Chapter 7 “Ionic and Metallic Bonding”
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Transcript of Chapter 7 “Ionic and Metallic Bonding”
Chapter 7
“Ionic and Metallic Bonding”
Valence Electrons are…? The electrons responsible for the
chemical properties of atoms, and are those in the outer energy level.
Valence electrons - The s and p electrons in the outer energy level
–the highest occupied energy level Core electrons – are those in the
energy levels below.
Keeping Track of Electrons Atoms in the same column...
1) Have the same outer electron configuration.
2) Have the same valence electrons. The number of valence electrons are
easily determined. It is the group number for a representative element
Group 2A: Be, Mg, Ca, etc.
– have 2 valence electrons
Electron Dot diagrams are… A way of showing & keeping
track of valence electrons. How to write them? Write the symbol - it
represents the nucleus and inner (core) electrons
Put one dot for each valence electron (8 maximum)
They don’t pair up until they have to (Hund’s rule)
X
The Electron Dot diagram for Nitrogen
Nitrogen has 5 valence electrons to show.
First we write the symbol. NThen add 1 electron at a time to each side.Now they are forced to pair up.
We have now written the electron dot diagram for Nitrogen.
The Octet Rule In Chapter 6, we learned that noble gases
are unreactive in chemical reactions In 1916, Gilbert Lewis used this fact to
explain why atoms form certain kinds of ions and molecules
The Octet Rule: in forming compounds, atoms tend to achieve a noble gas configuration; 8 in the outer level is stableEach noble gas (except He, which has
2) has 8 electrons in the outer level
Formation of Cations Metals lose electrons to attain a noble
gas configuration. They make positive ions (cations) If we look at the electron configuration,
it makes sense to lose electrons: Na 1s22s22p63s1 1 valence electron Na1+ 1s22s22p6 This is a noble gas
configuration with 8 electrons in the outer level.
Electron Dots For Cations Metals will have few valence electrons
(usually 3 or less); calcium has only 2 valence electrons
Ca
Electron Dots For Cations Metals will have few valence electrons Metals will lose the valence electrons
Ca
Electron Dots For Cations Metals will have few valence electrons Metals will lose the valence electrons Forming positive ions
Ca2+NO DOTS are now shown for the cation.
This is named the “calcium ion”.
Electron Dots For CationsLet’s do Scandium, #21The electron configuration is:
1s22s22p63s23p64s23d1
Thus, it can lose 2e- (making it 2+), or lose 3e- (making 3+)
Sc = Sc2+ Scandium (II) ion Scandium (III) ion
Sc = Sc3+
Electron Dots For CationsLet’s do Silver, element #47Predicted configuration is:
1s22s22p63s23p64s23d104p65s24d9
Actual configuration is: 1s22s22p63s23p64s23d104p65s14d10
Ag = Ag1+ (can’t lose any more, charges of 3+ or greater are uncommon)
Electron Dots For CationsSilver did the best job it
could, but it did not achieve a true Noble Gas configuration
Instead, it is called a “pseudo-noble gas configuration”
Electron Configurations: Anions Nonmetals gain electrons to attain
noble gas configuration. They make negative ions (anions) S = 1s22s22p63s23p4 = 6 valence
electrons S2- = 1s22s22p63s23p6 = noble gas
configuration. Halide ions are ions from chlorine or
other halogens that gain electrons
Electron Dots For Anions Nonmetals will have many valence
electrons (usually 5 or more) They will gain electrons to fill outer shell.
P 3-(This is called the “phosphide ion”, and should show dots)
Stable Electron Configurations All atoms react to try and achieve a
noble gas configuration. Noble gases have 2 s and 6 p electrons. 8 valence electrons = already stable! This is the octet rule (8 in the outer level
is particularly stable).
Ar
Ionic Bonding Anions and cations are held together
by opposite charges (+ and -) Ionic compounds are called salts. Simplest ratio of elements in an ionic
compound is called the formula unit. The bond is formed through the
transfer of electrons (lose and gain) Electrons are transferred to achieve
noble gas configuration.
Ionic Compounds
1) Also called SALTS
2) Made from: a CATION with an ANION (or literally from a metal combining with a nonmetal)
Ionic Bonding
Na ClThe metal (sodium) tends to lose its one electron from the outer level.
The nonmetal (chlorine) needs to gain one more to fill its outer level, and will accept the one electron that sodium is going to lose.
