Chapter 9 chemistry note

·         Isotopes are atoms of the same element that have different numbers if neutrons.

·         Most naturally occurring isotopes up to atomic number 19 have stable nuclei.

·         Elements with atomic numbers 20 and higher usually have one or more isotopes that have unstable nuclei, in which nuclear forces cannot offset the repulsions between the protons.

·         An unstable nucleus is radioactive, which means that it spontaneously emits small particles of energy, called radiation, to become more stable.

·         Radiation may take the form of particles such as alpha and beta particles, positrons, or pure energy such as gamma rays.

·         An alpha particle is identical to a helium (He) nucleus, which has 2 protons and 2 neutrons.

·         An alpha particle has a mass number of 4, an atomic number of 2, and a charge of 2+.

·         A beta particle is an electron that is emitted when a neutron in an unstable nucleus changes to a proton and electron. A beta particle has a charge of 1- and a mass number of 0.

·         A positron has a positive 1+ charge with a mass number of 0, which makes it similar to a beta particle.

·         Gamma rays are high energy radiation, released when an unstable nucleus under-goes a rearrangement of its particles to give a more stable, lower energy nucleus.

·         When radiation strikes molecules in its path, electrons may be knocked away, forming unstable ions.

·         The cells most sensitive to radiation are the ones undergoing rapid division- those of the bone marrow, skin, reproductive organs, and intestinal lining, as well as all cells of growing children.

·         Cancer cells are another example of rapidly dividing cells.

·         Alpha particles, the heaviest of the radiation particles, travel only a few centimeters in the air before they collide with air molecules, acquire electrons, and become helium atoms. A piece of paper, clothing, and our skin provide protection against alpha particles.

·         Beta particles move much faster and farther than alpha particles, traveling as much as several meters through the air. They can pass through paper and penetrate up to 4 to 5 mm into body tissue.

·         Gamma rays travel great distances through the air and pass through many materials, including body tissues. Because gamma rays can penetrate so deeply, exposure to these rays is extremely dangerous.

·         Symbols:

o   Alpha: α               Mass number:4                Charge: 2+

o   Beta: β                   Mass number: 0               Charge: 1-

o   Positron: β⁺                         Mass number: 0               Charge 1+

o   Gamma Ray: γ      Mass number: 0               Charge: 0

o   Proton: p               Mass number: 1               Charge: 1+

o   Neutron: n             Mass number: 1               Charge: 0

·         When radiation strikes molecules in its path, electrons may be knocked away, forming unstable ions.

·         The cells that are most sensitive to radiation are the ones undergoing rapid division: bone marrow, skin, reproductive organs, and intestinal lining, as well as all cells of growing children.

·         Alpha particles, the heaviest of the radiation particles, travel only a few centimeters in the air before they collide with air molecules, acquire electrons, and become helium atoms. Paper, clothing, and skin protect us from alpha particles. Dangerous if inhaled due to high ionization.

·         Beta particles move much faster and farther than alpha particles, traveling as much as several meters through the air. They can pass through paper and penetrate as far as 4-5 mm into the body tissue. External exposure can burn the surface of the skin. Use heavy clothing such as lab coats and gloves.

·         Gamma rays travel great distances through the air and pass through many materials including body tissues. Exposure is extremely hazardous, lead or concrete are required to stop them.

·         When a nucleus spontaneously breaks down by emitting radiation, the process is called radioactive decay.

o   Radioactive nucleus ànew nucleus + radiation (α β β+ γ)

§  It’s shown as a nuclear equation using the symbols for the radioactive nucleus, the new nucleus, the new nucleus, and the radiation emitted.

·         In a nuclear equation, the mass numbers and the atomic numbers must balance so the number of protons and neutrons are equal on both sides. It is often a change in the number of protons, which gives a different element.

·         An unstable nucleus undergoes alpha decay by emitting an alpha particle. Because an alpha particle consists of 2 protons and 2 neutrons, the mass number decreases by 4, and the atomic number decreases by 2.