Download ch 4 notes sept 30 oct 1.notebook

ch 4 notes sept 30 oct 1.notebook
CHAPTER FOUR:
THE STRUCTURE OF THE ATOM
Sep 24­4:05 PM
Section 4.1 Early Ideas About Matter
• Compare and contrast the atomic models of Democritus, Aristotle, and Dalton.
• Understand how Dalton's theory explains the conservation of mass.
October 01, 2013
The Structure of the Atom
Section 4.1
Section 4.2 Section 4.3 Section 4.4 Early Ideas About Matter
Defining the Atom
How Atoms Differ
Unstable Nuclei and Radioactive Decay
Sep 27­11:26 AM
The Atom
Smallest particle of an element that retains the properties of that element
* made of much smaller particles
* our concept is a result of generations of work
theory: an explanation supported by many experiments; is still subject to new experimental data, can be modified, and is considered successful if it can be used to make predictions that are true
Dalton's atomic theory
The ancient Greeks tried to explain matter, but the scientific study of the atom began with John Dalton in the early 1800's.
Sep 27­11:27 AM
Early atomic theory begins with...
Democritus
* 400 BC
* Claimed the world was nothing but empty space and atoms
"All matter is made of very small particles ­­ much too small to see."
Sep 24­11:24 AM
Aristotle *criticized Democritus*
(384­322 BC)
*thought the world was made of "hyle" (continuous matter)
*Did NOT believe in atoms
*Thought all matter was continuous
atomos: indivisible
* different types of atoms = different sizes, shapes and movement =
different types of properties
* believed that atoms could not be created, destroyed or further divided.
Sep 14­7:27 AM
* He couldn't wrap his mind
around the concept of
empty space!
Sep 24­10:40 AM
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ch 4 notes sept 30 oct 1.notebook
If these spheres represent atoms and molecules in the gas phase, what is between them?
October 01, 2013
Aristotle believed that
matter is made of...
Sep 30­10:35 AM
But really, what did it matter what philosophers thought when they had no experimental data to support their ideas?
Sep 24­4:11 PM
• Democritus (460–370 B.C.) was the first person to propose the idea that matter was not infinitely divisible, but made up of individual particles called atomos.
• Aristotle (484–322 B.C.) disagreed with Democritus because he did not believe empty space could exist.
• Aristotle’s views went unchallenged for 2,000 years until science developed methods to test the validity of his ideas.
Sep 24­4:13 PM
Sep 27­11:30 AM
Law of Conservation of Mass
Mass is neither created nor destroyed during ordinary chemical reactions or physical changes
2H2O 100.00g
Improved balances helped scientists accurately measure
masses of elements and compounds. This lead to several laws:
1. Law of Conservation of Mass
2. Law of Definite Proportions
3. Law of Multiple Proportions
Sep 24­10:46 AM
2H2 + O2
11.21g
H
H
Antoinne LaVoisier
H
H
88.79g
O
O
O
H
H
H
H
O
Sep 24­10:49 AM
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ch 4 notes sept 30 oct 1.notebook
Law of Definite Proportions
October 01, 2013
Not to be confused with THE LAW OF MULTIPLE PROPORTIONS
Proust
2 or more different compounds can be composed of the same elements
A chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound
H­2O2
vs
H2 O
water vs. hydrogen peroxide
H 2O
CO
vs CO2
carbon monoxide vs. carbon dioxide
2:1
Sep 14­8:24 AM
Sep 16­8:09 AM
John Dalton
* 1800's
* Studied experiments of others
* Came up with a feasible theory about atoms
Sep 24­10:37 AM
Sep 30­9:15 AM
Section 4.2 Defining the Atom Section 4.1 Assessment
Who was the first person to propose the idea that matter was not infinitely divisible? A. Aristotle B. Plato C. Dalton D. Democritus Dalton’s theory also conveniently explained what? A. the electron B. the nucleus C. law of conservation of mass D. law of Democritus • Define atom.
• Distinguish between the subatomic particles in terms of relative charge and mass.
• Describe the structure of the atom, including the locations of the subatomic particles.
model: a visual, verbal, and/or mathematical explanation of data collected from many experiments
atom
cathode ray
electron
nucleus
proton
neutron
An atom is made of a nucleus containing protons and neutrons; electrons move around the nucleus.
