Chapter Nineteen - PowerPoint PPT Presentation

Loading...

PPT – Chapter Nineteen PowerPoint presentation | free to view - id: ccee6-ZDc1Z



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Chapter Nineteen

Description:

Chapter Nineteen. Nuclear Chemistry ... Stable nuclides are not radioactive and are not the subject of this chapter. ... Review of isotopes, p, n, e: Chapter 2 ... – PowerPoint PPT presentation

Number of Views:33
Avg rating:3.0/5.0
Slides: 26
Provided by: joea152
Category:
Tags: chapter | nineteen

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Chapter Nineteen


1
Chapter Nineteen
  • Nuclear Chemistry
  • sections 19.1 19.7

2
  • Review
  • Atoms consist electrons, protons, and neutrons.
  • Atoms of elements are distinguished by number of
    protons in nucleus ( atomic number).
  • Isotopes of an element have different numbers of
    neutrons but same number of p and e-.
  • Isotopes of element react identically, in most
    instances.
  • Traditional chemical reactions focus primarily on
    interactions in the outer valence electrons of
    atoms.

3
Now we look at reactions that take place in the
nucleus radioactivity Stable nuclides are not
radioactive and are not the subject of this
chapter. Only the less common naturally
occurring and man-made isotopes that are
radioactive 14C, 32P, 3H (tritium), 86Rn, 60Co,
238U Review of isotopes, p, n, e Chapter 2
4
  • A nucleus with a specified number of protons and
    neutrons is a nuclide.
  • E
  • A mass number (number of P number of n)
  • Z atomic number
  • Together, protons and neutrons are called
    nucleons.

A Z
5
Introduction
  • Radioactivity, or radioactive decay, is the
    spontaneous change of the nuclei of certain
    atoms, accompanied by the emission of subatomic
    particles and/or high-frequency electromagnetic
    radiation.
  • There are five principal ways in which atomic
    nuclei may display radioactivity
  • 1. Alpha emission
  • 2. Beta emission
  • 3. Gamma emission
  • 4. Positron emission
  • 5. Electron capture

6
Types Of Radioactive Decay
  • An alpha (?) particle has the same composition as
    a helium nucleus (42He) two protons and two
    neutrons.
  • Beta (?-) particles are electrons (-10e).
  • Gamma (g) rays are a highly penetrating form of
    electromagnetic radiation (00g).
  • Positrons are particles having the same mass as
    electrons but carrying a charge of 1 (10e).
  • Electron capture (EC) is a process in which the
    nucleus absorbs an electron from an inner
    electron shell, usually the first or second, with
    the release of an X-ray.

7
Nuclear Equations
  • Basic principle in writing a nuclear equation
  • charge, mass number and atomic number must be
    conserved in a nuclear reaction.
  • The two sides of a nuclear equation must have
    the same totals of atomic numbers and mass
    numbers.

8
Three Types of Radiation
9
Summary Of Decay Types
10
Radioactive Decay Series
  • Most of the naturally occurring nuclides of the
    lighter elements have stable nuclei they are not
    radioactive.
  • Many naturally occurring nuclides with high
    atomic numbers are are radioactive.
  • A series of radioactive decays beginning with a
    long-lived radioactive nuclide and ending with a
    non-radioactive one is called a radioactive decay
    series.

11
Radioactive Decay Series For Uranium-238
238U start
238U ? 234Th ? 234Pa? 238U ? 234Th ? 226Rn ?
222Ra ? 218Po ? ? ?
12
Radioactive Decay Rates
  • The radioactive decay law states that the rate of
    disintegration of a radioactive nuclide, called
    the decay rate or activity, A, is directly
    proportional to the number of atoms present.
  • Rate of radioactivity decay (A) ? N
  • - Radioactive decay is a first-order process.
  • - A activity, measured in atom/time or
    disintegration/time, A lt-gt rate
  • - ? - decay constant, ? lt-gt k in the rate of
    reaction.
  • - N number of atoms of radioisotope present, N
    lt-gt conc.
  • Integrated rate law expression
  • Nt 0.690
  • ln ___ - ? t t1/2 ________
  • No ?

13
HalfLife (t1/2)
  • The half-life (t1/2) of a radioactive nuclide is
    the time required for one-half the nuclei in a
    sample of the nuclide to decay.
  • The shorter the half-life t1/2, the larger the
    value of ? (decay constant) and the faster the
    decay proceeds.

