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20 QUESTIONS · 5 TOPICS · TREND EXPLORER · ABOUT 15 MINUTES

Mendeleev left gaps in his table and predicted what would fill them.

In 1869 he forecast an unknown "eka-silicon" with a density of about 5.5 g/cm³. Germanium was found in 1886: 5.35. Twenty questions on the elements beyond carbon chains, each explained, then explore the patterns that made his prediction possible. No sign-up, nothing saved.

Start the test
EKA-SILICON (1871)PREDICTEDGERMANIUM
Atomic mass7272.6
Density (g/cm³)5.55.35
Oxide formulaEsO₂GeO₂
Chloride boils at< 100 °C86 °C
QUESTION 1 / 20 · PERIODIC TRENDSMedium

Going down group 1 (Li → Na → K), reactivity with water…

PERIODIC TREND EXPLORER

See the patterns in the first 36 elements

Colour the table by a property and the trends jump out: across a period and down a group, values change in a regular way. Click any element for its numbers.

Low: 31 pmMiddleHigh: 243 pmNo value
32GeGermaniumMetalloid · period 4, group 14
Atomic radius125 pm
Electronegativity2.01
1st ionisation energy762 kJ/mol
Atoms shrink across a period, as more protons pull electrons in, and grow down a group, as new shells are added. Potassium is about six times wider than fluorine.
Calculated atomic radii in picometres; Pauling electronegativity; first ionisation energy in kJ/mol. Noble gases He, Ne and Ar have no standard Pauling value. Figures are typical textbook values.

What this inorganic chemistry test covers, in short

Twenty multiple-choice questions at upper-secondary to first-year university level, four on each of five topics: periodic trends, the main groups, transition metals, ions and redox, and coordination chemistry.

Inorganic chemistry covers everything except most carbon compounds: metals, minerals, salts and catalysts. The test is our own and not normed.

By What's Your IQ · Reviewed 5 Oct 2026
Format
20 multiple-choice questions
Level
A-level / AP to first-year
Bonus
Periodic trend explorer, Z = 1–36
Milestone
Mendeleev's periodic table, 1869

Keep going

General chemistry testBonding, moles and the equation balancer.Organic chemistry testThe chemistry of carbon and the molecule builder.Quantum physics testWhy electron shells and these trends exist at all.

Mendeleev saw the pattern first. How quickly do you spot them?

Our full IQ test covers pattern, logical, numerical and verbal reasoning: 60 questions, about 30 minutes.

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