Sizing up the Atom Elements are able to be subdivided into
smaller and smaller particles these are the atoms, and they still
have properties of that element If you could line up 100,000,000
copper atoms in a single file, they would be approximately 1 cm
long Despite their small size, individual atoms are observable with
instruments such as scanning tunneling (electron) microscopes
Slide 4
An STM image of nickel atoms placed on a copper surface.
Source: IBM Research
Slide 5
Red ridge is a series of Cesium atoms
Slide 6
Image of a ring of cobalt atoms placed on a copper surface.
Source: IBM Research
Slide 7
Atom - smallest particle making up elements One teaspoon of
water has 3 times as many atoms as the Atlantic Ocean has teaspoons
of water!
Slide 8
Think about the technological advances of the past 100 years!
They have been nothing short of miraculous! RadiosCalculators
TelevisionsComputers AutomobilesCell phones Jet airplanesIpods
PlasticVelcro RefrigeratorsInternet (thanks, Al Gore) PenicillinCDs
& DVDs Insulinand, of course - Electric guitars Sliced
Bread!
Slide 9
Development of Atomic Theory This explosion of technology
occurred once we had a better understanding of the atom and how it
behaves!
Slide 10
Where did it all begin? The word atom comes from the Greek word
atomos which means indivisible. The word atom comes from the Greek
word atomos which means indivisible. The idea that all matter is
made up of atoms was first proposed by the Greek philosopher
Democritus in the 5th century B.C. The idea that all matter is made
up of atoms was first proposed by the Greek philosopher Democritus
in the 5th century B.C.
Slide 11
Then came the idea of The 4 Basic Elements Earth, Air, Fire,
& Water After that came Alchemy. The change to real Chemistry
didnt occur until the first true element was discovered! (1774) The
first element discovered was
Slide 12
The discovery of oxygen is attributed to 3 scientists (working
independently) Karl Scheele (1771) (German) Karl Scheele (1771)
(German) first to prepare and describe oxygen first to prepare and
describe oxygen Joseph Priestley (1774) (British) Joseph Priestley
(1774) (British) isolated oxygen gas from mercuric oxide. isolated
oxygen gas from mercuric oxide. observed accelerated burning
observed accelerated burning Antoine Lavoisier (1784) (French)
Antoine Lavoisier (1784) (French) made accurate measurements and
interpreted Priestleys results made accurate measurements and
interpreted Priestleys results
Slide 13
Carl Wilhelm Scheele beat Priestley to the discovery but
published afterwards. Carl Wilhelm Scheele beat Priestley to the
discovery but published afterwards. Too bad! So sad!
Slide 14
Priestley Medal Source: Roald Hoffman, Cornell University
Priestley gets the main credit for discovering oxygen!
Slide 15
Priestley produced a gas (oxygen) by using sunlight to heat
mercuric oxide kept in a closed container. The oxygen forced some
of the mercury out of the jar as it was produced, increasing the
volume about five times. Priestley produced a gas (oxygen) by using
sunlight to heat mercuric oxide kept in a closed container. The
oxygen forced some of the mercury out of the jar as it was
produced, increasing the volume about five times. 2HgO (s) 2Hg (l)
+ O 2 (g)
Priestley: Additional Scientific Contributions Discovered the
interconnection between photosynthesis and respiration Discovered
the interconnection between photosynthesis and respiration
Discovered carbonated water Discovered carbonated water Discovered
that India rubber removed graphite pencil marks - the first rubber
eraser Discovered that India rubber removed graphite pencil marks -
the first rubber eraser Now we can make mistakes!!
Slide 18
Antoine-Laurent Lavoisier Lavoisier: the Founder of Modern
Chemistry Lavoisier continued the investigations of Priestly
Quantitative experiments led to: Law of Conservation of Matter. He
systematized the language of chemistry, its nomenclature and
rhetoric. He was beheaded during the Reign of Terror for his role
as a tax farmer prior to the Revolution (Priestley escaped to
America!)