14
Selected Nuclide Half-lives
15
An Example
  • Example 19.2
  • The nuclide sodium-24 is used to detect
    constrictions and obstructions in the human
    circulatory system. It emits beta particles.
  • (a) What is the decay constant, in s-1, for
    sodium-24?
  • What is the activity of a freshly synthesized
    1.00-mg (1.00x10-3 g) sample of sodium-24?
  • What will be the rate of decay of the 1.00-mg
    sample after one week (168 h)?

16
Radiocarbon Dating
  • Carbon-14 is formed at a nearly constant rate in
    the upper atmosphere by the bombardment of
    nitrogen-14 with neutrons from cosmic radiation.
    The carbon-14 is eventually incorporated into
    atmospheric carbon dioxide.
  • Carbon-14 in living matter decays by ? emissions
    at a rate of about 15 disintegrations per minute
    per gram of carbon.
  • When the organism dies, no more carbon-14 is
    integrated into the system.
  • The half-life for carbon-14 is 5,730 years. This
    dating method works well if an object is between
    5,000 and 50,000 years old.

17
Synthetic Nuclides
  • For centuries, alchemists tried - without success
    - to change one element into another alchemy
    turn lead into gold.
  • The process of changing one element into another
    is called transmutation.
  • Modern scientists have learned to do this.
  • Rutherford, in 1919, was able to convert
    nitrogen-14 into oxygen-17 plus some extra
    protons by bombarding the nitrogen atoms with a
    particles. This is a naturally occurring isotope
    of oxygen and is not radioactive.
  • 147N 42He ? 178O 11H
  • Phosphorous-30 was the first synthetic
    radioactive nuclide.
  • Since its discovery, scientists have synthesized
    over a thousand others.

18
Transuranium Elements
  • In 1940, the first of the transuranium elements
    - elements with a Z gt 92 - was synthesized by
    bombarding uranium-238 nuclei with neutrons. This
    first element is plutonium.
  • 23892U 10n ? 23992U
  • 23992U ? 23993Np 0-1e
  • 23993Np ? 23994Pu 0-1e

19
Nuclear Stability
  • About 160 stable nuclides have an even number of
    protons and an even number of neutrons.
  • About 50 stable nuclides have an even number of
    protons and an odd number neutrons.
  • About 50 stable nuclides have an odd number of
    protons and an even number neutrons
  • Only four stable nuclides have an odd number of
    protons and an odd number of neutrons.
  • The magic numbers of protons or neutrons for
    nuclear stability are 2, 8, 20, 28, 50, 82, and
    126.

20
Stability of Nuclides
All the stable nuclides lie within the belt of
stability (as do some radioactive ones).
Nuclides outside the belt are radioactive. Their
modes of radioactive decay are indicated.
21
Energetics Of Nuclear Reactions
  • While working out the details of the theory of
    special relativity, Einstein derived the equation
    for the equivalence of mass and energy E mc2.
  • In a typical spontaneous nuclear reaction, a
    small quantity of matter is transformed into a
    corresponding quantity of energy.
  • Nuclear energies are normally expressed in the
    unit MeV (megaelectronvolt).
  • 1 u 931.5 MeV one atomic mass unit contains
    energy equivalent to 931.5 megaelectronvolts.
  • 1 amu 1 u

22
Nuclear Binding Energy
  • The energy released in forming a nucleus from its
    protons and neutrons is called the nuclear
    binding energy and is expressed as a positive
    quantity.
  • Alternatively, nuclear binding energy is the
    quantity of energy necessary to separate a
    nucleus into individual protons and neutrons.
  • This explains why there is a mass loss of 0.0304
    u in the formation of a helium nucleus from the
    two protons and two neutrons which comprise it.
    This quantity is called the mass defect of the
    nucleus.

23
Nuclear Binding Energy For Helium
24
Average Binding Energies
25
Summary
  • The five types of radioactive nuclides involve
    emission of alpha (?) particles, beta (?)
    particles, gamma (?) rays, positrons, and
    electron capture.
  • All known nuclides with Z gt 83 are radioactive,
    and many of them occur naturally as member of
    four radioactive decay series.
  • In the formation of an atomic nucleus from its
    protons and neutrons, a quantity of mass is
    converted into energy.
About PowerShow.com