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Transcript
Unit 3
Atomic Structure
Accelerated Chemistry
3.1 – The Discovery of the Atom – Identify and describe the contributions of Democritus
and John Dalton to the development of Modern Atomic Theory.
Democritus
- 400 BCE Greece
- First person to propose that all matter is made up
of tiny, indivisible particles.
- Atom is derived from “atomos,” which is Greek
for “indivisible.”
3.1 – The Discovery of the Atom – Identify and describe the contributions of Democritus
and John Dalton to the development of Modern Atomic Theory.
John Dalton
- Early 1800’s CE England
- Dalton’s Atomic Theory
1. All elements are composed of tiny indivisible particles called atoms.
2. Atoms of the same element are identical. The atoms of one element are different
from the atoms of another.
3.1 – The Discovery of the Atom – Identify and describe the contributions of Democritus
and John Dalton to the development of Modern Atomic Theory.
- Dalton’s Atomic Theory - Continued
3. Atoms of different elements can be physically mixed together or can chemically
combine with one another in simple whole-number ratios to form compounds.
4. Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms
of one element cannot be changed into atoms of another element as a result of a
chemical reaction.
3.1 – The Discovery of the Atom – Identify and describe the contributions of Democritus
and John Dalton to the development of Modern Atomic Theory.
Atom
- Smallest particle of an element that retains the properties of that element.
3.2 – Structure of the Nuclear Atom – Identify and describe the discoveries of early
scientists, specifically J.J. Thomson and Ernest Rutherford, and how these discoveries
led to our modern understanding of the atom.
J.J. Thomson
- 1897 CE England
- Discovered the first subatomic particle, the electron
- He was studying cathode ray tubes
3.2 – Structure of the Nuclear Atom – Identify and describe the discoveries of early
scientists, specifically J.J. Thomson and Ernest Rutherford, and how these discoveries
led to our modern understanding of the atom.
3.2 – Structure of the Nuclear Atom – Identify and describe the discoveries of early
scientists, specifically J.J. Thomson and Ernest Rutherford, and how these discoveries
led to our modern understanding of the atom.
J.J. Thomson
- Conclusions
- Renamed cathode rays “electrons”
- Electrons are negatively charged
- Electrons are a part of all atoms
3.2 – Structure of the Nuclear Atom – Identify and describe the discoveries of early
scientists, specifically J.J. Thomson and Ernest Rutherford, and how these discoveries
led to our modern understanding of the atom.
Robert Millikan
- 1916 CE - Conducted the Oil Drop Experiment and determined the
charge/mass ratio for the electron.
Eugen Goldstein
- 1886 CE - Discovered the proton.
James Chadwick
- 1932 CE - Discovered the neutron.
3.2 – Structure of the Nuclear Atom – Identify and describe the discoveries of early
scientists, specifically J.J. Thomson and Ernest Rutherford, and how these discoveries
led to our modern understanding of the atom.
Ernest Rutherford
- 1911 CE, England
- Discovered the nucleus using the Gold Foil Experiment
3.2 – Structure of the Nuclear Atom – Identify and describe the discoveries of early
scientists, specifically J.J. Thomson and Ernest Rutherford, and how these discoveries
led to our modern understanding of the atom.
Ernest Rutherford
3.2 – Structure of the Nuclear Atom – Identify and describe the discoveries of early
scientists, specifically J.J. Thomson and Ernest Rutherford, and how these discoveries
led to our modern understanding of the atom.
Ernest Rutherford
- Observations
1.Vast majority of alpha particles went straight through the metal.
2.A few alpha particles were deflected at a fairly wide angle.
3.Very, very few alpha particles were deflected back in the direction
they had come.
3.2 – Structure of the Nuclear Atom – Identify and describe the discoveries of early
scientists, specifically J.J. Thomson and Ernest Rutherford, and how these discoveries
led to our modern understanding of the atom.
Ernest Rutherford
- Conclusions
1.Atoms are mostly empty space.
2.Atoms have a tiny, positively charged area.
3.This tiny, positively charged area is extremely dense.
4.Rutherford named this area the nucleus.
3.3 – Distinguishing Between Atoms – Determine the number of protons, neutrons, and
electrons in an atom or isotope, and distinguish between atoms and isotopes.
Atomic Number
- The number of protons in the nucleus of that element.
- Since atoms are always electrically neutral, it is also the number of
electrons.