Slide 19
Lavoisier heated a measured amount of mercury to form the red
mercuric oxide. He measured the amount of oxygen removed from the
jar and the amount of red oxide formed. When the reaction was
reversed, he found the original amounts of mercury and oxygen.
Lavoisier heated a measured amount of mercury to form the red
mercuric oxide. He measured the amount of oxygen removed from the
jar and the amount of red oxide formed. When the reaction was
reversed, he found the original amounts of mercury and oxygen. 2Hg
(l) + O 2 (g) 2HgO (s)
Slide 20
Properties of Oxygen Colorless Colorless Odorless Odorless
Tasteless Tasteless Gas at room temperature Gas at room temperature
Slightly soluble in water Slightly soluble in water Inflammable
(does NOT burn) Inflammable (does NOT burn) Only part of air that
supports combustion Only part of air that supports combustion
Physical Property or Chemical Property? P PPPPCCPPPPCC
Slide 21
These properties of oxygen were later used to determine the
properties of other substances. By the late 18 th century,
scientists finally came to the conclusion that Oxygen was truly an
element (cant be broken down into simpler forms without losing its
properties) Scientists began to search for & test other new
elements.
Slide 22
Sometimes, when they tried to react substances together,
nothing happened! Substances that DO NOT react are Inert They found
that most materials will react to form new substances. These
elements are said to be chemically active (reactive) Oxygen is very
reactive, so is hydrogen which we will look at next! Increasing
chemical reactivity inert Oxygenhydrogen
Slide 23
Discovery of Henry Cavendish (1766) Reacted various metals with
acids producing a salt and hydrogen gas Acid + metal hydrogen gas +
salt Zinc + sulfuric acid Hydrogen + zinc sulfate Zn (s) + H 2 SO
4(aq) H 2 (g) + ZnSO 4 (aq) While testing the properties of
Hydrogen he While testing the properties of Hydrogen he found that
water is a compound found that water is a compound (1731 1810) Word
Equation Chemical equation
Slide 24
Hydrogen + Oxygen Water Hydrogen + Oxygen Water 2H 2 + O 2 2H 2
O
Slide 25
Antoine Lavoisier Named Priestlys newly discovered gas - oxygen
- meaning acid former Named Priestlys newly discovered gas - oxygen
- meaning acid former Named Cavendishs new gas hydrogen - meaning
water former Named Cavendishs new gas hydrogen - meaning water
former
Slide 26
Daltons Atomic Theory John Dalton (1766-1844) While his theory
was not completely correct, it revolutionized how chemists looked
at matter and brought about chemistry as we know it today (instead
of alchemy) So, its an important landmark in the history of
science.
Slide 27
Daltons Modern Atomic Theory (experiment based!) 3)Atoms of
different elements combine in simple whole-number ratios to form
chemical compounds 4)In chemical reactions, atoms are combined,
separated, or rearranged but never changed into atoms of another
element. 1)All elements are composed of tiny indivisible particles
called atoms 2)Atoms of the same element are identical. Atoms of
any one element are different from those of any other element.
Slide 28
Law of Definite Proportions n Each compound has a specific
ratio of elements by mass. n Ex: Water is always 8 grams of oxygen
for each gram of hydrogen.
Slide 29
Discovery of the Electron Began with the invention of the
Crookes Tube (cathode ray tube) c. 1875
Slide 30
Cathode Ray Tube Electric current sent through gases sealed in
tube at low pressure Anode- positive electrode Cathode- negative
electrode Voltage source Metal Disks - electrodes - + gas
Slide 31
Modern Cathode Ray Tubes Cathode ray tubes pass electricity
through a gas that is contained at a very low pressure.
TelevisionComputer Monitor
Slide 32
In 1897, J.J. Thomson used a cathode ray tube to study
gases.
