A Brief History of Chemistry

If we consider chemistry to be the controlled use of a chemical reaction, then we might suggest that it begins when we can make fire (somewhere around 750,000 years ago).

So when does chemistry begin?

Here are some highlights of the earliest examples of the use of chemistry (in chronological order):

For a very long time people have been using pigments to make dyes (not really sure for how long, certainly for 10’s of thousands of years).

Fire hardening of clay to make ceramics – Earlier than 8000 B. C.

Isolation of pure metals from ores (Cu, Au) – circa 4000 B.C.First alloy (bronze, from Cu and Sn) – circa 2000 B.C.

Smelting of Fe (iron age) – about 1500 B.C.And about 500 years later …

They added a little C to make steel.

Egyptians used natural pigments and juices to preserve human bodies – about 900 B.C.

In the 7th century B.C. Thales of Miletus speculated about whether one substance could be transformed into another.This began the movement known as khemeia, which lasted for approximately 1000 years in Greece.Pre-Socratic philosophers developed the idea that matter was composed of four elements -

Leucippus and Democritus did not challenge this idea, but they added their own twist –

Democritus 460 – 370 B.C.

atoms.

They held that the nature of things consists of an infinite number of extremely small particles, which they calledAtomos,the Greek word for indivisible.

Democritus described these particles as indestructible and containing no empty space. He felt these ‘atoms’ moved through space and that if they collided they could interlock, forming substances.

Unfortunately, Democritus ideas were not well received. The opposition included Platoand then, most notably,Aristotle.

Aristotle disregarded the atomistic ideas of Democritus for 3 reasons…

First, he felt it was far more important to understand the form of something rather than its substance.

Second, according to Aristotle, one of the reasons for discarding the concept of an infinite number of atoms moving in infinite space was that in infinite space no natural motion can take place, because in infinite space no place or point can be assigned unambiguously as the endpoint of any object's motion. Perhaps most importantly, he supported the school of thought that matter was infinitely divisible rather than made up of fundamental particles.

So the idea of fundamental particles making up atoms was pretty much ignored for the next 2000 years !!

In fact, in the western world, the end of the Golden Age of Greece was the end of scientific thought for quite a long time.

As one age was ending in the west, a new one was beginning in Egypt, Arabia, and China.This new movement, which began about the 2nd or 3rd century B.C. derives its name from the Arabic word for the khemeia, al-kimiya-- Alchemy

The goal of the alchemists in the east was immortality,a search for the elixir of life.

While they never achieved this, obviously, some significant discoveries were made.

One of the most renowned alchemists of this period was an Arab named Jabir ibn – Hayyan who lived during the 8th century A.D.

He described several chemicals, including some inorganic acids, acetic and nitric, for example, and developed several applied chemical techniques.His descriptions were so complicated and involved, a word was derived from his name - Gibberish

In the 9th century A.D., Another Islamic scientist, the Persian physician Al-Razi, invented the use of plaster of paris to immobilize broken bones. An early example of the use of chemistry for medical treatment.In China, about 1000 A.D., alchemists combined sulfur, salt peter, and honey to produced a recipe for eternal life.

The mixture came with a warning:

Use caution, or this may burn your house down.

The discovery?

Gunpowder !!!

Alchemy did not really develop in Europe until early in the 12th century A.D.Unlike their counterparts in the east, the goal of the European alchemists was wealth.They hoped to develop a way to transmute base elements, like Pb or Fe, into gold.Though never accomplishing this, by constantly messing around with metals, they improved element purification and developed even better alloys.While significant discoveries may have been made during this period, there was no real process or organization. For this reason, we would not call what was being done science.

The first idea for any type method for scientific study comes in the 13th century.

Roger Bacon, a Franciscan friar, proposed that speculation, analogy and even logic are not sufficient.Bacon said that it was necessary to utilize observation, experimentation,and verification.Apparently, the alchemical world wasn’t quite ready for a methodology. It didn’t catch on for several centuries.

