Periodic table

• Elements are arranged in order of increasing proton number
• groups run from top to bottom
• elements in the same group have the same number of valence electrons and thus have similar chemical properties
• periods are horizontal row of elements (left to right)
• the number of electron shells an element has is the same as its period number
• valency is the number of valence electrons used by an atom during chemical bonding
• metalloids have the properties of both metal and non-metal
• Elements in group 18 have full valence electron shells and do not form compounds
• elements in group 15 to 17 tend to gain electrons to form negative ions when bonded to a metal
• Group 1-13 metals tend to lose electrons to form positive ions
• Across the period there is a decrease in metallic properties and increase in non-metallic properties
• An atom displays more metallic properties when it is more likely to lose electrons than to gain electrons
• Across the period the number of protons in the nucleus increases while number of electron shells remain the same
• The increase in nuclear charge results in a stronger forces of attraction between the nucleus and valence electrons More energy is required to lose electrons resulting in lower tendency for the atom to lose electron. Thus the metallic property decreases
• Going down a group there is an increase in metallic properties and decrease in non-metallic properties
• down the group

  • The size of the atom increases due to an increase in the number of electron shells
  • The valence electrons are further away from the nucleus. Hence there is a weaker forces of attraction between the nucleus and the valence electrons.
  • There is a higher tendency for the atom to lose its valence electrons to form a positive ion
• Group 1 are alkali metals and they react with water to form soluble metal hydroxides, alkalis
• Physical property of alkali metals

  • Soft and can be cut easily
  • Good conductors of heat and electricity due to presence of delocalised mobile electrons
  • Low melting and boiling point
  • Low densities
• Down the group, the melting and boiling points of alkali metals decreases
• Down the group density of alkalis generally increases
• Alkali metals are highly reactive metal and are stored in oil to prevent them from reacting with air and water
• Group 1 metals lose 1 valence electrons to achieve noble gas electronic configuration
• Alkali loses their valence electrons easily and are powerful reducing agents
• Reactivity of group 1 elements increases down the group as:

  • size of atom increases due to the increase in number of electron Shells
  • The valence electrons are further away from the nucleus hence there is weaker forces of attraction between the nucleus and the valence electrons
  • increase in the ease of losing valence electrons
• reducing power of alkali metals increases down the group
• lithium reacts quickly with water. It floats on water
• Sodium reacts violently with water. It darts around the water surface. Reaction may be explosive
• Potassium reacts very violently with water. Reaction is explosive
• Elements in group 17 are known as halogens
• group 17 elements exist as diatomic molecules and are non metals
• halogens have low melting and boiling points, are coloured
• fluorine is pale yellow gas at r.t.p
• chlorine is yellow-green gas at r.t.p
• bromine is red-brown gas at r.t.p
• iodine is purple black solid at r.t.p
• astatine is black solid at r.t.p
• Melting point and colour intensity of halogens increases down the group
• reason for increase in melting and boiling point of halogens down the group

  • size of molecule increases resulting in stronger intermolecular forces of attraction
  • thus more energy is needed to overcome the stronger forces of attraction
• halogens are reactive non-metals. They have 7 valence electrons and have a tendency to gain one electron to achieve noble gas electronic configuration
• halogens are oxidising agents in chemical reactions