ATOMS
All matter is made of atoms. An individual atom is far too small to see, even with the most powerful microscope. But atoms joined together make up every solid object, substance, chemical and material in the Universe. A pinhead, for example, contains about one billion billion atoms.
Atoms able to move about make up liquids and gases. Atoms which are more fixed and unable to move much make up solids. Not all atoms are the same. There are about 92 different kinds of atoms that occur naturally. Scientists have made another 17 or so artificial kinds in laboratories. Each kind of atom has individual properties that distinguish it in some way from another kind. A substance made from just one kind of atom is known as a chemical element. Examples of six elements are:
Atoms of different chemical elements have different numbers of particles. Simplest is Hydrogen (1), a very light gas that makes up most of the Sun. Neon (2) is a gas used in coloured strip-lights. Egg yolks are rich in sulphur (3). Calcium (4) is needed for healthy bones. Silver (5) is a shiny valuable metal. Lead (6) has many particles and so is very heavy. It is used to make small weights or shot.
Atoms are not solid, like marbles. In fact, they are mostly empty space. But this space contains even smaller pieces of matter known as subatomic particles. There are three main kinds of subatomic particles – protons, neutrons and electrons. The protons and neutrons are gathered together in the middle of the atom, forming its central part or nucleus. The electrons are much smaller and move at speed around the nucleus. They do not move at random, but stay in certain layers known as shells.
Elements differ in their numbers of subatomic particles. Hydrogen is the simplest because its atom has just two particles, one proton and one electron. In most atoms there are the same numbers of protons as electrons. This is because a proton has a tiny positive electrical charge and an electron has the same amount of negative charge. The two sets of opposite charges balance each other out so the whole atom has no charge. This makes it stable or unlikely to break up.
Picture Credit : Google