Subtleties of the shell structure of the atomPhysically speaking why does the 4s level in neutral atoms lie below the 3d?

The s orbital has a small fraction of its probability density close to the nucleus.

3d orbitals do not have such inner regions, as they only have planar nodes

Hence an s electron from a higher

shell will sometimes occur at lower energy than a d electron in a lower shell

Effective nuclear charge

From Li to Ne, nuclear charge increases from 3 to 10

The charge that a 2s or 2p electron feels is different due to the shielding from the electrons in the 1s orbital

2 s orbital penetrate into the 1s orbital and therefore are shielded less on average than p orbitals

Note: Shielding effect increases as the number of e’s increases.

This is the result of additional shielding from the 2 s and 2 p e’s

-1.77-1.42-2.78-3.15

-3.51-3.87

Note: As Z* increases orbitals shrink towards nucleus as e’s are held more tightly dues to stronger electronic interactions.

E

Effect on atomic size

• Consider the size change from F to I

Decrease strongly

Increase significantly

Increase gently

Consider the change in size of the atoms from Li to F

Consider the size change from Li to Rb

Consider the size change from F to I

Size of Atoms and Ions

Atomic radius decreases along the period, and increases down the group

The radius of an anion is larger than its neutral atom.

Removing the electron decreases shielding without changing the charge of the nucleus.

Valence electrons of a cations are in a lower energy shell than in the neutral atom, decreasing the ionic radius.

Adding the extra electron increases shielding without changing the charge of the nucleus.

The radius of a cation is smaller than its neutral atom

Ie. Z* is smaller.

ie., Z* is larger.

Sizes of monatomic ions

Anions are larger than cations

This is always true across a period of the table

Ions in each group of the table get larger in size down the group

Isolectronic ions decrease in size across the period, as Z* increases dramatically. Ex) N3- to F- Na+ to Al3+

Ionization energy

1 ( ) ( ) ( ) for g g gIE E E E e

The energy that must be absorbed in order to remove a valence electron from a neutral atom in the gas phase

Z* and its effect on size and IE

3+

e-

e-

e-

9+

e-

e-

e-

e-

e-

e-e-

e-

e-

2 11 2s s 2 2 51 2 2s s pLi F

r = 152 pm

EA1 = 520 kJ/mol

r = 71 pm

EA1 = 1681 kJ/mol

Z*= 1.28 Z*= 5.13

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Periodic distribution of IE1 valuesList of the IE1 in kJ/mol for the elements

IE increases across the period

IE increases up the group

Z* increases

Shielding effect decreases ie. Z* increases

Enthalpy of Electronic Attraction

( ) ( )g gF e F

( ) ( )g gLi e Li

Energy released when an element attracts an extra electron into the lowest-energy unoccupied orbital to form an anion

For large Z* e’s are held closely to the nucleus therefore e-n interactions will be stronger for an additional electron coming in.

Compare Li (Z* = 1.28) with F (Z* = 5.13 )

DHEA increases in magnitude across period

DHEA decreases in magnitude down the group

Negative since energy is released

DHEA always negative

Electronegativity (c)i) How strongly does an element hold onto its own electrons ?

ii) How strongly is an element able to attract electrons from other elements?

A combination of ionization energy and enthalpy of electronic attraction.

Which element(s) should have the highest electronegativity?

Which element(s) should have the lowest electronegativity?

Pauling Electronegativity

General trend in element electronegativity

The Periodic Table Dmitri Mendeleev, In 1869, noticed that elements exhibited similar behaviour, in groups, in the ratios in which they form molecules with H and O.

Elements arranged by increasing mass so that similar elements form columns

Incomplete – noblegases are missing

Blank spaces left for elements yet to be discovered.

In 1913, H.G.J. Moseley- the periodic table is more descriptive if the elements were in order of increasing atomic number rather than increasing mass.

Order based on atomic masscausesmisalignments.

The Modern Periodic Table

C12

6

mass numbersymbol

atomic number

name & atomic weight 12.011Carbon

Law of Periodicity “The properties of the elements areperiodic functions of atomic number.”

Metals – Conducting, Ductile

Metalloids - Semiconductors Ductile ?

Nonmetals – insulatorsnot ductile

Group Period

Repetition of properties

Similar chemical properties