Sep 27­11:31 AM
Sep 27­11:34 AM
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ch 4 notes sept 30 oct 1.notebook
October 01, 2013
The Atom: smallest particle of an element that retains the
properties of the element.
The Atom
Xe on nickel
CO molecules on Pt
Made with atomic force microscope
• An instrument called the scanning tunneling microscope (STM) allows individual atoms to be seen.
Sep 24­4:42 PM
Sep 14­8:36 AM
Scanning Tunneling Microscope
Iron on copper
Nanotechnology
Sep 24­4:48 PM
How was the electron discovered?
* study of electricity and matter
Crooke's Tube
Sep 30­10:32 AM
Thomson found the charge/mass ratio of an electron
* JJ Thomson (1897)
* cathode ray tube: tubes with nearly a vacuum inside
Cathode rays = electrons
* determined the mass to be much tinier
than a H atom
* Dalton was wrong!
* Nobel Prize for Thomson in 1906! Woot!
Cathode rays were deflected by a magnet just like an electric current (­)
Cathode rays moved a small paddle wheel (had mass)
The mass of the particle was
much smaller than that of a
hydrogen atom.
Sep 14­8:15 AM
Sep 24­5:00 PM
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ch 4 notes sept 30 oct 1.notebook
Robert A Millikan
What he discovered:
October 01, 2013
The Electron (cont.)
• Matter is neutral.
* mass of the electron is about 1/1837 the mass of the simplest hydrogen atom
* confirmed the electron carries a negative electric charge
• J.J. Thomson's plum pudding model of the atom states that the atom is a uniform, positively changed sphere containing electrons.
* all elements produce identical cathode rays
* proved atoms are divisible
What still needed figuring out:
1. something must be in the atom to balance the charge
2. atoms must have some type of particle to produce so much mass
Sep 16­8:27 AM
Sep 27­2:39 PM
Ernest Rutherford
The Nucleus
• In 1911, Ernest Rutherford studied how positively charged alpha particles interacted with solid matter.
(with Geiger and Marsden)
The Gold Foil Experiment
•
By aiming the particles at a thin sheet of gold foil, Rutherford expected the paths of the alpha particles to be only slightly altered by a collision with an electron. 1. discovered the nucleus
2. nucleus was very small yet packed with matter
3. nucleus was +
Sep 27­2:39 PM
The Nucleus (cont.)
Sep 16­8:30 AM
The Nucleus (cont.)
• Rutherford refined the model to include positively charged particles in the nucleus called protons.
• All atoms are made of three fundamental subatomic particles: the electron, the proton, and the neutron.
• James Chadwick received the Nobel Prize in 1935 for discovering the existence of neutrons, neutral particles in the nucleus which accounts for the remainder of an atom’s mass.
• Atoms are spherically shaped.
• Atoms are mostly empty space, and electrons travel around the nucleus held by an attraction to the positively charged nucleus.
Sep 27­2:41 PM
Sep 27­2:42 PM
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ch 4 notes sept 30 oct 1.notebook
October 01, 2013
The Nucleus (cont.)
• Scientists have determined that protons and neutrons are composed of subatomic particles called quarks.
Section 4.2 Assessment
Atoms are mostly ____. A. positive B. negative C. solid spheres D. empty space •
•
•
•
A
B
C
D
• Chemical behavior can be explained by considering only an atom's electrons.
Section 4­2
Sep 27­2:42 PM
Sep 27­11:11 AM
Section 4.3 How Atoms Differ What are the two fundamental subatomic particles found in the nucleus? A. proton and electron B. proton and neutron C. neutron and electron D. neutron and positron •
•
•
•
A
B
C
D
• Explain the role of atomic number in determining the identity of an atom.
• Define an isotope.
• Explain why atomic masses are not whole numbers.
• Calculate the number of electrons, protons, and neutrons in an atom given its mass number and atomic number.
periodic table: a chart that organizes all known elements into a grid of horizontal rows (periods) and vertical columns (groups or families) arranged by increasing atomic number
atomic number
isotopes
mass number
atomic mass unit (amu)
atomic mass
Section 4­2
Sep 27­11:11 AM
Let's focus on the PROTONS:
What is going on inside the nucleus?
Protons:
p+
opposite the charge of an electron
Sep 27­2:44 PM
Atomic Number
Neutrons:
no
high energy particles
with no charge
same mass as proton
quarks, gluons, mesons...
