unit 6 chemical bonding
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Unit 6 Chemical Bonding. Chemistry I Mr. 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) - PowerPoint PPT PresentationTRANSCRIPT
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