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Mr. Shields Regents Chemistry U08 L03

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Valence ElectronsValence Electrons

Recall …Recall …

Electrons in the outermost principal energy levelElectrons in the outermost principal energy level(the Valence Shell) are called (the Valence Shell) are called VALENCEVALENCEELECTRONSELECTRONS

Ex. 2-8-18- 6

This element has 6 valence electrons.What element is it?

The valence shell(n=4)

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Main Group Valence shells

Grp 1 2 13 14 15 16 17 18

As we move from As we move from left to rightleft to right we add one electron at a time we add one electron at a timeTo the outermost Principal energy level – the Valence shellTo the outermost Principal energy level – the Valence shell

1e 2e 3e 4e 5e 6e 7e 8e

S Block P Block

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Valence electron trendsValence electron trends

1)As you go down a group the number of electrons in the valence shell stays the same

2) As you go across a period (left to right) the # of e- inthe valence shell of the main group elements increases one by one

- This ignores the transition metals(d orbitals are filling in n-1)

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Lewis dot Structures for theatoms of groups 1-2 and 13-18 ofThe periodic table

The Main group elements

Notice the e- trends in the Groups and Periods

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IonsIonsRecall that the electron configuration of the noble gasesIs the extremely stable electron configuration

It’s Known as the OCTET

Argon’s config is 2-8-8Potassium’s is 2-8-8-1 (why this config and not 2-8-9?)

By losing 1 electron the electron config of the potassium Ion (K+) becomes the same as Argon’s (2-8-8)

The Octet Configuration

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Lewis dot structures of Lewis dot structures of IonsIons

Lewis Dot structures for ions look similar to the Lewis DotLewis Dot structures for ions look similar to the Lewis DotStructures for atoms Structures for atoms Except brackets andExcept brackets andCharges are used:Charges are used:

[ Na ][ Na ]++ or just Na or just Na+

On the other hand, Br will fill it’s valence shell giving itOn the other hand, Br will fill it’s valence shell giving it8 valence electrons. It’s Lewis dot structure is:8 valence electrons. It’s Lewis dot structure is:

[ [ :: Br Br :: ] ] --

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Na is an S block element while bromine is a P block element

S block elements (metals) form pos. ions by losing e-

P block ions (the non-metals) form neg. ions by gaining e-.

The d and fBlocks elementsAre also metals

Therefore theyalso form Positive ionsEx. Co+3 or U+6

Na

BrCo

U

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Effective Nuclear ChargeEffective Nuclear ChargeWhether an atom gains or loses electrons will depend upon theEffective Nuclear Charge. For example K loses 1 e- and Cl gains 1 e-

The effectiveNuclear chargeIs the + charge felt by The Valence electrons.

Inner electrons shieldValence electrons from“Feeling” the nuclear charge

Val. e- held firmlyVal. e- held less firmly

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4+Cations Anions

Most common Oxidation nos.

Always!Electrons lost vary

Variation of nuclear charge across the Periodic Table

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Oxidation NumbersOxidation NumbersAn oxidation number represents the number of electronsan atom will typically gain or lose to achieve the octet.

For example:The oxidation number of Sodium is +1 The oxidation number of Oxygen is -2

Some Atoms can have more than one oxidation number

Open up your reference tables and look at the oxidation numbers. Oxidation numbers are located in the upperright. Check out various metal and non-metal oxidation nos.