atomic structure ? kenneth e. schnobrich. a brief history about 460 b.c. - a greek philosopher,...

ATOMIC STRUCTUREATOMIC STRUCTURE

?

Kenneth E. Schnobrich

A Brief HistoryA Brief History

• About 460 B.C. - a Greek Philosopher, About 460 B.C. - a Greek Philosopher, Democritus, developed the idea of Democritus, developed the idea of atoms (atoms (atomos)atomos) as small indivisible as small indivisible particlesparticles

• About 400 B.C. - a number of Greek About 400 B.C. - a number of Greek philosophers said matter consisted of philosophers said matter consisted of FIRE, EARTH, WATER, and AIR.FIRE, EARTH, WATER, and AIR.

A Brief HistoryA Brief History• NEXT 2000 YEARS - Alchemy (a pseudoscience) NEXT 2000 YEARS - Alchemy (a pseudoscience)

dominated - they were concerned with turning dominated - they were concerned with turning base metals into gold. During this time Hg, S, base metals into gold. During this time Hg, S, and Sb were discovered. Alchemists also and Sb were discovered. Alchemists also discovered how to make mineral acids.discovered how to make mineral acids.

• 1754-1826 Joseph Proust showed that a given 1754-1826 Joseph Proust showed that a given compound always had the same proportions by compound always had the same proportions by mass. mass. Law of Definite Proportions.Law of Definite Proportions.

A Brief HistoryA Brief History• 1766-1844 - John Dalton (following the work of 1766-1844 - John Dalton (following the work of

Robert Boyle) discovered that atoms can Robert Boyle) discovered that atoms can combine in more than one way. He proposed combine in more than one way. He proposed the the Law of Multiple Proportions.Law of Multiple Proportions. He theorized He theorized that the basic unit was the that the basic unit was the atomatom. .

• 1808 - Michael Faraday worked on the 1808 - Michael Faraday worked on the electrolysis of molten salts and coined the word electrolysis of molten salts and coined the word ion (ion (Greek meaning wanderers).Greek meaning wanderers).

A Brief HistoryA Brief History

• 1808 - John Dalton published “A New System 1808 - John Dalton published “A New System of Chemical Philosophy” which proposed his of Chemical Philosophy” which proposed his theory of atomstheory of atoms– All elements are composed of tiny, discrete, All elements are composed of tiny, discrete,

indivisible and indestructible particles called indivisible and indestructible particles called “atoms”.“atoms”.

– All atoms of a given element are identicalAll atoms of a given element are identical– Atoms of of different elements are different; they Atoms of of different elements are different; they

have different masses and properties.have different masses and properties.– Chemical combinations of these “atoms” compose all Chemical combinations of these “atoms” compose all

matter - different atoms combine differently to form matter - different atoms combine differently to form compounds.compounds.

DALTON’S ATOMDALTON’S ATOM

JOHN DALTON - he envisioned the atom as a hard spherical unit of matter (the ultimate unit)

Lithium

Chlorine

Sulfur

LiCl

Li2S

DALTON’S ATOMDALTON’S ATOM

JOHN DALTON - he envisioned the atom as a hard spherical unit of matter

Oxygen

Hydrogen

H2O

H2O2

HISTORY (cont.)HISTORY (cont.)

• 1875 - Eugen Goldstein discovered the 1875 - Eugen Goldstein discovered the existence of a charged stream from the existence of a charged stream from the cathode using a “Crookes Tube” and called cathode using a “Crookes Tube” and called them “Cathode Rays”them “Cathode Rays”


• 1886 - Eugen Goldstein discovered the 1886 - Eugen Goldstein discovered the existence of positively charged particles he existence of positively charged particles he called “Canal Rays”called “Canal Rays”


• 1897 - J.J. Thomson using a modified “Crookes 1897 - J.J. Thomson using a modified “Crookes Tube” determined that the “Cathode Rays” Tube” determined that the “Cathode Rays” behaved like charged particles and measured behaved like charged particles and measured the charge.the charge.


