Date post: | 02-Jan-2016 |
Category: |
Documents |
Upload: | cody-chapman |
View: | 213 times |
Download: | 0 times |
Atoms
The Building Blocks of Matter
Chapter 3
OBJECTIVES The Atom: Philosophy to Science 3.1 Explain the law of conservation of mass, the
law of definite proportions, and the law of multiple proportions.
Summarize the five essential points of Dalton’s atomic theory.
Explain the relationship between Dalton’s atomic theory and the 3 Laws
Foundations of Atomic TheoryThe Philosophers
400 B.C. – Particle Theory of Matter Greek Philosophers
Democritus“atmos” - indivisible
Aristotle matter is continuous, did
not believe in atomsNeither view was supported by experiments until the 18th century
Alchemy 700 B.C. – 1700’s
Transmutation – metals are made of varying proportions of sulfur and mercury - achieving the right combination would produce gold
Some used alchemy to make medicines
Balance Scale – Quantitative Analysis
The Laws of Chemistry
Measuring the masses of elements and compounds it was observed that when elements react to form compounds they combine in fixed proportions by mass.
Three basic laws of chemistry were proposed.
1. Law of Conservation of Mass
1782 - Antoine Lavoisier observed that the mass of the reactants before the reaction and the mass of the products after the reaction are the same.
Mass is neither created nor destroyed during ordinary chemical reactions or physical changes.
2. The Law of Definite Proportions
Regardless of the size of the sample or the source of a chemical compound, it is composed of a fixed ratio of elements by mass.
3. Law of Multiple Proportions
If two or more different compounds are made of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers.
Examples:
P. 87 #2
Dalton’s Atomic Theory
1808, an English school teacher and chemist, John Dalton, proposed a scientific explanation of these three laws based upon the idea of atoms of elements.
Dalton’s Atomic Theory1. All matter is made of tiny particles called
atoms.2. Atoms of the same element are identical,
those of different elements are different.3. Atoms cannot be subdivided, created , or
destroyed.4. Atoms of different elements combine in
small whole number ratios to form compounds
5. In chemical reactions, atoms are combined, separated or rearranged.
Dalton’s Atomic TheoryHow it Supported the laws: Conservation of mass - atoms are not created or destroyedDefinite proportions – a given compound is always the same proportion of atomsMultiple proportions – in 2 different compounds made of the same elements the ratio of the second atoms to the first atoms is a small whole number
Modern Atomic Theory
Dalton turned Democritus’ idea of the atom into a scientific theory that could be tested by experiment.
Not all aspects of Dalton’s theory have been proven correct. The theory has been modified by new discoveries.
OBJECTIVES The Structure of the Atom 3.2 Define atom. Summarize the observed properties of
cathode rays that led to the discovery of the electron.
Summarize the experiment carried out by Rutherford and his co-workers that led to the discovery of the nucleus.
List the properties of protons, neutrons, and electrons.
Atom
The smallest particle of an element that retains the chemical properties of the element.
Discovery of the electron
1897 -J. J. Thomson - English physicist.
Used a cathode ray tube.
It is a vacuum tube - all the air has been pumped out and replaced with a low pressure gas
Thomson’s ExperimentThomson’s Experiment
Voltage source
+-
An electric current was passed through the An electric current was passed through the tube from the tube from the cathodecathode (the negative (the negative electrode) to the electrode) to the anodeanode (the positive (the positive electrode). electrode).
Voltage source
Thomson’s ExperimentThomson’s Experiment
By adding an electromagnetic field By adding an electromagnetic field he found that the moving particles he found that the moving particles were negative were negative
+
-
Thomson’s Experiment
Movement of a paddlewheel in the path of the electrodes led scientist to conclude that the rays have mass.By using the cathode ray tube, Thomson determined that electrons have a very high charge and a very low mass.
Thomson’s Model
“plum pudding model”
An atom made of negative particles surrounded by positive material with the mass and charges uniformly distributed
Millikan Oil Drop Experiment.In 1909, Robert Millikan, an
American physicist, confirmed that the electron has the smallest possible negative charge and that all other negative charges are whole number multiples of the charge of the electron.
Rutherford’s experiment
(1910) Ernest Rutherford - English physicist.
Believed in the plum pudding model of the atom.
Used radioactivity to test it Alpha particles - positively charged pieces
given off by uranium Shot them at gold foil which can be made
a few atoms thick
Lead block
Uranium
Gold Foil
Florescent Screen
He expected the alpha particles to pass through He expected the alpha particles to pass through without changing direction very muchwithout changing direction very much
Because the positive charges were spread out Because the positive charges were spread out evenly. Alone they were not enough to stop the evenly. Alone they were not enough to stop the alpha particlesalpha particles
He thought the mass was evenly distributed in the atom
What he got
Most of the particles passed through the foil indicating that the atom is mostly empty space.
+
Very few of the particles bounced back, but Very few of the particles bounced back, but with great force,with great force,
What Rutherford concluded:
+
The atom is mostly empty space
A small, very dense, positively charged core within the atom
The nucleus
Protons and Neutrons
In 1919 Rutherford discovered the proton.
The neutron was discovered in 1932 by an English scientist, James Chadwick.
Composition of the Atom – Subatomic Particles
Protons are subatomic particles located in the nucleus of the atom with high mass and a positive charge equal in magnitude to the negative charge of the electron.
The nucleus also contains neutrons which are electrically neutral and have a mass ~ equal to a proton
Electrons surround the nucleus in an electron cloud. They have very little mass and a negative charge
Atoms are neutral due to the presence of equal numbers of protons and electrons.
