chem bonding14

A: to be happy (stable)… atoms are social creatures. Some share, some take but there is almost always interaction… ok, so they are not really social but they do need to be stable

To be Happy is to be stable… to be stable is to have a full valence shell

All bonds form due to some level of electrostatic attraction:

Attractive force is proportional to: (+ q) (- q)

+ q = magnitude of the positive charge - q = magnitude of the negative charge r2 = distance between the charges Bigger charges means stronger bonds Charges that are closer together are stronger, farther apart

is weaker bond

r2

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Cl2 Chlorine gas is very toxic Na is a highly explosive metal, even in

water

But Na + Cl2 makes NaCl which is table salt.

So we take a poison gas and an explosive metal, react them, and then put it on our food.

How is this possible? Because they become STABLE

Atoms tend to gain, lose or share electrons in their valence shells in order to have a full electron valence shell. This is usually 8 electrons, hence the octet rule

When atoms valence shells are full, they are stable, and “happy”

Note that these are trends… THERE ARE ALWAYS EXCEPTIONS

One quick note: Transition metals seem to be a major exception to the octet rule. That is because when they form ions, they tend to lose e- from their outer s orbital first then as many as necessary d orbital e- to be stable… This is counter intuitive as it requires more energy to hold e- in the lower d orbital due to its angular momentum. This is why so many have more than one oxidation number

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Reactions which require energy from their environment to occur are Endothermic

Reactions which release a net amount of energy into the environment are Exothermic

Note: this energy is almost always in the form of heat, but is sometimes electrochemical (release or require electron flow) or chemiluminescent (require or release of light)

A bond formed between 2 or more atoms, by the sharing, or transfer of 1 or more electrons in order to satisfy the octet rule

Important note: All chemical bonding occurs in the valence shell electrons (VSE). That is those electrons that are found in the outer most shell

Whenever elements come in contact with each other, they compete for electrons all based on electronegativity: the ability of an atom to take and hold electrons. The results are chemical bonds

A: because the Valence shell electrons (VSE) are getting closer to the nucleus, so the attraction is greater

Electron shielding does not allow this to be perfect increase

A: because there are more protons in the nucleus so the positive force is greater

Again, Electron shielding does not allow this to be perfect increase

BY FAR, as the electrons get closer the attractive force gets greater. This has a far greater impact than simply adding a proton to the nucleus

Ionic Covalent

◦ (to a lesser extent) hydrogen Metallic

A bond formed from a SEQUENTIAL transfer of electrons and electrostatic attraction. The sequence:

1) Transfer of one or more electrons 2) Ion formation 3) Attraction

More highly charged ions will form stronger bonds (+3 and -3 is stronger than +1

and -1) Also those ions that are smaller in radius

will form stronger bonds than those that are larger in radius (Na+1 and Cl-1 will form a stronger bond than Rb+1 and Br-1)

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NaCl or LiF

CuO or CuCl

MnP or ZnO

CaBr2 or CaF2

For ANY bond , ionic character is determined by finding the difference in electronegativity between the two elements (regardless of how many of each)

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Tend to occur between metals and nonmetals (some occur between nonmetals and polyatomic ions)

Always occur between oppositely charged particles (called ions)

Tend to be VERY polar compounds Result as a difference in electronegativity

Usually dissociate easily in water, but remain stable ions

Usually good conductors of electricity in water, BUT NOT conductors of electricity as a solid

Tend to be brittle compounds with significant (and identifiable) crystalline structures, called lattices

1) Electrons are transferred: Na loses one electron and becomes positive

Na --------> Na+ + (Cation)

2) Ions form:Cl gains one electron and becomes negative

Cl + -------> Cl -1 (Anion)

Na atom single valence electron

Sodiums lost VSE transferred to Cl

Ions are now attracted to each other because of the opposite charge

Na+ + Cl -1 -------> Na Cl Notice how the positive one and negative one charges are

neutralized by each other, yet the compound itself is very polar

(+)NaCl(-)

Electrostatic attraction: Based on Coulomb's law, which describes attraction of oppositely charged forces AP

Oppositely charged ions are strongly attracted to each other but the compound is very polar: Referring to oppositely charged (poles) of force.

