CHEM 103 Module 2

Waves

An oscillation or periodic movement that can transport energy from one point in space to another

Electromagnetic waves

Consist of both an electric and magnetic field, oscillating perpendicular to one another as well as the direction of travel.

Waves are characterized by?

Wavelength

Frequency

Amplitude

Wavelength

The distance between two consecutive peaks or troughs in a wave.

Measured in meters

Frequency

The number of wave cycles (complete wavelengths) that pass a specified point in space in a specified amount of time.

Measured in Hertz (Hz) - cycles per second

Amplitude

The magnitude of the wave’s displacement, which is one-half the height between the peak and troughs (measured from middle)

Speed of light

c = 2.988 x 10^8m/s

Formula for speed of light

The formula for speed of light is given by the equation c = λf.

c is the speed of light, λ is the wavelength, and f is the frequency.

Electromagnetic Spectrum

Range of energies that electromagnetic radiation can comprise, including radio, microwaves, infrared, visible, ultraviolet, x-rays and gamma rays.

Conversation factors for nanometers to meter

1nm = 1x10^-9m

10^9nm = 1m

Wave-Particle Duality Late 1600’s - Issac Newton: Particles

Light is made of particles.

Light travels in waves, but whenever the colors are separated in prisms, they separate into straight lines.

Wave-Particle Duality Late 1600’s - Christian Huygens: Waves

Reflection and refractions

Behavior explained as waves and not as particles

Wave-Particle Duality Early 1800’s - Thomas Young: Waves

Shining lights through 2 screens with slits.

If the light passed through the screen, it should hit the viewing screen in two lines = the light was a particle - but that’s not how he saw it.

He saw that when the light passes through 2 slits on the other side of the viewing screen, he had multiple lines with empty space between - called interference patterns.

Wave-Particle Duality Early 1800’s - James Clerk Maxwell: Waves

Able to produce first colored photograph.

First person to realize that light is made of 2 waves - electric and magnetic components.

Developed the theory of electromagnetism, describing light as electromagnetic waves that can travel through space.

Scientists viewed the physical universe as two separate domains

Matter - composed of particles moving according to Newton’s laws of motion.

Electromagnetic Radiation - consisting of waves governed by Maxwell’s equations.

Wave-Particle Duality defined

Observation that elementary particles can exhibit both wave-like and particle-like properties.

Blackbody Radiation Early 1900’s - Maxwell Planck: Particles

Objects that appear black because they absorb all colors, all wavelengths.

When heated, these blackbodies would emit all the energies absorbed and emit colors.

Worked well for a lot of objects, but in the UV range, the calculation and predictions fell apart - it didn’t work.

This was called the UV catastrophe or ultraviolet catastrophe.

Planck’s Constant

Able to explain UV catastrophe.

E = nhv

(h) = 6.626 x 10^-34 joule seconds (J*s)

This equation calculates the energy of light at a given frequency or wavelength, n= number of particles of light.

The Photoelectric Effect Early 190’s - Albert Einstein: Particles

A phenomenon where electrons are emitted from a metal surface when light shines on it at a high enough energy.

When changing the intensity of light, no changes were seen - it only changed when he changed the frequency of light.

Einstein explained this by suggesting that light comes in discrete packets of energy called photons.

Equation to calculate energy of a single photon of light at a given frequency or wavelength

E=hc/λ

The Bohr Model

Only works for hydrogen, no other elements.

But introduced several important features of all models used to describe the distribution of electrons in an atom:

1. The energies of electrons (energy levels) in an atom are quantized.

2. An electron’s energy increases with distance from the nucleus.

3. The discrete energies of light emitted by elements in an excited state result from quantized electronic energies.

Bohr Model - Ground State

State in which the electron in an atom, ion or molecule have the lowest energy possible.

Bohr model - Excited State

State having an energy greater than the ground-state energy.

Equation to calculate energy that’s either absorbed/emitted by electrons

Equation for energy

Understanding Quantum Theory of Electrons in Atoms 1920’s

Louis de Brogile: The wave nature of matter.

C. Davisson and L.H. Germer: Electron diffraction.

They were able to see that whenever electrons which are known to be particles were shot thru a screen with 2 slits, the electrons were scattered instead of straight thru and acted like a particle.

This pointed to the wave nature of electrons.

Relates properties of matter and velocity to properties of light.

Whenever we have mass x velocity = momentum (p=momentum).

This equation incorporates both properties of matter and waves.

Werner Heisenberg: Uncertainty principle

You can look at the position of an electron or you can look at its momentum - how fast its travelling and in what direction, BUT you cannot look at both at the same time and know both values with certainty.

Uncertainty principle arises from limitations of the math.

Electrons of small mass = higher degree of uncertainty in this equation.

Erwin Schrodiner: Wave Equation

We’re able to derive a mathematical expression to give a 3D map of where an electron is most properly located in an atom = Orbital.

Gave us a better understanding of how to describe the location and energy of electrons in an atom.

