CHAPTER 5

CHAPTER 5

The Structure of Atoms

Fundamental Particles

The following three fundamental particles make up atoms. The table below lists these particles together with their masses and their charges.

Particle Mass (amu) Charge

Electron (e-) 0.00054858 -1

Proton (p,p+) 1.0073 +1

Neutron(n,n0) 1.0087 0

Structure of the Atom Videos

1. The earliest modelshttp://www.youtube.com/watch?v=BhWgv0STLZs&feature=player_embedded

2. Smaller than the Smallesthttp://www.youtube.com/watch?v=WmmglVNl9OQ&feature=player_embedded

3. The Rutherford Modelhttp://www.youtube.com/watch?v=FfY4R5mkMY8&feature=player_embedded

4. The Bohr Modelhttp://www.youtube.com/watch?v=hpKhjKrBn9s&feature=player_embedded

5. Spectrahttp://www.youtube.com/watch?v=5z2ZfYVzefs&feature=player_embedded

6. Wave Mechanicshttp://www.youtube.com/watch?v=1bpG1lEjJfY&feature=player_embedded

Take notes over each video. Check calendar for due date.

The Atomic Weight Scale & Atomic Weights

define mass of 12C as 12 amu exactly1 amu = (1/12) mass of 12C

Ex. 1) Calculate the number of atomic mass units in one gram.

mass of one 24Mg atom = 24.3050 amuexperimentally determined1 mol of 24Mg atoms = 24.3050 g

atomic weight - weighted average of the masses of its constituent isotopes

Ex 2) Naturally occurring chromium consists of four isotopes. It is 4.31% 24

50Cr, mass = 49.946 amu, 83.76% 24

52Cr, mass = 51.941 amu, 9.55% 24

53Cr, mass = 52.941 amu, and 2.38% 24

54Cr, mass = 53.939 amu. Calculate the atomic weight of chromium.

Naturally occurring Lithium exists as two

isotopes, 6Li (mass = 6.015 amu) and 7Li (mass = 7.016 amu). The atomic weight is 6.941 amu. Which isotope is more abundant? Why?

Ex 3) The atomic number of boron is 10.811 amu. The masses of the two naturally occurring isotopes 5

10B and 511B, are 10.013

and 11.009 amu, respectively. Which isotope is most common? Calculate the fraction and percentage of each isotope.› requires a little algebra› remember X + (1-X) = 1

Ex 4) Nickel has five isotopes that occur in the following percentages and isotopic masses. What is the isotopic mass of 60Ni?

Isotope Mass (amu) % 58Ni 57.935 68.27 60Ni ? 26.10 61Ni 60.931 1.13 62Ni 61.928 3.59 64Ni 63.928 0.91

Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles. It is most generally used to find the composition of a sample by generating a mass spectrum representing the masses of sample components. The mass spectrum is measured by a mass spectrometer.

http://www.youtube.com/watch?v=J-wao0O0_qM

Mass Spectrometry & Isotopic Abundances

An analytical technique for identification of chemical structures, determination of mixtures, and quantitative elemental analysis, based on application of the mass spectrometer.

Francis Aston - devised first mass spectrograph

› In a mass spectograph ions pass down an evacuated path inside a magnet

Four factors which determine particle’s path in mass spectrometer1. accelerating voltage2. magnetic field strength3. masses of particles4. charge on particles

Mass spectrometers consist of three basic parts: an ion source, a mass analyzer, and a detector system. The stages within the mass spectrometer are:› Production of ions from the sample › Separation of ions with different masses › Detection of the number of ions of each

mass produced › Collection of data to generate the mass

spectrum

This technique is applicable in: identifying unknown compounds by the mass

of the compound molecules or their fragments determining the isotopic composition of

elements in a compound determining the structure of a compound by

observing its fragmentation quantifying the amount of a compound in a

sample using carefully designed methods studying the fundamentals of gas phase ion

chemistry (the chemistry of ions and neutrals in vacuum)

determining other important physical, chemical, or even biological properties of compounds with a variety of other approaches

How does a mass spectrometer work?

Since different chemicals have different masses, this info is used to determine what chemicals are present in a sample.

For example, table salt: NaCl, may be vaporized, turned into

gas and ionized into ions, electrically charged particles (Na+ and Cl-), in the first phase of the mass spectrometry.

