Chapter 3 Atoms and Elements

1
Chapter 3 Atoms and Elements

• 3.7
• Electron Energy Levels

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Energy Levels

• Energy levels
• are assigned numbers n 1, 2, 3, 4, and so on.
• increase in energy as the value of n increases.
• are like the rungs of a ladder with the lower
  energy levels nearer the nucleus.

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Energy Levels

• Energy levels have a maximum number of electrons
  equal to 2n2.
• Energy level Maximum number of electrons
• n 1 2(1)2 2(1) 2
• n 2 2(2)2 2(4) 8
• n 3 2(3)2 2(9) 18

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Orbitals

• An orbital
• is a three-dimensional space around a nucleus,
  where an electron is most likely to be found.
• has a shape that represents electron density (not
  a path the electron follows).
• can hold up to 2 electrons.

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Orbitals

• An s orbital
• has a spherical shape around the nucleus.
• is found in each energy level.

• A p orbital
• has a two-lobed shape.
• is one of three p orbitals in each energy level
  from n 2.

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Orbitals
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Electron Level Arrangement

• In the electron level arrangement for the first
  18
• elements
• electrons are placed in energy levels (1, 2, 3,
  etc.), beginning with the lowest energy level
• there is a maximum number in each energy level.
• Energy level Number of electrons
• 1 2 (up to He)
• 2 8 (up to Ne)
• 3 8 (up to Ar)
• 4 2 (up to Ca)

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Examples

• Write the electron level arrangement for each
• 1. N
• 2. Cl
• 3. K

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Examples

• Identify the element with each electron level
• arrangement
• 1. 2, 2
• 2. 2, 8, 3
• 3. 2, 7

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Chapter 3 Atoms and Elements

• 3.8
• Periodic Trends

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Valence Electrons

• The valence electrons
• determine the chemical properties of the
  elements.
• are the electrons in the highest energy level.
• are related to the group number of the element.
• Example Phosphorus has 5 valence electrons.
• 5 valence electrons
• P in Group 5A(15) 2, 8, 5

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Groups and Valence Electrons

• All the elements in a group have the same number
  of
• valence electrons.
• Example Elements in group 2A (2) have two (2)
  valence electrons.
• Be 2, 2
• Mg 2, 8, 2
• Ca 2, 8, 8, 2
• Sr 2, 8, 18, 8, 2

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Periodic Table and Valence Electrons

• Representative Elements Group Numbers
• 1 2 3 4 5
  6 7 8
• H He
• 1 2
• Li Be B C N
  O F Ne
• 2,1 2,2 2,3 2,4 2,5
  2,6 2,7 2,8
• Na Mg Al Si P
  S Cl Ar
• 2,8,1 2,8,2 2,8,3 2,8,4 2,8,5
  2,8,6 2,8,7 2,8,8

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Examples

• State the number of valence electrons for each.
• A. O
• 1) 4 2) 6 3) 8
• B. Al
• 1) 13 2) 3 3) 1
• C. Cl
• 1) 2 2) 5 3) 7

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Examples

• State the number of valence electrons for each.
• A. calcium
• 1) 1 2) 2 3) 3
• B. group 6A (16)
• 1) 2 2) 4 3) 6
• C. tin
• 1) 2 2) 4 3) 14

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Examples

• How many electrons are in energy level 3 of the
  following
• A. Sulfur b. Phosphorous

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Examples

• Identify the elements that have the following
  electron level
• Energy level 1 2 3
• 2 1 0
• 2 8 6
• 2 8 7

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Electron-Dot Symbols

• An electron-dot symbol
• shows the valence electrons around the symbol of
  the element.
• for Mg has 2 valence electrons as single dots on
  the sides of the symbol Mg.
• . .
• Mg or Mg or Mg or Mg

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Writing Electron-Dot Symbols

• Electron-dot symbols for
• groups 1A (1) to 4A (14) use single dots.
• Na Mg Al C
• groups 5A (15) to 7A (17) use pairs and single
  dots.
• P O

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Groups and Electron-Dot Symbols

• In a group, all the electron-dot symbols have the
• same number of valence electrons (dots).
• Example Atoms of elements in Group 2A (2) each
  have 2 valence electrons.
• Be
• Mg
• Ca
• Sr
• Ba

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Examples

• .
• A. X is the electron-dot symbol for
• 1) Na 2) K 3) Al
• . .
• B. . X .
• . is the electron-dot symbol of
• 1) B 2) N 3) P

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Examples

• What is the dot Lewis structure of
• Carbon
• Magnesium
• Aluminum
• Argon

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Atomic Size
Atomic size is described using the atomic radius
the distance from the nucleus to the valence
electrons.
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Atomic Radius Within A Group

• Atomic radius increases going down each group of
  representative elements.

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Atomic Radius Across a Period

• Going across a period from left to right,
• an increase in the number of protons increases
  attraction for valence electrons.
• atomic radius decreases.

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Examples

• Select the element in each pair with the larger
  atomic
• radius.
• A. Li or K
• B. K or Br
• C. P or Cl

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Ionization Energy

• Ionization energy is the energy it takes to
  remove a valence electron.
• Na(g) Energy (ionization) -gt Na(g)
  e-
• 
  
  

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Ionization Energy In a Group

• Going up a group of
• representative elements,
• the distance decreases between nucleus and
  valence electrons.
• the ionization energy increases.

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Ionization Energy

• Metals have lower ionization energies.
• Nonmetals have higher ionization energies.

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Examples

• Select the element in each pair with the higher
  ionization
• energy.
• A. Li or K
• B. K or Br
• C. P or Cl