The periodic table, Year 8: more practice

Iron

提示The symbol comes from its Latin name, not the English one.

为什么Fe comes from ferrum, the Latin word for iron. Some symbols do not match the English name, so it pays to look them up on the table.

Atomic number

提示It counts the protons in each atom.

为什么Each element has one more proton than the one before it, so atomic number goes up by one from box to box. Mendeleev first ordered them by mass, but atomic number is the modern rule.

Similar chemical properties (they react in similar ways)

提示Think of a group as a family.

为什么Elements in a group behave alike, so knowing one member lets you predict the others. For example, lithium, sodium and potassium all react with water.

Hydrogen

提示It is the gas that gives a squeaky pop with a lit splint.

为什么Sodium and water make sodium hydroxide and hydrogen. The fizzing you see is the hydrogen bubbling out.

They are less dense than water

提示Compare them with a stone, which sinks.

为什么Most metals are denser than water and sink. Group 1 metals are unusual because they are light for their size.

Low

提示They are soft enough to cut with a knife.

为什么Sodium melts at about 98 °C, but iron needs over 1500 °C. Their low melting points and softness set Group 1 apart from the typical metal.

Sodium chloride (common salt)

提示The name of the new compound ends in -ide.

为什么A Group 1 metal and a halogen join to make a salt. Sodium chloride is the same salt that seasons food.

2

提示The halogens go around in pairs.

为什么Chlorine is written Cl2: two chlorine atoms bonded together. Fluorine, bromine and iodine are also pairs.

Fluorine

提示The compound name comes from the name of the element.

为什么Fluoride compounds help make tooth enamel stronger against decay. Fluorine itself is a dangerous gas, but its compounds are safe in tiny amounts.

Helium is unreactive and will not burn, whereas hydrogen can catch fire or explode

提示Think about what could happen near a flame.

为什么Both gases are lighter than air, but hydrogen burns explosively. Helium belongs to the noble gases, which hardly react at all, so it is safe.