Slide 33
n Passing an electric current makes a beam appear to move from
the negative to the positive end so the beam was called a Cathode
Ray Thomsons Experiment Voltage source + -
Slide 34
Thomsons Experiment n Thomson found that cathode rays were
deflected from a negatively- charged plate. -
Slide 35
Voltage source Thomsons Experiment n and that cathode rays were
attracted to plates with a positive charge n Does light bend like
this? +
Slide 36
Light doesnt bend so the cathode ray must be made of particles
rather than Light! Since they are attracted to a positive plate
& repelled by a negative one the particles arent neutral What
charge must they have? Thats right! NEGATIVE!! Thomson called these
negative particles ELECTRONS
Slide 37
Mass of the Electron 1916 Robert Millikan determined the mass
of the electron: 1/1840 the mass of a hydrogen atom; and, has one
unit of negative charge The oil drop apparatus Mass of the electron
is 9.11 x 10 -28 g
Slide 38
Slide 39
Conclusions from the Study of the Electron: a)Cathode rays have
identical properties regardless of the element used to produce
them. Therefore, all elements must contain identically charged
electrons. b)Atoms are neutral, so there must be a positive
substance 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 their mass
Slide 40
Thomsons 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
Slide 41
Plum-Pudding Model Zumdahl, Zumdahl, DeCoste, World of
Chemistry 2002, page 56
Slide 42
In 1903, An important discovery leading to further
understandings of atomic structure happened by accident. Henri
Becquerel discovered radioactivity Radioactivity is the spontaneous
emission of energy from an object 1903: Shared a Nobel Prize with
Pierre andNobel PrizePierre Marie CurieMarie Curie for discovering
radioactivity.
Slide 43
Ernest Rutherford (1871-1937) The Nobel Prize in Chemistry 1908
Studied under J. J. Thomson
Slide 44
3 Types of Radiation discovered by Ernest Rutherford Alpha ( )
a positively charged helium nucleus 4 2 He +2 Alpha ( ) a
positively charged helium nucleus 4 2 He +2 Beta ( ) fast-moving
electrons - eBeta ( ) fast-moving electrons - e Gamma ( ) like
high-energyGamma ( ) like high-energyx-rays
Slide 45
Ernest Rutherfords Gold Foil Experiment - 1911 Shot alpha
particles at a thin sheet of gold foil Particles that hit on a
detecting screen (film) were recorded
Slide 46
Lead block Polonium Gold Foil Flourescent Screen
Slide 47
He Expected: The alpha particles to pass through the foil
without changing direction very much. The alpha particles to pass
through the foil without changing direction very much. Because
Because The positive charges were spread out evenly (according to
Thomsons atomic theory). Alone they were not enough to stop the
alpha particles. The positive charges were spread out evenly
(according to Thomsons atomic theory). Alone they were not enough
to stop the alpha particles.
Slide 48
What he expected
Slide 49
Again, because he thought the mass was evenly distributed in
the atom
Slide 50
What he got
Slide 51
Rutherfords Observations Most of the particles went straight
through the foil (what he expected) Most of the particles went
straight through the foil (what he expected) A few particles were
slightly deflected A few particles were slightly deflected Still
fewer actually bounced back towards the source! Still fewer
actually bounced back towards the source! Astonishing!!!
Astonishing!!! Rutherford said it was like firing a Howitzer shell
at a piece of tissue paper & having it bounce back & hit
you! Rutherford said it was like firing a Howitzer shell at a piece
of tissue paper & having it bounce back & hit you! Like
howitzer shells bouncing off of tissue paper!
Slide 52
+
Slide 53
Rutherfords Conclusions Since most of the particles went
through the foil - atoms are mostly empty space. Since most of the
particles went through the foil - atoms are mostly empty space.
Because a few particles were deflected they must have come close to
a positively charged core. Because a few + particles were deflected
they must have come close to a positively charged core. Since a
very few particles were deflected straight back, the
positively-charged core must be very dense. Since a very few
particles were deflected straight back, the positively-charged core
must be very dense. This small dense positive area is the nucleus.
This small dense positive area is the nucleus. +
Slide 54
The Rutherford Atomic Model Based on his experimental evidence:
Based on his experimental evidence: The atom is mostly empty space
The atom is mostly empty space All the positive charge, and almost
all the mass is concentrated in a small area in the center. He
called this a nucleus All the positive charge, and almost all the
mass is concentrated in a small area in the center. He called this
a nucleus The electrons are distributed around the nucleus, and
occupy most of the volume The electrons are distributed around the
nucleus, and occupy most of the volume His model was called a
nuclear model His model was called a nuclear model
Slide 55
Discovery of Protons Eugen Goldstein in 1886 observed particles
with a positive charge passing through a perforated cathode.
