Atoms: The Building Blocks of Matter - PowerPoint PPT Presentation


PPT – Atoms: The Building Blocks of Matter PowerPoint presentation | free to view - id: 7385e0-OWQ0Z


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation

Atoms: The Building Blocks of Matter


Atoms: The Building Blocks of Matter The History of Atomic Theory – PowerPoint PPT presentation

Number of Views:61
Avg rating:3.0/5.0
Slides: 49
Provided by: lewi124


Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Atoms: The Building Blocks of Matter

Atoms The Building Blocks of Matter
  • The History of Atomic Theory

Atomic Models
  • This model of the atom may look familiar to you.
    This is the Bohr model. In this model, the
    nucleus is orbited by electrons, which are in
    different energy levels.
  • A model uses familiar ideas to explain unfamiliar
    facts observed in nature.
  • A model can be changed as new information is

  • The atomic model has changed throughout the
    centuries, starting in 400 BC, when it looked
    like a billiard ball ?

Who are these men?
In this lesson, well learn about the men whose
quests for knowledge about the fundamental nature
of the universe helped define our views.
400 BC
  • This is the Greek philosopher Democritus who
    began the search for a description of matter more
    than 2400 years ago.
  • He asked Could matter be divided into smaller
    and smaller pieces forever, or was there a limit
    to the number of times a piece of matter could be

  • His theory Matter could not be divided into
    smaller and smaller pieces forever, eventually
    the smallest possible piece would be obtained.
  • This piece would be indivisible.

The word atom comes from the Greek word
atomos that means unable to be cut
and you kept on cutting the leftover piece in
Imagine you had a piece of gold that you then cut
in half
and then you cut one of these smaller pieces in
The word atom comes from a Greek word that
means unable to be cut
and kept going
Eventually you would have 1 piece of gold left.
If you cut it in half, you wouldnt have gold any
more youd have something else. This tiny,
tiny single piece of gold is called an atom of
gold. An atom is the smallest particle of an
element that acts like the element.
and kept going
and kept going
  • To Democritus, atoms were small, hard particles
    that were all made of the same material but were
    different shapes and sizes.
  • Atoms were infinite in number, always moving and
    capable of joining together.

  • This theory was ignored and forgotten for
    more than 2000 years!

  • The eminent philosophers of the time, Aristotle
    and Plato, had a more respected, (and ultimately
    wrong) theory.

Aristotle and Plato favored the earth, fire, air
and water approach to the nature of matter. Their
ideas held sway because of their eminence as
philosophers. The atomos idea was buried for
approximately 2000 years.
(No Transcript)
Daltons Model
  • In the early 1800s, the English Chemist John
    Dalton performed a number of experiments that
    eventually led to the acceptance of the idea of

Daltons Theory
  • He deduced that all elements are composed of
    atoms. Atoms are indivisible and indestructible
  • Atoms of the same element are exactly alike.
  • Atoms of different elements are different.
  • Compounds are formed by the joining of atoms of
    two or more elements.

  • This theory became one of the foundations of
    modern chemistry.

Thomsons Plum Pudding Model
  • In 1897, the English scientist J.J. Thomson
    provided the first hint that an atom is made of
    even smaller particles.

Thomson Model
  • He proposed a model of the atom that is sometimes
    called the Plum Pudding model.
  • Atoms were made from a positively charged
    substance with negatively charged electrons
    scattered about, like raisins in a pudding.

Thomson Model
  • Thomson studied the passage of an electric
    current through a gas.
  • As the current passed through the gas, it gave
    off rays of negatively charged particles.

Thomson Model
Where did they come from?
  • This surprised Thomson, because the atoms of the
    gas were uncharged. Where had the negative
    charges come from?

Thomson concluded that the negative charges came
from within the atom. A particle smaller than
an atom had to exist. The atom was divisible!
  • Thomson called the negatively charged particles
    corpuscles, today known as electrons.
  • Since the gas was known to be neutral, having no
    charge, he reasoned that there must be positively
    charged particles in the atom.
  • But he could never find them.

Rutherfords Gold Foil Experiment
  • In 1908, the English physicist Ernest Rutherford
    was hard at work on an experiment that seemed to
    have little to do with unraveling the mysteries
    of the atomic structure.

  • Rutherfords experiment Involved firing a stream
    of tiny positively charged particles at a thin
    sheet of gold foil (2000 atoms thick)

  • Most of the positively charged bullets passed
    right through the gold atoms in the sheet of gold
    foil without changing course at all.
  • Some of the positively charged bullets,
    however, did bounce away from the gold sheet as
    if they had hit something solid. He knew that
    positive charges repel positive charges.

