Chemistry ChapterChemistry Chapter 4 4
The Structure of The Structure of the Atoms the Atoms
Top Ten Top Ten
Table 3.1Table 3.1
Table Table 3.33.3
History of ChemistryHistory of Chemistry
• 400 B.C. Greeks proposed 4 elements– Earth– Fire– Water– Air
• Next 2000 years—alchemy• During this period discoveries were made
– Hg, S, Sb– prepared acids
Controversial Greek Controversial Greek ThinkingThinking!!
Democritus (460-370 B.C):-Matter is composed of “atomos” (now atoms)-Atoms were homogeneous & indivisible-Could not answer what holds atoms together
Aristotle (384 B.C.-322B.C.):-Matter was continuous and
indefinitely divisible (did not believe in atoms) -Matter made of earth, fire, air, & water-Idea was accepted for nearly 2000 years!
Indivisible or Divisible?Indivisible or Divisible?Democritis vs. AristotleDemocritis vs. Aristotle
Late 1700’sLate 1700’s
• Most chemists accepted element definition
• Understood elements combined to form compounds with various properties
• Disagreed whether compounds are always in the same ratio
What happened in 1790?What happened in 1790?
• Study of matter was revolutionized by new emphasis on Quantitative Analysis
• Aided by improved balances• Measurements were actually
ACCURATE!!!
Robert BoyleRobert Boyle
• Founder of Modern Chemistry (1627-1691)
• Took the “Al” out of Alchemy (although he started as one)
• First scientist to understand the importance of careful measurement
• Insisted science be based on experiments
• Famous for P=1/V
Antoine Lavoisier Antoine Lavoisier • Father of Modern
Chemistry (1743-1794)• Recognized and named
hydrogen and oxygen• Introduced the metric
system• Wrote first list of
elements and revised nomenclature
• Because of prominence in pre-revolutionary government, was beheaded at the height of the French revolution
John Dalton—Beginning of John Dalton—Beginning of Modern Atomic TheoryModern Atomic Theory
• Englishman from a Quaker family (1766-1844)
• Revolutionized chemistry by emphasizing that atoms can have weights and weights can be measured (quantitative)
• Opened a school at age 12
• Color blind/researched• Interested in botany• Theory not accepted
until 1905 Albert Einstein paper
Dalton’s Atomic Theory Dalton’s Atomic Theory (1808)(1808)
Atoms of a given element are identical in size, mass, and chemical properties.
Atoms of specific element are different from those of another element.
Different atoms combine in simple whole-number ratios to form compounds.
In chemical reactions, atoms are separated, combined, or rearranged
Matter is composed of extremely small particles called atoms
Atoms are indivisible and indestructible.
Dalton vs. Dalton vs. TodayTodayMatter is composed of extremely small particles called atoms.
True
Atoms are indivisible and indestructible.
Made up of smaller particles (protons, neutrons, & electrons)except in nuclear chemistry.
Atoms of a given elemet are identical in size, mass, and chemical properties.
Atoms of a given element have same p+ and e-, but may differ in # of neutrons
Atoms of a specific element are different from those of another element
True, how we identify them
Different atoms combine in simple whole-number ratios to form compounds
True, Law of Multiple Proportions
In chemical reactions, atoms are separated, combined, or rearranged
True
Law of Conservation of MassLaw of Conservation of Mass
Total mass of reactants =
Total mass of products
Antoine Lavoisier
Mass is neither created nor destroyed during chemical or physical reactions.
Law of Multiple ProportionsLaw of Multiple Proportions
• If two or more different compounds are composed of the same two elements, then the ratio is always small whole numbers. (CO, CO2)
Figure 3.2:Figure 3.2: Representation of NO, NO Representation of NO, NO22, and , and NN22O.O.
What does an atom look like? (Sketch it on your paper!)
This is The Modern Atomic This is The Modern Atomic ModelModel
• Atom: The smallest particle of an element that retains the properties of the element
• Only seen by STM (Scanning Tunneling microscope)
Subatomic ParticlesSubatomic Particles
Particle Charge
Mass (amu) Location
Electron (e-)J.J.Thomson 1897Nobel Prize 1906Robert Milllikan (1910s)
-1 5.486x10-4
amu9.1 x 10-28 g1/1840 of H
Electron cloud
Proton (p+)Thomson/Goldstein-1907Rutherford 1920
+1 1.007 amu1.673 x 10-24 g
Nucleus
Neutron (no)Chadwick 1932Nobel Prize 1935
0 1.0091.675 x 10-24 g
Nucleus
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.
Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.
Figure 3.7:Figure 3.7: Schematic of a cathode ray Schematic of a cathode ray tube.tube.
Some ModernSome ModernCCathode athode RRay ay TTubesubes
Mass of the ElectronMass of the Electron
1909 – Robert Millikan determines the mass of the electron.
The oil drop apparatus Mass of the
electron is 9.1 x 10-28 g
Conclusions from the Study Conclusions from the Study of the Electronof the Electron
Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons.
Atoms are neutral, so there must be positive particles in the atom to balance the negative charge of the electrons
Electrons have so little mass that atoms must contain other particles that account for most of the mass
Thomson’s Atomic Thomson’s Atomic ModelModel
Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.