This equation was able to reproduce Bohr’s expression for the energy, not only for hydrogen but for ALL atoms/elements.

Principle Quantum Number (n)

Aka shell - Specifies the size of the orbital and where the electron might be located in that space.

Ex: Electron is at n1 = very close to nucleus, the amount of space that electron can take up/the amount of space that electron can take up or the amount of space is very small.

As the energy of the electron increases, it’s able to orbit at a larger distance away from the nucleus.

When n=2, the amount of space that electron could inhabit becomes larger, so on and so on.

n can have values from 1 to infinity, but must be integer values.

Secondary Quantum Number (l)

Aka subshell - Specifies the shape of the orbital.

l value is baked on n value.

l can have values from 0 to n-1.

Ex: n=3, l= 0, 1, 2

s-subshell

l = 0

Has spherical shaped orbital.

p-subshell

l = 1

Has dumbbell shaped orbital.

d-subshell

l = 2

Has clover shaped orbitals except d0, all shapes don’t have to match.

f-subshell

l = 3

All not similar shaped orbitals.

Magnetic Quantum Number (ml)

Specifies the relative spatial orientation of a particular orbital; all possible values tell us how many orbitals in a subshell.

When l = 0…ml = 0

When l = 1…ml = -1, 0 or +1

When l = 2…ml = -2, -1, 0, +1 or +2

When l = 3…ml = -3, -2, -1, 0, +1, +2, or +3

Spin Quantum Number (ms)

Specifies the orientation/direction of the spin axis of an electron.

ms can have values of +½ or -½ ONLY.

The Pauli Exclusion Principle

No two electrons in the same atom can have exactly the same set of all the four quantum numbers.

Maximum of two electrons per orbital (limited by spin, ms).

Two electrons in the same orbital must have opposite spins.

Calculation for # of orbitals

n^2

Calculation for # of max electrons

2(n)^2

Electron Configuration

The arrangement of electrons in the orbitals of an atom.

Uses a symbol that constraints 3 pieces of info:

1. The number of principal quantum shell, n

2. The letter that designates the orbital type aka the subshell, l

3. The superscript number that designates the number of electrons in that particular subshell

Aufbau Principle

Procedure in which the electron configuration of the elements is determined by adding 1 proton to the nucleus and 1 electron to the proper subshell at a time.

Each added electron occupies the subshell of lowest energy available, subject to the limitations of the Pauli exclusion principle.

Electrons enter higher-energy subshells only after lower-energy subshells have been filled to capacity.

Orbital Diagrams

Pictorial representations of the electrons configuration, showing the individual orbitals and the pairing arrangement of electrons.

Valence Electrons

Electrons occupying the outermost shell orbital(s) or the highest value of n

Core Electrons

Electrons occupying the inner shell orbitals.

Correspond to noble gas electron configurations.

Can abbreviate electron configurations by writing the noble gas core.

Main group elements (aka, representative elements)

Are those in which the last electron added enters an s-orbital or a p-orbital in the outermost shell

Includes:

1. All the nonmetallic elements

2. Many metals (but not all metals)

3. Some metalloids

The valence electrons for main group elements are those with the highest n-level.

The completely filled d-orbitals count as core, not valence, electrons.

Transition Elements (aka transition metals)

Metallic elements in which the last electron added enters a d-orbital.

The valence electrons (those added after the last noble gas configuration) in these elements include the ns and (n-1) d-electrons.

Includes:

1. S-electrons AND d-electrons directly beneath the highest level

Inner Transition Elements

Metallic elements in which the last electron added occupies an f-orbital.

There are 2 inner transition series:

1. The Lanthanide Series - Lanthanum (La) thru Lutetium (Lu)

2. The Actinide Series - Actinium (Ac) thru Lawrencium (Lr)

The valence electrons of the inner transition elements consists of the (n-2)f, the (n-1)d and the ns subshells.

The valence electrons are not just the ones in the highest levels for these f-block elements.

They include the highest s-electrons, the electrons in the next level down and the f-electrons in the next level down.

Electron Configurations of Ions - Cations

Forms when one or more electrons are removed from a parent atom (original neutral atom).

Main Group Elements - The electrons that were added last are the first electrons removed.

Transition Metals and Inner Transition Metals - The highest ns electrons are lost first, and then the (n-1)d-electrons or (n-2)f-electrons are removed.

It doesn’t go in order from the last added, is the first removed, like the main group elements.

Electron Configurations of Ions - Anions

Forms when one or more electrons are added to a parent atom.

The added electrons fill in the order predicted by the Aufbau Principle to complete the next noble gas configuration.

Patterns in Chemical Properties on the Periodic Table

Size of atoms and ions

Ionization energies

Electron affinities

Covalent Radius

One-half the distance between the nuclei of two identical atoms when they are joined by a covalent bond.