If referenced correctly an atom is the neutral (but not necessarily stable form of an element) such as ◦ Mg or Cl

Ion ALWAYS refers to a charged form of an atom or polyatomic ion such as ◦ Mg+2 or Cl- or NO3

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animation

Notice when the VSE is transferred, the Na radius shrinks

When anions form from neutral atoms they actually get a little bigger because of the natural repulsion of el-

When cations form from neutral atoms, they get smaller because there are less electrons to repel each other AND because if the cation is stable it has shrunk to the next shell down

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Atomic: Single atoms with positive or negative charges- These can be found using the oxidation numbers on the periodic table

Polyatomic: 2 or more atoms bound together (usually covalently) acting together as an ion:

List of polyatomic ions (list is at top of link and also on next slide)

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Cations: Positively charged ions

Anions: Negatively charged ions

In atoms this is the charge an ion acquires after it becomes stable (these are sometimes referred to as ionic charges)… results from ionization process

Tendencies: Elements in groups tend to have common oxidation numbers in ionic compounds

GroupIA tend to be +1IIA tend to be +2VIIA tend to be -1VIA (nonmetals) tend to be -2 (ionic)VA (nonmetals) tend to be -3 (ionic)IVA (nonmetals) tend to be -4 (ionic)Boron tends to be +5 (ionic)Most transition metals can have more than one

Most transition metals can have more than one O.N. (refer to periodic tables)

Some very common transition metals have only one O.N. and you will need to know these: Ag=+1, Zn=+2, Al=+3

As a rule ions will arrange themselves to become a neutral compound

Ions possessing the same number of electrons…

N-3, O-2, F-1, Mg+2

These all have 10 electrons like the stable neon atom: 1S2, 2S2, 2P6

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A: yes, a wonderful place called the periodic table

Many elements have more than one ON

Click interactive table to find incredible amounts of information about all elements including oxidation numbers

Now that Ionic is over with, we get to the easy stuff!

Here elements, play nice and share valence shell electrons to become stable (satisfy the octet rule) and “happy”

Theoretically a nonmetal can form as many shared bonds as it has electrons in its valence shell

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Always occur between nonmetals Often form diatomic and sometimes polyatomic bonds

between atoms of the same element: O2 or O3

List of Diatomic molecules: H2, N2, O2, F2, Cl2, Br2, I2 This is how they naturally occur… free state

Tend to be very low and even NON-polar, and are therefore referred to as molecules (covalently bonded groups of atoms which tend to be mostly or completely neutral as a group)

Bond is very strong and can be single, double or triple bond

The first covalent BOND formed is called a sigma bond (all single-bonded molecules are sigma bonds)

Additional bonds between the SAME atoms are called Pi bonds

2 pi bond plus a sigma bond (triple bond) is the strongest and shortest

1 pi bond plus a sigma (double) is not quite as strong but not as short

A sigma (single) bond is weakest and longest

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Tend to be soft powders, liquids or gases at room temperature

Tend to have low melting points* points Do not dissociate easily in water Are not good conductors of electricity in

water

*Melting point: Point at which a pure substance goes from solid to liquid

Ionic compounds are always considered very polar

In general, the greater the ionic character, the greater the polarity

Covalent compounds are only nonpolar if they are exactly the same element, since one is not more electronegative than the other

Covalent compounds made of differing elements will have some polarity. The more electronegative element will exert more attraction to the valence electrons… keeping them more to one side of a molecule than another: we will discuss this later: intermolecular force

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Take note that in each of the following shared bonds, by sharing, they satisfy the octet rule and hence are stable

