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The Structure of the Atom


Title: The Structure of the Atom Author: Dan Martin Last modified by: lleeper Created Date: 9/1/2003 3:36:13 PM Document presentation format: On-screen Show – PowerPoint PPT presentation

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Title: The Structure of the Atom

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The Structure of the Atom
  • History, Structure, Properties and Forces
  • Chapter 4

Atomic Structure
History, Structure and Properties of the Atom
Atomic 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.

History of the Atom
  • Great Thinkers (2,000yrs. Ago)
  • Age of Reason and Thought
  • Democritus vs. Aristotle view on the make-up of

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

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?

John Daltons Atomic Theory
  • English school teacher
  • Proved Democritus atoms hypothesis using the
    scientific method.
  • His conclusions produced
  • Daltons Atomic Theory

Daltons 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

Thomsons 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.

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.
Goldsteins Cathode Tube Experiment
  • He discovered the positively charged particle,
    proton, using a cathode ray tube also.

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
  • 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.

Rutherfords Conclusion
  • Most of the atom is empty space.
  • Small dense region composed of
  • () charged particles.
  • (Nucleus)

Rutherfords Nuclear Atom Model

Subatomic 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 have a significant mass like protons.

Bell 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?

Bell Ringer 4. a. Identify and explain this
Atomic Model? b. Who concluded this atomic model?
Bell 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?

Kandium 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
  • Kandium isotope from amu to grams.

Distinguishing 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.

Neutral 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

Atoms 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

Atoms 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

Bell 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.

Atomic Structure Review
An 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

An Elements Isotopes
C-14 of p, n0, e-? of p,
n0, e-?
Elements 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
  • 3. What is the number of p, n0, and e- for each
    isotope of Oxygen ?

Atomic Mass Elements 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
  • 2. Add all the isotopes products together.

Carbons 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.

Mass Number vs. Atomic Mass
Compare mass number of an atom with elements
atomic mass using the Venn diagram below.
Atomic Mass
Atomic 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)
Atomic Properties
  • If most of the atom is empty space, why doesnt
    matter pass through one another?

Atomic Properties
  • If most of the atom is empty space, why doesnt
    matter pass through one another?
Atomic Properties
  • What keeps the protons from leaving the nucleus
    and being drawn towards the electrons?

Atomic Forces
  • Electrostatic Forces
  • Nuclear Forces

Bell 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

Atomic Forces
  • Electrostatic Forces
  • Forces between charged
  • particles.
  • Nuclear Forces
  • Forces that holds
  • nucleus together

Charged Atoms
  • Ions charged atoms.
  • How do ions form? Neutral atoms lose or gain
  • Two types of atoms
  • Cations positively charged atoms
  • (more p than e-)
  • Anions negatively charged atoms
  • (more e- than p)

Distinguishing 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