Atoms and the Periodic Table

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Chapter 3

• Atoms and the Periodic Table

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Matter

• What accounts for matters secrets?
• Atomists Democritus
• All things are made of Fire Herclitus
• Four Elements Aristotle

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Conservation of Mass and Law of Definite
Proportions

• Robert Boyle (16271691) Provided evidence for
  the atomic nature of matter.
• Element - A substance that cannot be chemically
  broken down further
• Joseph Priestley (17331804)

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Conservation of Mass and Law of Definite
Proportions

• Antoine Lavoisier (1743-1794)

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Conservation of Mass

• Law of Mass Conservation Mass is neither created
  nor destroyed in chemical reactions.
• Hg(NO3)2 2 KI ? HgI2 2KNO3
• 3.25g 3.32g ? 4.55g
  2.02g
• 6.57g
  6.57g

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Law of Definite Proportions

• Law of Definite Proportions In a unique compound
  the elements will always be found in the exact
  same ratio.

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Daltons Atomic Theory

• John Dalton (17661844) Proposed explanations
  for the laws of mass conservation and definite
  proportions.
• Postulate 1 Elements are made of atoms
• Postulate 2 Atoms of the same element have the
  same properties (including mass). Atoms of
  different atoms have different properties
• Postulate 3 Compound are comprise of elements
  joined together in small whole ratios
• Postulate 4 Chemical reactions only rearrange
  the way the atoms are combined

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The Structure of Atoms Electrons

• Elements are composed of atoms
• Compounds are composed of atoms of elements in a
  given ratio
• What does an atom look like?

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The Structure of Atoms

• Structure of the Atom

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The Structure of Atoms

• Comparison of Subatomic particles

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Atomic Number

• protons in an atom determines the element
• atomic number (Z) - Atomic number is found on the
  periodic table
• electrons protons in a neutral atom

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Mass Number

• mass of the atom neutrons protons
• Mass number protons neutrons
• An element may have more than one mass
• Isotopes Atoms with identical atomic numbers,
  but different mass numbers.
• Due to different of neutrons NOT protons

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Isotopes and Atomic Weight

• Atoms of an element that have a different mass
  are called isotopes

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Elements and Atomic Number
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Atomic Mass

• Atomic Mass A weighted average of the isotopic
  masses of an elements naturally occurring
  isotopes.
• Unit atomic mass unit (amu)

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Example

• Chlorine has two naturally occurring isotopes
  with an abundance of 75.77 and an isotopic mass
  of 34.969 amu, and with an abundance of 24.23
  and an isotopic mass of 36.966 amu. What is the
  atomic mass of chlorine?

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Isotopes and Atomic Weight

• Bromine has two naturally occurring isotopes
  79Br and 81Br, calculate the atomic mass of
  bromine.

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Problem

• Atoms X, Y, Z, and R have the following nuclear
  compositions  Which two are isotopes? 
• A.  X Y
• B.  X R
• C.  Y R
• D.  Z R
• E.  X Z

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Electronic Structure

• The Periodic Table Powerpoint
• Elements in a group react similarly
• Electronic Structure
• Atomic Size
• Why metals for cations and non-metals anions

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Electronic Structure of Atoms

• Structure based on an accepted quantum mechanical
  model
• Mathematical description of the location in which
  an electron can be found
• Quantum mechanical model electron cloud can be
  divided into
• Shells
• Subshells
• Orbitals

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Electronic Structure
Shell Each Floor
Subshell Row of rooms
Orbital - Room
2 beds per room opposite direction
Nucleus
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Electronic Structure of Atoms

• Shells layers in which the electrons are
  grouped around the nucleus
• As a layer is added the atomic size increases
• Shells agree with the period on periodic table
• Differ in energy requires more energy to remove
  an electron from a shell closer to the nucleus
• Electron capacity increases with higher shells
  cause e- can spread out more

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Electronic Structure of Atoms

• Subshells
• s, p, d, f
• 1st shell only s
• 2nd shell s, p
• 3rd shell s, p, d
• 4th shell s, p, d, f
• Note shell has the of subshells the shell
• 3s electron an electron is found in the s
  subshell of the 3rd shell

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Electronic Structure of Atoms

• Orbitals Subshells can further be divided into
  orbitals
• regions of space within an atom where the
  specific electrons are more likely to be found.
• Different orbitals have different shapes.
  Orbitals in s subshells are spherical (a), while
  orbitals in p subshells are roughly dumbbell
  shaped (b).

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Electronic Structure of Atoms

• 2 electrons in each orbital with opposite spins

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Electronic Structure of Atoms

• The overall electron distribution within an atom
  is summarized in Table 3.2 below.

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Electron Configurations

• Electron Configuration The exact arrangement of
  electrons in atoms shells and subshells. Rules
  to predict electron configuration
• Electrons occupy the lowest energy orbitals
  available first.
• Each orbital can hold only two electrons, which
  must be of opposite spin.
• If two or more orbitals have the same energy,
  each orbital gets one electron before any orbital
  gets two.

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Electron Configurations

• Order of orbital energy levels
• Electrons fill orbitals from the lowest-energy
  orbitals upward.
• Lower numbered shells fill before higher
  numbered shells at first.
• Some overlap in energy levels occurs starting
  with shell 3 and 4.

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Electron Configurations

• Electron configurations are described by
• write the shell number
• subshell letter in order of increasing energy.
• number of electrons actually occupying each
  subshell is indicated by a superscript.
• A graphic representation can be made by
  indicating each orbital as a line and each
  electron as an arrow. The head of the arrow
  indicates the electron spin.
• A shorthand using noble gas configurations is
  very useful for large atoms.

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Periodic Table and Electron Configurations
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Electron Configurations
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Electron Configurations
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Problem

• Select the correct electron configuration for
  sulfur (Z 16). 
• A.  1s21p62s22p6
• B.  1s22s22p83s23p4
• C.  1s22s22p83s23p2
• D.  1s22s22p63s23p4
• E.  1s22s22p63s23d4

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Problem

• Select the correct electron configuration for Te
  (Z 52). 
• A.  Kr5s25p64d8
• B.  Kr5s25d105p4
• C.  Kr5s24d105p6
• D.  Kr5s24f14
• E.  Kr5s24d105p4

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Problem

• The electronic structure 1s22s22p63s23p64s23d8
  refers to the ground state of 
• A.  Kr
• B.  Ni
• C.  Fe
• D.  Pd
• E.  none of these choices is correct

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Electron Configuration

• Allows determination of valence e- and core e-
• Indicates why elements of a group have similar
  reactivity
• Determine which element is present by the sum of
  the superscripts
• Ground state atom
• Excited state atom

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Optional Homework

• Text 3.31, 3.32, 3.33, 3.44, 3.46, 3.48, 3.50,
  3.52, 3.56, 3.70, 3.72, 3.74, 3.76, 3.78, 3.82,
  3.84, 3.86, 3.96, 3.100, 3.106, 3.108, 3.110,
  3.111
• Chapter 3 Homework from website