Where do the ionisation energy values come from?

From the NIST Atomic Spectra Database, which is the primary reference for spectroscopic data.

Why does ionisation energy dip between Groups 2 and 3?

The Group 3 electron sits in a higher-energy p orbital rather than an s orbital, so it is easier to remove.

Are the elemental composition percentages exact?

They are widely cited approximate values. Body composition varies between individuals; crustal composition varies by region.

What are the physical constants on the Data page exact by definition?

Since the 2019 SI redefinition, seven constants (including Avogadro's number, Planck's constant and Boltzmann constant) are exact by definition.

How is the scale of life chart made?

Sizes are plotted on a base-10 logarithmic scale from 0.1 nm to 1 mm, with positions computed from log₁₀(size).

Data

Numbers you can see
at a glance.

Every chart names what it measures, the unit, and whether it is sourced data or an illustrative model. Every value traces back to a primary source.

Sourced data Highlighted peaks

01 · Composition

What things are made of.

Switch between four systems to see how the same elements recur at every scale — from a single cell to the observable universe.

Human body

Approximate share of body mass

Oxygen
65%
Carbon
18.5%
Hydrogen
9.5%
Nitrogen
3.2%
Calcium
1.5%
Phosphorus
1%

Mostly oxygen, because the body is mostly water. Carbon is the backbone of every organic molecule.

Source: Emsley, J. The Elements, Oxford University Press, 1991.

02 · Ionisation energy

How tightly atoms hold their electrons.

First ionisation energy for elements 1–20. Noble gases spike at each period's end — a full outer shell holds electrons tightly. Select any column to read the exact value.

First ionisation energy, elements 1 to 20

Neon (Ne) 2,081 kJ/mol Noble gas: a full outer shell holds its electrons tightly.

Noble gas (row peak) Other elements

Source: NIST Atomic Spectra Database (physics.nist.gov). Values rounded to nearest kJ/mol. To verify before launch.

03 · Biology at scale

Size and redundancy in living systems.

The scale of life

Typical sizes on a logarithmic scale: each step right is ten times larger

Water molecule

~0.28 nm
DNA helix width

~2 nm
Ribosome

~25 nm
Influenza virus

~100 nm
E. coli bacterium

~2 µm
Red blood cell

~7.5 µm
Human egg cell

~120 µm

0.1 nm 1 mm

Molecules Structures and cells Track runs from 0.1 nm to 1 mm

Codon degeneracy

How many codons encode each amino acid (standard genetic code)

6 codons

LeuSerArg
4 codons

AlaGlyProThrVal
3 codons

Ile
2 codons

AspGluCysGlnHisLysAsnPheTyr
1 codon

MetTrp

Plus 3 stop codons (UAA, UAG, UGA) = 64 codons total. Source: NCBI, transl_table=1.

04 · Physical constants

Exact values, clearly labelled.

All values marked "exact" are exact by definition since the 2019 SI revision. Source: CODATA 2018 / NIST.

Constant Symbol Value Unit Status

Avogadro's number Nₐ 6.022 140 76 × 10²³ mol⁻¹ exact

Gas constant R 8.314 462 618 J mol⁻¹ K⁻¹ exact

Faraday constant F 96 485.332 12 C mol⁻¹ exact

Speed of light c 299 792 458 m s⁻¹ exact

Planck's constant h 6.626 070 15 × 10⁻³⁴ J s exact

Boltzmann constant kB 1.380 649 × 10⁻²³ J K⁻¹ exact

Molar mass of C-12 M(¹²C) 12 × 10⁻³ kg mol⁻¹ exact

Source: CODATA 2018 recommended values, NIST (physics.nist.gov/cuu/Constants). Values marked "exact" are exact by definition since the 2019 SI revision.

Questions about the data

: From the NIST Atomic Spectra Database, which is the primary international reference for spectroscopic and ionisation energy data. Values are given in kJ/mol, rounded to the nearest integer.
: The Group 3 electron (e.g. boron) sits in a higher-energy 2p orbital rather than a 2s orbital, so it is easier to remove than the Group 2 electron despite the higher nuclear charge. See Khan Academy: Periodic trends — ionisation energy for a full explanation.
: They are widely cited approximate values. Human body composition data follows Emsley, J. — The Elements (Oxford University Press, 1991). Crustal composition follows Rudnick & Gao, Treatise on Geochemistry (2003). These are consensus averages, not exact measurements.
: Since the 2019 SI redefinition (BIPM), seven fundamental constants are exact by definition — including Avogadro's number (6.022 140 76 × 10²³ mol⁻¹), Planck's constant and Boltzmann constant. Values are taken from CODATA 2018 / NIST.
: Sizes are plotted on a base-10 logarithmic scale from 0.1 nm (roughly the radius of a hydrogen atom) to 1 mm (visible without a microscope). Typical sizes follow Alberts et al., Molecular Biology of the Cell (NCBI Bookshelf) and the BioNumbers database (Harvard).

Want the story behind a chart?

Every dataset here has a guide that explains what the pattern means and why it matters. Start with ionisation energy or the periodic table.

Go to the guides →

Numbers you can seeat a glance.