The Periodic Table

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Emma Jones
The Periodic Table
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The modern periodic table. The periods are the
horizontal rows. The blue-shaded elements may be
omitted.
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• The modern periodic table has the elements
  arranged in order of increasing atomic number.
• A vertical column, called a group, contains
  elements with similar properties.
• A period runs from left to right with the atomic
  number of the elements increasing from left to
  right.
• The zig-zag red line shows the boundary between
  metals (on the left) and non-metals.

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Alkali Metals

• Group 1 is the vertical column on the far left of
  the periodic table.
• You can probably see lithium, sodium and
  potassium as a demonstration as they are the
  least reactive, but rubidium and caesium are
  considered to be too reactive to demonstrate.
• Francium is radioactive, very rare and the most
  reactive element in group one.

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Group one elements is shaded blue

• The common properties of Group one/Alkali Metals
  is that
• They have low melting and boiling points compared
  to most other metals in the periodic table.
• They are very soft and can be cut easily with a
  knife.
• They have low densities as lithium, sodium and
  potassium will float on water whereas the other
  elements will not
• They react quickly with water, producing
  hydroxides and hydrogen gas.

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Melting points

• The alkali metals have low melting and boiling
  points compared to most other metals.
• You can see from the graph that lithium, at
  the top of Group 1, has the highest melting point
  in the group.

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Density

• The density of a substance is a measure of how
  heavy it is for its size.
• The alkali metals have low densities
  (measured in grams/cubic centimetre) compared to
  most other metals.
• As you can see from the table that lithium
  has the lowest density in the group.

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Trends in Chemical Properties

• As well as knowing that alkali metals become more
  reactive as you go down the group.

Lithium and waterThis is the equation for the
reactionlithium water        lithium
hydroxide hydrogen 2Li(s) 2H2O(l)      
2LiOH(aq) H2(g)When added to
water, lithium floats. It fizzes steadily and
becomes smaller until eventually it disappears.
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Sodium and waterThis is the equation for the
reaction sodium water      sodium
hydroxide hydrogen2Na(s) 2H2O(l)     
 2NaOH(aq) H2(g)When added to water, sodium
melts to form a ball that moves around on the
surface. It fizzes rapidly, and may set on fire
with an orange flame before disappearing.
Potassium and waterThis is the equation for the
reactionpotassium water      potassium
hydroxide hydrogen2K(s) 2H2O(l)     
2KOH(aq) H2(g)When added to water, potassium
floats. It reacts so quickly that it sets on
fire with sparks and a lilac flame, and explodes
at the end of the reaction.
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Group 7 The Halogens

• The elements in Group 7 are called halogens.
  They belong to the column second from right in
  the periodic table.The halogens are non-metals
  with molecules that each contain two atoms. They
  have low melting points and boiling points, and
  they also form coloured vapours. They are poor
  conductors of heat and electricity.
• Group 7 is the vertical column second from right
  in the periodic table. Fluorine is far too
  dangerous to handle at school but you will
  probably see chlorine and iodine there. Bromine
  is a hazardous liquid but you may see a weak
  solution of it. Astatine is radioactive and very
  rare there are only a few grams of it in the
  whole of the Earth's crust at any time.

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Group 7 elements is the shaded blue

• The common properties of the Halogens are
• They are non-metals.
• They have low melting and boiling points.
• They are poor conductors of heat and electricity.
  
• They have coloured vapours.
• Their molecules each contain two atoms (they are
  diatomic).

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Melting point and boiling point

• The halogens have low melting points and boiling
  points.
• This is a typical property of non-metals.
• You can see from the graph that fluorine, at the
  top of Group 7, has the lowest melting point and
  boiling point in the Group.

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State at room temperature

• Room temperature is usually about 20C. At
  this temperature, fluorine and chlorine are
  gases, bromine is a liquid, and iodine and
  astatine are solids.
• Remember this trend as top two elements are
  gases, the bottom two are solids and the middle
  element is liquid.

Colour
The halogens become darker as you go down the
group. Fluorine is very pale yellow, chlorine is
yellow-green and bromine is red-brown. Iodine
crystals are shiny purple-black but easily turn
into a dark purple vapour when they are warmed
up.
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Trends in Chemical PropertiesReactions with
Metals

• The halogens react with metals to make salts
  called metal halides. For example, sodium reacts
  with chlorine to make sodium chloride (common
  salt)sodium chlorine     sodium chloride
• metal halogen metal halide

Sodium chloride is an ionic salt. It contains
sodium ions and chloride ions. Chloride ions
have a -1 charge. You will have come across
compounds containing fluoride ions in, for
example toothpaste.
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Reactions with Hydrogens

• The halogens react with hydrogen to make
  molecular compounds called hydrogen halides.
  These dissolve in water to form acidic solutions.
  For example, hydrogen reacts with chlorine to
  make hydrogen chloridehydrogen chlorine  
  hydrogen chloridehydrogen halogen hydrogen
  halideHydrogen chloride dissolves in water to
  make the familiar laboratory chemical,
  hydrochloric acid.

Trend in reactivityThe halogens become less
reactive as you go down the group. Fluorine, at
the top of the group, is the most reactive
halogen. It is extremely dangerous and will even
attack glass. Iodine, near the bottom of the
group, is much less reactive and is used as an
antiseptic.
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Halogen displacement reactions

• Remember that a more-reactive halogen can
  displace a less-reactive halogen from its salt
  dissolved in water. Here's an example
• Displacement of bromine from sodium
  bromideChlorine is more reactive than bromine
  (you know this because chlorine is above bromine
  in Group 7). Sodium bromide is a salt of bromine
  that will dissolve in water. So chlorine will
  displace bromine from sodium bromide solution.
• This means that if chlorine (as a gas or
  dissolved in water) is added to sodium bromide
  solution, bromine forms and the mixture turns
  brown. We say that bromine has been displaced
  from sodium bromide. Displaced is just a
  chemist's word for pushed out. The equation for
  the reaction is

chlorine sodium bromide -   sodium chloride
bromineCl2(aq) 2NaBr(aq) -
2NaCl(aq) Br2(aq)
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• You can see that the Cl and Br have swapped
  places.
• If you test different combinations of the
  halogens and their salts you can work out a
  reactivity series for Group 7.
• The most reactive halogen displaces all the
  other halogens from solutions of their salts,
  while the least reactive halogen is always
  displaced.
• It works just the same whether you use a
  sodium salt or a potassium salt.