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Transcript of Chapter 4 Compounds and Their Bonds 4.4 Polyatomic Ions 1 Copyright © 2009 by Pearson Education,...
Chapter 4 Compounds and Their Bonds
4.4 Polyatomic Ions
1
Copyright © 2009 by Pearson Education, Inc.
Polyatomic Ions
A polyatomic ion • is a group of atoms. • has an overall ionic charge.
Some examples of polyatomic ions are
NH4+ ammonium OH− hydroxide
NO3−
nitrate NO2−
nitrite
CO32− carbonate PO4
3− phosphateHCO3
− hydrogen carbonate(bicarbonate)
2
Some Compounds with Polyatomic Ions
3
Copyright © 2009 by Pearson Education, Inc.
Some Names of Polyatomic IonsThe names of common polyatomic anions
• end in ate.
NO3− nitrate PO4
3− phosphate
• with one oxygen less end in ite.
NO2− nitrite PO3
3− phosphite
• with hydrogen attached use the prefix hydrogen (or bi).
HCO3− hydrogen carbonate (bicarbonate)
HSO3− hydrogen sulfite (bisulfite)
4
Names and Formulas of Common Polyatomic Ions
5
Naming Compounds with Polyatomic Ions
• The positive ion is named first, followed by the name of the polyatomic ion.
NaNO3 sodium nitrate
K2SO4 potassium sulfate
Fe(HCO3)3 iron(III) bicarbonate
or iron(III) hydrogen carbonate
(NH4)3PO3 ammonium phosphite
6
Some Compounds with Polyatomic Ions
7
Learning CheckMatch each formula with the correct name.
A. MgS 1) magnesium sulfite
MgSO3 2) magnesium sulfate
MgSO4 3) magnesium sulfide
B. Ca(ClO3)2 1) calcium chlorate
CaCl2 2) calcium chlorite
Ca(ClO2)2 3) calcium chloride
8
Learning CheckName each of the following compounds:
A. Mg(NO3)2
B. Cu(ClO3)2
C. PbO2
D. Fe2(SO4)3
E. Ba3(PO3)2
9
Writing Formulas with Polyatomic IonsThe formula of an ionic compound
• containing a polyatomic ion must have a charge balance that equals zero (0).
Na+ and NO3− -> NaNO3
• with two or more polyatomic ions has the polyatomic ions in parentheses.
Mg2+ and 2NO3−
-> Mg(NO3)2
subscript 2 for charge balance
10
Learning CheckSelect the correct formula for each.
A. aluminum nitrate
1) AlNO3 2) Al(NO)3 3) Al(NO3)3
B. copper(II) nitrate
1) CuNO3 2) Cu(NO3)2 3) Cu2(NO3)
C. iron(III) hydroxide
1) FeOH 2) Fe3OH 3) Fe(OH)3
D. tin(IV) hydroxide
1) Sn(OH)4 2) Sn(OH)2 3) Sn4(OH)
11
Learning CheckWrite the correct formula for each.
A. potassium bromateB. calcium carbonateC. sodium phosphateD. iron(II) nitrite
12
Flowchart for Naming Ionic Compounds
13
Learning CheckName the following compounds:
A. Ca3(PO4)2
B. FeBr3
C. Al2S3
D. Zn(NO2)2
E. NaHCO3
14
Learning CheckWrite the formulas for the following:
A. calcium nitrate
B. iron(II) hydroxide
C. aluminum carbonate
D. copper(II) bromide
E. lithium phosphate
15
Chapter 4 Compounds and Their Bonds
4.5Covalent Compounds
16
Copyright © 2009 by Pearson Education, Inc.
Covalent Bonds
Covalent bonds form
• when atoms share electrons to complete octets.
• between two nonmetal atoms.
• between nonmetal atoms from Groups 4A (14), 5A (15), 6A (16), and 7A (17).
17
Hydrogen Molecule
A hydrogen molecule
• is stable with 2 electrons (helium).
• has a shared pair of electrons.
18
Forming Octets in Molecules
In a fluorine, F2,, molecule, each F atom
• shares 1 electron.
• attains an octet.
19
Carbon Forms 4 Covalent Bonds
In a CH4 (methane) molecule,
• 1 C atom shares electrons with 4 H atoms to attain an octet.
• each H atom shares 1 electron to become stable, like helium.
20
Multiple Bonds
In a nitrogen molecule, N2,
• each N atom shares 3 electrons.• each N attains an octet.• the bond is a multiple bond called a triple
bond.• the name is the same as the element.
