Walking Science Facts
These are the famous magnitudes from Dr. Laude's OnRamps list. Knowing them cold lets you sanity-check an answer — or skip the calculation entirely — on an exam.
Key Facts to Memorize
Mass of one atom
About 10⁻²³ g, which is 10⁻²⁶ kg.
Mass of an electron
About 10⁻³⁰ kg — roughly 2000 times lighter than a proton or neutron, which have about the same mass as each other.
Visible light
About 300–700 nm, or roughly 10⁻¹⁸ J per photon.
Electronegativity range
1 to 4, stepping by about 0.5 across the second row. Hydrogen is the exception at 2.2.
Hydrogen bond strength
About 20 kJ/mol per hydrogen bond.
ΔH(vap) of water
About 40 kJ/mol — two hydrogen bonds at roughly 20 kJ/mol each.
ΔH(vap) of methanol
About 35 kJ/mol — one hydrogen bond plus some dispersion forces.
ΔH(vap) ranges
Gases 1–10 kJ/mol; small organics around 30 kJ/mol; heavy hydrogen bonding above 40 kJ/mol.
Heat capacity
Liquid water 4 J/g°C; ice and water vapor about 2 J/g°C.
Density
Water 1 g/mL; air is about 1000 times less, roughly 1.3 g/L.
Bond breaking
Always endothermic — it always costs energy to break a bond.
Covalent bond energies
Single about 400 kJ/mol, double about 600 kJ/mol, triple about 800 kJ/mol.
RT (energy units)
About 2.5 kJ/mol at room temperature.
RT (liter-atm units)
About 25 L·atm/mol at room temperature.
Molar volume at STP
An ideal gas occupies 22.4 L per mole.
Al says…
You are not memorizing exact values, you are memorizing the size of things. If your answer for an atom's mass comes out at 10⁻³ g, you already know it's wrong.
Practice This Topic
External Tools
- Blooket review game
Coming soon — Mrs. Cauthron will post the game link here.
- UT OnRamps Chemistry
The course these 'walking facts' come from.