The periodic table, Year 8: more practice

Iron

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

The whyFe 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

HintIt counts the protons in each atom.

The whyEach 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)

HintThink of a group as a family.

The whyElements 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

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

The whySodium and water make sodium hydroxide and hydrogen. The fizzing you see is the hydrogen bubbling out.

They are less dense than water

HintCompare them with a stone, which sinks.

The whyMost metals are denser than water and sink. Group 1 metals are unusual because they are light for their size.

Low

HintThey are soft enough to cut with a knife.

The whySodium 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)

HintThe name of the new compound ends in -ide.

The whyA Group 1 metal and a halogen join to make a salt. Sodium chloride is the same salt that seasons food.

2

HintThe halogens go around in pairs.

The whyChlorine is written Cl2: two chlorine atoms bonded together. Fluorine, bromine and iodine are also pairs.

Fluorine

HintThe compound name comes from the name of the element.

The whyFluoride 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

HintThink about what could happen near a flame.

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