The sodium ions are monoisotopic, with mass 23 u. Chloride ions have two isotopes of mass 35 u (~75%) and mass 37 u (~25%). Since they have a charge, the speed and direction may be changed with an electric or magnetic field.

An electric field accelerates the ions to a high speed. Next they are directed into a magnetic field which applies a force to each ion perpendicular to the plane of the particles' direction of travel and the magnetic field lines.

This force deflects the ions (makes them curve instead of traveling in a straight line) to varying degrees depending on their mass-to-charge ratio. Lighter ions get deflected more than the heavier ions. This is due to Newton’s 2nd law of Motion. The acceleration of a particle is inversely proportional to its mass.

Therefore, the magnetic field deflects the lighter ions more than it does the heavier ions.

The detector measures the deflection of each resulting ion beam.

From this measurement, the mass-to-charge ratios of all the ions produced in the source can be determined. So the chemical composition of the original sample (both sodium and chlorine are present in the sample) and the isotopic compositions of its constituents (the ratio of 35Cl to 37Cl atoms) can be determined.

Electromagnetic Radiationrelationship for electromagnetic radiationc = l u

c = velocity of light - 3.00 x 108 m/s

Ex. 5) What is the frequency of green light of wavelength 5200 Å?

Max Planck - 1900› energy is quantized› light has particle character

Planck’s equation

sJ 10x 6.626 constant s Planck’ h

hc or E h E

34-

l

Ex. 6) What is energy of a photon of green light with wavelength 5200 Å?

Photoelectric EffectParticles – have mass, volume, and are countable.Photon – light composed of particles

•light has particle-like behavior•light can strike the surface of some metals and cause an electron to be ejected

Ex. ~ electronic door openers~ light switches for street lights~ exposure meters for cameras

• Albert Einstein explained the photoelectric effect in 1905› 1921 Nobel Prize in Physics

electrons are particle like b/c energy from a photon transfers to e- during collisions. If you increase energy, more electrons get kicked off. Each individual photon makes a spark, 1 e- per photon. The more intense the light, the more photons. Light strikes the surface of various metals and causes electrons to be ejected.

Atomic Spectraemission spectrum

electric current passing through a gas in a vacuum tube (at very low pressure) causes the gas to emit light

emission or bright line spectrum

absorption spectrumshining a beam of white light through a sample

of gas gives an absorption spectrum shows the wavelengths of light that have been

absorbed

Spectra are fingerprints of elements

use spectra to identify elementscan even identify elements in stars

The Origin of Spectral Lines Light of a characteristic wavelength (&

frequency) is emitted when electron falls from higher E (orbit) to lower E

(orbit)origin of emission spectrum

light of a characteristic wavelength (& frequency) is absorbed when

electron jumps from lower E (orbit) to higher E (orbit)

origin of absorption spectrum

Atomic Spectra how atoms talk to us”

› we have to interpret their language Bohr, Schrodinger, and Heisenberg

were some of the first scientists to translate the language of atoms

Ex. 7) An orange line of wavelength 5890 Å is observed in the emission spectrum of sodium. What is the energy of one photon of this orange light?

Quantum Mechanics Werner Heisenberg - 1927

› Uncertainty Principle

It is impossible to determine simultaneously both the position & momentum of an electron. Why? The act of measuring a very small particle changes its position, so it is impossible to precisely determine both the position and momentum of that object.

› electron microscopes use this phenomenon› devices for detecting motion of electron disturbs its

position

Quantum NumbersQuantum numbers are description of the orbitals; solutions of the Schrodinger, Heisenberg & Dirac wave equations

the quantum #’s help symbolize the solutions

There are four quantum numbers which describe the relative position and energy of an electron in an atom.

