Learn first: The periodic law and table
Non-metals occupy the upper right corner of the periodic table — above and to the right of the boron–astatine diagonal; there are 22 of them (including the noble gases). Although few, non-metals form the basis of nature: the atmosphere (N₂, O₂, Ar), water (H, O), living things (C, H, O, N, P, S — the organogenic elements) and the Earth’s crust (O, Si). Unlike metals they tend to gain electrons, so they usually act as oxidising agents. This topic covers the general patterns of non-metals, hydrogen and the noble gases; halogens, oxygen and sulfur, nitrogen and phosphorus, and carbon and silicon have topics of their own.
Most non-metal elements are molecular (H₂, N₂, O₂, Cl₂, P₄, S₈), so they melt easily and are volatile; some have giant covalent structures (diamond, silicon, boron) and are very hard. At room temperature the non-metals include gases (H₂, N₂, O₂, F₂, Cl₂, the noble gases), one liquid (bromine) and solids (C, Si, P, S, I₂). Most do not conduct electricity (graphite is the exception). Many non-metals show allotropy: oxygen and ozone, diamond and graphite, white and red phosphorus.
Hydrogen is the lightest element and the most abundant in the Universe (most of the mass of stars). Its configuration is 1s¹: by losing one electron it becomes H⁺ (like group I), by gaining one it becomes H⁻ (like group VII), so its place in the periodic table is ambiguous. Isotopes: protium ¹H, deuterium ²H (D) and tritium ³H (T, radioactive).
Preparation:
Laboratory: Zn + 2HCl → ZnCl₂ + H₂ (Kipp’s apparatus)
Industry: CH₄ + H₂O → CO + 3H₂ (steam reforming), electrolysis of water 2H₂O → 2H₂ + O₂
Hydrogen is a colourless, odourless gas, practically insoluble in water; M(H₂) = 2, so it is 29/2 = 14.5 times less dense than air and is collected in an upside-down test tube.
A mixture of hydrogen with air or oxygen explodes violently when ignited, so hydrogen is tested for purity before it is lit. Hydrogen is regarded as a clean fuel: burning it produces only water.
What volume of hydrogen (STP) is needed to reduce 23.2 g of Fe₃O₄ completely, and what mass of iron is obtained?
He, Ne, Ar, Kr, Xe and Rn make up group VIIIA. Their outer shell is full (ns² np⁶, helium 1s²), so they are chemically very inert and exist as single atoms. Only since 1962 have compounds of xenon and krypton with fluorine been made (XeF₂, XeF₄, KrF₂). Argon makes up 0.93 % of air by volume. Uses: helium in balloons and airships (it does not burn) and, as a liquid, for reaching extremely low temperatures; neon for the red light of advertising signs; argon as an inert atmosphere for welding and in filament lamps.
Across a period acidity increases: CH₄ (neutral) → NH₃ (basic) → H₂O (amphoteric) → HF (acidic)
Down a group acid strength increases: HF < HCl < HBr < HI; reducing power increases in the same order
Down a group the element–hydrogen bond gets longer and weaker, so the proton is lost more easily: H₂S is a stronger acid than water, and HI stronger than HF. The basicity of ammonia is due to the nitrogen lone pair accepting a proton.
For the oxoacids of one element, acid strength rises with the element’s oxidation state: HClO < HClO₂ < HClO₃ < HClO₄; H₂SO₃ < H₂SO₄; HNO₂ < HNO₃. The hydrates of the highest oxides get stronger across a period: H₂SiO₃ < H₃PO₄ < H₂SO₄ < HClO₄.
4.96 g of an element X reacted completely with 6.4 g of O₂, forming an oxide XₐOᵦ. Identify the element.
C + 2H₂SO₄(conc.) → CO₂ + 2SO₂ + 2H₂O and P + 5HNO₃(conc.) → H₃PO₄ + 5NO₂ + H₂O. In total 18 g of water formed, and the amount of H₃PO₄ equals the amount of gas from the first reaction. Find the total mass of the non-metals.