Slide 56
In 1920, Rutherford studied these particles & called them
protons. They have a charge of positive 1 and a mass of 1.7 x 10-
24 grams. This is not a handy number to work with so we use a mass
of 1 amu. Amu stands for atomic mass unit
Slide 57
1932 James Chadwick confirmed the existence of the neutron a
particle with no charge, but a mass nearly equal to a proton (1
amu). Discovery of the Neutron Rutherford predicted the existence
of the neutron in 1920. Twelve years later, his assistant found it!
So now we have a more complete picture of an atom!
Slide 58
Subatomic Particles ParticleCharge Mass (g) Location Electron
(e - ) (e - ) 9.11 x 10 -28 g (virtually 0) outside nucleus Proton
(p + ) (H + ) (H + )+1 1 amu (1.7 x 10 -24 g) in nucleus Neutron (n
o ) (n o )0 1 amu 1 amu (1.67 x 10 -24 g) (1.67 x 10 -24 g) in
nucleus
Slide 59
Elements are the new building blocks Hydrogen Nitrogen-7
Oxygen-8 Carbon-6
Slide 60
Between 1912 and 1914, the physicist H.G.J. Moseley conducted a
series of experiments where he bombarded targets made out of
different kinds of metals with cathode rays. Each metal he studied
emitted X-rays of a characteristic frequency, almost like a set of
"fingerprints". Henry Moseley (1887 1915)
Slide 61
The pattern that emerged when the observed X-rays were
organized in order of increasing frequency suggested to Moseley a
regular increase in the positive charge on the nuclei of the atoms.
He called this positive nuclear charge- the Atomic Number of the
element
Slide 62
Atomic Number Elements are different because they contain
different numbers of PROTONS The atomic number of an element is the
number of protons in the nucleus Since all atoms are neutral - the
# protons in an atom = # electrons Henry Moseley used x-ray spectra
& came up with the idea of the Atomic Number
Slide 63
Atomic Number, Z All atoms of the same element have the same
number of protons in the nucleus, Z 13 Al 26.981 Atomic number Atom
symbol AVERAGE Atomic Mass
Slide 64
Mass Number Mass number is the number of protons and neutrons
in the nucleus of an isotope: Mass # = # protons + # neutrons
Slide 65
Subatomic Particles Most of the atoms mass. NUCLEUS ELECTRONS
PROTONS NEUTRONS NEGATIVE CHARGE POSITIVE CHARGE NEUTRAL CHARGE
ATOM Atomic Number equals the # of... equal in a neutral atom
Slide 66
Isotopes Frederick Soddy (1877-1956) in 1912 (worked with
Rutherford) Frederick Soddy (1877-1956) proposed the idea of
isotopes in 1912 (worked with Rutherford) Isotopes are atoms of the
same element having different mass numbers, due to varying numbers
of neutrons. Isotopes are atoms of the same element having
different mass numbers, due to varying numbers of neutrons. Soddy
won the Nobel Prize in Chemistry in 1921 for his work with isotopes
and radioactive materials. Soddy won the Nobel Prize in Chemistry
in 1921 for his work with isotopes and radioactive materials.
