Page 62 - Curriculum Visions Dynamic Book

metals are more common in nonreactive elements such as gold than reactive ones such as calcium.
NATuRAL DyES: Dyes made from plants without any chemical alteration, for example, indigo.
NATuRAL FIBRES: Fibres obtained from plants or animals, for example, flax and wool.
NEuTRON: A particle inside the nucleus of an atom that is neutral and has no charge.
NOBLE GASES: The members of group 8 of the periodic table of the elements: helium, neon, argon, krypton, xenon, radon. These gases are almost entirely unreactive.
NONMETAL: A brittle substance that does not conduct electricity, for example, sulphur or nitrogen.
OIL-BASED PAINTS: Paints that are
not based on water as a vehicle. Traditional artists’ oil paint uses linseed oil as a vehicle.
OPAquE: A substance through which light cannot pass.
ORE: A rock containing enough of a useful substance to make mining it worthwhile, for example, bauxite, the ore of aluminium.
ORGANIC: A substance that contains carbon and usually hydrogen. The carbonates are usually excluded.
OxIDE: A compound that includes oxygen and one other element, for example, Cu2O, copper oxide.
OxIDIzE, OxIDIzING AGENT: A reaction that occurs when a substance combines with oxygen or a reaction in which an atom, ion, or molecule loses electrons to another substance (and in this more general case does not have to take up oxygen).
OzONE: A form of oxygen whose molecules contain three atoms of oxygen. Ozone high in the atmosphere blocks harmful ultraviolet rays from the Sun, but at ground level it is an irritant gas when breathed in and so is regarded as a form of pollution. The ozone layer is the uppermost part of the stratosphere.
PAINT: A coating that has both decorative and protective properties, and that consists of a pigment suspended in a vehicle, or binder, made of a resin dissolved in a solvent. It dries to give a tough film.
PARTIAL PRESSuRE: The pressure a
gas in a mixture would exert if it alone occupied the flask. For example, oxygen makes up about a fifth of the atmosphere. Its partial pressure is therefore about a fifth of normal atmospheric pressure.
PASTE: A thick suspension of a solid in a liquid.
PATINA: A surface coating that develops on metals and protects them from further corrosion, for example, the green coating
of copper carbonate that forms on copper statues.
PERIODIC TABLE: A chart organizing elements by atomic number and chemical properties into groups and periods.
PERMANENT HARDNESS: Hardness in the water that cannot be removed
by boiling.
PETROCHEMICAL: Any of a large group of manufactured chemicals (not fuels) that come from petroleum and natural gas. It is usually taken to include similar products that can be made from coal and plants.
PETROLEuM: A natural mixture of a range of gases, liquids, and solids derived from the decomposed remains of animals and plants.
PHASE: A particular state of matter.
A substance can exist as a solid, liquid, or gas and may change between these phases with the addition or removal of energy, usually in the form of heat.
PHOSPHOR: A material that glows when energized by ultraviolet or electron beams, such as in fluorescent tubes and cathode ray tubes.
PHOTOCHEMICAL SMOG: A mixture of tiny particles of dust and soot combined with a brown haze caused by the reaction of colourless nitric oxide from vehicle exhausts and oxygen of the air to form brown nitrogen dioxide.
PHOTOCHROMIC GLASSES: Glasses designed to change colour with the intensity of light. They use the property that certain substances, for example, silver halide, can change colour (and change chemically) in light. For example, when silver chromide is dispersed in the glass melt, sunlight decomposes the silver halide to release silver (and so darken the lens). But the halogen cannot escape; and when the light is removed, the halogen recombines with the silver to turn back to colourless silver halide.
PHOTOSyNTHESIS: The natural process that happens in green plants whereby the energy from light is used to help turn gases, water, and minerals into tissue and energy.
PIEzOELECTRICS: Materials that produce electric currents when they are deformed, or vice versa.
PIGMENT: Insoluble particles of colouring material.
PITH: The central strand of spongy tissue found in the stems of most plants.
PLASTIC: Material – a carbon-based substance consisting of long chains or networks (polymers) of simple molecules. The word plastic is commonly used only for synthetic polymers. Property – a material is plastic if it can be made to change shape easily and then remain in this new shape (contrast with elasticity and brittleness).
PLASTIC CHANGE: A permanent change in shape that happens without breaking.
PLASTICISER: A chemical added to rubbers and resins to make it easier
for them to be deformed and moulded. Plasticisers are also added to cement to make it more easily worked when used as a mortar.
PLATE GLASS: Rolled, ground, and polished sheet glass.
PLIABLE: Supple enough to be repeatedly bent without fracturing.
PLyWOOD: An engineered wood laminate consisting of sheets of wood bonded with resin. Each sheet of wood has the grain at right angles to the one above and below. This imparts stability to the product.
PNEuMATIC DEVICE: Any device that works with air pressure.
POLAR: Something that has a partial electric charge.
POLyAMIDES: A compound that contains more than one amide group, for example, nylon.
POLyMER: A compound that is made
of long chains or branching networks by combining molecules called monomers as repeating units. Poly means “many,” mer means “part.”
PORCELAIN: A hard, fine-grained, and translucent white ceramic that is made of china clay and is fired to a high temperature. Varieties include china.
PORES: Spaces between particles that are small enough to hold water by capillary action, but large enough to allow water to enter.
POROuS: A material that has small cavities in it, known as pores. These pores may or may not be joined. As a result, porous materials may or may not allow a liquid or gas to pass through them. Popularly, porous is used to mean permeable, the kind of porosity in which the pores are joined, and liquids or gases can flow.
POROuS CERAMICS: Ceramics that have not been fired at temperatures high enough to cause the clays to fuse and so prevent the slow movement of water.
POTENTIAL ENERGy: Energy due to the position of an object. Water in a reservoir has potential energy because it is stored up, and when released, it moves down to a lower level.
POWDER COATING: The application of a pigment in powder form without the use of a solvent.
POWDER FORMING: A process of using a powder to fill a mould and then heating the powder to make it fuse into a solid.
PRECIPITATE: A solid substance formed as a result of a chemical reaction between two liquids or gases.
PRESSuRE: The force per unit area measured in SI units in Pascals and also more generally in atmospheres.
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