chapter 4 atomic structure. by the end of the chapter you will be able to… describe democritus’s...

Chapter 4Chapter 4

Atomic StructureAtomic Structure

By the end of the chapter you WILL By the end of the chapter you WILL be able to…be able to…

Describe Democritus’s ideas about atomsDescribe Democritus’s ideas about atoms Explain Daltons atomic theoryExplain Daltons atomic theory ID the special instruments necessary to observe ID the special instruments necessary to observe

individual atomsindividual atoms ID 3 types of subatomic particlesID 3 types of subatomic particles Describe the structure of atoms according to the Describe the structure of atoms according to the

Rutherford atomic modelRutherford atomic model Explain what makes elements and isotopes different Explain what makes elements and isotopes different

from each otherfrom each other Calculate the number of neutrons in an atomCalculate the number of neutrons in an atom Calculate atomic mass of an elementCalculate atomic mass of an element

Quantum Model of the AtomQuantum Model of the Atom

http://science.discovery.com/videos/master-of-the-universe-stephen-hawking-atoms.html

Currently the most accepted modelCurrently the most accepted model ““shells” represent areas of probability of shells” represent areas of probability of

finding an electronfinding an electron Here are the majorHere are the major

contributors…contributors…

Erwin Schrødinger Erwin Schrødinger 1887-19611887-1961 educated in Vienna; serves educated in Vienna; serves

in Austrian Army in WWIin Austrian Army in WWI 1926 publishes 1926 publishes “wave “wave

equation”equation” model of model of electronselectrons

Goes to Germany in 1927 Goes to Germany in 1927 but leaves in 1933 with rise but leaves in 1933 with rise of Nazis; ends up in Austria of Nazis; ends up in Austria in 1937; recants opposition in 1937; recants opposition to Nazis but is harassed and to Nazis but is harassed and escapes in 1938escapes in 1938

1933 Nobel Prize in Physics 1933 Nobel Prize in Physics with Diracwith Dirac

1940 establishes Institute for 1940 establishes Institute for Advanced Studies in DublinAdvanced Studies in Dublin

Werner Heisenberg Werner Heisenberg 1901-19761901-1976 1923 PhD in Munich1923 PhD in Munich

1924-’25 works with Bohr 1924-’25 works with Bohr in Copenhagenin Copenhagen

establishes “quantum establishes “quantum mechanics” when only 23 mechanics” when only 23 years old in 1925 - includes years old in 1925 - includes Uncertainty PrincipleUncertainty Principle

1932 Nobel Prize in Physics1932 Nobel Prize in Physics 1941 director of Kaiser 1941 director of Kaiser

Wilhelm Institute in Berlin - Wilhelm Institute in Berlin - captured by US troops at captured by US troops at end of WWII & sent to end of WWII & sent to England; returns to England; returns to Germany after the warGermany after the war

Prince Louis-Victor Prince Louis-Victor deBrogliedeBroglie

1892-1987 1892-1987• educated and worked in educated and worked in

France - BA in 1913 & France - BA in 1913 & graduate work after graduate work after serving for France in WWIserving for France in WWI

• his 1924 doctoral thesis his 1924 doctoral thesis introduced “wave introduced “wave mechanics” - the idea mechanics” - the idea that that the electron could the electron could be treated as a wavebe treated as a wave

• 1929 Nobel Prize in 1929 Nobel Prize in PhysicsPhysics

computer-computer-generated generated images of images of “electron “electron

cloud” shapes cloud” shapes generated by generated by Schrødinger’sSchrødinger’s

wave equationwave equation

meta-synthesismeta-synthesis(chem education co.)(chem education co.)

Lets go back in time…Lets go back in time…

……and look at other and look at other modelsmodels

Bohr’s ModelBohr’s Model

Characterized by its concentric circles Bohr’s Characterized by its concentric circles Bohr’s model has probably been ingrained into your model has probably been ingrained into your headsheads

However Bohr was not the first to hypothesize However Bohr was not the first to hypothesize this modelthis model

The Rutherford Atomic ModelThe Rutherford Atomic Model Based on his experimental evidence:Based on his experimental evidence:

The atom is mostly empty spaceThe atom is mostly empty space All the positive charge, and almost all All the positive charge, and almost all

the mass is concentrated in a small area the mass is concentrated in a small area in the center. He called this a “in the center. He called this a “nucleusnucleus””

The nucleus is composed of protons The nucleus is composed of protons and neutronsand neutrons

The electrons distributed around the The electrons distributed around the nucleus, and occupy most of the volumenucleus, and occupy most of the volume

His model was called a “His model was called a “nuclear modelnuclear model””

Ernest Rutherford’sErnest Rutherford’sGold Foil Experiment - 1911Gold Foil Experiment - 1911

Alpha particles are helium nuclei - The alpha particles were fired at a thin sheet of gold foil Particle that hit on the detecting screen (film) are recorded

Rutherford’s problem:Rutherford’s problem:In the following pictures, there is a target hidden by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target?

