I Used To Know That Part 6

PERIODIC TABLE OF THE ELEMENTS.

The elements are traditionally designated by a one-, two-, or three-letter abbreviation, as you can see in the table, and there are 118 of them. The table above lists 103; listed below them are elements 104 through 118. From 93 upward the elements don't occur naturally but have been synthesized in particle accelerators. The last few are recent achievements, and they have temporary names based on their atomic numbers. Element 117, which will be called Ununseptium, hasn't been synthesized yet, but scientists are working on it. The lanthanides and actinides are usually separated from the rest of the table, as shown above, because-unlike the other rows-they have similar properties as you read across.

104 Rutherfordium Rf

105 Dubnium Db

106 Seaborgium Sg

107 Bohrium Bh

108 Ha.s.sium Hs

109 Meitnerium Mt

110 Darmstadtium Ds

111 Roentgenium Rg

112 Ununbium Uun

113 Ununtrium Uut

114 Ununquadium Uuq

115 Ununpentium Uup

116 Ununhexium Uuh

117 Ununseptium Uus

118 Ununoctium Uuo

* ACIDS, BASES, AND SALTS An acid is a substance (often sour and corrosive) that contains hydrogen atoms that, when dissolved in water, dissociate into ions and may be replaced by metals to form a salt.

A base is a compound that combines with an acid to form a salt plus water. Bases that are soluble in water are called alkalis. Many bases are oxides (so their formula ends in O, possibly with a little number after it) or hydroxides (OH).

A salt is a (usually crystalline) solid compound formed from the combination of an acid and a base by the replacement of hydrogen ions in the acid by positive ions in the base.

For example, combine sulphuric acid with the base cupric oxide in the right conditions and you have copper sulphate (that lovely bright blue stuff) and water:H2SO4 + CuO CuSO4 + H2O.

In a school lab you test whether a substance is an acid or a base with litmus paper. Acids turn litmus red; bases turn it blue. Serious scientists use the pH-potential of hydrogen-which is measured by sensors and electrodes and such. Pure water has a pH of 7, with anything less considered acidic and anything higher alkaline. Gardeners use this as a way of testing soil; you also sometimes see the pH listed on shampoo bottles.

Another term you might remember-and one worth mentioning here-is valency, which means the number of atoms of hydrogen that an atom or group displaces when forming a compound. Hydrogen has a valency of 1 and oxygen a valency of 2, which is why the formula for water is H2O and not just HO-because you need two atoms of hydrogen to "match" one of oxygen. Copper can have either of two valencies, which is why the one mentioned a moment ago is called cupric oxide, not just copper oxide. There's also cuprous oxide, CuO2.

* OXIDATION Oxidation is a commonly quoted chemical reaction, and the most common example of it is rust. In fact, anything that reacts when it comes into contact with oxygen is being subjected to oxidation: The green coating on an old copper coin is the result of oxidation; the browning of fruit is caused by oxygen burning away at the stuff that is released when you peel off the protective skin. Rust is, strictly speaking, the oxide that forms on iron or steel. Stainless steel doesn't rust, because it is protected by a layer of chromium, which doesn't react to oxygen in the same way.

* DIFFUSION AND OSMOSIS Molecules are constantly in motion and tend to move from regions where they are in higher concentration to regions where they are less concentrated-a process known as diffusion. Diffusion can occur in gases, in liquids, or through solids.

Osmosis is a form of diffusion that is specific to the movement of water. Water moves through a selectively permeable membrane (that is, one that lets some types of molecules through but not others) from a place where there is a higher concentration of water to one where it is lower.

In any form of diffusion, when the molecules are evenly distributed throughout a s.p.a.ce, they have reached equilibrium.

* BOILING AND FREEZING POINTS If the temperature is low enough, every known substance except helium becomes a solid. The temperature at which this happens is called its freezing point. Above its freezing point a substance is a liquid. At the other end of the scale, if the temperature is high enough, it becomes a gas, and this is called the boiling point.

Solid is the only state in which a substance retains its shape; a liquid a.s.sumes the shape of its container but does not necessarily fill it; a gas expands to fill the s.p.a.ce available.

Take water, for instance. In its solid state, it is ice and retains its shape-whether ice cube, icicle, or iceberg-until the temperature rises sufficiently for it to melt and become liquid (water). If you take a tray of melted ice cubes and pour the water into a pan, it will take the shape of the container-that is, spread out to cover the bottom-but it may only come a certain distance up the side. If, however, you then turn on the heat under the pan, put a lid on it, and boil the water, it will turn into gas (steam), fill the pan completely, and probably seep out under the lid as well.

Nonscientists commonly measure temperature according to one of two scales: Celsius and Fahrenheit, both named after the people who invented them. Celsius was also once called centigrade, from the Latin for one hundred degrees.

The freezing point of water is 0C, and its boiling point is 100C. The equivalent in Fahrenheit is 32F and 212F. This means that the difference between freezing and boiling is 100C and 180F (212 - 32).

To convert Celsius to Fahrenheit, you need to divide by 100 and multiply by 180, which can also be expressed as multiplying by 1.8, or . Then, because the freezing point of water is 32F, not 0F, you need to add 32:15C x 1.8 = 27; 27 + 32 = 59F.

To reverse the process, first deduct 32 from your Fahrenheit temperature, then divide by (or multiply by ; it's the same thing):104F - 32 = 72; 72 x = 40C.