In 1661, Robert Boyle, an Irish aristocrat, wrote a book calledThe Skyptical Chymist Among other things, the book argued that ideas about chem should be based on evidence.

Boyle also worked extensively with gases and one of his ideas was that gases were compressible because they were made up of small atoms, with empty space in between them.

That’s right,atoms!

In the 18th century scientific study really takes off.

At about the same time, in Germany, Hennig Brand becomes the first to isolate a non-metallic element,

Phosphorus.Wait ‘til you hear the recipe!

A main area of interest is combustion.One of the first significant ideas about combustion was developed by Georg Stahl in the early part of the century.

Stahl’s idea was that things which could burn gave off a substance he called phlogiston.When the substance had released all its phlogiston,

It stopped burning.

Stahl’s idea was not refuted until the 1770’s.

This was due primarily to the work of two scientists.

Joseph Priestly isolated gases from several types of reactions.He is most well-known for his discovery of oxygen.

The second scientist,

Antoine Lavoisier,Was a contemporary and it has been suggested, a competitor, of Priestly.He demonstrated that Priestly’s gas, which he named oxygen, was responsible for combustion.

This revelation finally ended the phlogiston theory of Stahl. He also showed that if it took place in a sealed container,

no mass was lost during combustion.

This discovery, combined with work on about 100 other reactions, allowed Lavoisier to propose the law of conservation of matter.

He also combined oxygen with a gas that had been discovered by Henry Cavendish (more on him later) and produced water.

This finally refuted the Greek’s 4-element theory for good. In 1778!!Lavoisier demonstrated the importance of carefully making and recording all measurements.He even wrote the first chemistry text.For all his contributions, Lavoisier is often referred to as the Father of Modern Chemistry.Unfortunately, his scientific career was… cut short

Want to hear the story?

Near the end of the 18th century, Joseph Proust showed that a given compound always contains the same proportion of elements by mass.This is known as the law of definite proportions.

In the early 1800’s an English school master used the work of Lavoisier, Proust, and his own research to develop the first modern atomic theory.His name wasJohn Dalton.Part of Dalton’s work was developing the law of multiple proportions.According to this law, different com-pounds made of the same elements,have mass ratios related by small whole numbers.

For example, there are two compounds made exclusively of hydrogen and oxygen.

In one, the ratio of O:H is 8 to 1. Its formula isH2O

In the other, the ratio of O:H is 16 to 1. Its formula is H2O2

Dalton’s atomic theory was comprised of 4 statements:All elements are composed of tiny, indivisible particles called atoms.

Atoms of the same element are identical. Atoms of any one element are different from those of any other element.

Atoms of different elements can combine with one another in simple whole number ratios to form compounds.

Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are not changed into atoms of another, by a chemical reaction.

Dalton’s theory was accepted, unchanged, for nearly a century, when the existence of the first subatomic particle is established.

Who did exactly what is not always clear, but what follows is a reasonably accurate description.

J. J. Thomson is given credit for discovering the electron in 1897.While working at the Cavendish, Thomson was using a device called a Crook’s – or cathode-ray - tube. The Cavendish was a famous lab, at the University of Cambridge, named after Henry. More on it, later.Anyway, Thomson deflected the beam with both charged electrodes and a magnetic field (see demo).Thomson was able to determine that the particles in the beam were negatively charged.

He was also able to calculate the charge to mass ratio.

Thomson’s work was enhanced by Robert Millikan.

In 1911, Millikan devised one of the classic experiments in atomic physics and chemistry,

the oil-drop experiment.

He constructed a chamber with a graduated view lens.

The chamber had oppositely-charged plates. He used an atomizer to spray tiny oil drops between the plates.By adjusting the charge on the plates until a drop was suspended, he determined the charge and mass of the electron (also thanks to Thomson’s results).

J. J. Thomson, who is now the director of the Cavendish, develops a model of the atom.

It is called the plum-pudding model .