Ionic Bonding
Na+ Cl -
Note: Remember that NO DOTS are now shown for the cation!
Ionic Bonding
All the electrons must be accounted for, and each atom will have a noble gas configuration (which is stable).
Ca P
Lets do an example by combining calcium and phosphorus:
Ionic Bonding
Ca P
Ionic Bonding
Ca2+ P
Ionic Bonding
Ca2+ P
Ca
Ionic Bonding
Ca2+ P 3-
Ca
Ionic Bonding
Ca2+ P 3-
Ca P
Ionic Bonding
Ca2+ P 3-
Ca2+ P
Ionic Bonding
Ca2+ P 3-
Ca2+ P
Ca
Ionic Bonding
Ca2+ P 3-
Ca2+ P
Ca
Ionic Bonding
Ca2+ P 3-
Ca2+P
3-
Ca2+
Ionic Bonding
= Ca3P2Formula Unit
This is a chemical formula, which shows the kinds and numbers of atoms in the smallest representative particle of the substance.
For an ionic compound, the smallest representative particle is called a: Formula Unit
Properties of Ionic Compounds1. Crystalline solids - a regular repeating
arrangement of ions in the solid: Fig. 7.9, page 197
– Ions are strongly bonded together.– Structure is rigid.
2. High melting points Coordination number- number of ions
of opposite charge surrounding it
- Page 198
Coordination Numbers:
Both the sodium and chlorine have 6
Both the cesium and chlorine have 8
Each titanium has 6, and each oxygen has 3
NaCl
CsCl
TiO2
Do they Conduct? Conducting electricity means allowing
charges to move. In a solid, the ions are locked in place. Ionic solids are insulators. When melted, the ions can move around.3. Melted ionic compounds conduct.
– NaCl: must get to about 800 ºC.– Dissolved in water, they also conduct
(free to move in aqueous solutions)
- Page 198
The ions are free to move when they are molten (or in aqueous solution), and thus they are able to conduct the electric current.
Metallic Bonds are…How metal atoms are held
together in the solid.Metals hold on to their valence
electrons very weakly.Think of them as positive ions
(cations) floating in a sea of electrons: Fig. 7.12, p.201
Sea of Electrons
+ + + ++ + + +
+ + + +
Electrons are free to move through the solid.
Metals conduct electricity.
Metals are MalleableHammered into shape (bend).Also ductile - drawn into wires.Both malleability and ductility
explained in terms of the mobility of the valence electrons
- Page 201
1) Ductility 2) Malleability
Due to the mobility of the valence electrons, metals have:
and
Notice that the ionic crystal breaks due to ion repulsion!
Malleable
+ + + ++ + + +
+ + + +
Force
Malleable
+ + + +
+ + + ++ + + +
Mobile electrons allow atoms to slide by, sort of like ball bearings in oil.
Force
Ionic solids are brittle
+ - + -+- +-
+ - + -+- +-
Force
Ionic solids are brittle
+ - + -
+- +-+ - + -
+- +-
Strong Repulsion breaks a crystal apart, due to similar ions being next to each other.
Force
Crystalline structure of metal If made of one kind of atom,
metals are among the simplest crystals; very compact & orderly
Note Fig. 7.14, p.202 for types:1. Body-centered cubic:
–every atom (except those on the surface) has 8 neighbors
–Na, K, Fe, Cr, W
Crystalline structure of metal2. Face-centered cubic:
–every atom has 12 neighbors
–Cu, Ag, Au, Al, Pb
3. Hexagonal close-packed
–every atom also has 12 neighbors
–different pattern due to hexagonal
–Mg, Zn, Cd
Alloys We use lots of metals every day,
but few are pure metals Alloys are mixtures of 2 or more
elements, at least 1 is a metal made by melting a mixture of the
ingredients, then cooling Brass: an alloy of Cu and Zn Bronze: Cu and Sn
Why use alloys? Properties are often superior to the pure
element Sterling silver (92.5% Ag, 7.5% Cu) is
harder and more durable than pure Ag, but still soft enough to make jewelry and tableware
Steels are very important alloys
– corrosion resistant, ductility, hardness, toughness, cost
More about Alloys… Table 7.3, p.203 – lists a few alloys Types? a) substitutional alloy- the
atoms in the components are about the same size
b) interstitial alloy- the atomic sizes quite different; smaller atoms fit into the spaces between larger
“Amalgam”- dental use, contains Hg
Atoms and Ions - Naming Atoms are electrically neutral.
