Elements, Compounds, Symbols and Formulae — Important Questions

Sulphur (S)

Sulphur is a non-metal. It is a yellow solid with a dull surface, is brittle, and is a bad conductor of heat and electricity. Iron, Copper, and Gold are all metals — they are shiny, malleable, ductile, and good conductors. Non-metals include elements like Sulphur, Oxygen, Hydrogen, Carbon, Nitrogen, and Chlorine. There are only about 18 non-metals compared to about 93 metals among the 118 known elements.

Definite proportion by mass

A key characteristic of compounds is that their elements always combine in a definite (fixed) proportion by mass. For example, in water (H₂O), hydrogen and oxygen always combine in the ratio 1:8 by mass — no matter where the water comes from. This is why water always has the same properties. If the proportion changes, a completely different compound is formed. For example, H₂O₂ (hydrogen peroxide) is different from H₂O (water) even though both contain hydrogen and oxygen.

Fe

The symbol for Iron is Fe, which comes from its Latin name 'Ferrum'. Like Sodium (Na from Natrium) and Copper (Cu from Cuprum), the symbol of Iron does not match its English name at all. 'Ir' might seem like a logical abbreviation but it is actually the symbol for Iridium, a different element. 'In' is the symbol for Indium. Memorising the Latin-based symbols is very important in chemistry.

Mercury

Mercury is the only metal that exists as a liquid at room temperature. All other metals are solids at room temperature — this makes Mercury a very important exception to the general property of metals. Sodium is a soft solid metal. Copper is a solid metal. Bromine is a liquid but it is a non-metal, not a metal. Mercury is used in thermometers because it expands and contracts uniformly with temperature changes.