The positively-charged, spherically-shaped, atom resembles the pudding part. And the electrons are spread throughout the atom, like the currants and raisins in the pudding.There would be enough electrons to offset the positive charge of the atom.In 1911, this model would be challenged by Rutherford, Geiger, and Marsden.

Ernest Rutherford was a New Zealander who studied under Thomson at the Cavendish laboratory.By 1911 he was at Victoria University, in Manchester.

His former mentor suggested that E. Ruth test the plum-pudding model.

So Ernie, along with his students Hans Geiger and Ernest Marsden, designed what has come to be known as …

The Gold Foil Experiment!

The experiment had a radioactive source, encased in a lead box. The box had a tiny opening to allow a stream of radioactive alpha particles to be emitted. The small,

dense, positively-charged alpha particles traveled thru a slit in circular, zinc sulfide-coated screen. When a particle hit the screen a flash of light was given off.

Since alpha particles are more dense than gold atoms they expected them to pass freely through the gold foil

-- not exactly what happened.

(let’s go back to the last slide)

Rutherford described his surprise the following way:

"It was as if you fired a 15-inch shell at a sheet of tissue paper and it came back to hit you." So what caused the particles to be deflected?

Rutherford explained it like this: An atom has a nucleus.

Rutherford explained that the mass and positive charge must be contained in a central dense core in the atom. He called this core

– the nucleus.

He said that the rest of the atom, outside the nucleus, was mainly empty space.Within this region of empty space, is where the electrons orbit around the nucleus.While this disproved the plum-pudding model,

Rutherford still didn’t know what caused the + charge.

In 1919 (shortly before he returned to the Cavendish to become director), Rutherford fired alpha particles at nitrogen nuclei causing them to release protons.Hydrogen had previously been shown to have these positively-charged particles, but Rutherford showed that these protons were present in all nuclei.Rutherford even predicted that there must be a third type of sub-atomic particle, a neutral particle,that would stabilize the proton repulsion in the nucleus.

This 3rd particle was finally discovered by James Chadwick (at the Cavendish) in 1932.It was called the neutron

.

So, here we are, 1932 and after all that history, this is our version of atomic structure:

ParticleParticle ChargeCharge MassMass LocationLocation

Proton (Proton (ρρ++)) +1+1 1 amu1 amu nucleusnucleus

Neutron Neutron (n(n00))

00 1 amu1 amu nucleusnucleus

Electron Electron (e(e--))

-1-1 0 amu0 amu ee- - cloudcloud

The atomic mass unit (amu) is a relative mass value.

It is equal to 1/12 the mass of the carbon-12 nucleus

The electron actually has a mass of 9.11 x 10-28 g.

This mass is insignificant (1/1840) compared to that of the proton, or neutron, so it is given a value of 0 amu.

IsotopesIsotopes

m

n X

Atoms of the same element with different Atoms of the same element with different masses.masses.

Same # of protons, different # of neutronsSame # of protons, different # of neutrons Isotopic Symbol:Isotopic Symbol:

m = mass number (sum of p+ & no) X = element symbol

n = atomic number (# of p+)

ExamplesExamples

12C 13C 14C 6 6 6#P _______ _______ _______ #N _______ _______ _______ #E _______ _______ _______

More Isotope ExamplesMore Isotope Examples

199F

p+ = no = e- =

184W p+ = no = e- =

Write the symbol for the element with 53 p+ and 74 no.

IsotopesIsotopes

Gallium is a metallic element found in small lasers used in compact disc players. In a sample of gallium, there is 60.2% of gallium-69 (68.9 amu) atoms and 39.8% of gallium-71 (70.9 amu) atoms. What is the atomic mass of gallium?

