Topics:

• Periodic Trends
  • Periodic table
  • Symbolic Representation
  • Groups and Periods
  • Metals and Non-metals
• Group Properties
  • Group I: Alkali Metals
  • Group II: Alkaline Earth Metals
  • Metalloids
  • Group VII: Halogens
  • Group VIII: Noble Gases
  • Transition Elements
• Transition Elements
  • Properties
  • Uses

Periodic Trends

Periodic Table:

• Periodic table is an arrangement of elements based on the increasing proton number.
• It is read like a book from left to right in order of proton number.
• Periodic Table includes all the discovered elements so far.
• The elements are also arranged in groups and columns which have specific properties.

Symbolic Representation:

Different tables have different symbolic representation. A common representation is with the symbol of the element together with its proton and mass number. The kind of periodic table provided in CIE is given below, with the proton number on top and mass number below the symbol:

Groups and Periods:

Groups:

• Vertical columns in the periodic table are called groups.

Group Properties:

• There are 8 major groups with 1-7 and group 0/8 as shown at the top of the table in Roman numerals.
• Elements in the same group have the same chemical properties since they have the same number of valence electron. Having same number of valence electron mean that the ion of the element will have the same charge and hence react in a similar way to other elements.
• For example, Group I elements all have one valence electron and hence their hydroxide will always have since OH radical in one molecule
  • NaOH
  • KOH
  • LiOH

Periods:

Periods are horizontal rows in the periodic table.

Period Properties:

• There are 7 periods in the period table
• Elements in the same periodic table have the same number of shells.
• The properties across a period change from metallic character to non- metallic character.
• Reactivity decreases across a period as the atom size decreases due to more attraction, making it harder for an atom to lose electron.

Group Properties:

Group I: Alkali Metals

Basic Properties:

• Group I elements are known as alkali metals since they form alkalis when dissolved in water.
• The alkali metals are soft, low density metals
• Their melting points decrease down the group
• They are more reactive (higher tendency to lose electron) as more distance between valence electron and nucleus making it easier to lose electron.
• They are found on the extreme left of the periodic table.
• Reactivity increases down the group.

Chemical Properties:

• When alkali metals react with oxygen, they form oxides.
  • 4Li + O₂ →2Li₂O (Red flame, slow reaction)
  • 4Na + O₂ → 2Na₂O (Yellow flame)
  • 4K + O₂ → 2K₂O (Lilac flame)
• When alkali metals react with water, they form alkalis
  • 2Li + 2H₂O → 2LiOH + H₂
  • 2Na + 2H₂O → 2NaOH + H₂
  • 2K + 2H₂O → 2KOH + H₂

Group II: Alkaline Earth Metals

Group II elements are called Alkaline Earth metals as they form alkalis with water and are found in our Earth’s surface.

Metalloids

• Metalloids are elements that act as both metals and non-metals.
• They gain and donate electron.
• They are found near the staircase as shown in the diagram
• Silicon and Germanium are used as solar plates.

Group VII: Halogens

Basic Properties:

• Halogens are found in group VII of the periodic table
• They are called halogens because they form salts
• They are non-metals with small size, making it easier for the nucleus to attract electron. Hence, they are more reactive.
• Reactivity of Halogens decrease down the group
• They make covalent bonds and exist in diatomic molecules as X₂
  • g. F₂, Cl₂, I₂

Physical Properties:

Chemical Properties:

• Displacement reaction:
  • In halogens, the element which lies above can displace the lower element from its salt.
  • This means that the elements above are more reactive and reactivity decreases down the group.
  • g. Cl₂ + 2KBr → 2KCl + Br₂

Group VIII: Noble Gases

Basic Properties:

• Inert or noble gases are found in the last group of the periodic table.
• They have a complete octet/ outermost shell and are very stable.
• As size affects MP and BP, the larger one has more melting and boiling point. Hence, Radon has the highest. MP and BP increase down the group.
• They were first discovered using fractional distillation
• They are monoatomic: exist as single atoms
• They are unreactive.

Uses of Noble Gases:

Transition Elements

Properties:

• Transition elements are found in the middle section of the periodic table, as shown in the diagram.
• They are called transition metals as their properties are changing from metals to non-metals
• They have high melting and boiling points
• They have high densities
• Transition metals have variable oxidation states.
• Their compounds are colored.
• Naturally, they are found in ores but not all of them
• They are used to form alloys. (discussed in metals)
• They are para magnetic (mostly): attracted by magnets.

Uses:

• Transition metals and their compounds are used as catalyst in many reactions.
• Two reactions already discussed are Haber Process and Contact Process:
  • Haber Process: Iron
  • Contact Process: Vanadium (V) oxide
• Nickel is used in the hydrogenation of Alkenes (discussed in Organic Chemistry)
• Catalysts are used to lower the energy demands of reactions in industry and this helps reduce the costs and saves energy conserves.
• Gold, copper and silver have increasing use in jewelry

Lesson Tags

Periodic Table | Groups and Periods | Alkaline Earth Metals | Detailed Notes For Preparation & Revision | O Level Chemistry 5070 and IGCSE Chemistry 0620

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