phys_chem-chptr_2
TRANSCRIPT
-
8/7/2019 Phys_Chem-Chptr_2
1/33
2010 Cosmopoint
HDF 111 : Physical ChemistryHDF 111 : Physical Chemistry
CHAPTER 2 :CHAPTER 2 :
Early Atomic Theory & StructureEarly Atomic Theory & Structure
-
8/7/2019 Phys_Chem-Chptr_2
2/33
Slide 2 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Learning Outcomes
After completing this chapter, you should
be able to do the following:
Define Daltons atom model Define atomic structure of the atom
Explain atomic number, isotopes, and atomic
mass concept
-
8/7/2019 Phys_Chem-Chptr_2
3/33
Slide 3 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
2.1 Early Thoughts
2.2 Daltons Model of the Atom
2.3 Composition ofCompounds
2.4 The Nature of Electric Charge
2.5 Discovery of Ions
2.6 Subatomic Parts of the Atom
2.7 The Nuclear Atom
2.8 Isotopes of the Elements
2.9 Atomic Mass
Topic Outlines
-
8/7/2019 Phys_Chem-Chptr_2
4/33
Slide 4 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Introduction
Pure substances are classified aselements or compounds
What makes a substance possessits unique properties?
How small a piece of salt will stilltaste salty?
Substances are in their simplestidentifiable form at the atomic, ionic,or molecular level
Further division produces a loss of
characteristic properties What particles lie within an atom orion?
How are these tiny particles alike?How do they differ? How far can wecontinue to divide them?
-
8/7/2019 Phys_Chem-Chptr_2
5/33
Slide 5 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Early Thoughts
The earliest models of the atom weredeveloped by the ancient Greek philosophers
About 440B.C. Empedocles stated that allmatter was composed of four elements earth, air, water, and fire
Democritus (about 470 370B.C.) thoughtthat all forms of matter were composed of tinyindivisible particles which he called atoms(Greek word atomos, meaning indivisible)
He held that atoms were in constant motionand they combined with one another invarious ways (no scientific observations)
Aristotle (384 322B.C.) opposed the theoryof Democritus; he endorsed and advancedthe Empedoclean theory and dominated thethinking of scientists and philosophers untilthe beginning of the 17th century
-
8/7/2019 Phys_Chem-Chptr_2
6/33
Slide 6 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Daltons Model of the Atom
English schoolmaster JohnDalton (1766-1844) revivedthe concept of atoms
He proposed an atomic modelbased on facts andexperimental evidence
He described his theory in aseries of paper published from
1803 1810 The idea was each element
consist of different kind ofatom
-
8/7/2019 Phys_Chem-Chptr_2
7/33
Slide 7 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Daltons Model of the Atom
The essence of Daltons atomicmodel: Elements are composed of minute,
indivisible particle called atom
Atoms of the same element are alike
in mass and size Atoms of different elements have
different masses and sizes
Chemical compounds are formed bythe union of2 or more atoms ofdifferent elements
Atom combine to form compounds insimple numerical ratios, such as oneto one , one to two, two to three, andso on
Atoms of two elements may combinein different ratios to form more thanone compound
-
8/7/2019 Phys_Chem-Chptr_2
8/33
Slide 8 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Daltons Model of the Atom
Later investigationhowever have shown: Atoms are composed of
subatomic particles Not all the atoms of a
specific element have thesame mass
Atoms, under specialcircumstances, can bedecomposed
-
8/7/2019 Phys_Chem-Chptr_2
9/33
Slide 9 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Composition of Compounds
Water Hydrogen peroxide
11.2% H 5.9%
88.8% O 94.1%Atomic composition 2H + 1O 2H + 2O
Law of definite composition: a compound
always contains two or more elementschemically combined in a definite proportion by
mass
-
8/7/2019 Phys_Chem-Chptr_2
10/33
Slide 10 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Composition of Compounds
Law of multiple proportions: states atoms of twoor more elements may combine in different ratios to
produce more than one compound
