Nuclear chemistry & biochemistry · Topic 14 of 15

Nuclear Chemistry

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Chemistry · nuclear

Nuclear Chemistry

Alpha (helium nucleus), beta (electron) and gamma (energy) come from unstable nuclei; balance mass and atomic numbers; half-life halves the sample each period.

01 · BalancingMass and atomic numbers both balance

02 · Half-lifeHalf-life: half decays each period

03 · ShieldingPaper stops α · metal β · lead γ

What it is

Half-life = time for half the radioactive atoms to decay must know

Fission = a heavy nucleus (U-235) splits into lighter ones + energy

Fission neutrons → chain reaction → nuclear power plants

Fusion = light nuclei join (hydrogen → helium): powers the sun

Parts & jobs

Alpha (α) = helium nucleus ⁴₂He: 2 protons + 2 neutrons, +2 must know

Beta (β) = electron ⁰₋₁e from a neutron turning into a proton must know

Gamma (γ) = high-energy radiation: no mass, no charge must know

The rules

Balance: top (mass) numbers and bottom (atomic) numbers each match must know

Alpha decay: mass number −4, atomic number −2

Beta decay: mass number same, atomic number +1

Gamma emission: no change in mass or atomic number

After n half-lives, (½)ⁿ remains: ½, ¼, ⅛, 1/16

Worked examples

80 g, half-life 6 h, after 24 h: 4 half-lives → 5 g left

²²⁶₈₈Ra → ²²²₈₆Rn + ⁴₂He (226 = 222 + 4; 88 = 86 + 2)

⁹⁰₃₈Sr → ⁹⁰₃₉Y + ⁰₋₁e (90 = 90 + 0; 38 = 39 − 1)

Don't confuse

Nuclear: the nucleus changes (new element) · chemical: bonds only

Stopped by: α paper or skin · β thin metal · γ thick lead or concrete

Fission or fusion?

Commonly confused

	Fission	Fusion
What happens	A heavy nucleus splits	Light nuclei join
Typical fuel	Uranium-235	Hydrogen
Where you find it	Nuclear power plants	The sun
What drives it	Neutrons → chain reaction	Extremely high temperatures

Common mistakes

Alpha: least penetrating, most ionizing — worst inside the body

More detail

Show 3 more facts

Positron ⁰₊₁e: atomic number −1, mass number same

Carbon-14 dating (half-life ~5,730 years) ages once-living material

Control rods (boron, cadmium) absorb neutrons to slow fission

Pearl

Paper stops alpha, thin metal stops beta, and only thick lead or concrete slows gamma.

Sources · OpenStax Chemistry 2e §21.2 Nuclear Equations · OpenStax Chemistry 2e §21.3 Radioactive Decay · OpenStax Chemistry 2e §21.6 Biological Effects of Radiation · OpenStax Chemistry 2e §21.4 Transmutation and Nuclear Energy · Union Test Prep — HESI Chemistry study guide, page 4 (nuclear chemistry: alpha, beta, gamma) · NurseHub — HESI A2 Chemistry review: Nuclear Chemistry lesson · Built from the verified NurseSavvy HESI A2 fact map (facts reviewed 2026-10-16). HESI is a trademark of Elsevier; NurseSavvy is not affiliated with Elsevier.

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