Periodic table structure – cells, periods and groups

What it shows

The periodic table arranges elements by increasing atomic number, and its layout follows from electron configuration: elements with the same number of occupied shells share a period, and elements with the same number of valence electrons share a group. The block (s, p or d) shows which subshell receives the last electron. The History tab shows how chemists got there: Döbereiner's triads (1829), Newlands' octaves (1865), Mendeleev's table ordered by atomic mass with gaps and predictions such as eka-silicon, later found as germanium, and Moseley's ordering by atomic number (1913), which removed exceptions such as tellurium and iodine.

How to use

In the Periodic table tab, set Color by to Element block, click cells and compare the shells with the period and the outer electrons with the group. In the History tab, work through the stages: test the mean rule on each triad, tap a note in Octaves to count eight, then in Mendeleev press Order by atomic mass and repair the table with Insert gap and Swap with next. In Modern, switch Order by between Atomic mass and Atomic number.

Parameters you can change

• Color by Element block, Metal – nonmetal – noble gas, No coloring
• Preselect element (atomic number) 1–36
• Show electron configuration
• View Periodic table, History of the table
• History stage Döbereiner's triads, Newlands' octaves, Mendeleev's table, Modern table (atomic number)

Questions to explore

1. In which period and group is the element with Z = 17, and how does its electron configuration explain this?
2. Why does potassium (Z = 19) start period 4 rather than continuing period 3?
3. Why did Mendeleev put tellurium before iodine, although tellurium has the larger atomic mass?