Title: The Structure of the Atom
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3The Structure of the Atom
- History, Structure, Properties and Forces
- Chapter 4
4Atomic Structure
History, Structure and Properties of the Atom
5Atomic Structure Objectives
- 1. I can illustrate and compare the different
atomic models proposed by scientists. - I can illustrate the organization of each
subparticle in a neutral atom. - I can distinguish between atoms of different
elements and of the same elements. - I can calculate the atomic mass for any element.
6History of the Atom
- Great Thinkers (2,000yrs. Ago)
- Age of Reason and Thought
- Democritus vs. Aristotle view on the make-up of
matter.
7 Democritus(400b.c.)Greek Philosopher
- Observed matter to be made up of atoms.
- Atoms are the smallest form of matter.
- Atoms cannot be broken down.
- The types of atoms in matter determine its
properties.
8 Aristotle Greek Philosopher (300b.c.)
- Aristotle observed matter to be composed of
one or more of these four elements - air, earth, fire and water.
- Most people believed Artistole.
- Why?
9John Daltons Atomic Theory
- English school teacher
- Proved Democritus atoms hypothesis using the
scientific method. - His conclusions produced
- Daltons Atomic Theory
10Daltons Atomic Theory
- Atoms are the building blocks of all matter.
- 2. Atoms cannot be subdivided.
- 3. Each element has the same kind of atoms.
- 4. In a compound, the different atoms chemically
combine in the same way (fixed composition). - 5. Atoms cannot be created or destroyed just
rearranged.
11Thomsons Cathode Ray Experiment
- J.J. Thomson (pg. 105)
- 1897 discovered electrons in gas atoms using a
cathode ray tube. - Determined electrons have a negative charge.
- Electrons have the same charge in all atoms.
-
-
12 Thomsons Plum Pudding Model
- If atoms are made of electrons how come most
matter does not shock us? - Atoms must have positive particles, too.
- He proposed the Plum Pudding Atomic Model
-
-
An atom is equally made up of positive and
negative particles.
13Goldsteins Cathode Tube Experiment
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- He discovered the positively charged particle,
proton, using a cathode ray tube also.
14 Rutherfords Gold Foil Experiment
- The laser beam consisted of positively charged
alpha particles. - Hypothesized that if the Plum Pudding model of
the atom was correct then the - charged alpha particles should deflect or bend
slightly when in contact with the gold foil
atoms. - His experimental results revealed something
different. Most alpha particles paths were not
affected by any charge when in contact with gold
foil. (Red straight lines on left diagram). Just
a few deflected back at large angles. Knew it
had to be of the same charge, because repelled.
15Rutherfords Conclusion
- Most of the atom is empty space.
- Small dense region composed of
- () charged particles.
- (Nucleus)
16Rutherfords Nuclear Atom Model
17Subatomic Particle Neutron
- What keeps the protons within the nucleus ?
- (Like particles repel each other)
- 1932 - James Chadwick discovers the nucleus also
has neutral particles present. He called them
neutrons. - Neutrons have a significant mass like protons.
18Bell Ringer
- 1. Compare the different views Aristotle and
Democritus had about what matter was made of. - 2. Which Greek philosopher was correct ?
- 3. Which later scientist proved his view?
19Bell Ringer4. a. Identify and explain this
Atomic Model?b. Who concluded this atomic model?
20Bell Ringer
- 5. Look at the following experiment below.
- What was this experiment called?
- Who developed this experiment?
- Did his experiment prove or disprove the Plum
Pudding Model?
21Kandium Lab Post Lab Question
Atomic Subparticles Charge mass (g) mass (amu) atoms contribution
Electron 9.11 x 10 -28 so tiny, no mass (10,000x smaller than p or no
Proton 1.674 x10-24 1 atomic mass unit for each proton.
Neutron 1.675 x10-24 1 atomic mass unit for each neutron
- Abbreviate each isotope of Kandium using the new
- symbol you assigned it and its mass number.
- Using the table above convert the mass number of
each - Kandium isotope from amu to grams.
22Distinguishing Atoms
- atomic number The number of protons within an
atoms nucleus. - Atoms I.D.
- Atoms of the same element always have the same
number of protons. - Elements are arranged numerically on the periodic
table based on their atomic number.
23Neutral Atoms
- Most matter in nature is neutral.