Based on the following facts: (1) atoms contain small, negatively charged particles called electrons and (2) the atoms of the element behave as if they have no charge at all
Ernest RutherfordErnest Rutherford
• 1871-1937• Learned physics in
JJ Thomson’s lab• Did much work
with alpha particles (+ charged part with mass)
• Most famous for his GOLD FOIL EXPERIMENT
Figure 3.5:Figure 3.5: Rutherford’s Rutherford’s experiment.experiment.
Try it Yourself!Try it Yourself!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?
The AnswersThe Answers
Target #1 Target #2
Figure 3.3:Figure 3.3: Plum Pudding model of an Plum Pudding model of an atom.atom.
Figure 3.6:Figure 3.6: Results of foil Results of foil experiment if experiment if Plum Pudding Plum Pudding
model had model had been correct.been correct.
Figure 3.6:Figure 3.6: Actual results. Actual results.
Rutherford’s FindingsRutherford’s Findings
The nucleus is small The nucleus is dense 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:
Disbelievers….Disbelievers….• Albert Einstein when
to his grave not totally believing it
• According to classical physics, the electron would have collapsed into the nucleus
• 1910-1930 began the Quantum Physics Revolution (the physics of atomic and subatomic particles)
The Atomic The Atomic ScaleScale
Most of the mass of the atom is in the nucleus (protons and neutrons) Electrons are found outside of the nucleus (the electron cloud) Most of the volume of the atom is empty space
“q” is a particle called a “quark”
The Quark…The Quark…
Oops…wrong Quark!
About Quarks…About Quarks…Protons and neutrons are NOT fundamental particles.Protons are made of two “up” quarks and one “down” quark.Neutrons are made of one “up” quark and two “down” quarks.
Quarks are held togetherby “gluons”
Figure 3.9:Figure 3.9: A nuclear A nuclear
atom viewed atom viewed in cross in cross section.section.
Atomic NumberAtomic NumberAtomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.
Element # of protons Atomic # (Z)
Carbon 6 6
Phosphorus 15 15
Gold 79 79
IsotopeIsotopess
Elements occur in nature as mixtures of isotopes.Isotopes are atoms of the same element that differ in the number of neutrons
Figure 3.10:Figure 3.10: Two isotopes of Two isotopes of sodium.sodium.
Mass NumberMass NumberMass number is the number of protons and neutrons in the nucleus of an isotope.Mass # = p+ + n0
Nuclide p+ n0 e- Mass #
Oxygen - 10
- 33 42
- 31 15
8 8 1818
Arsenic 75 33 75
Phosphorus 15 3116
Atomic Atomic MassesMasses
Isotope Symbol Composition of the nucleus
% in nature
Carbon-12
12C 6 protons6 neutrons
98.89%
Carbon-13
13C 6 protons7 neutrons
1.11%
Carbon-14
14C 6 protons8 neutrons
<0.01%
Atomic mass is the average of all the naturally isotopes of that element.Carbon = 12.011
Isotopes…Again Isotopes…Again (must be on the (must be on the test)test)
Isotopes are atoms of the same element having different masses due to varying numbers of neutrons.Isotope Proto
nsElectron
sNeutron
sNucleus
Hydrogen–1
(protium)
1 1 0
Hydrogen-2
(deuterium)
1 1 1
Hydrogen-3
(tritium)
1 1 2
Chlorine Practice ProblemChlorine Practice Problem• Chlorine exists as 2 isotopes in
nature. Cl-35 (atomic mass 34.969 amu) has a 75.77% relative abundance. Cl-37 has an atomic mass 36.966 amu.
1. What is the % abundance of the Cl-37 isotope?
Chlorine Practice ProblemChlorine Practice Problem• Chlorine exists as 2 isotopes in
nature. Cl-35 (atomic mass 34.969 amu) has a 75.77% relative abundance. Cl-37 has an atomic mass 36.966 amu
Calculate the atomic mass of Chlorine.
Chlorine Practice ProblemChlorine Practice Problem• Chlorine exists as 2 isotopes in
nature. Cl-35 (atomic mass 34.969 amu) has a 75.77% relative abundance. Cl-37 has an atomic mass 36.966 amu.
How many times more massive is Cl-37 than Cl-35?
Radioactivity
• Radioactivity: a process in which some substance spontaneously emit radiation
• Radiation: The rays and particles emitted by the radioactive materials.
• Nuclear Reaction: A change in an atom’s nucleus.
• Radioactive Decay: emitted radiation in a spontaneous process
• Major Breakthrough: 1890’s.• Only happens in radioactive atoms with
unstable nuclei
Types of Radiation
• Alpha Radiation– Made up of alpha particles– Deflected toward a negatively charged
plate• Beta Radiation
– Made up of beta particles– Deflected toward a positively charged plate
• Gamma Radiation– High E radiation that has no charge and
mass– Not deflected by electronic or magnetic
fields
Law of Definite (or Constant) Law of Definite (or Constant) CompositionComposition
• The fact that a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or the source of the compound.