• 1907 - J.J. Thomson proposed his 1907 - J.J. Thomson proposed his “Raisin Pudding Model” of the “Raisin Pudding Model” of the atom.atom.

--

--

---

- -

---

-

-

Negatively chargedElectrons

Positive Matrix

*Atoms are neutral


1911 - Ernest Rutherford suggested the 1911 - Ernest Rutherford suggested the atom was “nuclear” based on a famous atom was “nuclear” based on a famous experiment - “The Scattering experiment - “The Scattering Experiment”. He also suggested that Experiment”. He also suggested that the proton was the fundamental unit of the proton was the fundamental unit of positive chargepositive charge


AlphaParticles

Metal Foil(Au)

ASSUMPTIONSASSUMPTIONSRUTHERFORD’S WORKRUTHERFORD’S WORK

• Most of the atoms mass is concentrated Most of the atoms mass is concentrated in the nucleus.in the nucleus.

• All of the positive charge is concentrated All of the positive charge is concentrated in the nucleusin the nucleus

• Neutral atoms have equal numbers of Neutral atoms have equal numbers of protons and electrons.protons and electrons.

• The protons and neutrons are located in The protons and neutrons are located in the nucleus of the atom.the nucleus of the atom.


THOMSON MODEL

RUTHERFORD MODEL


• 1932 - Chadwick discovered and 1932 - Chadwick discovered and determined the properties of the determined the properties of the neutron. neutron.

Proton

Neutron

NucleusElectrons

SUBATOMIC PARTICLESSUBATOMIC PARTICLES

PARTICLEPARTICLE CHARGECHARGE MASSMASS LOCATIONLOCATION SYMBOLSYMBOL

PROTONPROTON +1+1 1 AMU1 AMU NUCLEUSNUCLEUS 11HH1 1 or or 11pp11

NEUTRONNEUTRON 00 1 AMU 1 AMU NUCLEUSNUCLEUS 00nn11

ELECTRONELECTRON -1-11/1836 1/1836 AMUAMU OUTSIDEOUTSIDE -1-1ee00

LOOKING AT THE ATOMS LOOKING AT THE ATOMS STRUCTURESTRUCTURE

• Atomic NumberAtomic Number = # protons and = # protons and electrons in a neutral atomelectrons in a neutral atom

• Atomic Mass Number*Atomic Mass Number* = sum of the = sum of the protons and neutrons protons and neutrons

• #Neutrons#Neutrons = Mass# - Atomic# = Mass# - Atomic#

*ATOMIC MASS MAY VARY (ISOTOPES)

ISOTOPESISOTOPESAVERAGE ATOMIC AVERAGE ATOMIC

MASSMASSMost of the elements on the periodic table have severalIsotopes. The Mass that you see is the weighted average of known isotopes.

Example: Carbon has two stable isotopesC12 = 98.89% and C13 = 1.108%

12(0.9889) + 13(0.01108) = 12.01

Average Atomic Mass

FORMING AN IONFORMING AN ION

• METALS - usually like to lose METALS - usually like to lose electrons to form electrons to form positive ionspositive ions called called CATIONSCATIONS..

• NONMETALS - usually like to gain NONMETALS - usually like to gain electrons to form electrons to form negative ionsnegative ions called called ANIONSANIONS..

