Ionic, Covalent and Metallic Bonding modified from Stephen L. Cotton.
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Transcript of Ionic, Covalent and Metallic Bonding modified from Stephen L. Cotton.
“Ionic, Covalent and Metallic Bonding”
modified from
Stephen L. Cotton
Valence Electrons are…? electrons in the outer energy level. Responsible for properties of
elements Valence electrons - The s and p
electrons in 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 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)
16
Bonds are…Bonds are… Forces that hold groups of Forces that hold groups of
atoms together and make them atoms together and make them function as a unit. Two types:function as a unit. Two types:
1)1) Ionic bondsIonic bonds – – transfertransfer of of electrons electrons (gained or lost; makes (gained or lost; makes formula unitformula unit))
2)2) Covalent bondsCovalent bonds – – sharingsharing of of electrons. The resulting electrons. The resulting particle is called a particle is called a ““moleculemolecule””
17
Covalent BondsThe word covalent is a
combination of the prefix co- (from Latin com, meaning “with” or “together”), and the verb valere, meaning “to be strong”.
Two electrons shared together have the strength to hold two atoms together in a bond.
18
MoleculesMolecules Many elements found in nature
are in the form of molecules: a neutral group of atoms joined
together by covalent bonds. For example, air contains oxygen For example, air contains oxygen
molecules, consisting of two molecules, consisting of two oxygen atoms joined covalentlyoxygen atoms joined covalently
Called a “Called a “diatomicdiatomic molecule molecule” (O” (O22))
19
How does H2 form?
The nuclei repel each other, since they both have a positive charge (like charges repel).
++
(diatomic hydrogen molecule)
+ +
20
How does H2 form?
++
But, the nuclei are attracted to the electrons
They share the electrons, and this is called a “covalent bond”, and involves only NONMETALS!
21
Covalent bondsNonmetals hold on to their valence
electrons. They can’t give away electrons to bond.
–But still want noble gas configuration. Get it by sharing valence electrons with
each other = covalent bonding By sharing, both atoms get to count
the electrons toward a noble gas configuration.
22
Covalent bonding Fluorine has seven valence
electrons (but would like to have 8)
F
23
Covalent bonding Fluorine has seven valence
electrons A second atom also has seven
F F
24
Covalent bonding Fluorine has seven valence
electrons A second atom also has seven By sharing electrons…
F F
25
Covalent bonding Fluorine has seven valence
electrons A second atom also has seven By sharing electrons…
F F
26
Covalent bonding Fluorine has seven valence
electrons A second atom also has seven By sharing electrons…
F F
27
Covalent bonding Fluorine has seven valence
electrons A second atom also has seven By sharing electrons…
F F
28
Covalent bonding Fluorine has seven valence
electrons A second atom also has seven By sharing electrons…
F F
29
Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons…
…both end with full orbitals
F F
30
Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons… …both end with full orbitals
F F8 Valence electrons
31
Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons… …both end with full orbitals
F F8 Valence electrons
32
33
Molecular Compounds The formula for water is written as
H2O–The subscript “2” behind hydrogen
means there are 2 atoms of hydrogen; if there is only one atom, the subscript 1 is omitted
Molecular formulas do not tell any information about the structure (the arrangement of the various atoms).
34
- Page 215
These are some of the different ways to represent ammonia:
1. The molecular formula shows how many atoms of each element are present
2. The structural formula ALSO shows the arrangement of these atoms!
3. The ball and stick model is the BEST, because it shows a 3-dimensional arrangement.
35
A Single Covalent Bond is... A sharing of two valence electrons. Only nonmetals and hydrogen. Different from an ionic bond
because they actually form molecules.
