Chem C6

6.1 Classifying elements

  • All elements can be divided into three main categories

    • metals,

      • solids (except Mercury (Hg))

      • shiny (usually)

      • usually high melting and boiling points (Except Sodium(Na))

      • usually hard and strong (Except Sodium(Na))

      • mellable and ductile(can stretch)

      • usually high density (Lithium(Li) is not)

      • good conductors of heat and electricity

    • non-metals,

      • Gases/solids (Except Bromine(Br))

      • Usually dull in appeareance (Iodine(I) is not)

      • usually low melting and boiling points (Carbon (C))

      • usually brittle (easy to break when force is applied)

      • not mellable and not ductile(for solids ofc)

      • usually low density

      • poor conductors of heat

      • poor conductors of electricity (Except graphite (C))

    • and metalloids

  • The nature of an element can be determined from its state at room temp and pressure.

6.2 Development of the periodic table

  • Elements are arranged in the order of increaseing atomic number

    • Periods:

      • Horizontal rows

      • 1-7

      • the period number = occupied electron shells

    • Groups:

      • Vertical columns of elements

      • 0, I to VII

      • the group number = valence electrons

      • certain groups have specific names

        • Group I: Alkali metals

        • Group II: Alkaline earth metals

        • Group VII: Halogens

        • Group 0: Noble gases

      • Exceptions:

        • Hydrogen(H) → no group

        • Helium (He) → Group 0 but has 2 valence elctrons

6.3 Patterns in the preiodic table

  • Metalic character (the ability of an element to lose e- during a reaction) decreases when going across a period while the non-metallic character (the ability of an element to gain e- during a reaction) increases → the elements on the right are usually non-metals while the elements on the left are usually metals.

  • Elements of the same group have similar chemical properties due to the same number of valence electrons.

  • There is a gradual change in physical and chemical properties down a group (group trend)

6.4 Group I: Alkali Metals

  • All alkali metals have 1 valence electron

  • soft metals

  • low densities

  • highly reactive in air/water

    • metal + water → metal hydroxide + hydrogen

    • e.g. Caesium + water → Caesium hydroxide + hydrogen

    • 2Cs + 2H2O → 2CsOH + H2

  • reacts with non-metal to form ionic compounds

  • reactivity of alkali metals increases down the group

    • → Lithium (Li) is the least reactive

    • Theoretically, Francium (Fr) is the most reactive but it is very rare.

    • → Caesium (Cs) is recogized as the most reactive alkali metal

6.5 Group II: Alkaline earth metals

  • All alkaline earth metals have 2 valence electrons

  • low densities 

  • less reactive than alkali metals

  • reacts with hydrochloric acid 

    • Alkaline earth metals + Hydrochloric acid → hydrogen + metal chloride

    • e.g. Calcium + Hydrochloric acid → Calcium chloride + Hydrogen

    • Ca + 2HCl → CaCl2 + H2

  • reacts with non-metals to form ionic compounds except Beryllium (Be) which has a concerning high ionization energy → it forms covalent bonds.

  • reacts with water

    • Alkaline earth metals + water → metal hydroxides + hydrogen

    • e.g. Magnesium + water → magnesium hydroxide + hydrogen

    • Mg + 2H2O → Mg(OH)2 + H2

  • reactivity of alkaline earth metals increase down the group

    • → Beryllium (Be) is the least reactive

    • Theoretically, Radium (Ra) is the most reactive but it is radioactive

    •  → Barium is recognized as the most reactive alkaline earth metal

6.6 Group VII: Halogens

  • halogens are non-metals with 7 valence electrons

  • their melting and boiling points increase down the group 

  • they are colored 

  • they react with metals to form ionic compounds

  • they react with non-metals to form covalent compounds

  • their reactivity decrease down the group

    • → Astatine (At) is the least reactive

    • → Fluorine (F) is the most reactive

  • Halogen solutions react with sodium sulphite to turn colorless

    • Halogen + water + sodium sulphite → sodium sulfate + hydrogen halide

    • E.g. Chlorine solution + sodium sulphite → sodium sulfate + chloride

    • Cl2 + H2O + Na2SO3 → Na2SO4 + 2HCl

    • Color change is observed because the sulphite ions reduces the elemental halogens to colorless halogen ions.

6.7 Group 0: Noble gases

  • follows the duet rule/ octet rule

  • → High stability, and are relatively inert

  • Electron arrangements:

    • Helium (He): 2

    • Neon (Ne): 2, 8

    • Argon (Ar) : 2, 8, 8

    • Krypton (Kr): 2, 8, 18, 8

    • Xenon (Xe): 2, 8, 18, 18, 8

    • Radon (Rn): 2, 8, 18, 32, 18, 8

  • Colorless, odorless and tasteless under room temp. and normal atmospheric pressure