Unit 6 Chemical Bonding

Unit 6Chemical Bonding

Chemistry IMr. Patel

SWHS

Topic Outline• MUST know all assigned ions and elements!!!• Review Ions and Octet Rule (7.1)• Ionic Bonding (7.2)• Naming Ionic Compounds (9.2)• Metallic Bonding (7.3)• Covalent Bonding (8.1, 8.2)• Polarity (8.4)• Naming Covalent Molecules (9.3)

Ionic Bonding Intro

Metallic Bonding Intro

Covalent Bonding Intro

Ions

• Ion – charged species – Must show the sign and value of charge

• Valence electrons – electrons in highest occupied energy level– How do we find the number of valence electrons?• For elements 1A-8A = Group Number (except He)

– Depict using Lewis Dot Structures

EX: Consider the element Aluminum. a) How many valence electrons does Al have?b) Draw the Lewis Dot Structure for Al.

The Octet Rule

• Octet Rule – Atoms try to have 8 valence electrons– Goal: Be like a noble gas = stable– Will lose or gain electrons– Results in ions…What do we call these ions?– Cations – Positive charge species (metals)– Anions – Negative charge species (nonmetals)

EX: Consider the element Phosphorus. a) How many valence electrons does P have?b) Draw the Lewis Dot Structure for P.c) Draw the Lewis Dot Structure for the ion

form of phosphorus.d) Will it form a cation or anion? Name it.

Ionic Bonding

• Bond between Metal and Nonmetal– Actually, it is between cations and anions– Metal always comes first

• Ionic bonding is due to the transfer of electrons

• Important: The compound is always neutral – Positive = Negative

Ionic Bonding• Consider sodium chloride, CaCl2

– Metal first then nonmetal– Subscript tells you number of ions – 1 calcium ion for 2 chloride ions– Repeated array of ions – crystal

• Chemical Formula – shows # of ions and smallest unit

• Formula unit – lowest whole-number ratio of ions

NaCl

CaCl2

CaCl2

Ionic Bond Formation

Ionic Bond Formation

Ionic Bond Formation

• There are 4 steps to diagram ionic bonding1. Draw neutral Lewis Dot Structures

(one with dots and other with x)2. Show transfer of electrons (follow Octet Rule)3. Show Resulting Ions4. Write Formula

Ex: Show the Ionic Bond formation between sodium and chlorine.

Nax Cl

Nax Cl

xNa Cl1+ 1-

NaCl

Step 1:Draw Lewis

Dot Structure

Step 2:Transfer the Electron(s)

Step 3:Resulting

Ions

Step 4:Chemical Formula

Use x and dots or different colors to show differences in valence electrons (VE).

- Metal lose e-, Nonmetal gains.- Metal must lose all VE- Nonmetal must have 8 VE

Show resulting ions – must have all charges. Anion must show the transferred electron.

Only show element symbols and subscripts – no charges, dots

Ex: Show the Ionic Bond formation between calcium and fluorine.

CaF2

Step 1:Draw Lewis

Dot Structure

Step 2:Transfer the Electron(s)

Step 3:Resulting

Ions

Step 4:Chemical Formula

- Metal lose e-, Nonmetal gains.- Calcium must lose 2 VE- Fluorine has 7 VE, can only take 1 more = Problem

We need to add another fluorine atom to take other VE from Calcium = Solution

There is one calcium and two fluoride ions in this bond.

Cax Fx

Cax Fx F2+ 1-

xCa F2

Ex: Show the Ionic Bond formation between elements X (Group 3A) and Z (Group 6A).

