Atomic structure, unit for radioactivity, half life calc

⚛ 1. Atomic Structure

🔹 Parts of an Atom

Particle

Charge

Mass

Location

Proton (p⁺)

+1

1

Nucleus

Neutron (n⁰)

0

1

Nucleus

Electron (e⁻)

-1

~0

Electron shells

🔹 Key Points

  • Protons = determine the element

  • Neutrons = determine isotope & contribute to mass

  • Electrons = involved in chemical reactions

  • Neutral atom = number of protons = number of electrons

☢ 2. Unit for Radioactivity

  • Becquerel (Bq) is the unit of radioactivity

  • 1 Bq = 1 decay per second

Key Notes

  • Radioactivity measures how many nuclei decay per second

  • Does not measure danger directly

⏳ 3. Half-Life Calculations

🔹 Definition

  • Half-life = the time it takes for half of the radioactive nuclei to decay

🔹 Stepwise Method

  1. Start with initial amount

  2. Each half-life → divide by 2

  3. Repeat for the number of half-lives

Example:

  • Initial nuclei = 80

  • After 1 half-life → 80 ÷ 2 = 40

  • After 2 half-lives → 40 ÷ 2 = 20

  • After 3 half-lives → 20 ÷ 2 = 10

🔹 Using Equation (Higher Level)

N=N0×(12)tTN = N_0 \times \left(\frac{1}{2}\right)^{\frac{t}{T}}N=N0​×(21​)Tt​

  • NNN = remaining nuclei

  • N0N_0N0​ = initial nuclei

  • ttt = elapsed time

  • TTT = half-life

🔹 Key Tips

  • Step method is safer for exams

  • Radioactive decay graphs are exponentially decreasing

  • Always write units for time & nuclei

🔗 Big Links

  • Atomic structure explains isotopes → some are radioactive

  • Radioactivity measured in Bq

  • Half-life shows rate at which a radioactive sample decays

⭐ Exam Tips

  • Draw nucleus with protons & neutrons clearly labeled

  • Unit = Bq, mention 1 decay per second

  • For half-life questions:

    • Stepwise division is simple & reliable

    • Graph interpretation questions are common