Target #1

Target #2

The Answers:The Answers:

Target #1 Target #2

Rutherford’s FindingsRutherford’s Findings

a) The nucleus is smallb) The nucleus is densec) The nucleus is positively

charged

Most of the particles passed right through A few particles were deflected VERY FEW were greatly deflected

“Like howitzer shells bouncing off of tissue paper!”

Conclusions:

Thomson’s Atomic ModelThomson’s Atomic Model

Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.

J. J. Thomson

John Dalton (1766-1844)John Dalton (1766-1844)

Published in 1808, Dalton’s Published in 1808, Dalton’s work became the basis for work became the basis for modern atomic theory.modern atomic theory.

Represented the atom as a Represented the atom as a simple sphere with no internal simple sphere with no internal structure. Sketch it!structure. Sketch it!

Showed that substances were Showed that substances were combinations of relatively few combinations of relatively few elementselements

Dalton’s Atomic TheoryDalton’s Atomic Theory

Includes four partsIncludes four parts1.1. All elements are composed of atomsAll elements are composed of atoms2.2. Atoms of the same element are identicalAtoms of the same element are identical3.3. Atoms of different elements can physically mix, or Atoms of different elements can physically mix, or

can chemically combine to form compoundscan chemically combine to form compounds4.4. Chemical reactions occur when atoms are Chemical reactions occur when atoms are

separated, joined, or combined. (atoms of one separated, joined, or combined. (atoms of one element cannot change into another element as a element cannot change into another element as a result of a chemical reaction)result of a chemical reaction)

See diagram on page 102See diagram on page 102

Structure of the Nuclear AtomStructure of the Nuclear Atom

One change to Dalton’s atomic One change to Dalton’s atomic theory is that atoms theory is that atoms are divisibleare divisible into into subatomic particles:subatomic particles: Electrons, protons, and neutronsElectrons, protons, and neutrons are are

examples of these fundamental examples of these fundamental particlesparticles

There are many other types of There are many other types of particles, but we will study these threeparticles, but we will study these three

Democritus of Abdera 460 B.C.E.-Democritus of Abdera 460 B.C.E.-370 B.C.E.370 B.C.E.

Believed atoms were Believed atoms were indivisible and indestructibleindivisible and indestructible

Believed matter was Believed matter was composed of atoms, the composed of atoms, the smallest part of an element smallest part of an element which retains its identity which retains its identity during a chemical reaction.during a chemical reaction.

Atom comes from the Greek Atom comes from the Greek work atomos, meaning work atomos, meaning indivisible .indivisible .

Why is the word “atom” a Why is the word “atom” a misnomer?misnomer?

400 BC 1803 1904 1910 1913 1926

Niels Bohr

J J Thomson

Democratus

John Dalton

Schroedinger / Heisenberg

Ernest Rutherford

Atomic Theory

Foundations of Atomic TheoryFoundations of Atomic Theory

Atoms and the Law of Conservation of Mass… Atoms and the Law of Conservation of Mass… (state it)(state it)

Atoms have mass, cannot be broken down, and Atoms have mass, cannot be broken down, and you CAN put them togetheryou CAN put them together

Therefore… A + B Therefore… A + B C and C C and C A+B A+B

(synthesis) (decomposition)(synthesis) (decomposition) What can we say about the masses of the What can we say about the masses of the

reactants and products?reactants and products?

Sizing up the AtomSizing up the Atom

Radii of most atoms fall within the range of Radii of most atoms fall within the range of 5x105x10-11-11 to 2x10 to 2x10-10-10mm

The unit, Angstrom (Å), can be used when The unit, Angstrom (Å), can be used when dealing with atomic radii. (1x10dealing with atomic radii. (1x10-10-10m)m)

Nanometers are also commonly used (1x10Nanometers are also commonly used (1x10 -9-9m)m) Using the factor label method convert the above Using the factor label method convert the above

measurements to angstroms.measurements to angstroms. You should have gotten…You should have gotten… .5 – 2 Å How many nanometers?.5 – 2 Å How many nanometers?

