Elementary atomic structure

All matter is made up of tiny particles known as atoms. There are only about a hundred different kinds of atoms, and they combine with each other in different ways to form groups called molecules. All matter is composed of atoms or molecules and some knowledge of how atoms are made will give us valuable information about the behaviour of matter.

In 1911, Rutherford in England discovered that an atom has a tiny nucleus which is positively charged and contains nearly all the mass of the atom. Distributed about the nucleus and revolving about it in orbits are much less massive negatively charged particles called electrons.

In a normal atom, there are exactly as many negatively charged electrons as are needed to neutralize the positive charge of the nucleus, so that the atom as a whole is electrically neutral. This is of course also true of all normal material substances, which are composed of atoms. The outermost electrons are less strongly bound to the atom than the inner ones, and there are the ones that take part in chemical reactions between atoms and that are responsible for the accumulation of an electric charge on bodies.

Words to be remembered:

matter

tiny

combine

behaviour

nucleus

charge

distribute

revolve

substance

outermost

bind /bound/

inner

to be responsible for

accumulation

вещество, материя

крошечный

соединять/ся/

поведение

ядро

заряд; заряжать

распределять

вращаться

вещество

крайний

связывать

внутренний

отвечать за

накопление

№ 10

Magnets and magnetic fields (I)

The ancient Chinese knew that pieces of certain natural iron ores, when suspended by a string, take a definite position with one end pointing approximately north and the other approximately south. It is clear from the behaviour of the magnetic compass of loadstones and other magnets, both natural and artificial.

We can use the magnetic field of the earth to magnetize steel rods if we hold them in the direction of the magnetic field of the earth and hitting them repeatedly with a hammer. The violent impacts shake the tiny particles of the rod and orient them, at least partially, in the direction of the field. As a matter of fact, all steel objects possess a certain small degree of magnetization induced by the terrestrial magnetic field.

If we bring two magnetized steel rods close together, we find the ends pointed the same way during the magnetization process, to repel each other and if one of the rods is turned around, the ends of the rods attract one another.

This behaviour shows that a long piece of magnetized material – a steel bar, or a compass needle - shows its magnetic properties most strongly in regions near its ends, known as the poles of the magnet. It also shows that like poles, i.e. poles that point toward the same direction, repel each other and that unlike poles attract. It is interesting to notice that the magnetic pole of the earth located near its geographic north pole is actually its magnetic south pole, and vice versa.

Words to be remembered:

ore

suspend

string

point

approximately

loadstone

steel rod

violent

impact

at least

partially

terrestrial

repel

steel bar

needle

vice versa

руда

подвешивать

веревка

указывать

приблизительно

природный магнит

стальной стержень

сильный

удар, толчок

по крайней мере

частично, отчасти

земной

отталкивать

стальной брусок

игла

наоборот

№ 11