Group 7 The Halogens

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• Group 7 The Halogens
• L.O.
• I know where the halogens are in the Periodic
  Table
• I know how the reactivity of the elements change
  as we go down Group 7.

17/01/2014
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Halogens and the Periodic Table

• These are the Halogens or Group 7 Elements

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Electronic Structure

• Draw the electronic configuration of the first
  two halogens, can you identify a pattern?

There are 7 electrons in the outermost shell.
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Halogen molecules

• All the Group 7 elements are molecules containing
  two atoms. (They are diatomic)
• Each atom is 1 electron short of a noble gas
  electron structure.
• By sharing electrons in a covalent bond full
  outer electron shells are achieved.

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Patterns colour

• The group 7 elements get darker as you go down
  the group.

What colour would you expect astatine to be?
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Patterns physical state

• Melting Points and boiling points increase as the
  molecules get bigger.

What is the physical state solid, liquid or gas?
Element Size Colour of gas Melting Point (oC) Boiling Point (oC) Physical State
Fluorine -220 -188
Chlorine
Bromine -7 59
Iodine 114 184
gas
gas
-101
-35
liquid
solid
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Patterns reactivity

• Reactivity increases up the group.

For example, their reaction with hydrogen For example, their reaction with hydrogen
F2 Reacts instantly even at -200 C
Cl2 Reacts slowly in dark.Explodes in light
Br2 Needs heating to 200 C in order to react
I2 Does not react completely even at 500 C
How will Astatine react?
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Reactivity and electron structures

• Most halogen reactions involve gaining an
  electron.

F

• The atoms get bigger as you go down the group.
  This reduces the attraction of the () nucleus
  for an additional (-) electron.
• Shielding by the inner electron shells also
  reduces the attraction from the nucleus.
• As we go down the group the tendency to gain
  electrons decreases and so does the reactivity

Cl
Reactivity decreases
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Uses of the Halogens

• Fluorine is used in toothpaste and in making
  non-stick pans.
• Chlorine is used in antiseptics and
  disinfectants, to kill bacteria in swimming pools
  and in pesticides.
• Bromine is used in pesticides and used in
  photographic film.
• Iodine is an antiseptic, it is dissolved in
  alcohol and put onto cuts.

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Reactivity trends of the Halogens