Exception: Hydrogen only needs 2 to have a full valence shell, but it is still stable at 2

single

H2 H2O

Oxygen gas O2 CO2

Nitrogen gas N2 6 shared electrons

As you might expect:◦ Single bond: weak◦ Double bond: stronger◦ Triple Bond: Strongest

Good conductor of heat Good conductor of electricity Many are highly malleable Many are highly ductile Many are hard and shiny

The bond itself forms as relatively fixed-position cations are surrounded by free-floating electrons. The free floating electrons are called the “sea of electrons.” As they surround the cations, they act as a flowing “glue” to hold the cations together but still give them the ability to flex and stretch without necessarily breaking… think of it like a Rice-Crispy treat…

Positive nucleii are

the rice Crispies

Free-floating

electrons are the

marshmallow “goo”

A blending of 2 or more metals or metal and Nonmetal NON-IONICALLY which leads to a new metal with different chemical and or physical characteristics

Many react with acids to produce salt and H2 gas

Oxidize fairly easily in presence of water or oxygen

Tend to form cations Some metals are more reactive than others

in a very predictable manner: see activity series on next frame

An important way to illustrate the process of bonding… particularly for covalent bonding

Process:◦ Count the total VSE◦ Adjust based on the charge of the molecule (PAI)◦ Design the structure with least EN element or the single

element in the middle◦ Start pairing up electrons (start with single bonds) between

bonds then place extra outside (starting with the central one) to satisfy the octet rule.

◦ Adjust the numbers in between the bonds to satisfy the octet rule

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1) Must be that correct number of e- 2) Must satisfy the octet rule 3) When there are more than one possible

structure that satisfy number 1 and 2 above, then use formal charge

CO3-2

Carbon: 4 = 4 Oxygen: 6 x 3 = 18 -2 charge means that there are 2 extra e-

Total: 24

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O

Are there 24 e- below? AND is the octet rule satsified?

O

O

C

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So we double bond one oxygen with the carbon:

Now the octet rule is satisfied AND there are 24 e-… You could put the double bond on any of the Oxygens… this means that this has resonance forms

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O

O

O

C

Used as a tool to help determine the best Lewis structure

When several Lewis structures are possible, the most stable one will be the one that:◦ Atoms have the smallest formal charges AND◦ Any negative charges are on the more EN atoms

1) All lone e- are assigned to that atom 2) Half of the bonding e- are assigned to it

Subtract the assigned e- from the ATOMS valence e-

The formal charges of all atoms should equal the compounds total charge

What is the formal charge of each of these Lewis dot structures?

Formal charge will equal molecular charge… if 0 then the formal charge should be 0… if -2 than it should be -2, etc

These are simple different forms of the same molecule

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Those elements that can be stable with less than 8 electrons. EG: H:2, Be (hydride):4, Li(hydride): 2B (freak): 6

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Atoms that have d subshells available, the central atom can have MORE than 8 electrons

Eg: PCl5

SF4

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There are some odd times when there is an odd number of e- in the valence shell… usually with nitrogen:

N O

N

O O

NO2 Has 2 resonance forms

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Valence shell electron pair repulsion model◦ Molecules with more than 2 atoms can have

varying shapes and are dictated by the electron pairs, regardless if they are in the bond or lone

◦ Each pair of electrons manifests a negative charge called an electron domain that repels other electrons which changes the molecular shape

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The best arrangement of a given number of electrons is the one that minimizes the repulsion among them

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Electron domain geometry: The arrangement of bonding or lone electron pairs around central atom ( a domain can be 1, 2, or 3 e- pairs in a bond)

Molecular geometry: the arrangement of the atoms which attach to the electrons around the central atom… Molecular shape as a result of the electron geometry

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1) diagram the Lewis dots model 2) count the e- domains and arrange them

in a way that minimizes the repulsion 3) Describe the geometry

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Table of molecular and electron pair geometry

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Orbitals around central atom which come from the combining of orbitals of differing atoms electrons…

SP orbitals

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1) Do the Lewis structure first2) Count the number of high density electron

areas (2 or more electrons, bonded or lone)

3) Each area represents an sp orbital

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A) SO2

B) NO3-

C) PCl3

Work these out

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A molecule has d2sp3 hybrid orbital… how many areas of high density electrons are there…

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d2=2 sp3=4

4+ 2 = 6

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Fundamental attractions between molecules… are weaker than intramolecular: Ionic, covalent, metallic

When there is a difference in EN of atoms in the same moment, it creates a dipole The side where electrons spend most of their time becomes partially negative compared with the other side which becomes partially positive

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The polarity of molecules is measured in the dipole moment. The larger the dipole moment the more polar the molecule is.