21
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Naming Covalent Compounds
In the names of covalent compounds, prefixes are used to indicate the number of atoms (subscript) of each element. (mono is usually omitted)
22
Naming Covalent CompoundsWhat is the name of SO3?
1. The first nonmetal is S sulfur.
2. The second nonmetal is O, named oxide.
3. The subscript 3 of O is shown as the prefix tri.
SO3 -> sulfur trioxide
The subscript 1 (for S) or mono is understood.
23
Naming Covalent CompoundsName P4S3.
1. The first nonmetal, P, is phosphorus.
2. The second nonmetal, S, is sulfide.
3. The subscript 4 of P is shown as tetra.
The subscript 3 of O is shown as tri.
P4S3 -> tetraphosphorus trisulfide
24
Formulas and Names of Some Covalent Compounds
25
Learning CheckSelect the correct name for each compound.
A. SiCl4 1) silicon chloride2) tetrasilicon chloride3) silicon tetrachloride
B. P2O5 1) phosphorus oxide2) phosphorus pentoxide3) diphosphorus pentoxide
C. Cl2O7 1) dichlorine heptoxide2) dichlorine oxide3) chlorine heptoxide
26
Learning CheckWrite the name of each covalent compound.
CO2 _____________________
PCl3 _____________________
CCl4 _____________________
N2O _____________________
27
Example: Writing Formulas for Covalent Compounds
Write the formula for carbon disulfide.
STEP 1: Elements are C and S
STEP 2: No prefix for carbon means 1 C
Prefix di = 2
Formula: CS2
28
Learning CheckWrite the correct formula for each of the following:
A. phosphorus pentachloride
B. dinitrogen trioxide
C. sulfur hexafluoride
29
Learning CheckIdentify each compound as ionic or covalent, and
give itscorrect name.
A. SO3
B. BaCl2
C. (NH4)3PO3
D. Cu2CO3
E. N2O4
30
Study Tip: Ionic or CovalentA compound is
• ionic if the first element in the formula
or the name is a metal or the polyatomic ion NH4+ .
K2O K is a metal; compound is ionic;
potassium oxide
• covalent if the first element in the formula or the name is a nonmetal.
N2O N is a nonmetal; compound is covalent;
dinitrogen oxide
31
Learning CheckIdentify each compound as ionic or covalent and
give itscorrect name.
A. Ca3(PO4)2
B. FeBr3
C. SCl2
D. Cl2O
32
Learning CheckDetermine if each is ionic (I) or covalent (C ), and
write the formula.
A. calcium nitrate
B. boron trifluoride
C. aluminum carbonate
D. dinitrogen tetroxide
E. copper(I) phosphate33
Chapter 4 Compounds and Their Bonds
4.6
Electronegativity and Bond Polarity
34Copyright © 2009 by Pearson Education, Inc.
Electronegativity
The electronegativity value
• indicates the attraction of an atom for shared electrons.
• increases from left to right going across a period on the periodic table.
• is high for the nonmetals, with fluorine as the highest.
• is low for the metals.
35
Some Electronegativity Values for Group A Elements
36
Low values
High values
` Electronegativity increases
` E
lectro
neg
ativity d
ecre
ase
s
Copyright © 2009 by Pearson Education, Inc.
Nonpolar Covalent Bonds
A nonpolar covalent bond
• occurs between nonmetals.• is an equal or almost equal sharing of electrons.• has almost no electronegativity difference (0.0 to 0.4).
Examples: Electronegativity Atoms Difference Type of BondN-N 3.0 - 3.0 = 0.0 Nonpolar covalentCl-Br 3.0 - 2.8 = 0.2 Nonpolar covalentH-Si 2.1 - 1.8 = 0.3 Nonpolar covalent
37
Polar Covalent Bonds
A polar covalent bond
• occurs between nonmetal atoms.• is an unequal sharing of electrons.• has a moderate electronegativity difference (0.5 to
1.7).
Examples: Electronegativity
Atoms Difference Type of BondO-Cl 3.5 - 3.0 = 0.5 Polar covalentCl-C 3.0 - 2.5 = 0.5 Polar covalentO-S 3.5 - 2.5 = 1.0 Polar covalent
38
Comparing Nonpolar and Polar Covalent Bonds
39
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Ionic BondsAn ionic bond • occurs between metal and nonmetal ions.• is a result of electron transfer.• has a large electronegativity difference (1.8 or
more).
