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4-1: Introduction to Atoms. How did the atomic theory develop and change into the modern model of the atom?. Anticipatory Set. Here come the atoms!. video. California Standards.

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4 1 introduction to atoms

4-1: Introduction to Atoms

How did the atomic theory develop and change into the modern model of the atom?


Anticipatory Set

Here come the atoms!


california standards
California Standards
  • Science Standard 8.3.a: Students know the structure of the atom and know it is composed of protons, neutrons, and electrons.
  • Science Standard 8.7.b: Students know each element has a specific number of protons in the nucleus (the atomic number) and each isotope of the element has a different but specific number of neutrons in the nucleus.
  • atom: smallest particle of an element.
  • electron: negatively charged particles in an atom.
  • nucleus: the central core of an atom
  • proton: positively charged particles in an atom’s nucleus.
  • energy level: the specific amount of energy an electron has.
  • neutron: small particle in the nucleus of an atom with no electrical charge
  • atomic number: the number of protons in the nucleus of an atom.
  • isotope: atoms of the same element that have different numbers of neutrons.
  • mass number: the sum of the protons and neutrons in the nucleus of an atom.
  • Development of Atomic Theory
    • Atomic theory has changed many times over the years. As more evidence was collected, the theory and models were revised.
    • Around 430 B.C.,
      • a Greek philosopher, Democritus,
      • Idea= matter is formed of small pieces that could not be cut into smaller parts.
      • atomoswhich means “uncuttable”
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Input & Modeling
  • Dalton’s Atomic Theory
    • thought that atoms were like smooth, hard balls

that could not be

broken into smaller


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Input & Modeling
  • Dalton’s Atomic Theory
    • All elements are composed of atoms that cannot be divided.
    • All atoms of the same element are exactly alike and have the same mass. Atoms of different elements are different and have different masses.
    • An atom of one element cannot be changed into an atom of a different element. Atoms cannot be created or destroyed in any chemical change, only rearranged.
    • Every compound is composed of atoms of different elements, combined in a specific ratio.
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  • Thomson’s Atomic Theory
    • In 1897, English scientist

J.J. Thompson found that

atoms contain negatively

charged particles.

    • The negatively charged

particles later became known as electrons.

Thomson suggested that atoms had negatively charged electrons embedded in a positive sphere.

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  • Rutherford’s Atomic Theory
    • In 1911, Ernest Rutherford found evidence that countered Thompson’s model.
    • His team discovered the

positive charge (proton) +

in an atom is clustered in

the center (nucleus).

According to Rutherford’s model, an atom was mostly empty space.

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  • Bohr’s Atomic Theory
    • In 1913, Niels Bohr, a Danish scientist, suggested that electrons

move in specific orbits

around the nucleus

of an atom.

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  • Cloud Model
  • In the 1920’s, scientists determined that electrons do not orbit the nucleus like planets, but rather could be anywhere in a cloudlike region.
  • An electron’s movement is

related to its energy level, or

the specific amount of energy

it has.

  • Electrons of different energy

levelsare likely to be found in

different places.

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Input & Modeling
  • The Modern Atomic Model
    • In 1932, English scientist James Chadwick discovered another particle, the neutron, in the nucleus of atoms.
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Input & Modeling
  • The Modern Atomic Model
    • At the center of the atom is a tiny, massive nucleus containing protons and neutrons.
    • Surrounding the nucleus is a cloudlike region of moving electrons.
    • The particle was difficult to detect because it has no charge.
  • Particles in an Atom
    • An atom is composed of positively charged protons, neutral neutrons, and negatively charged electrons. Protons and neutrons are about equal in mass. An electron has about 1/2,000 the mass of a proton or neutron.
  • Isotopes
    • Atoms of all isotopes of carbon contain six protons and six electrons, but they differ in their number of neutrons. Carbon-12 is the most common isotope.
check for understanding
Check forUnderstanding
  • What is located in a cloudlike region surrounding the nucleus in the modern atomic model?


  • According to Dalton, all elements are composed of atoms that cannot be ___.


guided practice
Guided Practice
  • Answer #1-4



  • Finish the


  • Complete the extension.


  • Write a detailed SUMMARY of the section and complete the UNANSWERED QUESTIONS section of your notes.
  • Choose two of the remaining Depth & Complexity ICONS in your notes and explain how they relate to this section.
  • Finish the Development of Atomic Theory Timeline Booklet.