FORMING IONSFORMING IONS

Na Na+1 + electron

Cl Cl-1+ electron

Mn25

54.94

2-8-13-2

+2+3+4+7

Electron Arrangement

Atomic Number

Atomic Mass OxidationStates

THE KERNELTHE KERNELANDAND

VALENCE ELECTRONSVALENCE ELECTRONS

19K39 2-8-8-1

Valence Electrons – those in the outer principal energylevel

Kernel – the nucleus and all of the electrons except those in the valence level

THE KERNELTHE KERNELANDAND

VALENCE ELECTRONSVALENCE ELECTRONS

19K39 2-8-8-1

Valence Electrons = 1

Kernel – has a charge of +1

*Now Lewis Dot Structures

LEWIS DOT STRUCTURES

19K39 2-8-8-1 K

16S-2 2-8-8 Sxx

[ ]-2

PUTTING IT TOGETHERPUTTING IT TOGETHER

PARTICLEPARTICLE PROTONSPROTONS ELECTRONSELECTRONS NEUTRONSNEUTRONS

NN

NN-3-3

SnSn

ScSc+3+3

NaNa

CONTINUOUSCONTINUOUSSPECTRUMSPECTRUM

VISIBLE REGION OF THE SPECTRUM

HYDROGEN AND HELIUM HYDROGEN AND HELIUM LINE SPECTRUMLINE SPECTRUM

HYDROGEN

HELIUM

More spectra

BRIGHT-LINE SPECTRABRIGHT-LINE SPECTRA

BRIGHT-LINE SPECTRA ARE LIKE FINGER PRINTS. EACH ELEMENT HAS ITS OWN CHARACTERISTIC SET OF BRIGHT LINES IN THE VISIBLE REGION OF THE SPECTRUM.

Carbon

Helium

Hydrogen

THE BOHR MODELTHE BOHR MODEL

Bohr’s Model was based on the simplest atom, Hydrogen. Bohr based his model on the following:(1) Electrons do not follow the rules of large

macroscopic bodies.(2) Electrons in atoms have only specific energies.(3) Electrons are only in specific orbits outside the

nucleus (ground state).(4) When an electron moves from one orbit to

another it absorbs or releases energy of a specific frequency.

(5) When electrons absorb energy they move to an excited state (higher energy orbit).

THE BOHR MODELTHE BOHR MODELHydrogenHydrogen

Excited State

Ground State

Energy ReleasedEnergy Absorbed

2

1

2

1

2

1

THE QUANTUM MODELTHE QUANTUM MODEL

As the science of spectroscopy grew and the resolution of the bright-line spectra of an element improved and the dual nature of the electron was explored scientists formulated a new picture of the atom.

This new model of the atom retains some of the original features but changes the concept of electron location. The electron, instead of occupying a specific orbit now is thought to occupy a region of 3-D space called the orbital.


Dual Nature of the Electron – the electron to this point, had been described as being “particle-like” in nature, but it also exhibits “wave-like behavior.”DeBroglie – was the first to suggest that, based on its extremely small size, the electron does have a measureable wavelength.

Double-click on the You Tube video


After viewing the video we see that Erwin Schrodinger allows us to describe the electrons in an atom with a set of 4 Quantum Numbers.• The quantum numbers help us to describe the relative energies and probable locations of the electrons. •The Principal Quantum Number (n) – corresponds very closely with the energy levels described in the Bohr Model. The PQN can only have small whole number values (n = 1, 2, 3, 4, 5, 6 etc). The greater the value of “n” the greater the energy and distance from the nucleus for the electron.


• The Sublevel Quantum Number (l) – describes the sublevels the electrons can occupy within a Principal Energy Level. •The SQN – has values that are determined by the value of the PQN.• It can have values from 0 … n-1• So, if n = 0, l = 0• If n = 2, l = 0, 1 (which means, in the second Principal Energy Level, there are two available sublevels the electron can occupy.• There are also corresponding letter values for the sublevels 0(s); 1(p); 2(d); 3(f)


• In the 2nd PEL there were two sublevels, 0, 1 or s and p.• Within a PEL, as the value of l increases the energy and distance from the nucleus increases.• In the 3rd PEL, there are three sublevels, 0, 1, and 2 or s, p, and d sublevels.

•The Orbital Quantum Number (m) (also sometimes called the Magnetic Quantum number) - describes the number of orbitals (3-D orientations in space) within a sublevel.