The law of definite composition and law ofmultiple proportions state that
(1) the composition of a particular substance will always
be the same no matter what its origin or how it is
formed,(2) the composition of different compounds formed from
the same elements will always be unique
-
8/7/2019 Phys_Chem-Chptr_2
11/33
Slide 11 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Combined Elements Giving More Than One Compound
Compound Formula Percent composition
Copper (I) chloride CuCl 64.2%Cu, 35.8%Cl
Copper (II) chloride CuCl2
47.3%Cu, 52.7%Cl
Methane CH4 74.9%C, 25.1% H
Octane C8H18 85.6%C, 14.4% H
Methyl alcohol CH4O 37.5%C, 12.6% H, 49.9% O
Ethyl alcohol C2H6O 52.1%C, 13.1% H, 34.7% O
Glucose C6H12O6 40.0%C, 6.7% H, 53.3% O
-
8/7/2019 Phys_Chem-Chptr_2
12/33
Slide 12 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
The Nature of Electric Charge
The properties of electric charge: Charge may be positive or negative
Unlike charges attract, like charges repel
Charges may be transferred from one object to another, by
contact or induction The less the distance between 2 charges, the greater the
force of attraction between unlike charges (or repulsionbetween identical charges)
The force of attraction (F) :
F = kq1
q2r2
q1 and q2 are the charges, r is the distance between thecharges and k is a constant
-
8/7/2019 Phys_Chem-Chptr_2
13/33
Slide 13 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Discovery of Ions
English scientist Michael Faraday (1791-1867) made thediscovery that certain substances when dissolved inwater conduct an electric current
He also noticed that certain compounds decompose into
their elements when an electric current is passedthrough the compound
Atoms of some elements are attracted to the positiveelectrode, while some other elements are attracted to thenegative electrode
He concluded that these atoms are electrically charged;he called them ions after the Greek word meaningwanderer
Any moving charge is an electric current
The electrical charge must travel through a substanceknown as a conducting medium
-
8/7/2019 Phys_Chem-Chptr_2
14/33
Slide 14 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Subatomic Parts of the Atom
Diameter of a singleatom ranges from 0.1to 0.5 nanometer
(1nm = 1 x 10-9
m) Hydrogen the
smallest atom diameter = 0.1nm
An atom containssubatomic particles:electrons, protons,and neutrons
-
8/7/2019 Phys_Chem-Chptr_2
15/33
Slide 15 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Electron
The electron is a particle
with a negative electrical
charge and a mass of
9.110 x 10-28g
This mass is 1/1837 the
mass of a hydrogen atom
Relative charge = -1
The size of electron has
not been determined
exactly; diameter is
believed to be < 10-12cm
-
8/7/2019 Phys_Chem-Chptr_2
16/33
Slide 16 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Proton
Proton firstobserved by Germanphysicist Eugen
Goldstein in 1886 Thompson calculated
its mass; approx.1837 times of themass of electron
Actual mass = 1.673 x10-24g; relative chargeof +1
-
8/7/2019 Phys_Chem-Chptr_2
17/33
Slide 17 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Thompson Model of The Atom
Electrons are negatively charged embedded in theatomic sphere
Atoms are electrically neutral, the sphere also containsan equal number of protons, or positive charges
A neutral atom could become an ion by gaining or losingelectrons
Positive ions: neutral atom loses electrons
Atom with net charge +1 has lost one electron
Atom with a net charge of +3 has lost 3 electrons
Negative ions gained additional electrons A net charge of-1 is produced by the addition of one
electron
-
8/7/2019 Phys_Chem-Chptr_2
18/33
Slide 18 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
The Third Major Subatomic Particle
Discovered by James
Chadwick (1891-
1974)
Neutron actualmass 1.675 x 10-24g;
slightly greater than
that of proton
-
8/7/2019 Phys_Chem-Chptr_2
19/33
Slide 19 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Class Activity 1
The mass of a helium atom is 6.65x10-24g.
How many atoms are in a 4.0g sample of
helium?