3.3 – Distinguishing Between Atoms – Determine the number of protons, neutrons, and
electrons in an atom or isotope, and distinguish between atoms and isotopes.
Mass Number
- Total number of protons and neutrons in the nucleus of the
atom. This is not found on the periodic table.
3.3 – Distinguishing Between Atoms – Determine the number of protons, neutrons, and
electrons in an atom or isotope, and distinguish between atoms and isotopes.
Atomic Mass (Weight)
- A weighted average mass of the atoms in a naturally occurring sample of the
element. It is based on the percentage of isotopes found in nature.
3.3 – Distinguishing Between Atoms – Determine the number of protons, neutrons, and
electrons in an atom or isotope, and distinguish between atoms and isotopes.
Isotope
- Atoms that have the same number of protons, but a different number of
neutrons.
3.3 – Distinguishing Between Atoms – Determine the number of protons, neutrons, and
electrons in an atom or isotope, and distinguish between atoms and isotopes.
Practice Answers
1. P = 53, E = 53, N = 73
2. P = 55, E = 55, N = 78
Practice Answers
3.
Atomic
Number
Mass
Number
20
74
1
80
# of protons
# of
neutrons
# of
electrons
Chemical
Symbol
20
20
20
Ca
74
W
184
Name
Tungsten
1
0
1
H
33
42
33
As
Arsenic
80
Hg
Mercury
80
Practice Answers
1. P = 27, E = 27, N = 32
2. P = 12, E = 12, N = 12
Practice Answers
3.
Atomic
Number
Mass
Number
50
119
# of protons
# of
neutrons
82
# of
electrons
Chemical
Symbol
Name
50
Sn
Tin
56
Ba
1
H
56
56
1
1
92
92
146
92
U
15
17
15
P
Hydrogen
Phosphorus
Practice Answers
5. Goldstein
6. Rutherford
7. Thomson
8. Thomson
9. Chadwick
10. Rutherford
11. Dalton
12. Democritus
Unit 3 Review
1. a. Dalton believed that all atoms were made of tiny indivisible particles called
atoms.
b. Atoms of the same element are the same, atoms of one element are
different from atoms of another.
c. Atoms of the same element are the same.
d. Atoms chemically combine to form compounds.
Unit 3 Review
2. a. The ray was attracted to the positive end of a magnet.
b. Dalton used different metals in his electrodes and got the same results.
3. Repel because similar charges repel.
4. Rutherford expected all the alpha particles to go straight through the gold foil.
When some of the alpha particles were deflected, this led Rutherford to conclude
that the atom is mostly empty space but that it contains a dense center called the
nucleus.
Unit 3 Review
5. Positive because protons are in the nucleus.
6. Because neutral atoms contain the same number of negative elections and
positive protons, so they cancel out.
7. The number of protons in that atom.
8. a. 15, b. 42, c. 13, d. 48, e. 24, f. 82
Unit 3 Review
Atomic
Number
Mass Number # of protons
19
14
22
25
# of neutrons
9
29
22
30
# of electrons
Chemical
Symbol
9
F
14
Si
22
Ti
25
Mn
Unit 3 Review
10. Isotopes of the same element have different numbers of neutrons and mass
numbers.
11. Isotopes are different versions of the same element and explain why there are
1,000 different atoms.
12. You need to know the number of neutrons and protons in that element.
13. Atomic Mass = Protons + Neutrons
14. The nucleus is incredibly dense and small compared to the rest of the atom,
which is mostly empty space.
Unit 3 Review
15. 1. Atoms are the smallest part of matter.
2. All atoms of the same element are the same.
3. Atoms of one element cannot be changed into atoms of another element.
16. a. The mass of that isotope
b.
195
78𝑃𝑡
Unit 3 Review
17. a. Lithium-6 p = 3, n = 3, e = 3
Lithium-7 p = 3, n = 4, e = 3
b. Calcium-42 p = 20, n = 22, e = 20
c. Selenium-78 p = 34, n = 44, e = 34
Calcium – 44 p = 20, n = 24, e = 20
Selenium-80 p = 34, n = 46, e = 34
18. They are weighted averages for the masses of all the isotopes for that
element.
Unit 3 Review
19. The atomic number is unique for every element. It also tells the number of
protons in that element. Every element on the periodic table has a unique number
of protons. It’s like an element’s Social Security Number.
20. Atomic number is the number of protons and electrons in an atom. To get the
number of neutrons, you take the Mass Number, round it to a whole number, and
subtract the atomic number from it.