Chapter 4. 8-E.

Polymers and Composites. Straight chain: a chain of carbon atoms that doesn’t branch or circle. Branched chain: a chain that branches. Carbon rings: a ring of carbons.

Carbon compounds form polymers. Polymer: a large complex molecule built from smaller molecules joined together. Monomers: smaller molecules joined together to form polymers. Polymers form when chemical bonds link large numbers of monomers in a repeating pattern.

Types of polymers. Plant polymers: made from cellulous; a flexible but strong polymer that gives shape to plant cells. Plant polymers are natural. Animal polymers: polymers produced by animals for survival. Example: spider web. Synthetic polymers: polymers made from simpler substances. Plastics- synthetic polymers that can be molded or shaped that consists of oil and coal.

Composites. Combine two or more substances as a new material with different properties. Uses the best properties of those substances. Natural composite: composites formed and found in nature. Example: a tree has cellulose and lignin that combine to support the tree. Synthetic composites: two or more man-made polymers combined to form a better polymer. Example: fiber glass.

Metals and alloys. – Alloys: a substance made of two or more elements that have the [properties of metals. – Properties of alloys: combine the best properties of the metals used; usually stronger than the individual metals. And less likely to react with air or water. – Properties of metal: shiny, hard, malleable, and ductile.

Ceramics and Glass Ceramics- Hard crystalline solids made by heating clay and other minerals to high temperatures Properties and uses of ceramics- they resist moisture, do not conduct electricity, and can withstand temperatures of molten metal. Glass- Clear solid material with no crystal structure, made by heating sand. Different materials may be added to glass to make it useful for other purposes. Example: using lead oxide to make glass that bends light. Optical fiber- thread like piece of glass that can be used for transmitting light.

Nuclear reactions Nuclear reactions- reactions involving the particles in the nucleus of the atom. Isotopes- Atom with the same number of protons but different number of neutrons. Mass Number- Sum of the protons and neutrons in the nucleus of an atom. Radioactive decay- release of fast moving particles and energy from the unstable isotopes of an atomic nuclei. Radio active decay produces alpha, beta and gamma decay, all nuclear radiation.

Alpha Particle Alpha Particle- consist of 2 protons and 2 neutrons. Increases the atomic number by 4 and decreases by 2. Move fast but cannot penetrate anything. Can cause injuries such as burns.

Beta particles When a neutron of an unstable atom breaks apart. Electrons are given off by the nucleus, so nucleus has one less neutron and one less proton. Because of this, it changes into a new element because the atomic number increases by one. Beta can travel faster than alpha, and can pass through an aluminum sheet, and human skin. Damages cells.

Gamma rays. H igh energy waves. The most penetrating type of radiation, gammas can pass through anything up to a one meter thick wall of concrete or several centimeters of lead. Can pass through a human body causing severe damage to cells.

Half Life The length of time needed for half the mass of a radioactive sample to decay. Half lives of certain radioactive isotopes are useful in determining the age of rocks and fossils in a process called radioactive dating.

Use of radioactive materials Tracers- radioactive isotopes that can be followed through a step of a chemical reaction in an industrial process. Uses in industry include detecting small cracks in the metal of bridges and building frames, and detecting flaws in metal.

Uses in medicine Include x-rays, tracers,and radiation therapy. Radiation therapy- is where radioactive elements are used to destroy unhealthy cells, such as cancer.

Nuclear Power Nuclear reactions- release enormous amounts of energy allowing them to be used to create electrical power. Safe use of radioactive material- because of the dangers, radioactive materials must be carefully managed.