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A solid is a compact substance, created by closely packed atoms that form a regular pattern called a lattice. There are strong forces holding the atoms together, which allow only slight movement. The hardness of a solid depends on the pattern and movement of its atoms. The element carbon, for example, can exist in a soft form called graphite, or in one of the hardest solid forms on Earth, the diamond. The difference is due to variations in the arrangements of atoms.

Text 2 

Metals are a group of elements that share certain properties. They conduct heat and electricity well, which is why cooking pans and electrical wires are made of metal. They are also strong and can be shaped easily; this is why they are used to make structures such as bridges. Although there are many similarities between metals, there are also differences that determine how suitable a metal is for a particular use. Of the 109 elements known today, 87 are metals. They are rarely used in their pure state – they are usually mixed with other metals or nonmetals to form combinations known as alloys.

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Only 22 of the elements are non-metals. The properties of non-metals are usually opposite to those of metals – the other group of elements. For example, they do not usually conduct heat and electricity and they cannot be formed into shapes easily. Useful non-metals include chlorine, which is used in swimming pools to kill germs, and hydrogen, which is a good fuel. Some elements, although classified as non-metals, have characteristics somewhere between those of a metal and those of a non-metal; they are known as semimetals or metalloids.

Text 4 

Many substances form crystals. A crystal is a type of solid matter that always forms the same shape. For example, crystals of common salt always for tiny cubes, and emerald crystals are always hexagonal (six-sided). Crystals often form when molten rocks cool down and solidify or when solutions containing minerals evaporate. Crystals can also be made in the laboratory. Some crystalline substances, such as rubies and diamonds, are used in jewelry. Others are useful in industry; quartz, for example, is used in watches.