TuesdayNovember 9, 2010

(Electronegativity, Valence Electrons)

Bell RingerTuesday, 11-9-10

Which one of the listed elements has

the largest atomic radius – K, Co, Br

the least ionization energy – Na, P, Cl

the greatest electron affinity – Li, B, F

the greatest ionization energy – Li, K, Fr

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WS: Atomic Structure

73-74

10/1 10/8

ElectronegativityThe outer-most, highest energy

level electrons in an atom’s electron cloud are called its

“valence” electrons.

Valence electrons are the ones that participate in chemical

bonding – the force that hold elements together to form

compounds.

When two atoms are bonded together, one of the atoms may “tug” harder at the participating

valence electrons harder than the other atom does.

Electronegativity is a measure of the ability of an atom in a

chemical compound to attract electrons.

Electronegativity values tend to increase across each period,

although there are exceptions.

Electronegativity

increase

Electronegativity values tend to either decrease down a group or remain about

the same.

Electronegativity

Decrease/remain same

The alkali and alkaline-earth metals are the least electronegative elements.

In compounds, their atoms have a low attraction for electrons.

Electronegativity

least electronegative

Nitrogen, oxygen, and the halogens are the most electronegative elements.

Their atoms attract electrons strongly in compounds.

Electronegativity

most electronegative

The Noble gases are unusual in that some of them do not form compounds and therefore cannot be assigned

electronegativity values.

Electronegativity

But when a Noble gas does form a compound, its

electronegativity is rather high, similar

to the values for the halogens.

The combination of the period and group trends in electronegativity results in the highest values belonging to the elements in the upper right of

the periodic table.The lowest values belong to the elements in the

lower left of the table.

Electronegativity

highest

lowest

The alkali metals cesium and francium have the lowest electronegativity values at 0.7.

The halogen fluorine has the highest electronegativy value at 4.0.

Electronegativity

highest

lowest

Valence ElectronsTwo very important conditions for atoms are:

electrical neutralityand, chemical stability

All atoms that have equal numbers of protons and electrons are electrically

neutral.However, only the Noble gases are also

stable.All other atoms bond to form chemical compounds because that’s the way to

become stable.

In the process of bonding, atoms either lose, gain, or share their

valence electrons.

Remember that these valence electrons are those in the atoms’ outermost, highest energy level, and as a result are the ones most subject to the influence of other

nearby atoms or ions.

Valence Electrons

In this chemistry class, we will deal primarily with valence electrons located in an atom’s highest energy

level s and p sub-levels.For example, the element sodium has an electron

configuration notation of1s2, 2s2, 2p6, 3s1

As you can see, sodium has only one electron in its highest energy level (3), and it’s in the s sub-level.This is the only electron sodium will use to bond.

Another example: the element chlorine has an electron configuration notation of

1s2, 2s2, 2p6, 3s2, 3p5

Chlorine has 7 electrons in its highest energy level (3), 2 in the s sub-level and 5 more in the p sub-level.

Chlorine counts all 7 of these valence electrons in its bonding considerations.

Valence Electrons

For main block (s and p) elements, the valence electrons are the

electrons in the outermost s and p sublevels.

The inner electrons are in filled energy levels and are held too

tightly by the nucleus to be involved in compound formation.

Valence Electrons

The alkali metals of group 1 have 1 valence electron.

The alkaline earth metals of group 2 have 2 valence electrons.

The elements in the p block (groups 13–18) have a number of valence electrons equal to

their group number minus 10.For example, group 13 has 3 valence

electrons, group 14 has 4, etc.In some cases, both the s and p sublevel valence electrons of the p-block elements

are involved in compound formation.In other cases, only the electrons from the p

sublevel are involved.

Valence Electrons