Slide 67
Isotopes Atoms of the same element (same Z) but different mass
number (A). Atoms of the same element (same Z) but different mass
number (A). Boron-10 (B-10) has 5 p and 5 n Boron-11 (B-11) has 5 p
and 6 n Boron-10 (B-10) has 5 p and 5 n Boron-11 (B-11) has 5 p and
6 n 10 B 11 B
Slide 68
Slide 69
Isotopes Radioisotopes (radioactive isotopes) - Radioisotopes
(radioactive isotopes) - unstable isotopes that spontaneously decay
emitting radiation They play an important part in the technologies
that provide us with food, water and good health. They play an
important part in the technologies that provide us with food, water
and good health. Radio-carbon dating of fossils Radio-carbon dating
of fossils In medicine, diagnosis, treatment, and research In
medicine, diagnosis, treatment, and research Sterilization of meat
Disinfestation of grain and spices Increasing shelf life (eg,
fruits)
Slide 70
Slide 71
Nuclear Symbols Contain the symbol of the element, the mass
number and the atomic number (represent isotopes of elements)
Contain the symbol of the element, the mass number and the atomic
number (represent isotopes of elements) X Mass number Atomic number
Subscript Superscript Element symbol REMEMBER! number of electrons
= number of protons So all atoms are neutral!
Slide 72
Rhenium Re 186 75 Protons: 75 Neutrons: 111 Electrons: 75
Slide 73
Nuclear Symbols n Find each of these: a) number of protons b)
number of neutrons c) number of electrons d) Atomic number e) Mass
Number Br 80 35
Slide 74
Nuclear Symbols n If an element has an atomic number of 34 and
a mass number of 78, what is the: a) number of protons b) number of
neutrons c) number of electrons d) Write the complete symbol Se 78
34 44 34
Slide 75
Naming Isotopes We can name isotopes by placing the mass number
after the name of the element: We can name isotopes by placing the
mass number after the name of the element: carbon-12 carbon-12
carbon-14 carbon-14 uranium-235 uranium-235 Mass numbers
IsotopeProtonsElectronsNeutronsNucleus Hydrogen1 (protium)
(protium)110 Hydrogen-2(deuterium)111 Hydrogen-3(tritium)112 The
element hydrogen has 3 isotopes
Slide 78
Examples of Isotopes
Slide 79
Learning Check Counting Naturally occurring carbon consists of
three isotopes, 12 C, 13 C, and 14 C. State the number of protons,
neutrons, and electrons in each of these carbon atoms. Naturally
occurring carbon consists of three isotopes, 12 C, 13 C, and 14 C.
State the number of protons, neutrons, and electrons in each of
these carbon atoms. 12 C 13 C 14 C 6 6 6 6 6 6 #p + _______ _______
_______ #n o _______ _______ _______ #e - _______ _______
_______
Slide 80
Answers 12 C 13 C 14 C 6 6 6 6 6 6 #p + 6 6 6 #n o 6 7 8 #e - 6
6 6
Slide 81
Learning Check An atom has 14 protons and 20 neutrons. A.Its
atomic number is 1) 142) 163) 34 B. Its mass number is 1) 142) 163)
34 C. The element is 1) Si2) Ca3) Se D.Another isotope of this
element is 1) 34 X 2) 34 X 3) 36 X 16 14 14 16 14 14
Slide 82
Atomic Mass How heavy is an atom of oxygen? It depends, because
there are different kinds of oxygen atoms. We are more concerned
with the average atomic mass. This is based on the abundance
(percentage) of each variety (isotope) of that element in nature.
We dont use grams for this mass because the numbers would be too
small
Slide 83
Measuring Atomic Mass Instead of grams, the unit we use is the
Atomic Mass Unit (amu) Instead of grams, the unit we use is the
Atomic Mass Unit (amu) It is defined as one-twelfth the mass of a
carbon-12 atom. It is defined as one-twelfth the 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 mass number, so we determine the average atomic mass from
the elements percent abundance. Each isotope has its own mass
number, so we determine the average atomic mass from the elements
percent abundance.
Slide 84
To calculate the average atomic mass: Multiply the mass of each
isotope by its abundance, then add the results. Multiply the mass
of each isotope by its abundance, then add the results. Abundance
may be expressed as a decimal or a %, (Divide by 100 if using %s)
Abundance may be expressed as a decimal or a %, (Divide by 100 if
using %s) Avg. Atomic Mass
Slide 85
IsotopeSymbol Composition of the nucleus % in nature
Carbon-12C-12 6 protons 6 neutrons 98.89% Carbon-13C-13 6 protons 7
neutrons 1.11% Carbon-14C-14 6 protons 8 neutrons