Despite their small size atoms are observable Despite their small size atoms are observable with instruments such as the scanning with instruments such as the scanning tunneling microscopetunneling microscope

First done in 1981First done in 1981 When observed they look like thisWhen observed they look like this

Problem!Problem! A sample of copper with a mass of 63.5g A sample of copper with a mass of 63.5g

contains 6.02x10contains 6.02x102323 atoms. What is the mass of atoms. What is the mass of a single atom of Cu?a single atom of Cu?

Answer…Answer… 1.05x101.05x10-22-22gg THINK ABOUT THIS!!!!!!!!!!!!!!!!THINK ABOUT THIS!!!!!!!!!!!!!!!!

-If you lined up 100,000,000 Cu atoms side by -If you lined up 100,000,000 Cu atoms side by side they would only measure 1cm longside they would only measure 1cm long

Other Major Contributors and Other Major Contributors and ContributionsContributions

Discovery of the ElectronDiscovery of the ElectronIn 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively

charged particle: the electron

See

pag

es 1

04 a

nd

105

Some ModernSome ModernCCathode athode RRay ay TTubesubes

Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

Mass of the ElectronMass of the Electron

1916 – Robert Millikan determines the mass of the electron: 1/1840 the mass of a hydrogen atom; has one unit of negative charge

The oil drop apparatus

Mass of the electron is 9.11 x 10-28 g

Conclusions from the Study Conclusions from the Study of the Electron:of the Electron:

a) Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons.

b) Atoms are neutral, so there must be positive particles in the atom to balance the negative charge of the electrons

c) Electrons have so little mass that atoms must contain other particles that account for most of the mass

Conclusions from the Study Conclusions from the Study of the Electron:of the Electron:

Eugen Goldstein in 1886 observed what is now called the “proton” - particles with a positive charge, and a relative mass of 1 (or 1840 times that of an electron)

1932 – James Chadwick confirmed the existence of the “neutron” – a particle with no charge, but a mass nearly equal to a proton

Subatomic ParticlesSubatomic Particles

ParticleParticle ChargeCharge Mass (g)Mass (g) LocationLocation

ElectronElectron

(e(e--)) -1-1 9.11 x 109.11 x 10-28-28 Electron Electron cloudcloud

ProtonProton (p(p++)) +1+1 1.67 x 101.67 x 10-24-24

NucleusNucleus

NeutronNeutron

(n(noo)) 00 1.67 x 101.67 x 10-24-24 NucleusNucleus

Atomic NumberAtomic Number Atoms are composed of protons, Atoms are composed of protons,

neutrons, and electronsneutrons, and electrons How then are atoms of one element How then are atoms of one element

different from another element?different from another element? Elements are different because they Elements are different because they

contain different numbers of contain different numbers of PROTONSPROTONS The “The “atomic numberatomic number” of an element is ” of an element is

the the number of protonsnumber of protons in the nucleus in the nucleus # protons in an atom = # electrons# protons in an atom = # electrons

Atomic NumberAtomic NumberAtomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.

ElementElement # of protons# of protons Atomic # (Z)Atomic # (Z)

CarbonCarbon 66 66

PhosphorusPhosphorus 1515 1515

GoldGold 7979 7979

IsotopesIsotopes

Dalton Dalton (thinking back to his theory) (thinking back to his theory) was wrong about all elements of was wrong about all elements of the same type being identicalthe same type being identical

Atoms of the same element Atoms of the same element cancan have different numbers of have different numbers of neutronsneutrons..

Thus, different mass numbers.Thus, different mass numbers. These are called These are called isotopesisotopes..

IsotopesIsotopesElements occur in nature as mixtures of isotopes.

Isotopes are atoms of the same element that differ in the number of neutrons.

Naming IsotopesNaming Isotopes

We can also put the We can also put the mass mass numbernumber afterafter the name of the the name of the element: nuclides…element: nuclides…carbon-12carbon-12carbon-14carbon-14uranium-235uranium-235

Mass NumberMass Number

Mass number is the number of protons and neutrons in the nucleus of an isotope: Mass # = p+ + n0

NuclideNuclide pp++ nn00 ee-- Mass #Mass #

Oxygen Oxygen - - 1010

- - 3333 4242

- - 3131 1515

8 8 1818

Arsenic 75 33 75

Phosphorus 15 3116

Nuclear SymbolsNuclear Symbols

Contain the symbol of the element, Contain the symbol of the element, the mass number and the atomic the mass number and the atomic number.number.

