Models to materials

bonding models

• bonding types can be used to explain chemical and physical properties of substances, but these have limitations

• bonding is best thought of as a continuum of the three different bonding types like the area of an equilateral triangle

bonding triangle

• location of an element or a compound on the bonding triangle is determined by electronegativity values of the elements present

• elements have 0 difference in electronegativity so would be found along the x-axis

• ionic compounds have a large diff, so would be found at the top

• covalent bonds have a small diff, so are found at the bottom

alloys

• an alloy is a mixture of metals, where the metals are mixed together physically but not chemically

• they can also be made of metals mixed with non-metals

• ions of different metals are spread throughout the lattice and are bound together by delocalised electrons

• it’s possible to form alloys due to the non-directional nature of metallic bonds

why do alloys have different properties to pure metals

• alloys have distinct properties due to different packing of cations in the lattice

• they have properties that can be very different to the metals they contain

• alloys contain atoms of different sizes, which distorts the regular arrangement of cations

  • makes it more difficult for the layers to slide over eachother, so they’re usually harder than the pure metal

examples of alloys

• brass

  • copper & zinc

  • strong and resistant to corrosion

  • door handles, hinges

• bronze

  • copper & tin

  • hard & strong, and resistant to corrosion

  • medals, sculptures

• stainless steel

  • iron, chromium, nickel, carbon

  • corrosion resistant

  • cutlery, surgical instruments