1 ch. 4: compounds and their bonds chem. 20 el camino college
TRANSCRIPT
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Ch. 4: Compounds and Their Bonds
Chem. 20
El Camino College
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Octet Rule
8 e-s is a magic number Main Group elements (except H and He)
will give, take, or borrow electrons to reach 8 electrons in the outermost shell
Noble Gases (except He) have 8 electrons in the outer shell, so they don’t give or take electrons
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Cations: Positive Ions
Atoms are neutral Ions have a charge Cations are positive, Anions are negative Metals lose e-s easily to form cations When electrons are lost, the particle left
over has a positive charge.
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Main Group. Cations: Positive Ions
Ex. Sodium atom has one valence electron. When Na loses 1 e-, a cation with a positive charge forms
The name of Na+ is sodium ion Note, for a +1 charge, just show +.
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Main Group. Cations: Positive Ions
Ex. Mg atom has 2 valence electrons When Mg loses 2 electrons, a cation with a
+2 charge forms The name of Mg2+ is magnesium ion Note, show the number, then the charge.
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Anions: Negative Ions Nonmetals gain electrons easily to form
anions When electrons are gained, the particle has
a negative charge Example: When Cl gains 1 e-, an anion with
-1 charge forms The name of Cl- is chloride ion.
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Anions: Negative Ions
Ex. How many valence e-s does N have? 5 How many e-s will N gain to reach 8? 3 The formula for nitride ion is N3-
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Names of Ions
For metal ions in groups. 1, 2, and 3, the name is the metal plus the word “ion”
K+ is potassium ion Ca2+ is calcium ion What is the name of Al3+? aluminum ion
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Names of anions
For anions (nonmetal ions), the name is the nonmetal in ide form, plus the word “ion”
F- is fluoride ion O2- is oxide ion What is the name of S2-? sulfide ion
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Name These
Li Li+
P3-
P Ba2+
Ba
lithium lithium ion phosphide ion phosphorus barium ion barium
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Charges from Group number
Gp 1 (1A) metals form + ions Gp 2 (2A) metals form 2+ ions Gp 13 (3A) metals form 3+ ions
Gp 15 (5A) nonmetals form 3- ions Gp 16 (6A) nonmetals form 2- ions Gp 17 (7A) nonmetals form - ions
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Ionic Compounds
An ionic bond occurs when one atom gives electrons to another
Compounds always have zero charge.
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Predicting Ionic Formulas Determine the charge of each ion Combine ions to get zero charge overall Use the lowest numbers possible Ex. A compound contains sodium ions and sulfide ions.
Write the formula. Sodium ion is Na+, sulfide ion is S2-
It will take 2 Na+ ions to cancel the charge in one S2- ion The formula is Na2S.
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Write the Formulascompound contains
potassium ions, iodide ions chloride ions, calcium ions aluminum ions, nitride ions beryllium ions, fluoride ions sulfide ions, lithium ions aluminum ions, oxide ions
KI CaCl2 AlN BeF2
Li2S
Al2O3
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Naming Ionic Compounds The 1st word is the cation name (metal ion) The 2nd word is the anion name Never use the word “ion” in a name
LiBr MgF2
CaS Ca3P2
K2O
AlCl3
lithium bromide magnesium fluoride calcium sulfide calcium phosphide potassium oxide aluminum chloride
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Transition Metal Ions Some transition metals may form many cations Know these transition metal ions
Cr2+, Cr3+ chromium(II) ion, chromium(III) ionFe2+, Fe3+ iron(II) ion, iron(III) ionCu+, Cu2+ copper(I) ion, copper(II) ionSn2+, Sn4+ tin(II) ion, tin(IV) ionPb2+, Pb4+ lead(II) ion, lead(IV) ion
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Transition Metal Ions Chromium can form two ions: Cr2+, Cr3+
To name, use a Roman numeral in parentheses and the word “ion” The name of Cr3+ is chromium(III) ion What is the name of Pb4+? lead(IV) ion (note--parentheses are only for elements that form
more than one ion such as Cr, Fe, Cu, Sn, Pb) What is the name of Ag? silver What is the name of Ag+? silver ion
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Transition Metals in Compounds
When a compound contains a transition metal with variable charge, you must determine what the charge is
Ex. Name FeCl2 Is that Fe2+ or Fe3+? Since chloride ion is Cl- and there are 2 of them, this must
be iron(II) ion Iron(II) chloride Write the formula for iron(III) bromide FeBr3
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Examples
Name CuO, Cu2O, Fe2S3, FeO, PbS, PbS2, AgCl copper(II) oxide copper(I) oxide iron(III) sulfide iron(II) oxide lead(II) sulfide lead(IV) sulfide silver chloride
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Formulas
chromium(III) bromide, chromium(II) sulfide, zinc oxide, tin(II) nitride, tin(IV) nitride, tin(II) oxide
CrBr3
CrS ZnO Sn3N2
Sn3N4
SnO
Jumbo Practice 1
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Polyatomic Ions
Polyatomic ions are ions that contain more than 1 atom Never change the numbers inside or the charge of a
polyatomic ion If you need more than one polyatomic ion, use
parentheses.
