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Periodic Table Trends

High schoolChemistryFirst-20-element reference map using Cordero covalent radii, NIST first ionisation energies and Pauling electronegativities

Atomic property map

Covalent radius

Select an element or a comparison element. Arrow keys move through atomic numbers. This map covers the first 20 elements.

Selected element

Carbon

76 pm

Comparison element

Oxygen

66 pm

Periodic property trace

Covalent radius
220.5168115.56310.515.7510.515.2520Atomic numberCovalent radius

Measurement notebook

Change the setup, test a prediction and save the result. Up to 12 snapshots are kept.

About this experiment

Map three different atomic properties on a periodic arrangement. Select and compare elements, then filter a period or group to discover broad trends and meaningful exceptions.

Learning goals

  • Compare trends across a period and down a group.
  • Distinguish covalent radius from an exact boundary of an atom.
  • Treat unassigned electronegativity as missing data rather than zero.

How to use it

  1. 1Compare lithium, beryllium and boron using radius and ionisation energy.
  2. 2Filter period two and identify the oxygen-nitrogen ionisation-energy exception.
  3. 3Compare sodium with potassium in group one.
  4. 4Choose a noble gas on the electronegativity map and interpret the missing value.

The model

Differences use the same property definition and units.
First ionisation energy refers to removing one electron from an isolated neutral gas-phase atom.

Assumptions

  • Only atomic numbers 1 through 20 are included. Values are fixed reference data, not predictions from an electronic-structure solver.
  • Radii use the Cordero 2008 covalent-radius definition in picometres; ionisation energies use NIST values in electronvolts. Pauling electronegativity is dimensionless.
  • Noble-gas Pauling entries are unassigned. Trace lines guide the eye between discrete elements and do not imply interpolated measurements.

Try this in class

  1. Q1Why is the first ionisation energy of boron lower than that of beryllium?
  2. Q2Why is a noble-gas electronegativity gap not evidence of zero attraction for electrons?

Frequently asked questions

Why can another periodic table list a different atomic radius?

Atomic size has several definitions, including covalent, metallic and van der Waals radii. Compare like definitions before interpreting a discrepancy.

Are periodic trends perfectly monotonic?

No. Subshell filling and pairing produce exceptions. Use the actual reference values rather than drawing an absolute rule from a trend arrow.