Elements are grouped in cElements are grouped in columnsolumns or g or groupsroups according to their number of according to their number of valencevalence electronselectrons..

Valence ElectronsValence Electrons

Valence ElectronsValence Electrons

HydrogenHydrogen and and helium’shelium’s outer outer

energy level can energy level can only hold up to only hold up to 22

electronselectrons..

In order to be In order to be stablestable, all atoms want a , all atoms want a fullfull outerouter energyenergy levellevel..

Since Since heliumhelium already has 2 valence electrons, its already has 2 valence electrons, its outer energy level is outer energy level is fullfull and Helium is and Helium is stablestable. .

HydrogenHydrogen, however, only has , however, only has 11 valence electron, valence electron, so hydrogen is so hydrogen is unstableunstable. .

Octet RuleOctet RuleAll the other elements, regardless of how many All the other elements, regardless of how many

energy levels they have, want energy levels they have, want 88 valencevalence electronselectrons in in their outer energy level. This is called the their outer energy level. This is called the octetoctet rulerule. .

All of the All of the noblenoble gasesgases have have 88 valencevalence electronselectrons, ,

so they are all so they are all stablestable..

Valence ElectronsValence ElectronsNone of the other representative elements have full None of the other representative elements have full

outer energy levels, so they are all outer energy levels, so they are all unstableunstable..

Gaining or Losing ElectronsGaining or Losing ElectronsIn order to In order to fillfill their their outerouter energy energy levellevel, the other , the other

atoms can either atoms can either gaingain or or loselose electronselectrons..

Sodium only has Sodium only has 11 valence valence electron. In order to become electron. In order to become

stable, sodium will stable, sodium will loselose its its valence electron and drop down valence electron and drop down

to only 2 energy levels.to only 2 energy levels.

Gains outer

Sodium Atom Sodium Ion

Chlorine Atom Chlorine Ion

Cl Cl _

Chlorine has Chlorine has 77 valence valence electrons. In order to become electrons. In order to become

stable, chlorine will stable, chlorine will gaingain 1 1 valence electron to fill its outer valence electron to fill its outer

energy level.energy level.

Gaining or Losing ElectronsGaining or Losing ElectronsAs a general rule, atoms with As a general rule, atoms with 44 oror lessless valence valence electrons will electrons will loselose their valence electrons, while their valence electrons, while

atoms with atoms with moremore than than 44 valence electrons will valence electrons will gaingain electrons.electrons.

Groups 1, 2, 13, Groups 1, 2, 13, and 14 will lose and 14 will lose

electrons electrons

Groups 15, 16, Groups 15, 16, and 17 will gain and 17 will gain

electronselectrons

++

++ ++ ++

----

----

IonsIonsWhen atoms gain or lose electrons, they develop a When atoms gain or lose electrons, they develop a

charge. charge. AtomsAtoms with a with a chargecharge are called are called ionsions..

Lithium atoms have three protons and three Lithium atoms have three protons and three electrons, making the overall charge of a lithium electrons, making the overall charge of a lithium

atom neutral.atom neutral.

(+3) (+3) ++ (-3)(-3) == 00

++

++ ++ ++

----

----

IonsIonsIf lithium loses an electron, then it will have one more If lithium loses an electron, then it will have one more

positively charged proton than it has negatively positively charged proton than it has negatively charged electrons, so it develops a + 1 charge.charged electrons, so it develops a + 1 charge.

(+3) (+3) ++ (-2)(-2) = +1 = +1

Ions and Oxidation NumbersIons and Oxidation NumbersAll of the atoms in the All of the atoms in the alkalialkali metalsmetals group have group have 11

valencevalence electronelectron which they which they loselose when they when they become ions with a +1 charge.become ions with a +1 charge.

The The +1+1 charge is called the charge is called the oxidationoxidation numbernumber..

Ions and Oxidation NumbersIons and Oxidation NumbersAll of the atoms in the All of the atoms in the alkalinealkaline earthearth metalsmetals group group

have have 22 valencevalence electronselectrons which they which they loselose when they when they become ions with a +2 charge.become ions with a +2 charge.

All alkaline earth metals All alkaline earth metals have an have an oxidationoxidation

numbernumber of of +2+2..

Ions and Oxidation NumbersIons and Oxidation NumbersAll of the atoms in the All of the atoms in the BoronBoron groupgroup have have 33 valencevalence electronselectrons which they which they loselose when they become ions when they become ions

with a +3 charge.with a +3 charge.

All ions in the Boron All ions in the Boron group have an group have an oxidationoxidation

numbernumber of of +3+3..

Ions and Oxidation NumbersIons and Oxidation NumbersAll of the atoms in the All of the atoms in the CarbonCarbon groupgroup have have 44 valencevalence electronselectrons which they which they loselose when they become ions when they become ions

with a +4 charge.with a +4 charge.

All ions in the Carbon All ions in the Carbon group have an group have an oxidationoxidation

numbernumber of of +4+4..

Ions and Oxidation NumbersIons and Oxidation NumbersAll of the atoms in the All of the atoms in the NitrogenNitrogen groupgroup have have 55

valencevalence electronselectrons. Each of these atoms will . Each of these atoms will gaingain 33 electronselectrons when they become ions with a -3 charge when they become ions with a -3 charge

All ions in the Nitrogen All ions in the Nitrogen group have an group have an oxidationoxidation

numbernumber of of -3-3..

Ions and Oxidation NumbersIons and Oxidation NumbersAll of the atoms in the All of the atoms in the OxygenOxygen groupgroup have have 66

valencevalence electronselectrons. Each of these atoms will . Each of these atoms will gaingain 22 electronselectrons when they become ions with a -2 charge when they become ions with a -2 charge

All ions in the Oxygen All ions in the Oxygen group have an group have an oxidationoxidation

numbernumber of of -2-2..

Ions and Oxidation NumbersIons and Oxidation NumbersAll of the atoms in the All of the atoms in the HalogenHalogen groupgroup have have 77

valencevalence electronselectrons. Each of these atoms will . Each of these atoms will gaingain 11 electronelectron when they become ions with a -1 charge when they become ions with a -1 charge

All ions in the Halogen All ions in the Halogen group have an group have an oxidationoxidation

numbernumber of of -1-1..

ReviewReview1.1. Atoms with full outer energy levels are stableAtoms with full outer energy levels are stable

2.2. Atoms seek stabilityAtoms seek stability

3.3. Atoms can lose or gain electrons to fill their outer Atoms can lose or gain electrons to fill their outer energy levelsenergy levels

4.4. When atoms lose electrons they develop a When atoms lose electrons they develop a positive chargepositive charge

5.5. When atoms gain electrons they develop a When atoms gain electrons they develop a negative chargenegative charge

6.6. Atoms with a charge are called ionsAtoms with a charge are called ions

ReviewReview7.7. The charge an atom develops when it gains or The charge an atom develops when it gains or

loses electrons is called its oxidation numberloses electrons is called its oxidation number

8.8. Ions in the same groups have the same oxidation Ions in the same groups have the same oxidation numbernumber

9.9. Groups on the left hand side of the periodic table Groups on the left hand side of the periodic table tend to lose electrons and have positive oxidation tend to lose electrons and have positive oxidation numbersnumbers

10.10.Groups on the right hand side of the periodic Groups on the right hand side of the periodic table tend to gain electrons and have negative table tend to gain electrons and have negative oxidation numbersoxidation numbers

Oxidation NumbersOxidation Numbers