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OH-
Hydroxide ion is OH-
To write the formula of sodium hydroxide Sodium ion is Na+
Hydroxide ion is OH-
NaOH
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OH-
To write the formula of calcium hydroxide Calcium ion is Ca2+
Hydroxide ion is OH-
Ca(OH)2
Note: Writing CaO2H2 or CaOH2 is incorrect
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Other Polyatomic Ions
Nitrate ion NO3-, sulfate ion SO4
2-, phosphate ion PO43-
Write the formulas for sodium nitrate, sodium sulfate, and sodium phosphate NaNO3
Na2SO4
Na3PO4
Write the formulas for calcium nitrate, calcium sulfate, and calcium phosphate Ca(NO3)2
CaSO4
Ca3(PO4)2
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Other Polyatomic Ions
Be careful with similar sounding ions sulfate ion SO4
2-, sulfite ion SO32-, sulfide ion S2-
hydrogen sulfate ion HSO4-
carbonate ion CO32-
hydrogen carbonate ion HCO3-
acetate ion C2H3O2-
ammonium ion NH4+
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Examples
Name CuNO3, Cu2SO3, ZnSO3, Sn(C2H3O2)4, KHCO3
copper(I) nitrate copper(I) sulfite zinc sulfite tin(IV) acetate potassium hydrogen carbonate
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Formulas
chromium(III) hydrogen sulfate, iron(II) phosphate, zinc hydroxide, tin(II) carbonate, ammonium acetate
Cr(HSO4)3
Fe3(PO4)2
Zn(OH)2
SnCO3
NH4C2H3O2
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Ionic vs. Covalent
All the compounds we’ve looked at so far are ionic
The cation of an ionic compound is a metal ion or ammonium ion
The anion of an ionic compound is a nonmetal ion or polyatomic ion
In ionic compounds, e-s are given from one atom to another.
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Ionic vs. Covalent
Covalent compounds are made of 2 nonmetals
In covalent compounds, e-s are shared (not given away)
Covalent compounds are called molecules Ionic compounds are never called
molecules.
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Diatomic Molecules are Formed by Covalent Bonds
H2 hydrogen
N2 nitrogen
O2 oxygen
F2 fluorine
Cl2 chlorine
Br2 bromine
I2 iodine
•There are 7 elements that form diatomic molecules•Formulas for these elements are always shown with subscript “2”
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Fig. 6-1, p. 137
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Examples• Write the formulas
• gold
• iodine• helium• nitrogen• oxygen• potassium
Au
I2
He
N2
O2
K
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Naming Compounds
• A compound is 2 or more elements bonded together
• The rules for naming covalent (nonmetal-nonmetal) compounds are different than the rules for ionic (metal-nonmetal) compounds
• Always check the periodic table to decide which rules to use.
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Molecular Compounds (Nonmetal-Nonmetal)
• We’ll only be naming binary molecular (nonmetal-nonmetal) compounds (made of 2 elements)
• The 1st word is the name of the 1st element• The 2nd word is the name of the 2nd element in
“ide” form• Use a prefix for the number.