1. Principal quantum number

2. Angular momentum quantum number

3. Magnetic quantum number

4. Spin quantum number

Principal Quantum Number

Symbol “n” – refers to energy level n = 1, 2, 3, …

The principal quantum number describes the relative distance from the nucleus. It is often referred to as Energy Level or Shell.

electron’s energy depends principally on n

Angular momentum, 2nd quantum number

angular momentum, tells shape of the atomic orbitals

Atomic Orbitals - regions of space where the probability of finding an electron around an atom is highest

~ volume that the electrons occupy 90-95% of the time

symbol ℓ to find ℓ plug into n-1n=1 n=2 n=3 …. n=8ℓ =0 ℓ = 0, 1 ℓ = 0, 1, 2 ℓ = 0, 1, 2, 3, 4, 5,

6, 7

represents the sublevels within an energy level: s, p, d, f (code letters for the shapes of orbitals) s=0 p=1 d=2 f=3

Quantum number - ℓℓ = 0, 1, 2, 3, 4, 5, .......(n-1)ℓ = s, p, d, f, g, h, .......(n-1)

s orbitalss orbitals are spherical in shape.Every energy level has an s orbitals orbitals have angular momentum quantum number (l) equal to 0.

p orbitalsp orbitals are shaped like dumbbells or peanuts.

They are oriented along the x, y, and z coordinates.

They have an angular momentum quantum number (l) equal to 1.3 per n level,

px, py, pzl = 1

p orbitals

d orbitals

start with n = 3

4 clover leaf shaped and 1 peanut shaped with a doughnut around it

on Cartesian axes and rotated 45o

5 per n level

l = 2m l = -2,-1,0,+1,+2 5 values of m l m l = Magnetic quantum number (info in a few slides)

d orbitals

f orbitals

start with n = 4 most complex shaped orbitals7 per n level, complicated names

l = 3 m l = -3,-2,-1,0,+1,+2, +3

7 values of m l important effects in lanthanides

& actinides

f orbitals

Magnetic quantum numbers 3rd quantum number symbol m l Helps tell orientation of orbitals

m l = - l to + l

theoretically, we can continue this series on to g, h, i, orbitals

l =0 m l =0

› only 1 value s orbital

l =1 m l = -1, 0, 1

› 3 values p orbitals

l =2m l = -2, -1, 0, 1, 2

› 5 values d orbitals

l =3 m l = -3, -2, -1, 0, 1, 2,

3› 7 values

f orbitals

Spin Quantum Number 4th quantum number, symbol = ms

› ms = +1/2 or -1/2

tells us the spin and orientation of the magnetic field of the electrons

spin effects› every orbital can hold up to two electrons› one spin up ­ one spin down ¯

spin describes the direction of their magnetic field

e- have charges two allowable magnetic states

Diamagnetic vs. paramagnetic paired electrons have spins unaligned ­¯

› no net magnetic field diamagnetic - repelled by a magnetic field,

all electrons are paired

unpaired electrons have their spins aligned ­­ or ¯¯› enhanced magnetic field

paramagnetic - attracted to a magnetic field, has unpaired electrons

Electronic ConfigurationsRules for assigning e- in orbitals:

1. Always fill orbitals in lowest energy level first. (Aufbau Principle)

Aufbau Principle - The electron that distinguishes an element from the previous element enters the lowest energy atomic orbital available. (in other words fill one energy sublevel before moving up)

2. No two e- can have same 4 quantum numbers in an atom. (Pauli Exclusion Principle)

Wolfgang Pauli - 1925 › No two electrons in an atom may have identical

sets of 4 quantum numbers.

3. Spread e- out on a sublevel if possible. (Hund’s Rule)

Electrons will spread themselves out among the orbitals individually and give unpaired, parallel spins. The pairing of electrons is an unfavorable process; energy must be expended in order to make it occur.

Exception: If you can achieve full or half-full orbitals by moving one e- between s ~ d or s ~ f orbitals, do so. It’s lower in energy because there is an increased stability due to the decrease in the screening of electron/nuclear attractions

Electronic Configurations

use periodic chart - best method

Electronic Configurations and Orbital Diagrams

1st row

22

11

1s He

1s H

ionConfigurat 1s

­¯

­

Orbital Order1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p 8s

2nd row

62210

5229

4228

3227

2226

1225

224

123

2p 2s 1s Ne

2p 2s 1s F

2p 2s 1s O

2p 2s 1s N

2p 2s 1s C

2p 2s 1s B

2s 1s Be

2s 1s Li

ionConfigurat 2p 2s 1s

­¯­¯­¯¯­­¯

­­¯­¯¯­­¯

­­­¯¯­­¯

­­­¯­­¯

­­¯­­¯

­¯­­¯

¯­­¯

­­¯

3rd row

62

18

5217

4216

3215

2214

1213

212

111

3p s3 Ne NeAr

3p s3 Ne Ne Cl

3p s3 Ne Ne S

3p s3 Ne Ne P

3p s3 Ne Ne Si

3p s3 Ne Ne Al

s3 Ne Ne Mg

s3 Ne NeNa

ionConfigurat 3p 3s

­¯­¯­¯­¯

­­¯­¯­¯

­­­¯­¯

­­­­¯

­­­¯

­­¯

­¯

­

4th row

orbitals. filled completely and filled-half withassociatedstability of measureextra an is There