This works for any temperature above freezing.

There are two other scales used by scientists-the Reaumur and the Kelvin. According to Rene Antoine Ferchault de Reaumur, water freezes at 0 and boils at 80. Kelvin is interesting because he invented the concept of absolute zero, a temperature at which particles cease to have any energy-so a scientific impossibility, although in the laboratory, scientists have achieved temperatures within a millionth of a degree of it. Absolute zero is 0K, or -273.15C, which is very, very cold. Imagine how much energy you would have at that temperature.

Physics

Physics deals with the properties and interactions of matter and energy, but its theories are constantly being redefined as physicists discover new things.

* OPTICS Optics is all about light and there are several terms that may ring a bell.

Remember "The angle of incidence equals the angle of reflection"? You probably do. But do you remember what it means? Well, the angle of incidence is the angle at which light hits a surface; with specular (mirrorlike) reflection the light is reflected at the same angle. If the surface is rough, you get diffuse reflection, which means that the light bounces off in all directions.

Light may also pa.s.s through a medium-such as gla.s.s or water-and be refracted (change direction). This is because of the difference in the velocity with which light pa.s.ses through the two different media (say, air and water), which is measured by the refractive index.

* CONDUCTION, CONVECTION, AND RADIATION There are three ways in which heat is transferred: Conduction can occur in solids, liquids, or gases and means (more or less) that a cool thing is warmed up by coming into contact with a hot thing. The different levels of conductivity in metals are reflected in their uses in anything from the science lab to kitchenware: Copper, for example, is highly conductive, and therefore it works well for fast cooking (although it may react with certain foods, which is why copper-bottomed pans are often lined with tin); whereas cast iron heats slowly but then cooks evenly.

Convection occurs in liquids and gases and is the basis of the principle that hot air rises. A hot liquid or gas is generally less dense than a cool one; as the hot particles rise, cooler ones rush in underneath to take their place. As the hot particles rise, they cool and come down again, and so on.

Radiation involves the energy that all objects, hot or cold, emit. It is the only one of the three that works in a vacuum and is how the sun's rays manage to warm the Earth from such a far distance away.

Heat is not the only commodity that is transferred in these ways. There is also electrical conduction, ma.s.s convection (of which evaporation is an example), and electromagnetic radiation. So, strictly speaking, you should insert the words "heat" or "therma" in front of conduction, convection, and radiation if that is what you mean.

* PHYSICAL LAWS Physics is based on properties that explain what matter and energy can or can't do; without these interactions the universe would probably fall apart. From the observation of the interactions, laws were developed. Some of the physical processes and phenomena are revealed in this section. But a few definitions might help first.

Ma.s.s is the quant.i.ty of matter a body contains. Newton defined it more precisely by bringing in inertia, which is "a property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless that state is changed by an external force." All this means is that a thing will sit still until you push it.

Force is calculated by multiplying ma.s.s by acceleration and concerns producing motion in a stationary body or changing the direction of a moving one.

Velocity is speed (the dictionary says, "measure of the rate of movement," but most people call that speed) in a given direction.

Acceleration is the rate of increase in velocity.

Work is the exertion of force overcoming resistance (which might be electrical resistance, or it could be physical resistance, such as friction).

And, regardless of what anyone else may tell you, in this context a body is a thing. The dictionary says, "an object or substance that has three dimensions, a ma.s.s, and is distinguishable from surrounding objects."

* THE LAWS OF THERMODYNAMICS Thermodynamics is the study of heat and its relationship with other forms of energy, and it is important in the study of heat engines such as gas-driven motors and gas turbines.

The other key term here is entropy, which is defined as "a measure of the disorder of a system." A solid has less entropy than a liquid, since the const.i.tuent particles in a solid are in a more ordered state. The flow of energy maintatins order and life. Entropy states the opposite. Entropy takes over when energy ceases.

If you have managed to follow along this far, then you are ready for the three laws of thermodynamics:1. Energy can change from one form to another, but it can never be created or destroyed.

2. In all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will be less than that of the initial state.

3. As the thermodynamic temperature of a system approaches absolute zero, its entropy approaches zero.

The British scientist and author C. P. Snow came up with a great way of remembering the three laws:1. You cannot win (you cannot get something for nothing, because matter and energy are conserved).

2. You cannot break even (you cannot return to the same energy state, because there is always an increase in disorder).

3. You cannot get out of the game (because absolute zero is unattainable).

Moving swiftly on.

* THE LAWS OF CONSERVATION OF ENERGY AND Ma.s.s The most common of these laws states that energy in a closed system cannot be created or destroyed (it's similar to the first law of thermodynamics), and nor can ma.s.s. At a more advanced level, similar laws apply to electric charge, linear momentum, and angular momentum, but most people never get that far.

* NEWTON'S THREE LAWS OF MOTION 1. A body remains at rest or moves with constant velocity in a straight line unless acted upon by a force.

2. The acceleration (a) of a body is proportional to the force (f) causing it: f = ma, where m is the ma.s.s of the body in question.

3. The action of a force always produces a reaction in the body, which is of equal magnitude but opposite in direction to the action.

Newton also came up with a law of gravity, which states that the force between two bodies is directly proportional to the product of their ma.s.ses and inversely proportional to the square of the distance between them. The universal gravitational constant that makes this equation work is called G, and its value is 6.673 x 10-11 newton m2 per kg2.