Ga-69 Ga-69

68.9 amu x 68.9 amu x 60.2 60.2 = = 41.5 amu for 41.5 amu for 6969GaGa

100100

Ga-71Ga-71

70.9 amu x 70.9 amu x 39.8 39.8 = = 28.2 amu for 28.2 amu for 7171GaGa

100100

Atomic mass Ga Atomic mass Ga = = 69.7 amu69.7 amu

IsotopesIsotopes

Lead has four different isotopes. 204Pb has a mass of 203.994 amu and an abundance of 1.32%. 206Pb has a mass of 205.993 and an abundance of 26.31%. 207Pb and 208Pb have masses of 206.991 and 207.899 amu and abundances of 20.78% and 51.59%, respectively. Calculate the relative (average) atomic mass of lead.

203.994 amu x .0132 = 2.69 amu

205.993 amu x .2631 =54.20 amu206.991 amu x .2078 =43.01 amu207.899 amu x .5159 =107.3 amu__________

207.2 amu

Finding Isotopes with Finding Isotopes with missing information.missing information.

If silicon had only two isotopes. What is the If silicon had only two isotopes. What is the percent abundance of it’s heavier isotope?percent abundance of it’s heavier isotope?

Mass NumberMass Number Exact WeightExact Weight Percent Percent AbundanceAbundance

2828 27. 97 27. 97 92.2392.23

2929 28.96 28.96 ??????

How a mass spectrometer worksNote: Samples must be vaporized gases

Different ions are deflected by the magnetic field by different amounts. The amount of deflection depends on:•the mass of the ion. Lighter ions are deflected more than heavier ones.•the charge on the ion. Ions with 2 (or more) positive charges are deflected more than ones with only 1 positive charge

Now that we have some knowledge about light, we can examine Niels Bohr’s solution to the electron orbit problem. Bohr combined the science of spectroscopy with Planck’s quantum theory to develop his explanation. What is spectroscopy? Let’s find out.

If white light is separated into its spectrum, the colors form a continuum.If the light given off from

a single element is separated, however, distinct lines are formed. emission spectrum.This is called an

Distinct dark lines are also formed when white light has passed through the gas of a single element.This is known as an absorption spectrum.

The important question was, Why was the spectrum of an element composed of separate lines, and not continuous like the spectrum of white light?Bohr’s answer to that question would be his explanation of how the electrons behaved in an atom. In 1885 Johann Balmer had shown mathematically that the wavelengths of the lines in the visible emission spectrum of hydrogen resulted from some whole number transition.

4 visible spectral lines of Hred

blue-greenblueviolet

Bohr suggested that this transition corresponded to an electron jumping from one possible orbit to another and emitting a photon of light energy.

In Bohr’s model of the atom, the electron can only exist in these specific orbits in an atom.Since an electron would have to possess a specific amount of potential energy to be in one of these orbits,they are known as energy levels. Here is how it works:

The electron is attracted to the positive charge of the nucleus, so the electron has to have more energy to be far from the nucleus than to

be close. Normally the electron would be in its low- est available energy level,this is called its ground state. If the atom is

exposed to an energy source the electron can absorb a quantum of energy (photon)

and the electron will make a quantum leap to a higher energy level. The electron

will then drop back down to a lower energy level.In order for this to happen,

the electron has to give off a quantum of light energy (photon). The energy of this photon would correspond exactly to the energy difference between the two levels. Using Planck’s equation, Bohr was able to calculate the energy value for each level in the hydrogen atom.It is important to note that the electron can jump from one level to another, but it cannot go in between them.

Bohr model

A little more than 30 years after that James Clerk Maxwell developed a set of equations that confirmed Faraday’s idea that electricity and magnetism are simply two parts of a single phenomenon, electromagnetism.

Maxwell showed that this phenomenon would produce waves which travel at the speed of light. He also suspected that there were light waves other than those that produced the light that we could see. We now refer to this collection of different waves of electromagnetic radiation (light) as the

Before we look at the EMS, let’s talk about waves.

electromagnetic spectrum (EMS)

http://paws.kettering.edu/~drussell/Demos/waves/wavemotion.html

There are two main types of waves,

transverse,and

longitudinal.Light moves through space as two interacting transverse wave disturbances, one caused by the electrical field and the other by the magnetic.

