Atoms

10-15 m

Neutron

Proton

Nucleus (protons and neutrons)

Space occupied by electrons

10-10 m

Periodic Table and Electron Configurations

• Build-up order given by position on periodic table; row by row.

• Elements in same column will have the same outer shell electron configuration.

The relation between orbital filling and the periodic table

Electron Configuration

• Orbitals have definite shapes and orientations in space

(insert Fig 2.11 of text)(if it will not all fit on one screen, put part (a) on one screen and part (b) on the next)

Orbital occupancy for the first 10 elements, H through Ne.

Atomic radii of the main-group and transition

elements.

Trends in the Periodic Table

Trend for atomic radii

• Left to right atoms get smaller• Why?

– Increase in nuclear charge– More protons and more electrons means greater

electrostatic attractions (stronger magnet)

• Top to bottom atoms get larger• Why?

– Increase in energy levels (You are adding floors to your hotel). Electrons are further from the nucleus

Atomic Radius• Atomic radii actually

decrease across a row in the periodic table. Due to an increase in the effective nuclear charge.

• Within each group (vertical column), the atomic radius tends to increase with the period number.

Atomic Radii for Main Group Elements

The Size of Atoms and IonsRadii of neutral atoms

The atomic radius of an atom is defined as half the distance between the nuclei in a homonuclear bond.

r decreases

r in

cre

ase

s

In general:

- radii decrease across a period because of increasing Z*.

-radii increase down a group because of the increasing distance of the electrons from the nucleus.

- increasing distance from the nucleus outweighs effective nuclear charge for atomic radii down a group.

Bohr model for H; radius(n) = n2a0

0.1 nm = 1 Å = 100 pm

Remember that the maximum probability for an orbital moves further away from the nucleus with increasing n.

The “d-block contraction” causes Ga to be about the same size as Al. This is caused by the introduction of the 3d elements which cause a vastly larger Z* for Ga.

Trend for Ion Size• Ion is a charged atom. • Metals lose electrons and nonmetals gain electrons to

create ions. • Cations are pawsitive (positive) and Anions are

negative.• Cations are smaller than their corresponding atom.

Why?• Loss of electrons means the positive nucleus has a

greater attraction on the remaining electrons• Anions are larger than their corresponding atom.

Why?• Gain of electrons means the nucleus has less

attraction for the electrons as well as the electrons are repulsing each other causing an increase in the size of the electron clouds

This is a “self-consistent” scale based on O-2 = 1.40 (or 1.38) Å.

Ionic radii depend on the magnitude of the charge of the ion and its environment. (more later)

Positively charged ions are smaller than their neutral analogues because of increased Z*.

Negatively charged ions are larger than their neutral analogues because of decreased Z*.

Radii of ions

Same periodic trends as atomic radii for a given charge

Trend for ion size

• Decrease across a period then jumps in size at nonmetals and continues to decrease

• Increases on the way down a group as you are adding energy levels (electrons are farther from the nucleus)

Ionization energy

• The energy required to remove an electron

First ionization energies of the

main-group elements

Trends in the Periodic Table

Ionization Energy• Ionization energy is a periodic property

• In general, it increases across a row. Why?• increasing attraction as the number of protons

in the nucleus increases (stronger magnet)• it decreases going down a group. Why?• Outer shell electrons are further from the

nucleus so less electrostatic attraction. Nucleus has less pull on them

Ionization energy

6) The trend across from left to right is accounted for by a) the increasing nuclear charge.

Electronegativity (electron affinity - This is the most important trend to

understand for this class.• The tendency for an atom to attract electrons

when chemically bonded.• Same trend as ionization energy.

– In general, it increases across a row. Why?– increasing attraction as the number of protons in

the nucleus increases (stronger magnet)– it decreases going down a group. Why?– Outer shell electrons are further from the nucleus

so less electrostatic attraction. Nucleus has less pull on them

Trends in three atomic properties

See chart in book for summary

Check for understanding

• Which of the following atoms has the largest atomic radii, ion size, electronegativity, and ionization energy

• Na, Mg, K, Ca, S, Cl, Se, Br

van der Waals radii are established from contact distances between non-bonding atoms in “touching” molecules or atoms

rVDW decreases

r VD

W in

crea

ses

van der Waals radii

VDW radii allow us to determine whether there can be a bonding interaction between two atoms:

If the distance between the nuclei is larger than the sum of the VDW radii, then the atoms are probability not bonded.