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Chemistry Atomic Theory

Chemistry Atomic Theory. Nuclear Equations & Half Life Do Now – Take out HW to check. CALCULATORS OPTIONAL PERIODIC TABLE REQUIRED. Radioactivity. Radioactivity is the spontaneous emission of radiation by an atom. It was first observed by Henri Becquerel .

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Chemistry Atomic Theory

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  1. ChemistryAtomic Theory Nuclear Equations & Half Life Do Now – Take out HW to check. CALCULATORS OPTIONAL PERIODIC TABLE REQUIRED

  2. Radioactivity Radioactivity is the spontaneous emission of radiation by an atom. It was first observed by Henri Becquerel. Becquerel studied light, and how certain substances emitted light after an energy source was removed (think glow-in-the-dark).He used film to study these. Quite by accident, Becquerel put film in the same drawer as some uranium, and found that the uranium exposed the film without light! This is the first exposure to radioactivity.

  3. Marie and Pierre Curie The Curies became obsessed with radioactivity. They discovered many new elements through their constant working with uranium, including polonium, and radium. X-rays and uranium rays (Becquerel rays) were discovered at the same time – the Curies studied the weaker uranium rays.

  4. How We Know Radioactivity Exists • There are four major ways we know radioactivity exists: • A Geigercounter detects Becquerel (uranium) rays. • Cloud chambers • If radiation is in the air, it makes air a conductor. • Radiation makes people ill and can cause cancer. • High energy radiation can mutate DNA, and causes sickness from as little as a sunburn to fatal cancers.

  5. Types of Radiation There are 4 kinds of radiation (Becquerel rays) Alpha particles (Helium nuclei) – Beta particles (electrons) – Gamma rays (high energy waves) Neutrons

  6. Why Are They Radioactive? When the neutron to proton ratio gets too large, the nucleus breaks down – that is why we called them nuclear reactions. The band of stability shows the stable isotopes that don’t break down.

  7. Balancing Nuclear Equations The total mass and the total atomic number must be the same on the left and right sides of the equation. Examples:

  8. Types of Nuclear Reactions Alpha Decay – emission of an alpha particle The alpha decay of seaborgium-263:

  9. Types of Nuclear Reactions Beta Decay – emission of a beta particle (a neutron turns into a proton) The beta decay of tritium, aka hydrogen-3:

  10. Types of Nuclear Reactions Neutron Bombardment – absorption of a neutron, increasing the mass number and releasing energy in the form of a gamma ray. Neutron bombardment of mercury-200:

  11. Half-Life • As a radioactive isotope decays, less of it remains. • The half-life (t1/2) of a radioactive isotope is the amount of time it takes for the isotope to decay by half. • 8 grams of a radioactive substance • After 1 half-life, 4 grams remain. • After 2 half-lives, 2 grams remain. • After 3 half-lives, 1 gram remains • Half-Life Simulation

  12. Half-Life Formulas • Uses a general decay equation • You will learn about these in Algebra II – exponential decay • Formula: • A0 = initial amount • A = final amount • If solving for A or A0, use 1st equation • If solving for time or half-life, use 2ndequation • Can you hit the log button on your calculator? Good – you can use these equations!

  13. Practice A 208 g sample of sodium-24 decays to 13.0 g of sodium-24 within 60.0 hours. What is the half-life of sodium-24?

  14. Practice Gold-198 has a half-life of 2.7 days. How much of a 96 g sample of gold-198 will be left after 8.1 days?

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