Subatomic particles
Electron
Proton
Neutron
Name Symbol ChargeRelative mass
Actual mass (g)
e-
p+
n0
-1
+1
0
.0005
1
1
9.11 x 10-28
1.67 x 10-24
1.67 x 10-24
Subatomic Particles
POSIT IVECHARG E
PROT ONS
NEUT RALCHARG E
NEUT RONS
NUCLEUS
NEG AT IVE CHARG E
ELECT RONS
AT OM
NUCLEUS ELECTRONS
PROTONS NEUTRONS NEGATIVE CHARGE
POSITIVE CHARGE
NEUTRAL CHARGE
ATOM
QUARKS
Homework
P. 74 # 1-5
OBJECTIVES Counting Atoms 3.3 Explain what isotopes are. Define atomic number and mass number, and
describe how they apply to isotopes. Given the identity of a nuclide,determine its
number of protons,neutrons, and electrons. Define mole in terms of Avogadro’s number,
and define molar mass. Solve problems involving mass in grams,
amount in moles, and number of atoms of an element.
Atomic NumberAtomic Number (Z) = number of
protons in the nucleus of atomAtomic Number Identifies the
element# of protons determines kind of
atom# protons = # electrons in the
neutral atom
Atomic Number – The identity
3LiLithium6.941[He]2s1
The atomic numberin this periodic-table entry revealsthat an atom of lithium has threeprotons in its nucleus
Mass Numbermass # = protons
+ neutrons
always a whole number
© Addison-Wesley Publishing Company, Inc.
Isotopes
Atoms of the same element with different numbers of neutrons –so different mass numbers.
C126Mass #
Atomic #
Nuclear symbol:
Hyphen notation: carbon-12
Isotopes
© Addison-Wesley Publishing Company, Inc.
Designating Isotopes
Isotopes of Hydrogen and Helium – p. 77
Isotopes
Chlorine-37
atomic #:
mass #:
# of protons:
# of electrons:
# of neutrons:
17
37
17
17
20Cl37
17
Symbols of Nuclides
Find the # p+
# n0
# e-
Atomic numberMass Number
F19 9
Symbols of Nuclides Find the Find the
# p# p++
# n# n00
# e# e--
–Atomic numberAtomic number
–Mass NumberMass Number
Br80 35
Nuclides 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
–number of protonsnumber of protons
–number of neutronsnumber of neutrons
–number of electronsnumber of electrons
–Complete symbolComplete symbol
Nuclides if an element has 91 protons if an element has 91 protons
and 140 neutrons what is the and 140 neutrons what is the
–Atomic numberAtomic number
–Mass numberMass number
–number of electronsnumber of electrons
–Complete symbolComplete symbol
Nuclides if an element has 78 if an element has 78
electrons and 117 neutrons electrons and 117 neutrons what is the what is the
–Atomic numberAtomic number
–Mass numberMass number
–number of protonsnumber of protons
–Complete symbolComplete symbol
Using the periodic table for nuclides
How many protons, neutrons, and electrons are in an atom of
Uranium-235
Uranium-238
Relative Atomic MassThe mass of an atom expressed in atomic mass
units is called the atomic mass of the atom.
1 p = 1.007276 amu
1 n = 1.008665 amu
1 e- = 0.0005486 amu
© Addison-Wesley Publishing Company, Inc.
atomic mass unit (amu or u)
1 amu = 1/12 the mass of a 12C atom
Average Atomic Mass
weighted average of all naturally occurring isotopes of an element
Periodic Table shows the average
100
(%)(mass(mass)(%) )
Avg.AtomicMass
Avg.AtomicMass
Average Atomic Mass
EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O.
100
(18)(0.20)(17)(0.04))(16)(99.76 16.00amu
Avg.AtomicMass
Average Atomic Mass
Ex. copper consists of 69.17% copper-63, which has an atomic mass of 62.94 u, and copper-65, which has an atomic mass of 64.93 u.
10
.83)(64.93)(30.17)(62.94)(69
63.55 amu
Magnesium has three isotopes. 78.99% magnesium - 24 with a mass of 23.99 amu,
10.00% magnesium - 25 with a mass of 24.99 amu,
magnesium - 26 with a mass of 25.98 amu.
What is the average atomic mass of magnesium?
The Mole
Avogadro
What is the Mole?
A counting number (like a dozen)
Avogadro’s number
1 mol = 6.022 1023 items
A large amount!!!!
1 mole of pennies would cover the Earth 1/4 mile deep!
1 mole of basketballs would fill a bag the size of the earth!
Molar Mass
Mass of 1 mole of an element or
compound.
Molar mass tells the … grams per mole (g/mol) Use average atomic mass on the
periodic table – same # different unit
Molar Mass Examples
carbon
aluminum
zinc
12.01 g/mol
26.98 g/mol
65.39 g/mol
Molar Conversions
molar mass
(g/mol)
MASS
IN
GRAMS
MOLESNUMBER
OF
PARTICLES
6.022 1023
(particles/mol)
Mole
Molar Conversions – grams to mol
How many moles of carbon are in 26.0 g of carbon?
26.0 g C 1 mol C
12.01 g C= 2.16 mol C
Molar Conversions – mol to grams
What is the mass in grams of 3.50 mol of Cu?
3.50 mol Cu 63.55 g Cu
1 mol Cu= 222 g Cu
Molar Conversions Using Avogadro’s numberHow many atoms are in 2.50
moles of lead?
2.50 mol
6.022 1023
atoms
1 mol= 1.51 1024
atoms Pb
Molar Conversions Using Avogadro’s numberHow many moles of Ag are in
3.01 1023 atoms of silver?
3.01 1023 atoms 1 mol Ag
= 0.500 mol Ag6.022 1023 atoms
Molar Conversions
Find the mass of 2.1 1024 atoms of Copper.
2.10 1024
atoms 1 mol
6.022 1023
atoms
= 222 g Cu
63.55 g
1 mol