Examples: Electronegativity
Atoms Difference Type of BondCl-K 3.0 – 0.8 = 2.2 IonicN-Na 3.0 – 0.9 = 2.1 IonicS-Cs 2.5 – 0.7 = 1.8 Ionic
40
Electronegativity and Bond Types
41
Predicting Bond Types
42
Learning CheckUse the electronegativity difference to identify the type of bond [nonpolar covalent (NP), polar covalent (P), or ionic (I)] between the following:
A. K-NB. N-OC. Cl-ClD. H-Cl
43
Chapter 4 Compounds and Their Bonds
4.7Shapes and Polarity of
Molecules
44
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°
VSEPRIn the valence-shell electron-pair repulsion
theory(VSEPR), the electron groups around a central
atom
• are arranged as far apart from each other as possible.
• have the least amount of repulsion of the negatively charged electrons.
• have a geometry around the central atom that determines molecular shape.
45
Four Electron Groups
In a molecule of CH4,
• there are 4 electron groups around C.
• repulsion is minimized by placing 4 electron groups at angles of 109°, which is a tetrahedral arrangement.
• the shape with four bonded atoms is tetrahedral.
46
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Three Bonding Atoms and One Lone Pair
In a molecule of NH3,
• 3 electron groups bond to H atoms, and the fourth one is a lone (nonbonding) pair.
• repulsion is minimized with 4 electron groups in a tetrahedral arrangement.
• with 3 bonded atoms, the shape is pyramidal.
47
Two Bonding Atoms and Two Lone PairsIn a molecule of H2O,
• 2 electron groups are bonded to H atoms and 2 are lone pairs (4 electron groups).
• 4 electron groups minimize repulsion in a tetrahedral arrangement.
• the shape with 2 bonded atoms is bent.
48
Shapes with 4 Electron Groups
Electron Pairs
Bonded Atoms
Lone Pairs
Molecular Shape
Example
4 4 0 Tetrahedral CH4
4 3 1 Pyramidal NH3
4 2 2 Bent H2O
Copyright © 2009 by Pearson Education, Inc. 49
Learning CheckState the number of electron groups, lone pairs, and use VSEPR theory to determine the shape of the following molecules or ions.
1) tetrahedral 2) pyramidal 3) bent
A. PF3
B. H2S
C. CCl4
50
Study TipTo determine shape, 1. draw the electron-dot structure.2. count the electron pairs around the central atom.
3. count the bonded atoms to determine shape.
4 electron pairs and 4 bonded atoms = tetrahedral 4 electrons pairs and 3 bonded atoms = pyramidal
4 electron pairs and 2 bonded atoms = bent
51
Polar MoleculesA polar molecule • contains polar bonds.
• has a separation of positive and negative charge called a dipole, indicated with + and -.
• has dipoles that do not cancel. + -
• •
H–Cl H—N—H dipole
H dipoles do
not cancel
52
Nonpolar MoleculesA nonpolar molecule • contains nonpolar bonds.
Cl–Cl H–H
• or has a symmetrical arrangement of polar bonds.
O=C=O Cl
Cl–C–Cl
Cl
dipoles cancel
53
Determining Molecular Polarity STEP 1: Write the electron-dot formula. STEP 2: Determine the shape. STEP 3: Determine if dipoles cancel or not.
Example: H2O
. .
H─O: H2O is polar
│ H
dipoles do not cancel
54
Learning CheckIdentify each of the following molecules as 1) polar or 2) nonpolar. Explain.
A. PBr3
B. HBr
C. Br2
D. SiBr4
55
Chapter 4 Compounds and Their Bonds
4.8 Attractive Forces in Compounds
56
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°
Ionic Bonds
In ionic compounds, ionic bonds • are strong attractive forces.• hold positive and negative ions
together.
57
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Dipole-Dipole Attractions
58
In covalent compounds, polar molecules •exert attractive forces called dipole-dipole attractions.
•form strong dipole attractions called hydrogen bonds between hydrogen atoms bonded to F, O, or N, and other very electronegative atoms.
Dispersion Forces
Dispersion forces are• weak attractions between nonpolar
molecules.• caused by temporary dipoles that develop
when electrons are not distributed equally.
59
Attractive Forces
60
Melting Points and Attractive Forces• Ionic compounds require large amounts of energy to
break apart ionic bonds. Thus, they have high melting points.
• Hydrogen bonds are the strongest type of dipole-dipole attractions. They require more energy to break than other dipole-dipole attractions.
• Dispersion forces are weak interactions and very little energy is needed to change state.
61
Melting Points of Some Substances
62
Learning CheckIdentify the main type of attractive forces for each:1) ionic 2) dipole-dipole 3) hydrogen bonds 4) dispersion
A. NCl3
B. H2O
C. Br-BrD. KClE. NH3
63