-
8/7/2019 Phys_Chem-Chptr_2
20/33
Slide 20 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Answer
(4.0g) (1 atom He)
(6.65 x 10-24g)
= 6.0 x 1023 atoms He
-
8/7/2019 Phys_Chem-Chptr_2
21/33
Slide 21 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Atomic Numbers of the Elements
Atomic number of an
element is the number of
protons in the nucleus of
an atom of that element
The atomic number
determines the identity of
an atom
Hydrogen = atomic
number = 1; contains oneproton in its nucleus
Uranium = 92; 92 protons
-
8/7/2019 Phys_Chem-Chptr_2
22/33
Slide 22 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Isotopes of the Elements
Isotopes: atoms of anelement having the sameatomic number butdifferent atomic masses
called isotopes of thatelement
Hydrogen (1), deuterium(2), tritium (3)
Mass number: the sum ofthe number of protonsand the number ofneutrons in the nucleus
-
8/7/2019 Phys_Chem-Chptr_2
23/33
Slide 23 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Isotopes of the Elements
Isotopes: atoms of anelement having the sameatomic number butdifferent atomic masses
called isotopes of thatelement
Hydrogen (1), deuterium(2), tritium (3)
Mass number: the sum ofthe number of protonsand the number ofneutrons in the nucleus
-
8/7/2019 Phys_Chem-Chptr_2
24/33
Slide 24 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Atomic Mass
The mass of a single atom canbe determined precisely withmass spectrometer
The mass of a single hydrogen
atom = 1.673 x 10-24g. However, it is not
convenient/practical to comparethe actual masses of atoms ingrams => a table of relative
atomic masses using atomicmass units was devised
The term atomic weight issometimes used instead ofatomic mass
-
8/7/2019 Phys_Chem-Chptr_2
25/33
Slide 25 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Atomic Mass Unit
Carbon isotope having 6 protons & 6neutrons and designated carbon-12, or12C,was chosen as the standard for atomicmasses
This reference isotope was assigned avalue of exactly 12 atomic mass units (amu)
1 atomic mass unit is defined as equal toexactly 1/12 of the mass of a carbon-12atom
The actual mass of a carbon-12 atom =1.9927 x 10-23g => one atomic mass unit =1.6606 x 10-24g
6
-
8/7/2019 Phys_Chem-Chptr_2
26/33
Slide 26 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Average Atomic Mass
Hydrogen atoms, with a mass of about 1/12 that of acarbon atom, have an average atomic mass of1.00797amu.
Magnesium atoms, which are about twice as heavy as
carbon, have an average mass of24.305 amu. Most elements occurs as mixtures of isotopes withdifferent masses.
The atomic mass determined for an element representsthe average relative mass of all naturally occurringisotopes of that element.
The atomic masses of the individual isotopes areapproximately whole numbers because the relativemasses of the protons and neutrons are approximately1.0 amu each
-
8/7/2019 Phys_Chem-Chptr_2
27/33
Slide 27 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Average Atomic Mass
Isotope Isotopic mass Abundance Average atomic mass
(amu) (%) (amu)
63Cu 62.9298 69.0963.55
65Cu 64.9278 30.91
29
29
Average atomic mass:
(62.9298 amu)(0.6909) = 43.48 amu
(64.9278 amu)(0.3091) = 20.07 amu
63.55 amu
-
8/7/2019 Phys_Chem-Chptr_2
28/33
Slide 28 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Example 1
How many protons,
neutrons, and electrons arefound in an atom of14C ?
6
-
8/7/2019 Phys_Chem-Chptr_2
29/33
Slide 29 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Answer
The element is carbon.
Atomic number = 6
Number of protons orelectrons are equal to theatomic number = 6
The number of neutrons =14 6 = 8
-
8/7/2019 Phys_Chem-Chptr_2
30/33
Slide 30 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Class Activity 1
How many protons, neutrons, andelectrons are in each of theseisotopes
16O8 80Br35 235U92
64Cu29
-
8/7/2019 Phys_Chem-Chptr_2
31/33
Slide 31 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Class Activity 2
What is the atomic number and themass number of the elements thatcontains:
a)9 electrons
b)24 protons and 28 neutrons
c)197X79
-
8/7/2019 Phys_Chem-Chptr_2
32/33
Slide 32 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
Class Activity 3
Chlorine is found in nature as twoisotopes, 37Cl17 (24.47%) and
35Cl17
(75.53%). The atomic masses are36.96590 and 34.96885 amurespectively. Determine the averageatomic mass of chlorine.
-
8/7/2019 Phys_Chem-Chptr_2
33/33
Slide 33 of 18 2010 Cosmopoint
Chapter 2: Early Atomic Theory and Structure
THANK YOU !THANK YOU !