Unit 5: Atoms and the Periodic Table

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Unit 5 Atoms and the Periodic Table

• Chapter 4

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Part 1 Atomic Structure Objectives

• Explain Daltons atomic theory, and describe why
  it was more successful than Democrituss theory.
• State the charge, mass, and location of each part
  of an atom according to the modern model of the
  atom.
• Compare and contrast Bohrs model with the modern
  model of the atom.

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Atomic Models

• Atom comes from the Greek word that means unable
  to be divided.
• Democritus (4 b.c.) - came up with the first
  theory of atomic structure said that the
  universe was made of invisible units called
  atoms, but was unable to provide evidence.

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• John Dalton (1808) - used scientific research to
  claim that atoms could not be divided, that all
  atoms of an element were exactly alike, and that
  atoms of different elements could join to form
  compounds.

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• Neils Bohr (1913) - said that the electrons in an
  atom orbit around the nucleus like planets around
  the sun. The path of an electron is determined by
  how much energy it has, which puts it in a
  specific energy level.

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• Modern wave model (1925) - says that electrons
  behave more like waves on a vibrating string, and
  move back and forth between energy levels. Thus,
  an electrons exact location at any given moment
  cannot be determined.

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An Atoms Contents

• Atoms contain smaller pieces called subatomic
  particles.

PARTICLE CHARGE LOCATION MASS
proton positive in nucleus 1 amu
electron negative around nucleus almost 0 amu
neutron neutral in nucleus 1 amu
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• Unreacted atoms (atoms that are not part of a
  chemical compound) have no overall charge.
• That means the number of positive charges
  (protons) must equal the number of negative
  charges (electrons).
• Neutrons do not affect the overall charge.

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Electrons and Energy Levels

• If an electron does not have much energy, it will
  be closer to the nucleus in the first or second
  energy level.
• The first energy level will hold only 2
  electrons.
• If an atom has more than 2 electrons, the first
  two will fill the first level, and the rest will
  begin filling the second energy level.
• The second level will hold 8 electrons.

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• If the first and second levels are full and there
  are still leftover electrons, they will go to the
  third level, which holds 18 electrons.
• Once the first three levels are full (thats 28
  electrons!), electrons must go to the fourth
  level, which holds 32 electrons.

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Orbitals

• There are four different types of orbitals that
  can be found within the energy levels. They are
  s, p, d, and f.
• An s orbital has the lowest amount of energy and
  can hold 2 electrons.
• A p orbital has more energy than s orbitals, and
  there are 3 of them. Each one can hold 2
  electrons, for a total of 6.
• There are 5 d orbitals and 7 f orbitals. F
  orbitals have the most energy, and each one holds
  2 electrons.

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Valence Electrons

• Electrons found in the outermost energy level of
  an atom.
• Each atom contains between 1 and 8 valence
  electrons.
• These electrons are the ones that are used to
  form chemical bonds with other atoms to form
  molecules or compounds.

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Part 2 The Periodic Table Objectives

• Relate the organization of the periodic table to
  the arrangement of electrons within an atom.
• Explain why some atoms gain or lost electrons to
  form ions.
• Determine how many protons, neutrons, and
  electrons at atoms has given its symbol, atomic
  number, and mass number.
• Describe how the abundance of isotopes affects an
  elements average atomic mass.

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• Locate alkali metals, alkaline-earth metals, and
  transition metals in the periodic table.
• Locate semiconductors, halogens, and noble gases
  in the periodic table.
• Relate an elements chemical properties to the
  electron arrangement of its atoms.

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The Periodic Table

• The periodic law says that if the elements are
  arranged in a specific order, similarities in
  their properties will occur in a regular pattern.
• Period - horizontal row the number of protons
  (and therefore, the number of electrons)
  increases by one as you move from left to right.
• Group (or family) - vertical column elements in
  the same group have the same number of valence
  electrons, so they have similar characteristics.

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The Periodic Table
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Groups

• Group 1 - Alkali metals (1 v.e.)
• Group 2 - Alkaline-earth metals (2 v.e.)
• Groups 3 -12 - Transition metals (number of v.e.
  varies)
• Group 13 - Boron family (3 v.e.)
• Group 14 - Carbon family (4 v.e.)
• Group 15 - Nitrogen family (5 v.e.)
• Group 16 - Oxygen family (6 v.e.)
• Group 17 - Halogens (7 v.e.)
• Group 18 - Noble (or inert) gases (8 v.e.)

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• If an atom has only 1 v.e., it will be very
  reactive because it will want to stabilize itself
  by giving away its v.e. The goal of an atom is to
  become stable by having a totally full or totally
  empty outer energy level. This will cause it to
  be an ion with a 1 charge.
• Likewise, an atom with 7 v.e. will be very
  reactive because it only needs 1 v.e. to be
  stable. Where can it find 1 v.e.?

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Calculating P, N and E

• Atomic number - the number of protons in an atom
  (and thus, the number of electrons)
• Mass number - the number of protons plus neutrons
  in an atom
• Isotope - atoms of an element that have the same
  number of protons, but different number of
  neutrons. This will not affect the number of
  electrons, but will affect the mass.
• Average atomic mass - the average mass of all the
  isotopes of an element

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• To calculate the number of neutrons in an atom
• Mass number - atomic number neutrons
• Mass is measured in atomic mass units (amu).
• 1 amu 1/12 the mass of a standard C-12 atom

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Part 3 Using Moles to Count Atoms Objectives

• Explain the relationship between a mole of a
  substance and Avogadros constant.
• Find the molar mass of an element by using the
  periodic table.
• Solve problems converting the amount of an
  element in moles to its mass in grams, and vice
  versa.

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Using Moles to Count Atoms

• We use moles to count atoms because they are so
  small and so numerous. If we know the mass of the
  atom, we can estimate how many atoms are in a
  sample of a substance by counting them in groups.
• The mole has a value of 6.022 x 1023 particles in
  exactly 1 mole of substance. This value is called
  Avogadros constant.

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Molar Mass

• The mass in grams of 1 mole of a substance is its
  molar mass, which is the same as its average
  atomic mass on the periodic table.

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Using Conversion Factors

• A fraction that equals 1.
• For example 12 in/1 ft 1 5280 ft/ 1 mi
  1 365.25 d/1 yr 1
• Example If you have 5.50 mol of Fe, and Fe has a
  molar mass of 55.85 g/mol, what is its mass in g?
• 5.50 mol Fe x 55.85 g Fe 307 g Fe
• 1 mol Fe

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Examples

• If you have 2.50 mol of S, and S has a molar mass
  of 32.07 g/mol, what is its mass in g?
• 2.50 mol S x 32.07 g S 80.18 g S
• 1 mol S

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• A) 1.80 mol Ca
• B) 0.50 mol C
• C) 3.20 mol Cu

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• A) 72.14 g Ca
• B) 6.01 g C
• C) 203.36 g Cu

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• How many moles are in 620 g of Hg?
• 620 g Hg x 1 mol Hg 3.09 mol Hg
• 200.59 g Hg

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• A) 352 g Fe
• B) 11 g Si
• C) 205 g He

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• A) 6.30 mol He
• B) 0.39 mol Si
• C) 51.25 mol He