An Animation of the Gold Foil Experiment
  • http//

  • This could only mean that the gold atoms in the
    sheet were mostly open space. Atoms were not a
    pudding filled with a positively charged
  • Rutherford concluded that an atom had a small,
    dense, positively charged center that repelled
    his positively charged bullets.
  • He called the center of the atom the nucleus
  • The nucleus is tiny compared to the atom as a

  • Rutherford reasoned that all of an atoms
    positively charged particles were contained in
    the nucleus. The negatively charged particles
    were scattered outside the nucleus around the
    atoms edge.

Bohrs Model
  • In 1913, the Danish scientist Niels Bohr proposed
    an improvement.
  • By studying what happens to atoms when they have
    gained energy and then lose it, he was able to
    propose that each electron exists in a specific
    energy level.

The Hydrogen-Atom Line-Emission Spectrum
  • The lowest energy state of an atom is its ground
  • A state in which an atom has a higher potential
    energy than it has in its ground state (energy
    has been added) is an excited state.

The Hydrogen-Atom Line-Emission Spectrum,
  • When investigators passed electric current
    through a vacuum tube containing hydrogen gas at
    low pressure, they observed the emission of a
    characteristic pinkish glow.
  • When a narrow beam of the emitted light was
    shined through a prism, it was separated into
    four specific colors of the visible spectrum.
  • The four bands of light were part of what is
    known as hydrogens line-emission spectrum.

Hydrogen Line Emission Spectrum
Hydrogen Line Emission Spectrum
Emission and Absorption Spectrums
  • When an electron falls to a lower energy level, a
    photon is emitted, and the process is called
  • Energy must be added to an atom in order to move
    an electron from a lower energy level to a higher
    energy level. This process is called absorption.

Emission and Absorption Spectrums
Bohr Model
  • Niels Bohr proposed a hydrogen-atom model that
    linked the atoms electron to photon emission.
  • According to the model, the electron can circle
    the nucleus only in allowed paths, or orbits.
    Sort of like the planets around the sun.
  • The energy of the electron is higher when the
    electron is in orbits that are successively
    farther from the nucleus.

Modern Quantum Model
The Modern Model
  • Todays atomic model is based on the principles
    of wave mechanics.
  • According to the theory of wave mechanics,
    electrons do not move about an atom in a definite
    path, like the planets around the sun.

Electrons as Waves
  • French scientist Louis de Broglie suggested that
    electrons be considered waves confined to the
    space around an atomic nucleus.
  • It followed that the electron waves could exist
    only at specific frequencies.
  • According to the relationship E h?, these
    frequencies corresponded to specific energiesthe
    quantized energies of Bohrs orbits.

Electrons as Waves, continued
  • Electrons, like light waves, can be bent, or
  • Diffraction refers to the bending of a wave as it
    passes by the edge of an object or through a
    small opening.
  • Electron beams, like waves, can interfere with
    each other.
  • Interference occurs when waves overlap.

Electrons as Waves
The Heisenberg Uncertainty Principle
  • German physicist Werner Heisenberg proposed that
    any attempt to locate a specific electron with a
    photon knocks the electron off its course.
  • The Heisenberg uncertainty principle states that
    it is impossible to determine simultaneously both
    the position and velocity of an electron or any
    other particle.

The Heisenberg Uncertainty Principle
The Schrödinger Wave Equation
  • In 1926, Austrian physicist Erwin Schrödinger
    developed an equation that treated electrons in
    atoms as waves.
  • Together with the Heisenberg uncertainty
    principle, the Schrödinger wave equation laid the
    foundation for modern quantum theory.
  • Quantum theory describes mathematically the wave
    properties of electrons and other very small

The Modern Quantum Model
  • Since it is impossible to determine the exact
    location of an electron, the probable location of
    an electron is based on how much energy the
    electron has.
  • According to the modern atomic model, at atom has
    a small positively charged nucleus surrounded by
    a large region in which there are enough
    electrons to make an atom neutral.

Electron Cloud
  • Is made up of areas known as orbitals. An orbital
    is a three-dimensional region around the nucleus
    that indicates the probable location of an
  • Electrons whirl about the nucleus billions of
    times in one second.
  • They are not moving around in random patterns,
    but are moving around in a certain orbital.
  • Location of electrons depends upon how much
    energy the electron has.

Different Orbitals
Electron Cloud
  • Depending on their energy, electrons are locked
    into a certain orbital in the cloud.
  • Electrons with the lowest energy are found in the
    energy level closest to the nucleus
  • Electrons with the highest energy are found in
    the outermost energy levels, farther from the

Indivisible Electron Nucleus Orbit Electron Cloud
Greek X
Dalton X
Thomson X
Rutherford X X
Bohr X X X
Modern X X X
The Different Models