11 Mr. Shields Regents Chemistry U09 L01

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Elements found in Abundance in the Earth’s Crust

Only Five Elements account for 93% of the mass ofThe earth’s crust

What do you think they might be?

5 elements make up 93% of the earths crust

And only 8 make up 99% of the entire mass

But consider the diversity of compounds in our world! How Can there be so many different combinations?

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Types of BondsTypes of Bonds

Elements combine by forming what is called theCHEMICAL BOND

So … What is a Chemical Bond?

“ A Chemical Bond is a FORCE OF ATTRACTION holding two or more atoms together”

Compound diversity found in the world is aconsequence of the many possible ways elementscan combine with one another.

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Types of BondsTypes of Bonds

There are several different types of Chemical Bonds:

IonicMetallicNetworkCovalentPolar Covalent

All these bond types involve ONLY the electrons in the atoms valence shell, i.e. the valence electrons

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Ionic BondsIonic BondsIn this unit we’ll discuss Ionic compounds first.

Everyone is familiar with STATIC ELECTRICITY

- Such as when you get a shock touching a doorknob after walking across a rug in the winter

- In this case you’re neg. and the doorknob is +

- Electrons are transferred in the process

- So… From what to what?

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Ionic BondsIonic Bonds

Static electricity is also the basis for ionic bond formation

In Ionic bonds there are metal atoms & non-metal atoms

- We know metals want to lose electrons and Non-metals want to gain electrons. WHY?

Remember effective nuclear charge?

- During the formation of IONIC BONDS metals TRANSFER valence electrons to the non-metal

e-

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Ionic bonds are formed by the Attraction between positive andnegative ions

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Electron Transfer between Sodium and Chlorine

How many electrons are transferred?

And from where to where?

2Na + Cl2 2NaCl

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We know the valence electrons are involved in electron transfer to form the ionic bond

A quantum mechanical representation of the electron transfer

But WHICH electrons (i.e. what orbitals) are involved?

Formation ofThe Octets

BOTH NOW HAVE AN OCTET

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What are The oxidationNos. ofThese Atoms?

Remember that the number of valence electrons an atom hasdetermines its OXIDATION NUMBER

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Group 1 & 17Group 1 & 17The oxidation number determines how many atomsAre needed to form the ionic compound

                                                                                                                

Ox. No: +1 -1 +1 -1

Chemical Formula: M1X1 (i.e. MX) -WHY?

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Ox. No: -1 +2 -1

Chemical Formula: M1X2 (i.e. MX2) - WHY?

Group 2 & 17Group 2 & 17

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Ox. No: -2 +3 -2 +3 -2

Chemical Formula: M2X3 – WHY?

Group 13 & 16Group 13 & 16

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Ionic BondsIonic Bonds

So… The driving force for ionic bond formation is the Attainment of the octet

Remember: Metals with Low IE lose electrons more readily than non-metals with higher IE

Non-metals with High Electronegativitiesattract electrons more readily than metals with Lower Electronegativities

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And… for Metals lower Ionization energy means High Reactivity.For Non-metals lower Electronegativity means Lower Reactivity.

Therefore Francium and Fluorine are the most Reactive elements.

Dec. IncreasingI.E. Reactivity

Na

FrIE and EN decreases down a group and…IE and EN both increase L to R across a period

Dec. DecreasingEN Reactivity

F

I

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Electronegativity DifferenceElectronegativity DifferenceThe ability to fully transfer or accept electronsDefines ionic bonds we can determine which bonds areMore ionic than others by calculating the difference inEN Between the Atoms

When the difference inElectronegativityBetween 2 elementsIs greater than 1.7 theElements will form anIonic bond

For Example

Fr+ F-

EN Diff = 3.3Most ionic compound

Non-ionic ionic ionic

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Diatomic molecules Like H2, O2, Cl2 etc ∆EN =0

3.2

2.1

Most Ionic –Least covalent

Least Ionic -Most covalent

1.7

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We saw that when Na and Cl2 react there is a largeamount of heat released

We’ve burned Mg in air (O2) and saw that inthis reaction there is also a lot ofHeat & light released

All IONIC REACTIONS areCharacterized by the release of heati.e. they are EXOTHERMIC

Reaction of sodium metal and chlorine gas

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Bond FormationBond FormationWhen we release heat we are releasing energy

Therefore ionic reaction products have less energyThan the starting reactants

- Decreasing energy means greater stability

NaCl

Na + Cl

Pote

nti

al Energ

y

Potential Energy isStored in the Chemical Bond

Bonds have An ideal bondLength.

Push atomsCloser together& PE inc.