If the EN differential is greater on the two ends of the molecule then the dipole moment is greater

Also, the greater the distance between the charges, also the greater the value of the dipole moment

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Delta used for partial charge

Similar to the dipole-dipole attraction of molecules (although this is stronger than dipole-dipole). The positive hydrogen part of a molecule (like water) is attracted to the negative portion of another molecule which contains a highly electronegative element like F, O, N.

These have higher MP than dipole-dipole attractions because they are a stronger bond

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Fundamental attraction between neutral nonpolar molecules

Occurs because e- move randomly and at any instant there may be more on one side of a molecule than on the other, giving it momentary polarity

This is a temporary nonshielding by the electrons moving out of the way

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An attractive force between molecules often (not always) generated by (weak) partial polarity such as in water. Tutorial

Intermolecular bond: Here the delta (partial

charge0 is greater than dipole-dipole attraction

Intermolecular: Van DER Waals forces: dipole-dipole

Hydrogen London dispersion

Intramolecular: ionic, covalent, Metallic

Intramolecular is always stronger than intermolecular force

There are rules which vary slightly for Ionic and covalent compounds formula writing… fortunately the only rule for writing metallic formulas is the metal itself

Almost always write the cation (not the atom) first and the anion (not the atom) second

Mg+2Cl-1 (Note: Sometimes you will only see + or – next to the ion. It is an implied value of +1 or -1)

Now some basic math skills: Q: How many -1 charges are required to cancel out a +2

and make the net 0? A: 2

MgCl2 So for every Magnesium, there is 2 Chlorine

because we need 2 Chlorine ions to cancel out 1 Magnesium ion and make the whole thing neutral

Write the resulting formula for K and N Write ions: K+1N-3

It takes 3 positive ones to cancel out a negative three, so we need 3 K and 1 N

Result: K3N

There is a quick correlation here… do you see it?... See how the number 3 went from the N to the K?

Shortcut to follow…

Simply eliminate the charge signs, criss-cross the numbers down and simplify

K+1N-3

K3N Obviously there is no reason to show

the 1 from the K… That’s like saying 1X in algebra

Ca+2 S-2

◦ Ca2S2 should simplify to ◦ CaS◦ Don’t forget to simplify

Ba+2 N-3

◦ Ba3N2

◦ Done, since you can not simplify this any further

Same process

NH4+Cl-

NH4Cl

Treat Polyatomic ions as if they were their own element… don’t change them… just add more

Calcium ion and Phosphate Polyatomic ion Ca+2PO4

-3

Ca3(PO4)2

Notice how we used parenthesis around the polyatomic ion to multiply the phosphate to the number we needed?

UNLESS otherwise directed, do NOT change the polyatomic ion

Ammonium ion and Sulfate ion NH4

+SO4-2

What did you get? (NH4)2SO4

Covalent:

For all intent and purpose, you can use the same method as ionic. When two nonmetals bond to each other ONE possible formula can be made by criss-crossing. The more electronegative element will be Partially negative and the less electronegative element will be partially positive

By using the criss-cross method and simplifying you canDetermine ONE form of the covalent compound, although this compound doesn’t form the same way as ionic.

Trouble is, that since there single, double, and triple bondsThey can combine in different ways

Example

C + O

C+4 O-2

C2O4simplify

CO2 This is one form of carbon and oxygen but they also exist as just CO. CO has completely different physical characteristics than CO2

Covalent bonds are formed in necessary ratios to share electrons and satisfy the octet rule… the math is really tough!