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Prefixes in Molecular Compounds
• One: mono- • Two: di-• Three: tri-• Four: tetra-• Five: penta-
• Six: hexa-• Seven: hepta-• Eight: octa-• Nine: nona-• Ten: deca-
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Putting it all Together
• CO2 is a molecular compound
• The 1st word is the name of the 1st element: carbon (the prefix mono is omitted in the 1st word)
• The 2nd word is the 2nd element in “ide” form, with the prefix “di”
• The name is carbon dioxide.
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Examples
• Name these: NF3, S2Br4, CCl4, N2
• nitrogen trifluoride• disulfur tetrabromide• carbon tetrachloride• nitrogen
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Awkward Vowel Combinations
• When the combinations “ao” or “oo” appear, remove the first awkward vowel
• Example: SiO4 is silicon tetroxide
• Name P2O5, I2O, and SI2
• diphosphorus pentoxide• diiodine monoxide• sulfur diiodide
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Water and Ammonia
The name of H2O is water
The name of NH3 is ammonia.
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Sharing electrons between Different Nonmetals
Most nonmetals share electrons to reach 8 electrons
Except: H reaches 2e-s, B reaches 6 e-s e- dot formulas show how e-s are shared
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e- Dot Formulas
Electrons in covalent compounds exist as bonding pairs or as lone pairs
A bonding pair is 2 elctrons shared between 2 atoms A lone pair is a pair of electrons around the outside
of an atom
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e- Dot Formulas
Use this guide to help you connect the dots H gets 1 bond B gets 3 bonds C, Si get 4 bonds N, P get 3 bonds and 1 lone pair O, S get 2 bonds and 2 lone pairs F, Cl, Br, I get 1 bond and 3 lone pairs
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e- Dot Formulas
:: :
H B NC
Si:
P:
O::
S
::X
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e- Dot Formulas
X represents any halogen. Halogens get 1 bond and 3 lone pairs.
Halogens never get 2 bonds.
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Examples
Draw these molecules. Be careful about how many bonds and lone pairs each atom prefers to have.
BI3 SCl2 CH4
Cl
S
Cl
::
::
::: :
C
H
HH
H
:
B
I
II ::
::
::
: :
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Examples
Draw these molecules. Be careful about how many bonds and lone pairs each atom prefers to have.
BH3 H2O PCl3
B
H
HH
::
H
O
H
:
::
::
::
:
P
ClCl
Cl
::
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Double and Triple Bonds are also possible
Draw CO2 (C is in the center)
Draw CH2O (all atoms attached to C)
Draw N2
O C O
O
C
HH
::
N N: :
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VSEPR: Valence Shell Electron Pair Repulsion Theory
VSEPR Theory predicts the shapes of molecules
e- sets (bonds or lone pairs) get as far away from each other as possible
Geometry is determined around one atom at a time.
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VSEPR
One “set” is a lone pair or a single bond or a double bond or a triple bond
A single, double, or triple bond connects to a bonded atom (BA).
A lone pair (LP) is not bonded to anything
Molecular shapes use bonded atoms (BA) only.
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Ex: How many sets are around each indicated atom? How many bonded atoms and how many lone pairs?
Sets BA LP
a. 4 4 0
b. 3 3 0
c. 3 1 2
d. 4 3 1
e. 4 4 0
f. 2 2 0
g. 2 2 0
h. 4 2 2
CC
NC
C
C
O
H
H
H
H
O
H
H H
ab
c
d
e fg
h
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Fig. 12-1, p. 325
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Atoms with 2 Sets When an atom has 2 sets around it, e- repulsion
pushes the sets as far apart as possible from each other
The two sets will be 180o apart
The molecular shape is linear
O C O
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Fig. 12-2a, p. 325
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Atoms with 3 Sets When an atom has 3 sets around it, the 3 sets
will be 120o apart due to e- repulsion. When the 3 sets are bonded atoms, the
molecular shape is trigonal planar When 2 sets are BA and 1 set is an LP, the
molecular shape is bent.
B
H
HH
:
O
N
O:
:: :
:
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Fig. 12-2b, p. 325
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Atoms with 4 Sets When an atom has 4 sets around it, the 4 sets
will be 109.5o apart When the 4 sets are bonded atoms, the
molecular shape is tetrahedral When 3 sets are BA and 1 set is an LP, the
molecular shape is trigonal pyramidal When 2 sets are BA and 2 sets are LP, the
molecular shape is bent.
