The Modern View of Atomic Structure

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Section 2.3

• The Modern View of Atomic Structure

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Three Subatomic Particles

• Proton
• Neutron
• Electron

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Proton

• Positively charged particle
• Located in the nucleus of the atom
• Charge of 1.602 x 10-19 C
• Expressed in multiples of the charge 1

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Electron

• Negatively charged particle
• Orbit the nucleus of the atom
• Account for most of the volume of the atom
• Charge of -1.602 x 10-19 C
• Expressed in multiples of the charge -1

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Neutron

• Uncharged and electrically neutral particle
• Located in the nucleus of the atom

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The Atom
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Every atom has an equal number of protons and
electrons, and so atoms have no net electrical
charge.
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Mass of the Atom

• Expressed in the atomic mass unit (amu)
• 1 amu 1.66054 x 10-24 g
• 1 g 6.02214 x 1023 amu

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Particle Charge Mass (amu)
Proton Positive (1) 1.0073
Neutron None (neutral) 1.0087
Electron Negative (-1) 5.486 x 10-4
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Atomic Number

• References the number of protons in the nucleus
  of an atom of a particular element
• Every element has a unique atomic number

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Question

• If Pb has an atomic number of 82, how many
  protons are in the nucleus of every atom of Pb?
• How many electrons must be orbiting the nucleus
  of every Pb atom?

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Mass Number

• Total number of protons plus neutrons in the
  nucleus of an atom of an element.
• Uses the number of neutrons in the most abundant
  form of the element

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• How many protons?
• How many electrons?
• How many neutrons?

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Isotopes

• Atoms with identical atomic numbers but different
  mass numbers

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