s-, p-, d- and f-Block Elements: MDCAT Chemistry notes
s-, p-, d- and f-Block Elements for MDCAT: block classification by subshell, group configurations, metals and non-metals, aluminium and uses of elements.
Basis of the blocks
The modern periodic table is arranged in increasing order of atomic (proton) number, not atomic mass. Elements are placed in blocks according to the subshell that receives the last (differentiating) electron.
| Block | Groups | Valence configuration | Examples |
|---|---|---|---|
| s-block | IA, IIA | $ns^{1\text{–}2}$ | Alkali and alkaline earth metals |
| p-block | IIIA–VIIIA | $ns^2\,np^{1\text{–}6}$ | B, C, N, O, halogens, noble gases |
| d-block | B groups (IIIB–IIB) | $(n-1)d^{1\text{–}10}\,ns^{1\text{–}2}$ | Outer transition elements: Fe, Cu, Zn |
| f-block | Lanthanides, actinides | $(n-2)f^{1\text{–}14}$ | Inner transition elements |
Reading the group from a configuration
For s- and p-block elements, the group number equals the number of valence electrons. Some examples:
- $1s^2\,2s^2\,2p^1$ has 3 valence electrons, so it is group IIIA (boron).
- $2s^2\,2p^2$ is group IVA (carbon).
- $2s^2\,2p^4$ is group VIA (oxygen).
- $2s^2\,2p^5$ is group VIIA (fluorine).
Metals, non-metals and metalloids
- Group IVA shows the full change in one group. Carbon is a non-metal, silicon and germanium are metalloids, and tin and lead are metals.
- Silicon is the classic semiconductor. Al and Mg are metals and P is a non-metal.
- The halogens (group VIIA) are F, Cl, Br, I and At. Iron is a d-block transition metal, not a halogen.
Aluminium (group IIIA)
- The main ore is bauxite, hydrated aluminium oxide ($\mathrm{Al_2O_3\cdot 2H_2O}$). Haematite is an iron ore. Cryolite ($\mathrm{Na_3AlF_6}$) is used as a solvent, not as the ore.
- Aluminium is extracted by electrolysis of purified alumina dissolved in molten cryolite. Cryolite lowers the melting point.
- With nitrogen it forms aluminium nitride, AlN: $\mathrm{2Al + N_2 \to 2AlN}$.
- Aluminium halides are electron deficient (Al has only 6 electrons) and act as Lewis acids (electron-pair acceptors). This is why anhydrous $\mathrm{AlCl_3}$ is a Friedel–Crafts catalyst and why it dimerizes to $\mathrm{Al_2Cl_6}$.
Uses and occurrence asked in MDCAT
- Chlorine kills bacteria in drinking water.
- Argon fills electric bulbs because it is inert, cheap and plentiful, and it stops the filament oxidizing.
- Galvanized iron is iron coated with zinc. Zinc corrodes in preference to iron (sacrificial protection).
- Gold occurs in the free (native) state because it is very unreactive. Iron, copper and mercury are mainly found as ores.
Common MDCAT traps
- The table is ordered by proton number. Atomic mass, nucleon number and mass number are all wrong answers.
- d-block elements are outer transition elements and f-block elements are inner transition elements.
- Bauxite is the ore. Cryolite is the flux.
- Galvanizing uses zinc. Tin-plating is a different process.
- Count only the valence-shell electrons ($ns + np$) when finding the group.
Quick revision
- The alkali metals are in the s-block.
- Group IVA contains a non-metal, metalloids and metals.
- Aluminium is extracted by electrolysis of fused bauxite (alumina in cryolite).
- $\mathrm{AlCl_3}$ is a Lewis acid.
- Argon is used in bulbs and chlorine in water treatment.