Another important feature of wave motion is the inverse relationship between wavelength and frequency.

That is, as one increases the other decreases.

waveParts of a wave you should be familiar with:

This relationship is expressed in the following equation:c=(the speed of light)λ(wavelength)ν(frequency)What about units, you ask?Well…

What is the highest point on a What is the highest point on a wave called?wave called?

a.a. TroughTrough

b.b. CrestCrest

c.c. AmplitudeAmplitude

d.d. ColgateColgate

the speed of light has a constant value of 3.00 x 108 m/sWavelength is in meters.

Frequency is in:cycles/s;or 1/s; or s-1.These are also known as 1 hertz (Hz)Sample problem 1: Calculate the frequency of light with a wavelength of 5.22 x 10-10 m.c = λνManipulating the variables to solve for ν gives,v = c/λ = 3.00 x 108 m/s/5.22 x 10-10 m/ / =

5.75 x 1017/s = 5.75 x 1017 Hz

Sample problem 2 (You try): Calculate the wavelength of a radio station signal with a frequency of 99.7 MHz.c = λν λ = c /ν = 3.00 x 108 m/s/ 99.7 x 106/s

3.01 m

/ /

=

OK, now let’s discuss Review the EMS.

microwaves Radio waves

The spectrum goes from radio waves (long λ) on the rightto gamma rays (short λ) on the left. The visible part of the spectrum goes from red (7 x 10-7m) to violet (4 x 10-7m),

ROYGBIVin this sequence v increases.,

At the end of the 19th century, there were two things about which science was certain: Matter was particles;

and light was waves.Then,in 1900, everything was messed up, by a German scientists named Max Planck.

Planck was trying to determine how the color of light radiated by a body was related to its temperature.Two separate mathematical explanations already existed.One failed to work for light at high frequencies,the other at low frequencies.

Planck demonstrated that the problem could be solved by treating light as being given off in discrete units – he called them quanta - rather than being given off continuously, as previously assumed.

Planck found that light energy was proportional to its frequency. The relationship is given by:E = hνE is energy.h is Planck’s constant,6.63 x 10-34 J . s

If light is only emitted or absorbed in a discrete quantum of energy, If it’s not continuous,then what is it? A particle?

Evidence to support Planck’s theory came in 1905when a Swiss patent clerk explained the photo-electric effect. When UV light is shined on a piece of metal connected to a circuit, electrons are ejected into the circuit and a current is produced.What no one had yet explained was why the intensity of light had no effect on the energy of the electrons.

The patent clerk proposed that if, like Planck said, light consisted of discrete quanta - photons -they would interact with the electrons like particles. He even showed

the electrons had energy related to hv !!Who was this clerk?

Albert Einstein

Sample Problem #1 Calculate the energy of a photon of light with a frequency of 5.45 x 1014 Hz.E = hv = (6.63 x 10-34 J . s)(5.45 x 1014/s)/ / =

3.61 x 10-19 J

Wave-Particle DualityWave-Particle Duality Louis De Broglie (1924)Louis De Broglie (1924)

Proposed that ALL matter has wave and Proposed that ALL matter has wave and particle properties, not just electrons.particle properties, not just electrons.

E = E E = E E = h E = hυυ or E = hc/ or E = hc/λλ & E = mc & E = mc22

hc/hc/λλ = mc = mc22 hc = mc hc = mc22λλ h = mc h = mcλλ λλ = h/mc OR = h/mc OR λλ = h/m = h/mυυ Example:Example:

λλ of baseball (mass = .2 kg and of baseball (mass = .2 kg and υυ = 30 m/s) = 30 m/s) λλ of an electron (mass = 9.11 x 10 of an electron (mass = 9.11 x 10-31-31 kg and kg and υυ

= 3 x 10= 3 x 1088 m/s) m/s)

Wave-Particle DualityWave-Particle Duality Heisenberg (1927)Heisenberg (1927)

Said that because of size and speed it is Said that because of size and speed it is impossible to know both exact position and impossible to know both exact position and momentum of and electron at the same time.momentum of and electron at the same time.

