Early atomic theory and structure
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Early Atomic Theory and Structure. Chapter 5. What are the building blocks of matter?. Early Greeks Air, Earth, Water, Fire Democritus (470-370 BC) Atoms John Dalton (1766-1844) Modern Atomic Theory. Dalton’s Atomic Theory.

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Early Atomic Theory and Structure

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Early Atomic Theory and Structure

Chapter 5


What are the building blocks of matter?

  • Early Greeks

    • Air, Earth, Water, Fire

  • Democritus (470-370 BC)

    • Atoms

  • John Dalton (1766-1844)

    • Modern Atomic Theory


Dalton’s Atomic Theory

  • Elements (matter) is composed of small, indivisible particles called atoms.

  • Atoms of a given element are identical in mass and behavior.

  • Atoms of different elements differ in mass and behavior.

  • Chemical combination of elements to make different substances occurs when atoms join together in small whole number ratios.

  • Chemical reactions only rearrange the way the atoms are combined; the atoms themselves are not changed.


Law of Constant Composition

  • The composition of a substance is always the same, regardless of how the substance was made or where the substance is found.

Law of Multiple Proportions

  • Atoms of two or more elements may combine in different ratios to form different compounds.

Both explained by Dalton’s Law.


Sub Atomic Particles


Atoms are composed of


Isotopes

  • Atoms which differ only in the number of neutrons present in the nucleus.

  • Neutrons help keep the protons together by adding to the strong nuclear force without adding to the mutually repulsive electrical force of the protons.

    • Generally 1-1.5 neutrons per proton in an atom’s nucleus.


Atomic Number = Z = number of protons in an atom. = number of electrons in a neutral atom. Mass Number = number protons + number neutrons in an atom


  • Fill in the missing information in the following table of four neutral atoms:


  • Fill in the missing information in the following table of ions:


Atomic Mass

  • The average relative mass of the isotopes of an element compared to the atomic mass of carbon-12 (exactly 12 amu)

  • Atomic mass unit (amu)

    • 1/12 the mass of a carbon-12 atom

    • 1.6606 x 10-24 g


Isotopes of Neon


Isotopes of Neon


The precious metal platinum (Z=78) has six isotopes with these abundances:

Use these data to calculate the average atomic mass of platinum.


  • Boron, lithium, nitrogen, and neon each have two stable isotopes. In which of the following pairs of isotoopes is the heavier isotope more abundant?


  • Using the following table of abundances and masses of the three naturally occurring argon isotopes, calculate the mass of 40Ar.


  • Silver (Ag) has two stable isotopes: 107Ag, 106.90 amu and 109Ag, 108.90 amu. If the average atomic mass of silver is 107.87 amu, what is the natural abundance of each isotope?


  • It takes nearly twice the energy to remove an electron from a helium atom as it does to remove an electron from a hydrogen atom. Propose an explanation for this.


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