If you can subtract single digits you should be OK

Ready?

Best to use an example to explain:

How would Nitrogen and hydrogen combine?

N-3 H+1 Yes this has ionic qualities but technically this is a covalent molecule because they are both nonmetals: NH3

Hydrogen is a weird element that can act as both a metal (H+) and a nonmetal (H-)

If you are not given the actual formula, then you can use a criss-cross method to determine ONE of the possible molecules.

Other forms will have to be named for you first… so let’s get to naming compounds

Different structural modifications of an element

This often leads to different chemical formulas of that element: S, S2, O2, O3

Again, naming ionic and covalent compound have different rules, but have some similarities

1) Name them in order of appearance (except acetate)… this is same for covalent naming

2) the cation is NOT modified at all unless it has multiple oxidation numbers. If so then you MUST state which one

3) The anion is modified to end with “ide” unless it is a poly atomic ion (never change the name of a poly atomic ion)

Let’s try some

1) Name the cation (only has one oxidation number): ◦ Calcium

2) Name the anion but change the end to “ide” since it is NOT a polyatomic ion◦ Oxide

3) Put it together: Calcium Oxide

Here’s some more…

NaSO4

Sodium Sulfate (Remember that you do not change the name of a polyatomic ion)

NH4NO3

Ammonium Nitrate (since they are both poly atomic ions, there is no change)

FeCl3 Iron has more than one Oxidation Number-so how do we write it?

It is still Iron but which species? Fe+2 or Fe+3

Here’s what you do: Look at the ANIONEvery Cl has a -1 in an ionic bond. Since there are 3

of them then there must be a total of -3 charge attached to iron, SO the iron HAS to be +3 to cancel out the -3 … Express this using roman numerals:

Iron (III) Chloride

1) BaBr2

2) Li3N

3) NaHCO3

4) Cu2O

5) (NH4)4C Answers on next frame

1) Barium Bromide

2) Lithium Nitride

3) sodium bicarbonate or sodium hydrogen carbonate

4) Copper (I) Oxide

5) Ammonium Carbide

Ionic naming games:

Naming covalent molecules/compounds requires more information because covalent compounds can have single, double or triple bonds:

Name each element in order but also adding a prefix which indicates how many there are unless there is only one:

From above example: hexacarbon decahydrogen

As with ionic compounds, the ending is changed to “ide”: hexoxide

So: hexacarbon decahydrogen hexoxide

Mono-1 Di-2 Tri-3 Tetra-4 Penta-5 Hexa-6 Hepta-7 Octa-8 Nona-9 Deca-10

1) C2H4

2) CH4

3) S2O2

4) SiO2

5) HF6) C6H8

Answers on next slide

1) Dicarbon Tetrahydride2) Carbon TetrahydrideDo not need to say monocarbon because if there is only ONE of the first element, it is

understood to be mono

3) Disulfur Dioxide4) Silicon Dioxide5) Hydrogen MonofluorideHere we are using covalent naming rules because they are both nonmetals but we can

(and usually do) use the ionic naming rules here because hydrogen acts as a metal. This would be hydrogen fluoride using ionic rules

6) Hexacarbon Octahydride

If Hydrogen is bonded to poly atomic ion, then use ionic naming

H2SO4 is hydrogen sulfate compound, where HSO4- is

hydrogen sulfate ion

If, however hydrogen is bonded to single nonmetalic elements, then use covalent rules:

H2O is dihydrogen monoxide

Finally, if hydrogen is bonded to a metal than it is an anion and uses ionic naming:

MgH2 is magnesium hydride

Games:

Lewis dots are a way to represent ionic and covalent compounds based on the valence shell electrons. Each valence electron is represented by a dot.

So where do we find the number of valence electrons???

Mg atom Mg

Mg ion Mg

Cl Atom Cl

Cl ion Cl