Properties of Ionic Compounds

• Arranged into a crystal lattice– Large attractive forces = stable, strong structure

• Solid at room temperature• High melting points• Poor conductor as a solid• Good conductor when

molten or in solution• Overall exothermic

Covalent Bonding

• Bond between Nonmetal and Nonmetal– Can also include semimetals– NO IONS (cations/anions)

• Covalent bonding is due to the sharing of electrons

• Molecule – group of neutral atoms held together by covalent bonds

Covalent Bonding

• Covalent molecules are defined structures– No crystal lattice– Has a specific 3-D structure

• Molecular Formula – shows how many atoms of each element are in a molecule– We do not reduce formulas like ionic compounds– Ex: H2O, CO, CH4, C6H12O6

Depictions of Covalent Molecules

Covalent Molecule Shapes

• Sharing of electrons are caused by overlapping and hybridizing orbitals (electron location)

• VSEPR Theory – Valence Shell Electron Pair Repulsion Theory

• VSEPR helps explain and predict the shape of molecules– Theory states that shape of molecules based on minimizing

the repulsion of valence electron pairs– Keep electrons as far apart as possible

Methane = CH4 - Tetrahedral

Properties of Covalent Molecules

• Distinct groupings of atoms = molecule• Solid, liquid or gas at room temperature• Low melting points• Poor conductor• Polar or Nonpolar

Diatomic Molecules

• There are 7 elements that can not be found as individual atoms – found in pairs

• Diatomic molecule – two atoms• H2 , N2 , O2 , F2 , Cl2 , Br2 , I2 (Group 7 + HON)

Types of bonds

• Covalent molecules share bonds to complete octets – octet rule still applies!

• Three types of bonds: single, double, triple

Comparing Bonds

Bond Electrons Involved

Bond Length Bond Strength Diatomics

Single Bond 2 electrons Longest Weakest H2 , F2 , Cl2 , Br2 , I2

Double Bond 4 electrons Moderate Intermediate O2

Triple Bond 6 electrons Shortest Strongest N2

Valence Electrons not participating in bonding are called non-bonding electrons or lone pairs.

Polarity

• Covalent Bonding is sharing of electrons• Electrons can be shared equally or unequally

depending on the strengths of the atoms• If electrons have different electronegativities,

the molecule will be polar• Like dissolves Like

Polarity

• Polar – electrons shared unequally– Align themselves with an electric field– Ex: Water

• Nonpolar – electrons shared equally– All diatomics are nonpolar

Metallic Bonding

• These are the forces that hold metals together• Valence electrons are a sea of electrons

around nuclei– Excellent conductors

• Metals atoms arranged in compact and orderly patterns.

Comparing Ionic and Covalent Bonding

Characteristic Ionic Bonding Covalent Bonding

Elements Metal and Nonmetal Nonmetal and Nonmetal

Bond Formation Transfer electron Share electron

Product of bond Formula Unit (salt) Molecule

Physical State Solid Solid, Liquid, Gas

Melting Point High Low

Conductivity Good Conductor Poor to Non-conductor

Nomenclature No PrefixesCan Have Roman Numerals

Always Prefixes No Roman Numerals

Follow Octet Rule YES YES

Force Intramolecular Intramolecular

NOMENCLATURE

RULES

Nomenclature: Type 1Ionic Compounds with Fixed Charges

• Groups 1A-7A have fixed charges…memorize these charges (Skip 4A and 8A)

1A: 1+ 2A: 2+ 3A: 3+5A: 3- 6A: 2+ 7A: 1-

• Must be able to go from formula to name AND name to formula

Nomenclature: Type 1Ionic Compounds with Fixed Charges

• Rules for Formula Name:– Write down full name of the cation– Write down name of the anion (-ide)– Ex: K2O = potassium oxide

• Practice:– H2S LiF Al2O3

– hydrogen sulfide, lithium fluoride, aluminum oxide

Nomenclature: Type 1Ionic Compounds with Fixed Charges

• Rules for Name Formula:– Write symbol and charge of cation and anion– Use subscripts to make all positive = negative

(cross charges and reduce)– EX: Lithium Phosphide = Li1+ P3- Li3P

• Practice:– Magnesium bromide, barium sulfide, Calcium nitride– MgBr2 BaS Ca3N2

Nomenclature: Type 2Ionic Compounds with Variable Charges

• Groups 1A-7A have fixed charges- charge always the same (Skip 4A and 8A)