– Because there is the same number of protons (+) and electrons (-).
Ions are atoms, or groups of atoms, with a charge (positive or negative)– They have different numbers of protons
and electrons. Only electrons can move, and ions
are made by gaining or losing electrons.
An Anion is… A negative ion. Has gained electrons. Nonmetals can gain electrons. Charge is written as a superscript on
the right.
F1-Has gained one electron (-ide is new ending = fluoride)
O2- Gained two electrons (oxide)
A Cation is… A positive ion. Formed by losing electrons. More protons than electrons. Metals can lose electrons
K1+ Has lost one electron (no name change for positive ions)
Ca2+ Has lost two electrons
Predicting Ionic ChargesGroup 1AGroup 1A:: Lose 1 electron to form Lose 1 electron to form 1+1+ ions ions
HH11++ LiLi11++ NaNa11++ KK11++ RbRb11++
Predicting Ionic ChargesGroup 2AGroup 2A:: Loses 2 electrons to form Loses 2 electrons to form 2+2+ ions ions
BeBe2+2+ MgMg2+2+ CaCa2+2+ SrSr2+2+ BaBa2+2+
Predicting Ionic ChargesGroup 3AGroup 3A:: Loses 3 Loses 3
electrons to form electrons to form 3+3+ ions ions
BB3+3+ AlAl3+3+ GaGa3+3+
Predicting Ionic ChargesGroup 4AGroup 4A:: Do they Do they loselose 4 electrons or 4 electrons or gaingain 4 electrons? 4 electrons?
Neither! Neither! Group 4A Group 4A elements rarely form elements rarely form
ions ions (they (they tend to tend to share)share)
Predicting Ionic ChargesGroup 5AGroup 5A:: Gains 3 Gains 3 electrons to form electrons to form 3-3- ions ions
NN3-3-
PP3-3-
AsAs3-3-
Nitride
Phosphide
Arsenide
Predicting Ionic ChargesGroup 6AGroup 6A:: Gains 2 Gains 2 electrons to form electrons to form 2-2- ions ions
OO2-2-
SS2-2-
SeSe2-2-
Oxide
Sulfide
Selenide
Predicting Ionic ChargesGroup 7AGroup 7A:: Gains 1 Gains 1 electron to form electron to form 1-1- ions ions
FF1-1-
ClCl1-1-
BrBr1-1-Fluoride
Chloride
Bromide
II1-1- Iodide
Predicting Ionic ChargesGroup 8AGroup 8A:: Stable Stable noble gases noble gases do notdo not form ions!form ions!
Predicting Ionic ChargesGroup B elementsGroup B elements:: Many Many transitiontransition elements elements
have have more than onemore than one possible oxidation state. possible oxidation state.Iron (II) = Fe2+
Iron (III) = Fe3+
Note the use of Roman numerals to show charges
Naming cations Two methods can clarify when
more than one charge is possible:
1) Stock system – uses roman numerals in parenthesis to indicate the numerical value
2) Classical method – uses root word with suffixes (-ous, -ic)• Does not give true value
Naming cations We will use the Stock system. Cation - if the charge is always the
same (like in the Group A metals) just write the name of the metal.
Transition metals can have more than one type of charge.– Indicate their charge as a roman
numeral in parenthesis after the name of the metal (Table 9.2, p.255)
Predicting Ionic Charges Some of the Some of the post-transitionpost-transition elements also elements also have have more than onemore than one possible oxidation state. possible oxidation state.Tin (II) = Sn2+ Lead (II) = Pb2+
Tin (IV) = Sn4+ Lead (IV) = Pb 4+
Predicting Ionic ChargesGroup B elementsGroup B elements:: Some Some transitiontransition elements elements have have only oneonly one possible oxidation state, such possible oxidation state, such as these three:as these three:
Zinc = Zn2+Silver = Ag1+ Cadmium = Cd2+
Exceptions:Some of the transition metals
have only one ionic charge:
–Do not need to use roman numerals for these:
–Silver is always 1+ (Ag1+)
–Cadmium and Zinc are always 2+ (Cd2+ and Zn2+)
Practice by naming these: Na1+ Ca2+ Al3+ Fe3+ Fe2+ Pb2+ Li1+
Write symbols for these:
Potassium ionMagnesium ion Copper (II) ionChromium (VI) ionBarium ionMercury (II) ion
Naming AnionsAnions are always the
same chargeChange the monatomic
element ending to – ideF1- a Fluorine atom will
become a Fluoride ion.
