03. Atoms, Elements and Compounds

• State the relative charges and approximate relative masses of protons, neutrons and electrons

• Define proton number (atomic number) as the number of protons in the nucleus of an atom

• Define nucleon number (mass number) as the total number of protons and neutrons in the nucleus of an atom

• Use proton number and the simple structure of atoms to explain the basis of the Periodic Table (see section 9), with special reference to the elements of proton number 1 to 20

• Define isotopes as atoms of the same element which have the same proton number but a different nucleon number

• State the two types of isotopes as being radioactive and non-radioactive

• State one medical and one industrial use of radioactive isotopes

• Describe the build-up of electrons in ‘shells’ and understand the significance of the noble gas electronic structures and of the outer shell electrons. (The ideas of the distribution of electrons in s and p orbitals and in d block elements are not required.)

Note: a copy of the Periodic Table, as shown in the Appendix, will be available in Papers 1, 2, 3 and 4.

• Understand that isotopes have the same properties because they have the same number of electrons in their outer shell

• Describe the formation of ions by electron loss or gain

• Describe the formation of ionic bonds between elements from Groups I and VII

• Describe the formation of ionic bonds between metallic and non-metallic elements

• Describe the lattice structure of ionic compounds as a regular arrangement of alternating positive and negative ions

• Describe the formation of single covalent bonds in H2, Cl2, H2O, CH4, NH3 and HCl as

the sharing of pairs of electrons leading to the noble gas configuration

• Describe the differences in volatility, solubility and electrical conductivity between ionic and covalent compounds

• Describe the electron arrangement in more complex covalent molecules such as N2, C2H4, CH3OH and CO2

• Explain the differences in melting point and boiling point of ionic and covalent compounds in terms of attractive forces