• The OQN’s are determined by the values for l• m can have values from 0… +/- l• So, if l = 0, m = 0, which means that there is only one possible 3-D description (or orbital) in that sublevel.• If l = 1, m = 0, +1, -1, which means in the “p” sublevel there are three, 3-D descriptions (or orbitals), in that sublevel.

Along the X axis Along the Y axis Along the Z axis


• If an orbital is located in an s sublevel it is referred to as an s-orbital and has a spherical distribution along the X, Y, and Z axes.

• If an orbital is located in an p sublevel it is referred to as an p-orbital and has a “dumbell” distribution”along the X, Y, and Z axes.


• Of course there are other orbital shapes but they are complicated and for our purposes, our concerns will be limited to the s and p orbital shapes.• The fourth quantum number is the Spin Quantum Number – based on the Stern/Gerlach experiment it is thought that an electron can have one of two possible spins, +1/2 and -1/2 (it spins on its axis).• Since no two electrons can have exactly the same set of four quantum numbers, only two electrons can occupy an orbital, provided they have opposite spins.


• Based on the work of many scientists, including deBroglie, Shrodinger, and Heisenberg, we now know that –• we can only speak in terms of the probable location of the electrons• the bright line spectra available for the elements gives us additional information on the energy associated with the electrons

THE QUANTUM MODEL THE QUANTUM MODEL OFOF

HYDROGENHYDROGEN

Note: the electron is pictured as a cloud or region of space where you will most probably find the electron.

Nucleus

Quantum AtomQuantum AtomRelationshipsRelationships

1 orbital

s

3 orbitals

p

5-orbitals

d

7-orbitals

f

SUBLEVELS

ORBITPrincipal

Energy LevelIncreasing Energy

Electron FillingElectron Filling

When we fill the energy sublevels that are several rules we must follow –• The Aufbau Principle – you must always fill from lowest energy to highest energy• Hund’s Rule – you must completely half-fill an energy sublevel before you start pairing electrons• Pauli Exclusion Principle – no two electrons can have the same set of four quantum numbers in a given orbital, they must have opposite spins to exist in the same orbital.

Filling the Sublevels & OrbitalsFilling the Sublevels & Orbitals

• When filling the sublevels and orbitals remember the rules• It is also important to remember that for multi-electron atoms some of the sublevels do overlap from an energy standpoint.• there is a simplified relationship to help us with this overlap – Sublevel Energy = n + l (n is the PQN and l is the SQN ). It is why the 4s sublevel fills before the 3d sublevel (see the diagram on the next slide).• 4s = 4 + 0 = 4 and 3d = 3 + 2 = 5• the sublevel energy of 4s is lower than that of 3d, therefore, the 4s sublevel fills before the 3d sublevel.

General SublevelGeneral SublevelArrangementArrangement

En

ergy

Dis

tan

ce f

rom

Nu

cleu

s

1s

2s

2p

3s

3p

4s

3d


1s2s 2p

3s 3p 3d4s 4p 4d 4f

5s 5p 5d 5f

* The idea of sublevel overlap can be much more complicated for larger atoms


En

ergy

Dis

tan

ce f

rom

Nu

cleu

s

1s

2s

2p

3s

3p

4s

3d

For 19K39 the sublevel filling would look like this


En

ergy

Dis

tan

ce f

rom

Nu

cleu

s

1s

2s

2p

3s

3p

4s

3d

For 7N14 the sublevel filling would look like this

Note: the sublevel is half-filled, the electrons have parallel spins (the same)

Electron ArrangementElectron Arrangement

Let’s take a sample and show you how the electron arrangement can be written in three formats.

19K39 2-8-8-1

19K39 1s22s22p63s23p64s1

19K39 [Ar]4s1

4s1 # of electronsEnergy sublevel

Principal EnergyLevel

atomic structure ? kenneth e. schnobrich. a brief history about 460 b.c. - a greek philosopher,...

Documents

matter different atoms

s slide

identical atoms

daltons atom john dalton

brief history

schnobrich slide

idea of atoms atomos

law of definite proportions