This is referred to as This is referred to as ““Heisenberg Uncertainty Heisenberg Uncertainty PrinciplePrinciple””

To To ““seesee”” an electron we strike it with something an electron we strike it with something of similar size and observe its behavior.of similar size and observe its behavior.

We cannot see an electron directly.We cannot see an electron directly. We use photons of energy to do this.We use photons of energy to do this.

Quantum MechanicsQuantum Mechanics The work of de Broglie and Heisenberg The work of de Broglie and Heisenberg

led to the study of led to the study of ““quantum mechanicsquantum mechanics”” (motion in increments)(motion in increments)1. classical physics1. classical physics describes the motion of bodies much larger describes the motion of bodies much larger

than the atoms of which they are composed.than the atoms of which they are composed. energy can be gained or lost in any amountenergy can be gained or lost in any amount

2. quantum physics2. quantum physics describes the motion of atoms and describes the motion of atoms and

subatomic particles as waves.subatomic particles as waves. particles gain or lose energy in packets particles gain or lose energy in packets

called called ““quantaquanta””

Quantum Mechanical ModelQuantum Mechanical Model Schroedinger (1887-1961)Schroedinger (1887-1961)

Developed the Developed the ““quantum mechanical modelquantum mechanical model”” of the of the atomatom

He used the following equation to produce He used the following equation to produce scatterplots that are now called scatterplots that are now called ““electron cloudselectron clouds””

E = 2E = 222meme22/h/h22nn22

These electron clouds are areas in which there is a These electron clouds are areas in which there is a great probability of finding an electron (90%).great probability of finding an electron (90%).

The cloud is more dense where the probability of The cloud is more dense where the probability of finding an electron is high.finding an electron is high.

The cloud is less dense where the probability of The cloud is less dense where the probability of finding an electron is low.finding an electron is low.

This is called an This is called an ““orbitalorbital”” – a region in space in – a region in space in which there is a high probability of finding an which there is a high probability of finding an electron.electron.

http://scienceworld.wolfram.com/physics/SchroedingerEquation.htmlhttp://www.uark.edu/misc/julio/orbitals/index.html

Electrons and Electron Electrons and Electron Configurations (Not on note Configurations (Not on note

sheet)sheet) Electrons have an Electrons have an ““addressaddress”” with four quantum with four quantum numbers.numbers.

We have 3 General rules for We have 3 General rules for ““distributingdistributing”” these these electrons.electrons. Pauli Exclusion Principal: Orbitals contain no Pauli Exclusion Principal: Orbitals contain no

more than two electrons. Or…Each address more than two electrons. Or…Each address describes the location of only one electron.describes the location of only one electron.

Hund Rule: When filling orbitals, assign one Hund Rule: When filling orbitals, assign one electron to each orbital (of that type) before electron to each orbital (of that type) before doubling up with two electrons per orbital.doubling up with two electrons per orbital.

Aufbau: Electrons fill lowest orbitals first, then Aufbau: Electrons fill lowest orbitals first, then procede to higher energy levels. procede to higher energy levels.

Energy Components in Energy Components in ElectronsElectrons

Each component is given a letter & a name – Each component is given a letter & a name – we call them we call them ““quantum number valuesquantum number values””1. n = principal1. n = principal distance from the nucleus (energy level)distance from the nucleus (energy level)2. l = azimuthal2. l = azimuthal indicates the type of orbital in which the indicates the type of orbital in which the

electron moves (sublevel)electron moves (sublevel)3. m = magnetic3. m = magnetic indicates the orientation about the three axes in indicates the orientation about the three axes in

space of the orbital (specific orbital)space of the orbital (specific orbital)4. s = spin4. s = spin indicates the direction of the spin of the electron indicates the direction of the spin of the electron

– either clockwise or counterclockwise.– either clockwise or counterclockwise. Using these we can pinpoint the exact Using these we can pinpoint the exact

location of an elocation of an e--..

