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⚗️ The Periodic Table

How 118 elements line up to reveal the hidden logic of matter.

lessons

~30 min

to learn

🔬 Science

subject

Teens

level

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What you’ll learn

Explain what the periodic table organizes and how it is ordered by atomic number.The periodic table charts all 118 elements. Mendeleev's 1869 version, ordered by mass, revealed repeating properties and predicted new elements. The modern table is ordered by atomic number into seven periods and eighteen groups.
Use an element's group and position to predict its properties and reactivity.Valence electrons drive chemistry, so groups share behavior. The table splits into metals, nonmetals, and metalloids, with named families and smooth periodic trends in size, ionization energy, and electronegativity.
Interpret the full structure of the table, including special rows and synthetic elements.The lanthanides and actinides float below for readability. Elements past uranium are mostly synthetic and radioactive. Each element box encodes identity, mass, and behavior, making the table a living predictive map.

Questions this course answers

What determines an element's position and identity on the modern periodic table?

The modern table is ordered by atomic number, the number of protons, which uniquely defines each element.

Why is Mendeleev's 1869 table considered so important?

Mendeleev left gaps for missing elements and accurately predicted their properties, which later discoveries confirmed.

How many elements are confirmed on the modern periodic table?

There are 118 confirmed elements, from hydrogen up to oganesson.

Elements in the same vertical group behave similarly mainly because they share the same:

Members of a group have the same number of valence electrons, which controls their chemical behavior.

Why are the noble gases in group 18 so unreactive?

Noble gases have complete outer electron shells, so they have little tendency to gain or lose electrons.

As you move left to right across a period, atomic radius generally:

Increasing nuclear charge pulls electrons in tighter, so atoms shrink across a period.

Grounded in trusted sources

Britannica, 'Periodic table' (britannica.com/science/periodic-table)
Royal Society of Chemistry, Periodic Table (rsc.org/periodic-table)
Chemistry LibreTexts, '2.5: Mendeleev and the Periodic Table' (chem.libretexts.org)
Scerri, Eric R., 'The Periodic Table: Its Story and Its Significance' (Oxford University Press, 2019)

Every Wunder lesson is built from real, reputable sources — never invented.

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