Two specific atoms are joined. In an ionic solid, you can’t tell which
atom the electrons moved from or to
36
Water
H
O
Each hydrogen has 1 valence electron
- Each hydrogen wants 1 more
The oxygen has 6 valence electrons
- The oxygen wants 2 more They share to make each
other complete
37
Water Put the pieces together The first hydrogen is happy The oxygen still needs one more
H O
38
Water So, a second hydrogen attaches Every atom has full energy levels
H OH
Note the two “unshared” pairs of electrons
39
Multiple Bonds Sometimes atoms share more than
one pair of valence electrons. A double bond is when atoms share
two pairs of electrons (4 total) A triple bond is when atoms share
three pairs of electrons (6 total) Table 8.1, p.222 - Know these 7
elements as diatomic:
Br2 I2 N2 Cl2 H2 O2 F2 What’s the deal with the oxygen dot diagram?
40
Dot diagram for Carbon dioxide CO2 - Carbon is central
atom ( more metallic ) Carbon has 4 valence
electrons Wants 4 more Oxygen has 6 valence
electrons Wants 2 more
O
C
41
Carbon dioxide Attaching 1 oxygen leaves the
oxygen 1 short, and the carbon 3 short
OC
42
Carbon dioxide Attaching the second oxygen
leaves both of the oxygen 1 short, and the carbon 2 short
OCO
43
Carbon dioxide The only solution is to share more
OCO
44
Carbon dioxide The only solution is to share more
OCO
45
Carbon dioxide The only solution is to share more
OCO
46
Carbon dioxide The only solution is to share more
OCO
47
Carbon dioxide The only solution is to share more
OCO
48
Carbon dioxide The only solution is to share more
OCO
49
Carbon dioxide The only solution is to share more Requires two double bonds Each atom can count all the
electrons in the bond
OCO
50
Carbon dioxide The only solution is to share more Requires two double bonds Each atom can count all the electrons in
the bond
OCO8 valence electrons
51
Carbon dioxide The only solution is to share more Requires two double bonds Each atom can count all the electrons in
the bond
OCO8 valence electrons
52
Carbon dioxide The only solution is to share more Requires two double bonds Each atom can count all the electrons in
the bond
OCO
8 valence electrons
53
HCN Put single bond between each atom Need to add 2 more bonds Must go between C and N (Hydrogen is full)
NH C
54
HCN Put in single bonds Needs 2 more bonds Must go between C and N, not the H Uses 8 electrons – need 2 more to
equal the 10 it has
NH C
55
HCN Put in single bonds Need 2 more bonds Must go between C and N Uses 8 electrons - 2 more to add Must go on the N to fill its octet
NH C
56
A Coordinate Covalent Bond... When one atom donates both
electrons in a covalent bond. Carbon monoxide (CO) is a good
example:
OCBoth the carbon and oxygen give another single electron to share
57
Coordinate Covalent Bond When one atom donates both
electrons in a covalent bond. Carbon monoxide (CO) is a good
example:
OC
Oxygen gives both of these electrons, since it has no more singles to share.
This carbon electron moves to make a pair with the other single.
58
Coordinate Covalent Bond When one atom donates both
electrons in a covalent bond. Carbon monoxide (CO)
OCC O
The coordinate covalent bond is shown with an arrow as:
59
Resonance is... When more than one valid dot
diagram is possible. Consider the two ways to draw ozone
(O3) Which one is it? Does it go back and
forth? It is a hybrid of both, like a mule; and
shown by a double-headed arrow found in double-bond structures!
60
Resonance in OzoneResonance in Ozone
Neither structure is correct, it is actually a hybrid of the two. To show it, draw all varieties possible, and join them with a double-headed arrow.
Note the different location of the double bond
61
ResonanceResonanceOccurs when more than one valid Lewis structure can be written for a particular molecule (due to position of double bond)
•These are resonance structures of benzene.•The actual structure is an average (or hybrid) of these structures.
62
Resonance in a carbonate ion (CO3
2-):
Resonance in an acetate ion (C2H3O2
1-):
Polyatomic ions – note the different positions of the double bond.
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