NUCLEAR CHEMISTRY (Sections 4.4, )

 Notes: Read Section 4.4 in your text. Define all vocabulary words (words in bold). For each type of radiation, include the sample reaction. Add Problem 24 (p 107) to your notes

 Atomic Number tells us:  The identity of the element; the number of protons (and number of electrons in a neutral atom)  Atomic Mass tells us:  The average mass in amu of all naturally occuring isotopes Mass

REVIEW All atoms of the same element have the same number of ______. PROTONS (6 protons = carbon) Elements with different numbers of neutrons are called… ISOTOPES

 REVIEW: Isotope Naming Using the element symbol:

 Chemical v. Nuclear Reactions In a chemical reaction (CHEMICAL CHANGE), atoms gain, lose or share electrons and a new SUBSTANCE is formed.

 Chemical v. Nuclear Reactions In a nuclear reaction, the nucleus of an atom changes and becomes a new ELEMENT.

 Nucleus Stability What particles are in the nucleus? Protons (+ charge) and neutrons (neutral) STRONG NUCLEAR FORCE holds the neutrons and protons together.

 Nuclear Reactions In nuclear reactions, an unstable nucleus changes (LOSES MASS and ENERGY) to become more stable. Stability of a nucleus depends on the ratio of protons (p + ) to neutrons (n 0 )

 Radioactivity Marie Curie ( ) was a Polish scientist whose research led to many discoveries about radiation and radioactive elements. She won 2 Nobel prizes. In 1934 she died from leukemia caused by her long-term exposure to radiation. The element polonium that she helped discover is named after her homeland, Poland

 Radioactivity Marie Curie showed that rays emitted by uranium atoms caused fogging in photographic plates. Marie Curie named the process by which materials give off such rays radioactivity. The penetrating rays and particles emitted by a radioactive source are called radiation.

 Radioactivity DEFINITIONS: Radioactivity – the release or decay of particles or energy caused by the spontaneous disintegration of the atomic nucleus.  Spontaneous: on its own; no energy is required to start it

 Radioactivity Three main types of radioactive decay: Alpha decay Beta decay Gamma radiation

 Summary – 3 Types of Radiation Radiation TypeSymbolMass (amu)Charge 42+ ~0 (very small) 1- 00

 Radioactive Decay – Nuclear Equations Nuclear equations written similarly to chemical reactions Mass numbers and atomic numbers are conserved

 Alpha Decay Alpha particles  are released  is 2 protons & 2 neutrons (a helium nucleus with no electrons) Produced in large nuclei

 Alpha Decay Mass number: 238 = Atomic number: 92 = The new element has two less protons and mass 4 amu less compared with the original atom.

 Balancing Nuclear Equations

 Beta Decay Occurs in elements with more neutrons than protons: a neutron splits into a proton and electron. The proton stays in the nucleus and the electron is emitted.

 Balancing Nuclear Equations

 Gamma Radiation Occurs if nucleus is in an excited state and it releases energy (gamma rays). Usually occurs with alpha or beta decay.

 Gamma Radiation

 Balancing Nuclear Equations

 Alpha particles can be stopped by paper.  Beta particles can be stopped by wood  Most (but not all) Gamma rays can be stopped by lead or thick concrete. Radiation

 Alpha particles are the least penetrating. Gamma rays are the most penetrating. Radiation

 Damage Caused by 3 Types of Radiation Radiation Type ExposureDamage Stopped by clothing and your outer skin layer. Inhaled or ingested Lung cancer (i.e., radon gas) Can penetrate the first few mm of skin or ingested. Stopped by wood. Burns, tissue damage, radiation sickness Can pass through your body. Stopped by lead or thick concrete. Cancer, radiation sickness, tissue and organ damage

1.Certain elements are radioactive because their atoms have  more neutrons than electrons.  an unstable nucleus.  a large nucleus.  more neutrons than protons.

2.An unstable nucleus releases energy by  emitting radiation.  thermal vibrations.  a chemical reaction.  giving off heat.

3.What is the force that holds the neutrons and protons together in the nucleus?  electronegativity  strong nuclear force  gravity  electrostatic force

4.When a radioactive nucleus releases a high-speed electron, the process can be described as  oxidation.  alpha decay.  beta decay.  gamma radiation.

 Homework Problems 7, 8, 9, 11, 12 on p. 814 in your book

 Radioactivity No elements have stable nuclei for atomic numbers above ~83 protons Large elements are reactive because they spontaneously decay to return a nucleus to the band of stability. The most stable isotope is Iron-56

A radioactive nucleus reaches a stable state by a series of steps. Ex: thorium-232 undergoes , ,  decay. Graphic – Wikimedia Commons User Tosaka

 Half-Life A half-life (t 1/2 ): the time required for one-half of the nuclei of a radioactive sample to decay. After each half-life, half of the atoms have decayed into atoms of a new element.

 Half-Life

 Half-Life – Sample Problem

 Homework