3d 4s Ar ArCr

3d 4s Ar Ar V

3d 4s Ar Ar Ti

3d 4s Ar Ar Sc

4s Ar ArCa

4s Ar ArK

ionConfigurat 4p 4s 3d

5124

3223

2222

1221

220

119

­­­­­­

­¯­­­

­¯­­

­¯­

­¯

­

4th row continued

reason. same y theessentiallfor andCr like exceptionAnother

3d 4s Ar Ar Cu

3d 4s Ar Ar Ni

3d 4s Ar Ar Co

3d 4s Ar Ar Fe

3d 4s Ar Ar Mn

ionConfigurat 4p 4s 3d

10129

8228

7227

6226

5225

­­¯­¯­¯­¯­¯

­¯­­­¯­¯­¯

­¯­­­­¯­¯

­¯­­­­­¯

­¯­­­­­

4th row continued

6102

36

510235

410234

310233

210232

110231

4p 3d 4s Ar ArKr

4p 3d 4s Ar ArBr

4p 3d 4s Ar Ar Se

4p 3d 4s Ar Ar As

4p 3d 4s Ar Ar Ge

4p 3d 4s Ar ArGa

ionConfigurat 4p 4s 3d

­¯­¯­¯­¯­¯­¯­¯­¯­¯

­­¯­¯­¯­¯­¯­¯­¯­¯

­­­¯­¯­¯­¯­¯­¯­¯

­­­­¯­¯­¯­¯­¯­¯

­­­¯­¯­¯­¯­¯­¯

­­¯­¯­¯­¯­¯­¯

Finding Quantum numbers Let’s find the complete set of quantum

numbers for the electrons in Na and Fe

(look at electron configurations/orbital diagrams 1st) 11Na

› must have one set of 4 quantum numbers for each of the 11 electrons in Na

26Fe› should have one set of 4 quantum numbers

for each of the 26 electrons in Fe

Some vocab Ground State – lowest energy/most stable

state of an atom, molecule, or ion. Fills one sublevel before moving up, follows Aufbau Principle.

Excited State – orbitals skipped, does not follow Aufbau Principle

Forbidden State – very wrong or not possible

Isoelectronic – different elements that have the same electron configuration b/c of gaining or losing electrons.

Shielding effect - negatively charged electrons prevents higher orbital electrons from experiencing the full nuclear charge by the repelling effect of inner-layer electrons

Effective nuclear charge - the net positive charge experienced by an electron in a multi-electron atom

group names on the P.T. ~ Representative elements

Representative elements: group A(the last electron fills s or p levels) IA – alkali metals IIA – alkaline earth metals IIIA – boron famly IVA – carbon family VA – pnictogens or nitrogen family VIA – chalcogens or oxygen family VIIA – halogens VIIIA – noble gases

group names on the P.T. ~ the rest… Transition metals (filling d level) 3 - the scandium family 4 - the titanium family 5 - the vanadium family 6 - the chromium family 7 - the manganese family 8 - the iron family 9 - the cobalt family 10 - the nickel family 11 - the coinage or copper family 12 - the zinc family

Lanthanide series (filling 4f level) Actinide series (filling 5f level)

Extra credit1) In a universe far far away, the laws

of quantum mechanics are the same as ours with one small change. Electrons in this universe have three spin states, -1, 0, and +1, rather than the two, +1/2 and -1/2, that we have. What two elements in this universe would be the first and second noble gases? (Assume that the elements in this different universe have the same symbols as in ours.)

2) A) What is the atomic number of the element that should theoretically be below Ra? B) Its chemical behavior would be most similar to which elements? C) How many valence electrons would it have?D) Its electron configuration would be?E) An acceptable set of 4 quantum numbers for the last electron in this element would be?F) What would you name it?