LocationLocation n = principal energy leveln = principal energy level n + l = energy sublevel, defines the n + l = energy sublevel, defines the

type of orbital that the electron is intype of orbital that the electron is in n + l + m = specific orbital (axis n + l + m = specific orbital (axis

orientation)orientation) n + l + m + s = spin (exact n + l + m + s = spin (exact

electron), identifies the exact electron), identifies the exact electron and its locationelectron and its location

ANALOGYANALOGY

Orbital TypesOrbital Types

S-orbital = spherical shape, only 1 of themS-orbital = spherical shape, only 1 of them P-orbital = gumdrop or dumbell shape, 3 of P-orbital = gumdrop or dumbell shape, 3 of

them – one on each axis (x,y,z)them – one on each axis (x,y,z) D-orbital = donut shape, 5 of themD-orbital = donut shape, 5 of them F-orbital = cigar shape, 7 of themF-orbital = cigar shape, 7 of them Each orbital contains a max of 2 electronsEach orbital contains a max of 2 electrons Orbit – path of an electron (according to Bohr)Orbit – path of an electron (according to Bohr) Orbital – region in space where there is a high Orbital – region in space where there is a high

probability of finding an electronprobability of finding an electron

Orbital Shapes

Orbital SitesOrbital Sites

http://www.colby.edu/chemistry/http://www.colby.edu/chemistry/OChem/DEMOS/Orbitals.htmlOChem/DEMOS/Orbitals.html

http://micro.magnet.fsu.edu/http://micro.magnet.fsu.edu/electromag/java/atomicorbitals/electromag/java/atomicorbitals/index.htmlindex.html

http://itl.chem.ufl.edu/ao_pict/ao_pict.html

http://winter.group.shef.ac.uk/orbitron/AOs/1s/index.html

ENERGY ENERGY LEVELSLEVELS

ORBITAL ORBITAL TYPESTYPES

# OF # OF ORBITALSORBITALS

# OF # OF ELECTROELECTRO

NSNS

n = 1n = 1 ss 11 22

n = 2n = 2 s,ps,p 44 88

n = 3n = 3 s,pd,s,pd, 99 1818

n = 4n = 4 s,p,d,fs,p,d,f 1616 3232

n = 5n = 5 s,p,d,f,s,p,d,f,””gg ”” 2525 5050

Energy level = the number of orbital typesTotal number of orbitals in an energy level = n2

Total number of electrons in any energy level = 2n2

Not on Notes Outline…..Not on Notes Outline…..Now with the idea of orbitals firmly in-Now with the idea of orbitals firmly in-hand. hand. •How manyHow many•What shapeWhat shape•How many electrons they can holdHow many electrons they can hold

Now we can actually do something Now we can actually do something with this knowledge!with this knowledge!

Electron Configurations!!!Electron Configurations!!!

(Hint: Saying electron configurations (Hint: Saying electron configurations are a big deal in Chemistry would be are a big deal in Chemistry would be an understatement)an understatement)

Not on Notes Outline…..Not on Notes Outline…..Electron Configurations!!!Electron Configurations!!!

Indicate where all the electrons are Indicate where all the electrons are located.located.•Which energy levelWhich energy level•Which type of orbitalWhich type of orbital•Which orbital of Which orbital of thatthat type type•What direction they spinWhat direction they spin

Not on Notes Outline…..Not on Notes Outline…..Electron Configurations!!!Electron Configurations!!!

We will always start at the lowest We will always start at the lowest possible energy level and fill upwards possible energy level and fill upwards until all possible electrons are until all possible electrons are assigned.assigned.

Electron ConfigurationA method we use to keep track of how electrons are arranged in an atom.

It helps us to explain why atoms react the way they do.

