Ionic, Covalent and Metallic Bonding modified from Stephen L. Cotton.

transcript

“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)

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

Electron Dots For Cations Metals will have few valence electrons Metals will lose the valence electrons

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)

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””

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.

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))

How does H2 form?

The nuclei repel each other, since they both have a positive charge (like charges repel).

(diatomic hydrogen molecule)

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!

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.

Covalent bonding Fluorine has seven valence

electrons (but would like to have 8)

electrons A second atom also has seven

electrons A second atom also has seven By sharing electrons…

Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons…

…both end with full orbitals

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

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

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).

- 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.

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

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

Water Put the pieces together The first hydrogen is happy The oxygen still needs one more

Water So, a second hydrogen attaches Every atom has full energy levels

Note the two “unshared” pairs of electrons

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?

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

Carbon dioxide Attaching 1 oxygen leaves the

oxygen 1 short, and the carbon 3 short

Carbon dioxide Attaching the second oxygen

leaves both of the oxygen 1 short, and the carbon 2 short

Carbon dioxide The only solution is to share more

Carbon dioxide The only solution is to share more Requires two double bonds Each atom can count all the

electrons in the bond

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

the bond

OCO8 valence electrons

the bond

8 valence electrons

HCN Put single bond between each atom Need to add 2 more bonds Must go between C and N (Hydrogen is full)

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

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

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

Coordinate Covalent Bond When one atom donates both

electrons in a covalent bond. Carbon monoxide (CO) is a good

example:

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.

Coordinate Covalent Bond When one atom donates both

electrons in a covalent bond. Carbon monoxide (CO)

The coordinate covalent bond is shown with an arrow as:

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!

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

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.

Resonance in a carbonate ion (CO3

Resonance in an acetate ion (C2H3O2

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).

Lets do an example by combining calcium and phosphorus:

Ionic Bonding

Ca2+ P

Ionic Bonding

Ca2+ P

Ionic Bonding

Ca2+ P 3-

Ionic Bonding

Ca2+ P 3-

Ionic Bonding

Ca2+ P 3-

Ca2+ P

Ionic Bonding

Ca2+ P 3-

Ca2+ P

Ionic Bonding

Ca2+ P 3-

Ca2+ P

Ionic Bonding

Ca2+ P 3-

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

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:

Notice that the ionic crystal breaks due to ion repulsion!

Malleable

+ + + ++ + + +

+ + + +

Malleable

+ + + +

+ + + ++ + + +

Mobile electrons allow atoms to slide by, sort of like ball bearings in oil.

Ionic solids are brittle

+ - + -+- +-

Ionic solids are brittle

+ - + -

+- +-+ - + -

Strong Repulsion breaks a crystal apart, due to similar ions being next to each other.

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

Ionic, Covalent and Metallic Bonding modified from Stephen L. Cotton.

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