Group I

What is Group I?

The first vertical column of the Periodic Table, whose elements are the alkali metals. Each atom has one electron in its outer shell, so each forms an ion with a charge of one plus. Lithium, sodium and potassium are the three required by the syllabus; all three are relatively soft metals.

This definition is part of the The Periodic Table chapter in Cambridge IGCSE Chemistry.

Concepts related to Group I

• alkali metal
• one outer electron
• \(+1\) ion

Common mistakes with Group I

• 1 · Rows and columns swapped Defect Calling a vertical column a period, or a horizontal row a group. Fix Period is the horizontal row — think of a sentence running left to right and ending in a full stop. Group is the vertical column — a family standing in a line. Period number = number of occupied shells; group number = number of outer electrons.
• 4 · Treating the density trend as exact Defect Writing that density increases down Group I as though every step were guaranteed. Fix The syllabus calls all three Group I trends general trends, and density is where you can see why. Density generally increases, and the data has a wobble in it — potassium is slightly less dense than sodium. Keep the word “generally” and the statement is safe; drop it and the statement is falsifiable from a data table the examiner may well print.
• Error 1 · “The groups are the horizontal rows.” Defect Row and column swapped. Chemistry A group is a chemical family, and family resemblance comes from a shared outer-shell arrangement, which is what the columns share. The rows share only the number of shells. Repair Period \(=\) row. Group \(=\) column. Transfer Sodium and potassium are in the same what? Group.
• Error 7 · “Density increases down Group I.” Defect A missing qualifier turns a true statement into a false one. Chemistry The data is not perfectly regular: potassium \((0.86\;\mathrm{g/cm^3})\) is slightly less dense than sodium \((0.97\;\mathrm{g/cm^3})\). The syllabus calls all three Group I trends general trends, and density is the one where you can see why. Repair Insert one word: density generally increases down Group I. Transfer Which of the three trends most needs the word “generally”, and why? Density — the potassium value dips below sodium's.
• Error 8 · “Melting point increases down Group I.” Defect Direction reversed. Chemistry The data runs \(181\,{}^\circ\mathrm{C}\), \(98\,{}^\circ\mathrm{C}\), \(63\,{}^\circ\mathrm{C}\) for lithium, sodium and potassium — falling at every step. Repair Melting point decreases down Group I. Transfer Rubidium is below potassium. Higher or lower melting point? Lower.
• Error 9 · “Reactivity decreases down Group I, like Group VII.” Defect One group's trend copied onto the other. Chemistry The two run in opposite senses. Group I reactivity increases down the group; Group VII reactivity decreases. Repair Learn them as a contrasting pair, never separately. Transfer Which is more reactive, potassium or lithium? Potassium. Chlorine or iodine? Chlorine.

Examiner tips on Group I

• A question style worth recognising. Questions on this topic often use letters — element \(\mathrm{A}\), element \(\mathrm{Q}\) — rather than real symbols, so that you cannot answer from memory. Treat that as a gift rather than a trap: when a proton number, a configuration or a group is supplied, the answer is derivable from it — and when none of those is supplied, saying what is missing is the answer, as cases G and H in the position studio show. If you find yourself trying to remember which element \(\mathrm{Q}\) “really is”, you have left the method.