X Massnumber

Atomicnumber

Subscript →

Superscript →

SymbolsSymbols Find each of these: Find each of these:

a)a) number of protonsnumber of protons

b)b) number of number of neutronsneutrons

c)c) number of number of electronselectrons

d)d) Atomic numberAtomic number

e)e) Mass NumberMass Number

Br80 35

SymbolsSymbols If an element has an atomic If an element has an atomic

number of 34 and a mass number of 34 and a mass number of 78, what is the: number of 78, what is the:

a)a) number of protonsnumber of protons

b)b) number of neutronsnumber of neutrons

c)c) number of electronsnumber of electrons

d)d) complete symbolcomplete symbol

SymbolsSymbols If an element has 91 If an element has 91

protons and 140 neutrons protons and 140 neutrons what is the what is the

a)a) Atomic numberAtomic number

b)b) Mass numberMass number

c)c) number of electronsnumber of electrons


SymbolsSymbols If an element has 78 If an element has 78

electrons and 117 neutrons electrons and 117 neutrons what is the what is the

a)a) Atomic numberAtomic number

b)b) Mass numberMass number

c)c) number of protonsnumber of protons


Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons.

IsotopeIsotope ProtonsProtons ElectronsElectrons NeutronsNeutrons NucleusNucleus

Hydrogen–1Hydrogen–1

(protium)(protium) 11 11 00

Hydrogen-2Hydrogen-2

(deuterium)(deuterium) 11 11 11

Hydrogen-3Hydrogen-3

(tritium)(tritium)

11 11 22

Atomic MassAtomic Mass How heavy is an atom of oxygen?How heavy is an atom of oxygen?

It depends, because there are different It depends, because there are different kindskinds of oxygen atoms. of oxygen atoms.

We are more concerned with the We are more concerned with the average average atomic mass.atomic mass.

This is based on the abundance This is based on the abundance (percentage) of each variety of that (percentage) of each variety of that element in nature.element in nature. We don’t use grams for this mass because We don’t use grams for this mass because

the numbers would be too small.the numbers would be too small.

Measuring Atomic MassMeasuring Atomic Mass

Instead of grams, the unit we use Instead of grams, the unit we use is the is the Atomic Mass UnitAtomic Mass Unit (amu)(amu)

It is defined as one-twelfth the It is defined as one-twelfth the mass of a carbon-12 atom.mass of a carbon-12 atom. Carbon-12 chosen because of its isotope purity.Carbon-12 chosen because of its isotope purity.

Each isotope has its own atomic Each isotope has its own atomic mass, thus we determine the mass, thus we determine the average from percent abundance.average from percent abundance.

To calculate the average:To calculate the average:

Multiply the atomic mass of Multiply the atomic mass of each isotope by it’s each isotope by it’s abundance (expressed as a abundance (expressed as a decimal), then add the decimal), then add the results.results.

If not told otherwise, the mass of the If not told otherwise, the mass of the isotope is expressed in isotope is expressed in atomic mass atomic mass unitsunits (amu) (amu)

Atomic MassesAtomic Masses

IsotopeIsotope SymbolSymbol Composition of Composition of the nucleusthe nucleus

% in nature% in nature

Carbon-12Carbon-12 1212CC 6 protons6 protons

6 neutrons6 neutrons

98.89%98.89%



1.11%1.11%



<0.01%<0.01%

Atomic mass is the average of all the naturally occurring isotopes of that element.

Carbon = 12.011

Law of Multiple ProportionsLaw of Multiple Proportions If two elements form more than one compound If two elements form more than one compound

between them, then the ratios of the masses of the between them, then the ratios of the masses of the second element which combine with a fixed mass of second element which combine with a fixed mass of the first element will be ratios of small whole the first element will be ratios of small whole numbers. (not decimals) For example, Hnumbers. (not decimals) For example, H22O and HO and H22OO22..

Law of Constant ProportionsLaw of Constant Proportions Every pure substance always contains the same Every pure substance always contains the same

elements combined in the same proportions by weightelements combined in the same proportions by weight

Question

Solution

Answer

Knowns and Unknown

The Periodic Table:The Periodic Table:A PreviewA Preview

A “periodic table” is an arrangement of elements in which the elements are separated into groups based on a set of repeating properties

The periodic table allows you to easily compare the properties of one element to another

The Periodic Table:The Periodic Table:A PreviewA Preview

Each horizontal row (there are 7 of them) is called a periodEach vertical column is called a group, or family

Elements in a group have similar chemical and physical propertiesIdentified with a number and either an “A” or “B”More presented in Chapter 6

chapter 4 atomic structure. by the end of the chapter you will be able to… describe democritus’s...

Documents

rutherford atomic model

atomic structure slide

quantum model

structure of atoms

atomic mass

individual atoms id

nobel prize

war slide