Understanding the Periodic Table: PERIODS

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Understanding the Periodic TablePERIODS
The periodic table can help youuse your
imagination to visualize the nano-world of
atomic structure.
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Look at your periodic table
How many rows?
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• Rows (there are 7)
• Row 1 has only 2 elements
• Row 2 and 3 each have 8 elements
• Rows 4, 5, and 6 each have 18 elements
• Row 7 is shown below the main body with total of
  28 elements
• Horizontal (across)
• The elements of a single period have the same
  number of energy levels.

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Whats an energy level?
Electrons have characteristic distances from the
nucleus where they orbit. Each distance
requires a certain amount of energy to resist the
pull of the nucleus. Electrons farthest from
the nucleus have the highest energy level.
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Each periods elements have the same number of
energy levels.
Group 1 Bohr Diagram Lewis Dot
PATTERNS TO NOTICE

• What is different?
• Period 1 has 1 energy level.
• Period 2 has 2 energy levels.
• Period 3 has 3 energy levels.
• Period 4 has .
• How many energy levels do you expect period 5 to
  have?
• What is the same?
• 1 electron in outermost shell. (group)

H ? Li ? Na ? K ?
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Electron Configuration, Group 8 (8A column)

• What is the same?
• 8 electrons in outermost shell.
• What is different?
• Period 2 has 2 energy levels.
• Period 3 has 3 energy levels.
• Period 4 has 4 energy levels.
• How many energy levels do you think He in period
  1 has?
• How many for Xe in period 5?

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Electron Configuration, Period 2
Li Be B C N O F
Ne
1s22s1 1s22s2 1s22s22p1
1s22s22p2 1s22s22p3 1s22s22p4
1s22s22p5 1s22s22p6

• What is the same?
• 2 energy levels all across the period.
• 2 electrons in first energy level all across the
  period

What is different? Increase in number
ofelectrons from left to right.
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Atomic Radius

• As the period increases, the size of the electron
  cloud increases
• Looking across a period, the size of the electron
  cloud decreases.
• Looking across a period, each next atom has one
  additional proton which pulls the electrons in
  tighter.

1 2 3 4 5 6
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Atomic Radius vs Ionic Radius
Ion lost an electon
Neutralatom
Neutralatom
Ion gained an electon
Positive ions -- smaller than the atoms they come
from. Sodium loses a whole layer of electrons,
and the remaining 10 electrons are being pulled
in by the full force of 11 protons.
Negative ions -- bigger than the atoms they come
from. Chlorine the incoming electron causes the
atom to expand. There are still only 17 protons,
but they now have to hold 18 electrons.
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Ionization Energy

• the amount of energy it takes to detach one
  electron from a neutral atom.

(Electrostatic attraction is the attraction of
opposite charges.)
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Ionization Energy Trends
F
K
Why does it take more energy to remove an
electron from Fluorine than Potassium?
Across a Period, there are more protons to
attract the electrons.
Up the Group, the distance from nucleus to
electrons is shorter so the attraction is
stronger.
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Electronegativity

• measures the tendency of an atom to attract a
  bonding pair of electrons.

The Pauling scale is the most commonly
used. Fluorine (the most electronegative
element) is assigned a value of 4.0, and values
range down to caesium and francium which are the
least electronegative at 0.7.
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Electronegativity

• No electronegativity difference between two atoms
  leads to a pure non-polar covalent
  bond.Electrons are shared evenly.
• A small electronegativity difference leads to a
  polar covalent bond.
• Electrons are drawn towards the stronger atom.
• A large electronegativity difference leads to an
  ionic bond. Electrons are drawn to the stronger
  atom.

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Test Yourself

• 1. Which pairs of atoms will have electrostatic
  attraction?

ANSWER D Sodium has 1 electron to give,
Chlorine has a strong pull to gain 1 electron.
Becoming ions, they attract each other.
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Test Yourself

• 2. Which pairs of elements are in the same period?

ANSWER A Elements in the same period have the
same number of energy levels.
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Test Yourself

• 3. Which atom would require the least energy to
  detach an electron from?

ANSWER C One single electron in the outermost
shell is easiest to remove. Potassium has the
lowest ionization energy of all the elements
shown.
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Test Yourself

• 4. What happens to the ionization energy of
  elements when moving from the bottom to the top
  of a group in the periodic table?

ANSWER DAtoms at the top of the periodic table
have fewer electrons, therefore fewer energy
levels. The closer the electrons are to the
nucleus, the stronger the pull, and therefore the
more energy required to escape the pull.