFF F

F

AX5E1 - Square Pyramidal

AX

XX



PRACTICE: MOLECULAR GEOMETRY

EXAMPLE: Draw each of the following compounds and determine their molecular geometries.

PH2 – XeCl2

PRACTICE 1: Draw the following compound and determine its molecular geometry.

OBr2

PRACTICE 2: Draw the following compound and determine its molecular geometry.

SO42-



CONCEPT: IDEALIZED BOND ANGLES

According to the ___________________________________________ (VSEPR) model bond and lone electron pairs will

position themselves around the central element so that they are as far apart as possible.



PRACTICE: IDEALIZED BOND ANGLES

EXAMPLE: Determine the bond angles of each of the following compounds.

CO2 BrF4+

PRACTICE 1: Determine the bond angle of the following compound.

AsCl5

PRACTICE 2: Determine the bond angle of the following compound.

IF3



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