The periodic table, Year 7: more practice

Metals are good conductors of heat

提示Think about what has to travel from the hob into the food.

为什么Heat passes quickly through a metal base from the hob to the food. A poor conductor such as plastic would stay cool underneath and cook the food slowly.

Iron

提示Its symbol is Fe.

为什么Iron, cobalt and nickel are the magnetic metals. Copper, aluminium and gold are not, so magnetism is a useful test for iron but not for metals in general.

Solid

提示There is just one well-known exception, and it is not the rule.

为什么Most metals have high melting points, so they are solid at room temperature. Mercury is the exception and is a liquid.

Sonorous

提示Think of a bell, a gong or a cymbal.

为什么Bells and gongs are made of metal because metals ring when struck. Non-metals such as wood or plastic give a dull thud instead.

It resists being scratched or dented

提示Think about what you could do to its surface with a key.

为什么Diamond is very hard because almost nothing can scratch it. Hard is about the surface, and a hard material can still be brittle.

Strong

提示It is about how large a force the material can take before it breaks.

为什么A strong material withstands a big force without breaking. Steel is strong, while chalk is easily crushed even though it feels solid.

Flexible

提示Think about what you can do to it without it snapping.

为什么A flexible material bends and returns, or can be bent, without cracking. It is the opposite of brittle, which snaps when you try to bend it.

No, most are poor conductors (insulators)

提示Compare them with copper wire.

为什么Non-metals such as sulfur, oxygen and plastic carbon compounds do not let electricity pass easily. That is why plastic is used to cover wires.

Graphite

提示It is also a form of carbon, but not the hard, sparkling one.

为什么Graphite is a non-metal that conducts electricity, so it is used in electrodes. It is a famous exception to the rule that non-metals are poor conductors.

It shatters, because solid non-metals are brittle

提示Compare it with how a metal copes with being hammered.

为什么Solid non-metals are usually brittle and break into pieces. Metals are malleable and change shape without breaking.