Photoelectron Spectroscopy (PES)

PES

Provides explanation for shells and orbitals in quantum theory

Photoelectric effect— Utilization of photons to remove electrons from atoms Photons have been energized, analyzing the energy

needed to remove electrons from an atom/compound

Photoelectric spectrum— Energy on x-axis Number of electrons in a subshell on y axis

Photoelectric Spectrum

Peaks— Number of subshells/orbitals

Peak heights— Number of electrons in subshell

Electrons within the same subshell have similar energy values but different orbital energies, energy values vary among subshells

Shells with high energies indicate electrons located close to nucleus

Example 1: Na

Example 2:

A third period element in the periodic table forms a PES spectrum with three peaks, in the ratio 2:2:1. Name this element. A) Aluminum

B) Boron

C) Carbon

D) Sodium

Example 3:

Aluminum has the following electron configuration: 1s22s22p63s23p1

A) How many peaks should be expected in a PES spectrum for Al?

B) Which electrons will show the highest energies? Why?

Example 3: (cont.)

Aluminum has the following electron configuration: 1s22s22p63s23p1

C) Which peak on the spectrum will be the most intense/largest? Why?

D) Explain why the peaks for the 3s and 3p electrons would be closely grouped and why they are different than electrons in the 2s and 2p orbitals.

Periodic Trends

Elemental Properties and Patterns

The Periodic Law

Dimitri Mendeleev (1869/1871) was the first scientist to publish an organized periodic table of the known elements.

He was taking a chemistry course in Russia and tried to find a way to organize the periodic table.

The Periodic Law

Mendeleev even went out on a limb and predicted the properties of 2 at the time undiscovered elements.

He was very accurate in his predictions, which led the world to accept his ideas about periodicity and a logical periodic table.

The Periodic Law

Mendeleev understood the ‘Periodic Law’ which states:

When arranged by increasing atomic number, the chemical elements display a regular and repeating pattern of chemical and physical properties.

The Periodic Law

Atoms with similar chemical properties and behavior appear in groups or families (vertical columns named by Roman numerals with A or B) on the periodic table.

They are similar because they all have the same number of valence (outer shell) electrons, which governs their chemical behavior.

Periods– horizontal rows on periodic table

Periodic Trends

There are several important atomic characteristics that show predictable trends that you should know.

Atomic properties— Deal with only single atoms

Atomic Radius

Enables us to gain information on atom’s size Outer electrons hard to locate

Radius is the distance from the center of the nucleus to the “edge” of the electron cloud. Measurement of distance between nuclei of 2 atoms

Since a cloud’s edge is difficult to define, scientists use define covalent radius, or half the distance between the nuclei of 2 bonded atoms.

1. Covalent Radius

Half the distance between the nuclei of 2 bonded atoms.

Radius of nonmetallic atoms

Ex. Br 2.86 Å1.43 Å 1.43 Å

Half the distance between nuclei of adjacent atoms in a metal

Radius of metallic atoms

2. Metallic Radius

Atomic Radius Trend

Decreases

Increases

Atomic Radius

The effect is that the more positive nucleus has a greater pull on the electron cloud.

The nucleus is more positive and the electron cloud is more negative.

The increased attraction pulls the cloud in, making atoms smaller as we move from left to right across a period.

Identify the atom with the largest radii

1) Ca, F

2) Cl, O

3) N, P

Affected by distance between nuclei of 2 ions

Defined by the distance between the nuclei occupied by the particular ion Studies with crystal structures

Radii related to original atomic radii

Isoelectronic— Atoms/ions with SAME number of electrons SO ------ electron

configuration same as well

Ionic Radii

Larger size than original neutral atom Generally nonmetals Electrons repel as increase in number, causes

size to increase

Ionic Radii: 1) Anions

Smaller size than original neutral atom

Generally metals

Less electrons, more attractive force from nucleus

Ionic Radii: 2) Cations

Ionization Energy If an electron is given enough energy (in the

form of a photon) to overcome the effective nuclear charge holding the electron in the cloud, it can leave the atom completely.

Amount of energy needed to remove ONE electron from a neutral atom Removal from ground state in neutral atom of

gaseous state to form positive ion

Ionization Energy (cont.)

The energy required to remove an electron from an atom is ionization energy.

The larger the atom is, the easier its electrons are to remove.

Ionization energy and atomic radius are inversely proportional.

1st ionization energy Energy required to remove 1st electron from

atom Taken from highest energy level Easiest to remove

Energy increases as more electrons are removed

Ionization Energy (cont.)

Ionization Energy Trend

Increases

Decreases

Ionization Energy

Identify the highest ionization energy

1) F, Mg

2) Na, Rb

3) P, O

What does affinity mean?

Electron Affinity

energy change that occurs when electrons added to gaseous atom

Greater value with smaller atoms

Energy released when electron added Exothermic, negative value

An atom’s “desire/affinity” for more electrons, wants to get more electrons ! ! !

Metals—decrease electron affinity. Nonmetals—increase electron affinity, more reactive Stable atoms—full octet

Electron Affinity Trend

Increases

Decreases

Metals, Nonmetals, Metalloids

How can you identify a metal?

What are its properties?

What about the less common nonmetals?

What are their properties?

And what the heck is a metalloid?

A Different Type of Grouping

Besides the 4 blocks of the table, there is another way of classifying element:

Metals

Nonmetals

Metalloids or Semi-metals.

The following slide shows where each group is found.

Metals Metals are shiny, malleable, ductile, and are good conductors of heat and electricity.

They are mostly solids at room temp.

Want to LOSE valence electrons

Form positive ions

s block (not H and He), d/f blocks, some p block elements

Nonmetals

Nonmetals are the opposite.

No color, no shine

They are dull, brittle, nonconductors (insulators).

Gases at room temperature

Want to GAIN electrons

Form negative ions

p block elements, H and He

Transition Metals Middle of the periodic table

Forms positive ions, multiple types

Shine, malleable, ductile, good conductors

s/d orbitals—electrons lost from these subshells.

Metalloids/Semi-Metals Metalloids, aka semi-metals are just

that.

They have characteristics of both metals and nonmetals.

They are shiny (like metals) but brittle.

And they are semiconductors.

“on the fence, middle of the road”

B, Si, As, Te, At, Ge, Sb, Po

Noble Gases Group 18

Do NOT react with other elements

Atomspheric gases

Naturally in elemental form , single atoms

Not completely unreactive

Metallic Character

This is simply a relative measure of how easily atoms lose or give up electrons.

Tendency to LOSE electrons

Related to atomic radius/ionization energy, how easy to remove electrons

Metallic Character

Decreases

Increases

Atoms with a tendency to GAIN electrons

Nonmetallic Character

Increases

Decreases

Classwork: Ionization Energy

Circle the atom with the highest first ionization energy.

1) Al, B 5) Fr, Li 9) Se, Cl

2) Mg, Na 6) Mg, Al 10) Rb, Mg

3) P, As 7) C, F

4) I, At 8) K, Sc

Classwork: Metal IdentityIdentify each element as a nonmetal, metal, or

metalloid

1) Na 6) Cl

2) P 7) Mg

3) Se 8) Al

4) Ge 9) Sb

5) N 10) Si