8th Grade 11/8 Do Now:

1
8th Grade11/8 Do Now

• Calcium is in period 4. Its atomic number is 20.
  Draw the Bohr diagram for Calcium.

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In your copybook

• What pattern do you notice with the Bohr diagrams
  for noble gases? How does this relate to the
  reactivity of noble gases?
• What pattern do you notice with the Bohr diagrams
  for halogens? How does this relate to the
  reactivity of noble halogens?
• What pattern do you notice with the Bohr diagrams
  for alkali metals? How does this relate to the
  reactivity of alkali metals?

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Noble Gases

• Do not combine with other elements
• All have stable outer level
• 8 electrons in outer level stable for levels
  2-7
• 2 electrons stable in first level

4
Halogens

• Need 1 electron to have a stable outer energy
  level
• Flourine is the most reactive because it s outer
  level is closest to the nucleus
• Reactivity decreases down the group

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Alkali Metals

• 1 electron in outer energy level
• This electron is removed during reactions
• Less energy is needed to remove an electron from
  an energy level that is farther from the nucleus
• Reactivity increases down the group

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Electron Dot Diagrams

• Symbol for the element surrounded by as many
  electrons as there are electrons in the outer
  energy level (valence electrons)
• Also known as Lewis Structures

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Why do atoms combine?
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How to Write Them

• The dots are written in pairs on four sides of
  the element symbol.

• Start by writing one dot on the top of the
  element symbol, then work your way around adding
  dots to the right, bottom, and left.

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Why do atoms combine?
1
How to Write Them

• Add a fifth dot to the top to make a pair.

For elements with more than 5 valence electrons,
continue drawing dots as pairs, moving clockwise.