Down the Column

Zeff decreases

Size increases

IE decreases

EA decreases

Across the Column

Zeff increases

Size decreases

IE increases

EA increases

Effective Nuclear Charge (Zeff)

The pull exerted on a specific electron by the nucleus, taking into account shielding effects of the other electrons in the atom/ion.

Shielding happens when another electron is in between the electron of interest and the nucleus.

Or when the electron of interest experiences repulsion from any other electron in the atom.

Ionic Radius

The measure used to describe the size of an ion.

Can’t look at periodic table and look for trend, doesn’t increase as you go right or decrease as you go left - Instead, we have to compare size of neutral parent atom to size of the ion.

A cation (positive ion) has fewer electrons and the same number of protons as the parent atom

Smaller than the parent atom, because of the greater Zeff.

The electrons feel a stronger pull towards nucleus than parent atom.

Cations with larger charges are smaller than cations with smaller charges.

The larger the charge = more electrons have been lost.

The more electrons that have been lost from an atom, the greater the difference the number of protons and electrons.

If there’s an excess of protons, that nucleus has a very strong attraction for all of the valence electrons and pulls it in very close = decreasing in size.

An anion (negative ion) has more electrons and the same number of protons as the parent atom.

Larger than the parent atom, because of the smaller Zeff.

The number of protons that an atom has never changes, but when you add extra electrons, you’re adding an excess of negative charge that the nucleus will have more trouble attracting with the same number of protons.

Anions with larger charges are larger than anions with smaller charges.

Because they have an excess of electrons and the number of protons doesn’t change.

Ionization Energy (IE)

The amount of energy required to remove an electron from a gaseous atom or ion.

First ionization energy (IE1)

IE for most loosely bound electron

1st electron removed

Second ionization energy (IE2)

IE for second most loosely bound electron

2nd electron removed

Electron Affinity (EA)

The energy change for the process of adding an electron to a gaseous atom to form an anion (negative ion).

Adding an electron can either require or release energy, depending on the element.

Formation of a more stable ion releases energy

Exothermic (lets off energy), EA value is negative.

Whenever it gains an extra electron, it lets go of energy - becomes more stable.

Formation of a less stable ion requires energy, a positive energy charge

Endothermic (absorb or require energy), EA value is positive.

Energy must be put into the atom to force the atom to accept extra electron.

Metallic Character

Increases as atomic size increases (ease of removing electrons).

Dimitri Meneleev

Generally accepted as correct, placing different elements in groups based on their reactivity.

Predicted the existence of 3 undiscovered elements (Gallium, Scandium, Germanium).

Periodic Law

Established by Mendeleev

The properties of the elements are periodic functions of their atomic numbers.

Metals

Elements that are shiny, malleable and ductile, and conduct heat and electricity well.

Easily loses electrons

Nonmetals

Elements that are not shiny, malleable and ductile, and are poor conductors of heat and electricity.

Don’t loses electrons easily

Metalloids

Elements that conduct heat and electricity moderately well and possess some properties of metals and some properties of nonmetals.

Main-Group Elements (or representative elements)

In the columns labeled 1, 2, and 13-18.

Transition Metals

In the columns labeled 3-12

Inner Transition Metals

In the two rows at the bottom of the table

Group 1

 Alkali metals

Group 1 metals always form ions with +1 charge

Group 2

Alkaline earth metals

Group 2 all ions will always form +2 charge

Group 13

Boron group

Group 13 Aluminum will always form +3 charge

Group 14

Carbon group

Group 14 Carbon is four spaces away from noble gases.

Fill valence by gaining 4 electrons = ion with -4 charge.

Group 15

 Pnictogens

Group 15 Nitrogen and Phosphorus are three spaces away from noble gases.

Will gain 3 electrons to form ion with -3 charge.

Group 16

Chalcogens

Group 16 Oxygen, Sulfur and Selenium will gain 2 electrons to form ion with -2 charge.

Group 17

Halogen

Group 17 will gain one electron to form an ion with -1 charge

Group 18

 Noble gases

Group 18 noble gases do not form ions - they’re already stable

Group 3-12

Transition metals

Transition metals have variety of possible charges.

Will assume any transition metal will be a variable charge metal.

Ionic and Molecular Compounds

The transfer and sharing of electrons among atoms govern the chemistry of the elements.

Atoms that gain or lose electrons from electrically charged particles called ions.

Metals lose valence electrons

Form cations

Fixed Charge

Only one possible charge

Variable Charge

More than one possible charge.

Depends on the element and valence electron configuration.

Nonmetals gain electrons to fill valence

Form anions

Monatomic Ions

Ions formed from only one atom

Polyatomic Ions

Electrical charged molecules (a group of bonded atoms with an overall charge)

Oxyanions

Polyatomic ions that contain one or more oxygen atoms

Ammonium

NH₄+

Hydroxide

OH-

Acetate

CH₃COO-

Cyanide

CN-

Carbonate

CO₃²-

Nitrate

NO₃-

Nitrite

NO₂-

Sulfate

SO₄²-

Sulfite

SO₃²-