• Each element contains a unique positive charge in their nucleus.
• The number of protons in the nucleus of an atom identifies the element and is known as the element’s atomic number.
Nuclear forces: short­range p/n, p/p and n/n forces that make them sticky
Sep 16­8:31 AM
Oct 1­8:54 AM
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ch 4 notes sept 30 oct 1.notebook
October 01, 2013
# OF PROTONS = IDENTITY
Z = atomic
number
47
• All atoms of a particular element have the same number of protons and electrons but the number of neutrons in the nucleus can differ.
Ag
average atomic mass
107.8682
Sep 16­8:36 AM
Sep 27­2:46 PM
Remember this guy?
• Atoms with the same number of protons but different JJ Thomson
numbers of neutrons are called isotopes.
* he was the first to discover that • Adding the # of protons to the # neutrons =
atoms of neon could have different masses.
Neon-22
Neon-20
MASS NUMBER (A)
* he was the first to discover the existence of stable isotopes
Oct 1­8:58 AM
Oct 1­9:05 AM
ISOTOPES
# of Neutrons =determines which isotope
Isotope
Protium
hyphen notation
# protons
1
# neutrons
0
Mass number
1
Nuclide Hyphen symbol
notation
1
H
Hydrogen-1
H
Hydrogen-2
1
2
nuclide symbol
Deuterium
1
1
2
1
3
A
X
Hydrogen­1
Z
1
name of element
mass number (A)
Sep 16­8:36 AM
1
Tritium
1
2
3
1
H
Hydrogen-3
H
Oct 1­3:50 PM
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ch 4 notes sept 30 oct 1.notebook
October 01, 2013
Although isotopes have different masses, they do not differ significantly in their chemical behavior.
Isotopes of the same element can have different uses:
Sep 27­2:46 PM
Oct 1­9:11 AM
Relative atomic mass: use carbon­12 as the standard
Mass of Atoms
• One atomic mass unit (amu) is defined as 1/12th the mass of a carbon­12 atom.
atomic mass units
• One amu is nearly, but not exactly, equal to one proton and one neutron.
• When we are talking about the mass of ONE atom, we label it as amu.
Carbon­12 = 12 amu
Sep 16­8:40 AM
Sep 27­2:46 PM
Carbon­14
Carbon­13
Half­life = 5730 years
Natural abundance
Isotopic tracing
Notice that isotopes of the same for metabolism
radioactive dating
Sep 17­8:19 AM
element do NOT occur in the same amounts in nature.
Oct 1­9:16 AM
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ch 4 notes sept 30 oct 1.notebook
October 01, 2013
For the isotope Mg-24:
The actual mass of Mg-24 is
a) Find the # of protons, electrons and neutrons
atomic mass is 23.985 042 amu
b) Using the number of protons, neutrons and electrons, calculate WHY????????????
the mass of an atom of Mg-24:
Oct 1­10:24 AM
Oct 1­10:26 AM
Calculating the average atomic mass on * Protons and neutrons are not exactly 1 amu
the periodic table
Isotope
* electrons have mass
6
* small amount of mass is changed to energy in the creation of a nucleus
7
X
X
mass (amu)
6.015
7.59%
7.016
92.41%
Sep 16­8:42 AM
Oct 1­8:03 AM
Calculate the average atomic mass of Isotope
% natural
abundance
Atomic Mass
(amu)
Copper­63
Copper­65
69.17%
30.83%
62.929 599
64.927 793
magnesium:
Isotope
atomic mass
% abundance
% abundance
Mg-24
23.985
78.99%
Mg-25
24.986
10.00
Mg-26
25.983
11.01
Average atomic mass?
Oct 1­10:27 AM
Sep 16­8:48 AM
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ch 4 notes sept 30 oct 1.notebook
October 01, 2013
Section 4.3 Assessment
Elements with the same number of protons and differing numbers of neutrons are known as what? A. isotopes B. radioactive C. abundant D. ions •
•
•
•
A
B
C
D
An unknown element has 19 protons, 19 electrons, and 3 isotopes with 20, 21 and 22 neutrons. What is the element’s atomic number? A. 38 B. 40 C. 19
D. unable to determine • A
• B
• C
• D
Section 4­3
Sep 27­11:11 AM
Section 4­3
Sep 27­11:11 AM
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