chap 8 patterns in the periodic table

• element in the same group has the same number of valence electrons
• elements in the same period has the same number of electron shells
• why atomic radius of atom decreases across the period ?

  the number of protons increases, it causes valence electrons to be attracted more strongly to the protons in the nucleus bringing the valence shell closer to the nucleus
• why atomic radius of atom increases down the group ?

  number of electron shells increases down the group, distance from nucleus to valence shell increases
• group 1: MP & BP decreases down the group
• group 1: density, reactivity and reducing property increases down the group
• across the period: metallic properties and atomic radius decrease
• down the group: metallic properties and atomic radius increases
• physical properties of alkali metals

  soft, low MP and BP, low density and conducts electricity
• why does reactivity of atom increases down the group ?

  because the number of electron shells increases. this causes the distance between the positively- charged nucleus and negatively- charged valence electrons increases, resulting in a weaker electrostatic forces of attraction between them. this leads to less energy required to lose one valence electron
• alkali metals react with cold water to form hydrogen gas and metal hydroxide
• observation of lithium and cold water

  lithium dissolves quickly, darts and floats on the water surface, effervescence
• observation of sodium, and cold water

  sodium darts and floats on the water surface, burns with yellow orange flame, reacts vigorously with a sizzling sound, effervescence
• observation of potassium and cold water

  potassium darts and floats on the water surface, burns with lilac flame, reacts explosively with a spluttering sound, effervescence
• group 17: reactivity and oxidising property decreases down the group
• group 17: MP and BP, density and colour intensity increases down the group
• physical properties of halogens

  low MP and BP, does not conduct electricity, coloured substances
• fluorine is a pure yellow gas at rtp
• chlorine is a yellow- green gas at rtp
• bromine is a red- brown liquid at rtp
• iodine is a red- brown solid at rtp
• astatine is a black solid at rtp
• aq iodine is brown
• physical properties of group 18

  low MP and BP, colourless and odourless, unreactive
• chemical properties of transition metals

  form coloured compounds and acts as catalyst to speed up reactions