Atoms and Elements

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Atoms and Elements

• Chapter 2

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Learning Objectives

• Students understand
• Composition and structure of atoms and the terms
  atomic number and mass number
• The various representations of masses of atoms
• Composition of isotopes
• Importance of Coulombs law
• Mole concept and molar mass application
• How mass spectrometry is used

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Learning Objectives

• Students will be able to
• Carry out calculations relating atomic weights,
  isotopic masses, and isotopic abundances
• Carry out calculations involving masses, moles,
  and numbers of particles
• Interpret, predict, and write formulas for ionic
  and molecular compounds
• Determine empirical and molecular formulas and
  percent composition

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2.1 Atomic Structure

• Electrons
• Protons
• Neutrons
• Atoms have no net charge. The number of
  electrons outside the nucleus equals the number
  of protons within the nucleus.

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2.2 Atomic Number and Atomic Mass

• All atoms of a given element have the same number
  of protons in the nucleus.
• Number of protons in the nucleus is its atomic
  number.
• One atomic mass unit (1 u) is one twelfth of the
  mass of an atom of carbon with six protons and
  six neutrons.
• 1 u 1.661x10-24 g

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Mass Number

• protons and neutrons have mass of approximately 1
  u (electrons are about 1/2000 of this mass)
• sum of protons and neutrons is defined as the
  mass number
• symbolized by an A
• can be expressed as sodium-23 or 23Na

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2.3 Isotopes

• Data from mass spectroscopy demonstrate evidence
  that Daltons model is incorrect these data then
  require a modification of that model.
• These data demonstrate direct evidence of
  different isotopes from the same element.

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Isotopes

• atoms with same atomic number but different mass
  numbers are called isotopes, named by mass number
• isotopes of hydrogen each have separate names
• protium hydrogen with one proton
• deuterium 2H or heavy hydrogen (1 neutron)
• tritium 3H radioactive hydrogen (2 neutrons)

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Isotope Abundance

• percent abundance is the number of atoms of a
  given isotope divided by the total number of all
  isotopes of that element multiplied by 100
• the atomic mass of an element is affected by the
  percent abundance of each isotope

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2.4 Atomic Weight

• the atomic weight is the average mass of a
  representative sample of atoms
• usually closer to the mass of the most abundant
  isotope(s)
• Atomic mass is the mass of an atom at rest.
  Relative atomic mass (atomic weight) is the
  average of the atomic masses of all the elements
  isotopes.

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Practice Problems

• Review and Check for Section 2-4
• P. 52

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2.5 The Periodic Table

• Mendeleev discovered that elements with similar
  properties appeared in a regular pattern when
  organized by increasing atomic mass.
• law of chemical periodicity the properties of
  the elements are periodic functions of atomic
  number

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The Periodic Table

• vertical columns of groups or families have
  similar characteristics
• A groups are main group elements
• B groups are the transition elements
• horizontal rows are called periods
• metals, nonmetals, metalloids
• allotropes are different forms of the same
  element (diamond, graphite, bucky balls)

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Overview of Elements

• Group 1A alkali metals
• Group 2A alkaline earth metals
• Group 3A B, Al, Ga, In, Tl
• Group 4A C, Si, Ge, Sn, Pb
• Group 5A N, P, As, Sb, Bi
• Group 6A O, S, Se, Te, Po
• S, Se, Te are called the chalcogens
• Group 7A halogens
• Group 8A noble gases

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Overview of Elements

• The Transition Elements
• B group elements all metals
• reactivity varies
• commercial uses (structures, paints, vehicles,
  coins, batteries)
• lanthanides and actinides are below the table

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Homework for Chapter 2

• After reading sections 2.1 2.5, you should be
  able to do the following problems
• P. 95a-b (10-11, 18, 23-24, 32)
• Be familiar with the key experiments involved in
  the development of the current atomic model
  (p.54-55)