Practice by naming these:Cl1- N3- Br1- O2-
Ga3+
Write symbols for these:
Sulfide ionIodide ionPhosphide ionStrontium ion
Polyatomic ions are… Groups of atoms that stay together and
have an overall charge, and one name. Usually end in –ate or -ite
Acetate: C2H3O21-
Nitrate: NO31-
Nitrite: NO21-
Permanganate: MnO41-
Hydroxide: OH1- and Cyanide: CN1-?
Sulfate: SO42-
Sulfite: SO32-
Carbonate: CO32-
Chromate: CrO42-
Dichromate: Cr2O72-
Phosphate: PO43-
Phosphite: PO33-
Ammonium: NH41+
Know Table 9.3 on page 257
If the polyatomic ion begins with H, then combine the word hydrogen with the other polyatomic ion present: H1+ + CO3
2- → HCO3
1-
hydrogen + carbonate → hydrogen carbonate ion
(One of the few positive polyatomic ions)
Writing Ionic Compound Formulas
Example: Barium nitrate (note the 2 word name)
1. Write the formulas for the cation and anion, including CHARGES!
BaBa2+2+ NONO33--
2. Check to see if charges are balanced. 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance subscripts.
Not balanced!
( )( ) 22
Now balanced.
= Ba(NO3)2
Writing Ionic Compound Formulas
Example: Ammonium sulfate (note the 2 word name)
1. Write the formulas for the cation and anion, including CHARGES!
NHNH44++ SOSO44
2-2-
2. Check to see if charges are balanced.
3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance the subscripts.
Not balanced!
( )( )22
Now balanced.
= (NH4)2SO4
Writing Ionic Compound Formulas
Example: Iron (III) chloride (note the 2 word name)
1. Write the formulas for the cation and anion, including CHARGES!
FeFe3+3+ClCl--
2. Check to see if charges are balanced.
3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance the subscripts.
Not balanced!
33
Now balanced.= FeCl3
Writing Ionic Compound Formulas
Example: Aluminum sulfide (note the 2 word name)
1. Write the formulas for the cation and anion, including CHARGES!
AlAl3+3+ SS2-2-
2. Check to see if charges are balanced.
3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance the subscripts.
Not balanced!
22 33
Now balanced.= Al2S3
Writing Ionic Compound Formulas
Example: Magnesium carbonate (note the 2 word name)1. Write the formulas for the cation and anion, including CHARGES!
MgMg2+2+ COCO332-2-
2. Check to see if charges are balanced.
They are balanced!
= MgCO3
Writing Ionic Compound Formulas
Example: Zinc hydroxide (note the 2 word name)
1. Write the formulas for the cation and anion, including CHARGES!
ZnZn2+2+ OHOH--
2. Check to see if charges are balanced. 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance the subscripts.
Not balanced!
( )( )22
Now balanced.= Zn(OH)2
Writing Ionic Compound Formulas
Example: Aluminum phosphate (note the 2 word name)
1. Write the formulas for the cation and anion, including CHARGES!
AlAl3+3+ POPO443-3-
2. Check to see if charges are balanced.
They ARE balanced!
= AlPO4
Naming Ionic CompoundsNaming Ionic Compounds 1. Name the cation first, then anion
2. Monatomic cation = name of the element
Ca2+ = calcium ion
3. Monatomic anion = root + -ide
Cl = chloride
CaCl2 = calcium chloride
Naming Ionic CompoundsNaming Ionic Compounds
some metals can form more than one charge (usually the transition metals)
use a Roman numeral in their name:
PbCl2 – use the anion to find the charge
on the cation (chloride is always 1-)
Pb2+ is the lead (II) cation
PbCl2 = lead (II) chloride
(Metals with multiple oxidation states)(Metals with multiple oxidation states)
Things to look for:
1) If cations have ( ), the number in parenthesis is their charge.
2) If anions end in -ide they are probably off the periodic table (Monoatomic)
3) If anion ends in -ate or –ite, then it is polyatomic
Practice by writing the formula or name as required…
Iron (II) PhosphateStannous FluoridePotassium SulfideAmmonium ChromateMgSO4
FeCl3