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Fig. 12-2c, p. 325
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Atoms with 4 Sets
In CH4, the shape is tetrahedral
In NH3, the shape is trigonal pyramidal
In H2O, the shape is bent
C
H
HH
H H
N
H
H
:
H
O
H
::
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Fig. 12-5, p. 328
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# e- sets
molecular shapebond angle
2 2BA: linear 180o
33BA: trigonal planar 120o
2BA, 1LP: bent <120o
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4BA: tetrahedral 109.5o
3BA, 1LP: trigonal pyramidal <109.5o
2BA, 2LP: bent <109.5o
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Electronegativity & Bond Polarity
Electronegativity is the ability to attract e-s The most electronegative element is F The closer on the periodic table to F, the
higher the electronegativity Electronegative elements “pull” e- density
towards themselves.
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Bond Polarity
You can show bond polarity in two ways, with partial charges or with polarity arrows
:: :H-F
:: :H-F
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Example For BCl3, draw partial charges on all the
atoms
For BCl3, draw polarity arrows next to all the bonds
Cl
B
ClCl
:
::
:
:
:
: ::
Cl
B
ClCl
:
::
::
:
: ::
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Electronegativity & Bond Polarity
There are 2 types of covalent bonds nonpolar covalent bonds polar covalent bonds
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Electronegativity & Bond Polarity
In a nonpolar covalent bond, the 2 nonmetal atoms are the same
In a polar covalent bond, the 2 nonmetal atoms are different.
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Electronegativity & Bond Polarity
Ex. Electronegativities (H=2.1, Cl=3.0) Is an H-H bond nonpolar covalent or
polar covalent? Is a Cl-Cl bond nonpolar covalent or
polar covalent? Is an H-Cl bond nonpolar covalent or
polar covalent?
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Polarity of Molecules
You determined whether a bond was polar covalent or nonpolar covalent
Using that information and the correct shapes, you can determine whether a whole molecule is polar or nonpolar.
Remember, polarity of bonds and polarity of molecules are different
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Review: Polarity of Bonds
Draw BF3 and NF3 in the correct shapes. Draw a polarity arrow next to each bond.
:
B
F
FF :::
:
::
: : :
::
F
N
F
F :
::
:
:: :
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Polarity of Molecules
To determine if a molecule is polar or nonpolar, add the polarity arrows.
The polarity arrows cancel (have no overall pull) in a nonpolar molecule
The polarity arrows demonstrate an overall pull in one direction in a polar molecule
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Polarity of Molecules Determine whether BF3 and NF3 are polar
or nonpolar.
:
B
F
FF ::
::
::
: : :
::
F
N
F
F :
::
::
: :
In BF3, the polarity arrows cancel. The molecule is nonpolar.In NF3, the arrows don’t cancel. There is overall pull and the molecule is polar.
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Notes on Polarity of Molecules
You must draw the structure in the correct shape to get polarity of molecules correct
Polarity of bonds is different than polarity of molecules
BF3 has polar covalent bonds, but BF3 is a nonpolar molecule
NF3 has polar covalent bonds and is a polar molecule.
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Notes on Polarity of Molecules
The size of the polarity arrow represents the relative difference in electronegativity
A B-F bond would have a bigger polarity arrow than a B-Cl bond
When polarity arrows cancel, both the size and direction are taken into account.
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Examples Draw CHCl3 and CCl4
What are the approx. bond angles? Which molecule contains nonpolar covalent
bonds? Which molecule contains polar covalent bonds? Which molecule is polar?
Cl
C
ClCl
Cl:
::
:
:
:
:
::
::
:
H
C
ClCl
Cl:
::
:
::
:
::
109.5o
neitherboth
CHCl3
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Fig. 12-10, p. 335
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Examples: Draw Each One and Answer the Questions
H2O CH3NH2 PCl3 C2H4
a) Does it contain nonpolar covalent bonds?
b) Does it contain polar covalent bonds?
c) Is the molecule or ion polar or nonpolar overall?
a) a) a) a)
b) b) b) b)
c) c) c) c)
:
::
Cl
P
Cl
Cl :
:::
:: :
no
polaryes
H
O
H
::
no
polaryes
C
H
NH
H
HH
:
no
polar
yes
C C
H
HH
H
nonpolaryes
yes