What does this mean? (What does this mean? (Law of Law of Definite CompositionDefinite Composition))
• 50.0 g sample of pure H2O decomposed into its elements– would find 5.6 g H and 44.4 g oxygen – % mass would be:
mass H = 5.60 g x 100 = 11.2% Htotal mass 50.0 g
mass 0 = 44.4 g x 100 = 88.8% Ototal mass 50.0 g
Atomic # and Atomic MassAtomic # and Atomic Mass
The Periodic LawThe Periodic Law
Chinese Periodic TableChinese Periodic Table
Triangular Periodic TableTriangular Periodic Table
““Mayan” Mayan” Periodic Periodic
TableTable
Stowe Periodic TableStowe Periodic Table
A Spiral Periodic TableA Spiral Periodic Table
Modern Russian TableModern Russian Table
• First International Congress of Chemists– 60 to 70 of 113 elements had been
discovered– Italian chemist Cannizzaro presented
method for measurement of atomic mass that all could agree on.
The Year 1860….The Year 1860….
– Writing a book about the same time.
– Wanted to include new information of atomic masses
– Wanted to find an arrangement for all of the information on the 60-70 elements
Dimitri MendeeleevDimitri Mendeeleev
– Properties of the elements recur in regular cycles (periodically) when the elements are arranged in order of increasing atomic mass.
Law of Mendeleev:Law of Mendeleev:
Missing?Missing?
14Si
28.09
??
50Sn
118.71
Named missing element “Ekasilicon”
From base word “eka” meanging next in order
““Ekasilicon”Ekasilicon”
Predicted Properties
Observed Properties
Atomic Mass 72 amu
Density 5.5 g/cm3
Melting Point 825° C
““Ekasilicon”Ekasilicon”
Predicted Properties
Observed Properties
Atomic Mass 72 amu 72.61 amu
Density 5.5 g/cm3 5.32 g/cm3
Melting Point 825° C 938° C
““Ekasilicon”Ekasilicon”
Predicted Properties
Observed Properties
Oxide Formula XO2 GeO2
Chloride Formula
XCl4 GeCl4
Mendeleev’s Periodic TableMendeleev’s Periodic Table
Dmitri Mendeleev
Figure 3.11:Figure 3.11: The periodic table The periodic table
Figure 3.11:Figure 3.11: The periodic table The periodic table
Periodic Table with Group NamesPeriodic Table with Group Names
The Periodic TableThe Periodic Table
Period
Group or family
PeriodGroup or Family
Periodic Table with Group NamesPeriodic Table with Group Names
Figure 3.12:Figure 3.12: Elements Elements classified classified
as metals and nonmetals.as metals and nonmetals.
Properties of MetalsProperties of Metals Metals are good conductors of heat and electricity
Metals are malleable
Metals are ductile
Metals have high tensile strength
Metals have luster
Figure 3.17:Figure 3.17: Spherical atoms packed closely Spherical atoms packed closely together.together.
• Mostly brittle solids• Properties between metal and non-
metal (semi-conductors)• With exception of Bismuth, found in
nature only as compound• Once obtained as free metals, that
are stable in the presence of air
Metalloids:Metalloids:
PropertiesProperties of Nonmetalsof Nonmetals
Carbon, the graphite in “pencil lead” is a great example of a nonmetallic element. Nonmetals are poor conductors of heat and electricity Nonmetals tend to be brittle Many nonmetals are gases at room temperature
Examples of NonmetalsExamples of Nonmetals
Sulfur, S, was once known as “brimstone”
Microspheres of phosphorus, P, a reactive nonmetal
Graphite is not the only pure form of carbon, C. Diamond is also carbon; the color comes from impurities caught within the crystal structure
Figure 3.14:Figure 3.14: Nitrogen gas contains N Nitrogen gas contains N22 molecules.molecules.
Figure 3.13:Figure 3.13: A collection of argon A collection of argon atoms.atoms.
Figure 3.14:Figure 3.14: Oxygen gas contains O Oxygen gas contains O22 molecules.molecules.
Table 3.5Table 3.5
AllotropesAllotropes
• Different forms of a given element• Different properties b/c different
arrangement of atoms• EX: diamond, graphite,
Buckminsterfullerene (All Carbon!) • Look in your book—p. 70
TYPES OF IONSTYPES OF IONS (Remember an (Remember an ion ion is an is an atom or group of atoms that has a net + atom or group of atoms that has a net +
or net – charge.or net – charge.Cations Positively charged ions
Smaller than the corresponding atom (lost e’/closer together)Anions
Negatively charged ions Larger than the corresponding atom (gained e’/spread apart
Table of Ion SizesTable of Ion Sizes
Figure 3.11:Figure 3.11: The periodic table The periodic table
Figure 3.19:Figure 3.19: The ions formed by selected The ions formed by selected members of groups 1, 2, 3, 6, and 7.members of groups 1, 2, 3, 6, and 7.
Figure 3.20:Figure 3.20: Pure water does not conduct a Pure water does not conduct a current.current.
Figure 3.20:Figure 3.20: Water containing Water containing dissolved salt dissolved salt
conducts a current.conducts a current.