H 1s1

Energy LevelSub-level

# of electrons in sub-level

The arrangement of the electrons may be represented in one of three ways.

This is how hydrogen would be shown using spectroscopic notationElectron configuration may also be shown with box diagrams.

Electron Configuration

A box is used to represent each orbital.

An arrow is used to represent each electron.

H 1s1 These may also be called orbital box diagrams or orbital filling diagrams.

Circles may also be used instead of boxes.Helium has 2 electrons:

He 1s2

Electron Configuration

Here are some more:

Li 1s2 2s1

Be 1s2 2s2

B 1s2 2s2 2p1

C 1s2 2s2 2p2

N 1s2 2s2 2p3

O 1s2 2s2 2p4

F 1s2 2s2 2p5

Ne 1s2 2s2 2p6

This arrangement (filled s & p in the outer energy level) is called a stable octet.

Not on Notes Outline…..Not on Notes Outline…..Review Slide:Review Slide:

Electrons move around the nucleus in orbitals of Electrons move around the nucleus in orbitals of distinct shapes and sizes. Starting with 1s then distinct shapes and sizes. Starting with 1s then building around this with another sphere, the 2s, building around this with another sphere, the 2s,

and moving on to fill higher and progressively more and moving on to fill higher and progressively more complex shapes and energy levels as more complex shapes and energy levels as more

electrons are added.electrons are added.

•The Orbitals and their shapes are?The Orbitals and their shapes are?•How many can each orbital hold?How many can each orbital hold?•How many of each can occur in a How many of each can occur in a given energy level.given energy level.

Not on Notes Outline…..Not on Notes Outline…..

Not on Notes Outline…..Not on Notes Outline…..Review Slide:Review Slide:

We have 3 General rules for We have 3 General rules for ““distributingdistributing”” these these electrons.electrons.

Pauli Exclusion Principal: Orbitals contain no Pauli Exclusion Principal: Orbitals contain no more than two electrons. Or…Each address more than two electrons. Or…Each address describes the location of only one electron.describes the location of only one electron.

Hund Rule: When filling orbitals, assign one Hund Rule: When filling orbitals, assign one electron to each orbital (of that type) before electron to each orbital (of that type) before doubling up with two electrons per orbital.doubling up with two electrons per orbital.

Aufbau: Electrons fill lowest orbitals first, then Aufbau: Electrons fill lowest orbitals first, then procede to higher energy levels. procede to higher energy levels.

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Configurations can be written in Configurations can be written in four waysfour ways

•Spectroscopic notationSpectroscopic notation•Box diagramBox diagram•Dot notationDot notation•IB short handIB short hand

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We finished with several new revelations/tricks:We finished with several new revelations/tricks:

1.1.Noble Gas shorthand!Noble Gas shorthand!

2.2.There are exceptions :^(There are exceptions :^(1.1. The energy levels do not always fill in the designated order The energy levels do not always fill in the designated order

and will fill the 4s before the 3d or 5s before the 4d…etc The and will fill the 4s before the 3d or 5s before the 4d…etc The diagonal rule!diagonal rule!

2.2. A half or fully filled A half or fully filled ““dd”” orbital is MORE stable than the orbital is MORE stable than the exception above and so when you encounter a 3d4 or 3d9 exception above and so when you encounter a 3d4 or 3d9 situation nature will make an exception to the above situation nature will make an exception to the above exception. See Copper or Chromiumexception. See Copper or Chromium

3.3.The periodic table is arraigned to match electron The periodic table is arraigned to match electron configurations! You donconfigurations! You don’’t need the t need the ““diagonal rulediagonal rule””!!

4.4.The The ““dot notationdot notation”” that you write is a summary of that you write is a summary of the outmost energy level, the one that interacts the outmost energy level, the one that interacts

with the world. These are known as an elements with the world. These are known as an elements VALENCE ELECTRONS and also correspond to the VALENCE ELECTRONS and also correspond to the

column number in the table.column number in the table.

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