- (Doesnt shock us!)
- This means the atoms making up the matter is
neutral. ? - What are the two charged subatomic particles?
- p and e-
- For an atom to be neutral the of p of
e-.
24Atoms Mass
- Mass number (amu)
- What contributes mass to the atom?
- Sum of protons and neutrons in nucleus of atom.
- Problem A Selenium(Se) has an atomic of 34
and a mass of 80 amu. How many p, e-, and n0
are there in selenium? p (proton) 34
(atomic ) - e- (electron) 34
(balance p) - n0 (neutron) 80 34
46
25Atoms Subatomic Particles
- Problem B A cesium (Cs) atom has a mass of 133
and an atomic number of 55 amu. How many p, e-,
and no are there? - P 55 e- 55 no 78
- Problem C An iron atom has an atomic number of
26 and 30 neutrons. - How many p and e- are there?
- P 26 e- 26
- What is irons mass number?
- Mass number 56 amu
26Bell Ringer Atomic Structure
Element Symbol protons (p) neutrons (no) Electrons (e-)
N 8
F 9
C 8
O 9
- Complete the table above. Each atom is neutral.
- Rank the atoms in increasing order based on
atomic number. -
- 3.Rank the atoms in decreasing order based on
mass number. - 4.Pick one of the atoms from the table to
illustrate the number of protons, electrons, and
neutrons using Rutherfords model of the atom.
27Atomic Structure Review
28An Elements Isotopes
- Isotopes atoms with different number of
neutrons in their nucleus. - Elements can have several isotopes.
- Ex. Carbon C-12 and C-14 (mass )
- Mass changes. (varied neutrons)
- The number of protons and electrons stay the
same.
29An Elements Isotopes
C-12
C-14 of p, n0, e-? of p,
n0, e-?
30Elements Isotopes
- Oxygen has three isotopes. They are O-16,
- O-17, and O-18.
- What is the mass number for each isotope of
oxygen in amu? - 2. What is the atomic number for each isotope of
oxygen? - 3. What is the number of p, n0, and e- for each
isotope of Oxygen ?
31Atomic MassElements average mass
- Atomic mass the average mass of all the
elements isotopes present within a naturally
occuring sample of matter. - Calculate Atomic Mass of an Element
- 1. Multiply the mass of each isotope by its
natural abundance ( common occurance) in decimal
form. - 2. Add all the isotopes products together.
32Carbons Atomic Mass
- Calculate the atomic mass for Carbon
- Carbon-12 natural abundance is 98.
- Carbon-14 natural abundance is 2.
- Carbons atomic mass?
- 12 x 0.98 11.76 amu
- 14 x 0.02 0.28 amu
- 12.04 amu
- Just remember to convert natural abundance
from percentage to decimal form. -
33Isotopes
34Mass Number vs. Atomic Mass
Compare mass number of an atom with elements
atomic mass using the Venn diagram below.
35Atomic Mass
36Atomic Mass
- Calculate Iodines atomic mass. Watch
significant figures.
Isotope Natural Abundance ()
I-127 80
I-126 17
I-128 3
Answer 126.86 126.9 (sig. figs)
37Atomic Properties
- If most of the atom is empty space, why doesnt
matter pass through one another?
38Atomic Properties
- If most of the atom is empty space, why doesnt
matter pass through one another?
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39Atomic Properties
- What keeps the protons from leaving the nucleus
and being drawn towards the electrons?
40Atomic Forces
- Electrostatic Forces
- Nuclear Forces
41Bell Ringer Atomic Forces
- What are the two primary forces within an atom?
- Distinguish between these forces.
- a. Which one of the forces is stronger ?
- b. Why is this important to the atoms
existence?
42Atomic Forces
- Electrostatic Forces
- Forces between charged
- particles.
- Nuclear Forces
- Forces that holds
- nucleus together
43Charged Atoms
- Ions charged atoms.
- How do ions form? Neutral atoms lose or gain
electrons. - Two types of atoms
- Cations positively charged atoms
- (more p than e-)
- Anions negatively charged atoms
- (more e- than p)
44Distinguishing Between Atoms
Type of Atom of p of n0 of e- Mass Number Neutral or Charged atom Atoms Symbol
Calcium 20 41
28 18 48
7 10 15
36 28 65