• Other metals (transition metals) do not have fixed charges – multiple possibilities for charge– We must indicate the specific charge

• Example: Mg – always Mg2+

• Example: Mn – can be Mn1+, Mn5+, Mn6+, Mn7+

Nomenclature: Type 2Ionic Compounds with Variable Charges

• Rules for Formula Name:– Write down full name of the cation and anion (-ide)– Find total negative charge = total positive charge– Find charge on each cation– Write charge as Roman Numeral between cation and

anion in name

– Ex: FeCl3 = iron(III) chloride• Each Cl is 1- charge = b/c there are 3 Cl there is total of 3-• This means there is a total of 3+ so Fe must be 3+• Write charge of Fe as roman numeral in name

Nomenclature: Type 2Ionic Compounds with Variable Charges

Practice Formula Name:

1. SnS2

2. Cu2O

3. Fe3P2

1. Tin(IV) sulfide

2. Copper(I) oxide

3. Iron(II) phosphide

Nomenclature: Type 2Ionic Compounds with Variable Charges

• Rules for Name Formula:– Write symbol and charge of cation and anion– Charge of cation comes from Roman Numeral– Use subscripts to make all positive = negative

(cross charges and reduce)

– EX: Cobalt(II) nitride = Co2+ N3- Li3N2

• Charge of cobalt came from roman numeral• Charge of anion came from periodic table• Cross charges (positive = negative)

Nomenclature: Type 2Ionic Compounds with Variable Charges

Practice Name Formula:

1. Manganese(II) chloride

2. Iron(III) oxide

3. Copper(II) sulfide

1. MnCl2

2. Fe2O3

3. CuS

Nomenclature: Type 3Ionic Compounds with Polyatomic Ions

• The compounds have more than two elements– Must know polyatomic ions (page 257)

• Treat the polyatomic ion as a single unit that WILL NOT CHANGE– Nitrate = NO3

1- 2 nitrates = (NO31-)2

• Must be able to go from formula to name AND name to formula

Nomenclature: Type 3Ionic Compounds with Polyatomic Ions

• Rules for Formula Name:– Write down full name of the cation– Use Roman Numerals is cation is transition metal– Write down name of anion (-ide or polyatomic ion)– Ex: Ba(OH)2 = barium hydroxide

– Ex: Pb3(PO4)2 = lead(II) phosphate

• Practice:– Fe(CN)3 Li2SO4 NH4C2H3O2

– Iron(III) cyanide, lithium sulfate, ammonium acetate

Nomenclature: Type 3Ionic Compounds with Polyatomic Ions

• Rules for Name Formula:– Write symbol and charge of cation and anion– Use subscripts to make all positive = negative

(cross charges and reduce)– EX: Tin(IV) sulfite= Sn4+ (SO3

2-) Sn(SO3)2

• Practice:– Calcium hydroxide, copper(I) nitrite, ammonium phosphate– Ca(OH)2 CuNO2 (NH4)3PO4

Nomenclature: Type 4Covalent Molecules

• The molecules do not contain metals.

• Need to know Greek prefixes

Nomenclature: Type 4Covalent Molecules

• Rules for Formula Name:– Write down full name of the first element– Write down modified name of second element (-ide)– Place Greek prefixes before each element name to denote the

number of atoms – No mono prefix on first element– Ex: CO2 = carbon dioxide

• Practice:– N2O5 NO3 XeF6

– Dinitrogen pentoxide, nitrogen trioxide, xenon hexafluoride

Nomenclature: Type 4Covalent Molecules

• Rules for Name Formula:– Write symbol of both elements– Use prefixes as subscripts– EX: phosphorus pentafluoride = PF5

• Practice:– Dihydrogen monoxide, sulfur heptachloride– H2O SCl7