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Atomic Structure

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Atomic Structure Chapter 4 – PowerPoint PPT presentation

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Title: Atomic Structure


1
Atomic Structure
  • Chapter 4

2
4.1 Defining the Atom
  • Democritus (460 BC 370 BC)
  • Had an atomic philosophy
  • Matter was made of small invisible particles
    called atoms
  • No scientific evidence, but it was logical

3
Daltons Atomic Theory
  • John Dalton (1766-1844) was an English chemist
    and school teacher
  • Daltons theory was the first scientific theory
    of the atom

4
John Dalton looks like another famous John
5
Daltons Atomic Theory
6
Daltons Atomic Theory
  1. Matter is composed of tiny indivisible atoms
  2. All atoms of a given element are exactly the same
  3. Different elements are made of different atoms
  4. Atoms of different elements can combine in simple
    whole number ratios to form compounds
  5. Chemical reactions involve separating, combining,
    or rearranging atoms.

7
How big are atoms?
  • Pretty small
  • Just 4 grams of helium (He) contains 6.02 x 1023
    atoms!
  • Most atoms have a radius in the range of 5 x
    10-11 m to 2 x 10-10 m
  • Atomic sizes are in the pico- and nanometer range

8
Can we see atoms?
  • Amazingly, yes!
  • STM
  • Scanning tunneling microscope has made it
    possible to see atoms.
  • These are gold atoms
  • They are only 2.3 Å apart!

9
Here is a picture of a mixture of tin, lead, and
silicon atoms!
Custance's team demonstrated their
"fingerprinting" technique by using an atomic
force microscope (AFM) to distinguish atoms of
tin (blue) and lead (green) deposited on a
silicon substrate (red). (Credit Oscar Custance)
physicsworld.com/cws/article/news/27208
The colors are added to help distinguish the atoms
10
4.2 Structure of the Nuclear Atom
  • When do I know I have learned this section?
    When
  • I can describe 3 types of subatomic particles
  • I can describe the structure of the nuclear atom
  • I can explain Thomsons discovery
  • experiment and model of the atom
  • I can explain Millikans discovery
  • I can explain Rutherfords discovery
  • experiment and model of the atom

11
Subatomic Particles
4.2
  • A cathode ray is deflected by electrically
    charged plates.

12
Subatomic Particles
  • In Daltons theory, atoms had no charge
  • Thomson studied cathode rays (the cathode ray
    experiment)
  • Resulted in discovery of the electron
  • Electrons are negatively charged particles
  • Discovered the charge to mass ratio of electron

13
JJ Thomsons Plum Pudding Model
  • Atom was a sphere
  • Atoms were electrically neutral
  • (-) charged electrons embedded in a () charged
    matrix
  • Like a chocolate chip cookie

14
Millikans Oil Drop Experiment
  • Discovered the actual quantity of charge for the
    electron
  • Using Thompsons charge/mass ratio, Millikan was
    also able to determine the mass of the electron
  • Mass of electron is 1/1840 the mass of a hydrogen
    atom.

15
Protons
  • If H atoms are neutral, and they give off
    negatively charged electrons, what must be left?
  • Positive charge
  • Proton discovered by Eugen Goldstein noticed a
    ray traveling in opposite direction of the
    electrons in the cathode ray tube
  • Toward the negative end (cathode)

16
Neutrons
  • Discovered by James Chadwick

17
Quarks
  • Quarks are subnuclear particles
  • Protons and neutrons are composed of quarks

18
The Atomic Nucleus
  • Ernest Rutherford discovered the nucleus
  • Gold foil experiment

19
Simulation of Rutherfords Gold Foil Experiment
20
Interpretation of Rutherfords Findings
21
Rutherfords Conclusions
  • All positive charge and nearly all the mass of
    the atom are concentrated in a very small nucleus
  • Atom contains mostly empty space
  • Rutherfords model of the atom was like a mini
    solar system

22
Summary of Atomic Models
  • Democritus Invisible particles
  • Dalton Tiny homogeneous sphere
  • 5 (4) statements
  • Thomson Plum pudding
  • Rutherford Nuclear atom

23
Thomsons Model of the Atom
  • Plum Pudding
  • Negatively charged electrons embedded in a
    positive matrix

24
Rutherfords Model
  • Nuclear Atom
  • Most of the volume of the atom is empty space
  • All positive charge most mass in a small
    nucleus
  • Nucleus contains protons and neutrons
  • Electrons occupy space outside the nucleus

25
Distinguishing Among Atoms
  • Atomic Number
  • number of protons in nucleus
  • Each element has unique atomic number
  • Mass Number
  • number of protons and neutrons in nucleus
  • neutrons mass - atomic

26
Practice
27
Symbols of Elements
  • Elements are symbolized by one or two letters.
  • First letter is always capitalized.
  • Second letter, if there is one, is always lower
    case.

28
Atomic Number
  • All atoms of the same element have the same
    number of protons
  • The atomic number (Z)

29
Mass Number
  • The mass of an atom in atomic mass units (amu)
    is the total number of protons and neutrons in
    the atom.

30
Isotopes
  • Isotopes are atoms of the same element with
    different masses.
  • Isotopes have different numbers of neutrons.

31
Different Ways of Indicating Isotopes
  • Chemical symbols
  • 168O 188O
  • Symbol and mass number
  • O-16 O-18
  • Name and mass number
  • oxygen-16 oxygen-18

32
Isotopes of Neon
Atomic Mass
33
Atomic Mass
  • Measured in amus (atomic mass units) because
    their mass is so small
  • Definition one atom of carbon-12 equals exactly
    12 amus
  • 1 amu exactly 1/12 the mass of a C-12 atom
  • 1 amu 1.6605 x 10-24g

34
Different Isotopes Have Different Abundance
Atomic Masses
Isotope Abundance Atomic mass (amu)
Chlorine-35 75.77 34.969
Chlorine-37 24.23 36.966
What is the atomic mass of chlorine on the
periodic table?
35
Average Atomic Mass
  • Determining abundance of isotopes when average
    atomic mass is known
  • Multiply the mass of each isotope by its relative
    abundance (decimal equivalent) and add the
    products

Isotope Atomic Mass Abundance
R-125 125 ________ ________
R-120 120 ________ ________
124
36
Periodic Table - Preview
  • Allows you to easily compare and predict
    properties of elements
  • Groups Columns
  • Numbered 1-18 or
  • 1A-8A (representative elements)
  • 1B-8B (transition metals)
  • Periods Rows
  • Numbered 1-7
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