Answers to Chapter 5 Review Questions

1. Charges: proton: +1, neutron: 0, electron: -1, Masses: proton: 1, neutron: 1, electron: almost 0.

2. The element’s atomic number will determine the extent to which its outer layers are populated with electrons. If the outer shell is not quite full, the atom may gain electrons to fill them and become an anion (negative charge). If the outer shell has only a few electrons, it may lose them and become a cation (positive charge). Cations and anions attract each other to form molecules with ionic bonding.

3. Helium and neon (and the other noble gases) have complete outer shells and therefore no tendency to form ionic bonds.

4. Electrons are transferred from one atom to another to form an ionic bond. Electrons are shared between atoms to form a covalent bond.

5. An anion has a negative charge and a cation has a positive charge.

6. Minerals are classified into groups based on their anion or anion group.

7. Name the mineral group for the following minerals:

calcite CaCO3   carbonate biotite silicate pyrite FeS2 sulphide
gypsum CaSO4 sulphate galena PbS sulphide orthoclase KAlSi3O8 silicate
hematite Fe2O3 oxide graphite C native magnetite Fe3O4 oxide
quartz SiO2 silicate fluorite CaF2 halide olivine MgSiO4 silicate

8. An unbonded silica tetrahedron has one Si ion (+4 charge) and 4 oxygens (-2 charge each) so the overall charge is 4 – 8 = -4 for SiO4-4

9. Magnesium can substitute freely for iron in olivine and several other minerals because they have similar charges (+2) and similar ionic radii.

10. Pyroxene is made up of single chains of tetrahedra while amphibole is made up of double chains.

11. The two end-members of the plagioclase series are Albite (NaAlSi3O8) and Anorthite (CaAl2Si2O8)

12. In quartz each silica tetrahedron is bonded to four other tetrahedra, and because oxygens are shared at each bond the overall ratio is silicon (+4) to two oxygens (2 x -2 = -4), which is balanced.

13. Some minerals have distinctive colours, but many have a wide range of colours due to differing impurities.

14. Glass has a Mohs hardness of about 5.5 while porcelain is close to 6.5. The mineral is between these two, so it must be close to 6.