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The periodic table
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The periodic table puts all the elements in order. Elements in the same column behave in similar ways.
Mendeleev's table
In 1869 Dmitri Mendeleev arranged the elements in order of their atomic mass, and put elements with similar properties in the same column.
He left gaps for elements not yet discovered and predicted their properties. When those elements (such as germanium) were found, his predictions were very close, so scientists accepted his table.
He left gaps for elements not yet discovered and predicted their properties. When those elements (such as germanium) were found, his predictions were very close, so scientists accepted his table.
Groups and periods
A group is a column. Elements in the same group have similar chemical properties.
A period is a row.
Metals are on the left and in the middle; non-metals are on the right.
Metals are usually shiny, good conductors of heat and electricity, and malleable. Non-metals are usually dull, brittle when solid, and poor conductors.
Metal oxides are bases (those that dissolve make alkalis). Non-metal oxides that dissolve in water make acids.
A period is a row.
Metals are on the left and in the middle; non-metals are on the right.
Metals are usually shiny, good conductors of heat and electricity, and malleable. Non-metals are usually dull, brittle when solid, and poor conductors.
Metal oxides are bases (those that dissolve make alkalis). Non-metal oxides that dissolve in water make acids.
Patterns in groups
Group 1, alkali metals (lithium, sodium, potassium): soft metals that react with water to make hydrogen and an alkaline solution. They get more reactive down the group.
Group 7, halogens (fluorine, chlorine, bromine, iodine): non-metals that get less reactive down the group.
Group 0, noble gases (helium, neon, argon): very unreactive.
Group 7, halogens (fluorine, chlorine, bromine, iodine): non-metals that get less reactive down the group.
Group 0, noble gases (helium, neon, argon): very unreactive.
Rubidium is below potassium in group 1. Predict how it reacts with water compared with potassium.
- Group 1 metals get more reactive down the group.
- Rubidium is lower than potassium.
Answer: Rubidium reacts even more vigorously with water than potassium.
Mendeleev ordered elements and left gaps for undiscovered ones. Groups are columns with similar properties; periods are rows. Metals on the left, non-metals on the right. Group 1 more reactive down; group 7 less reactive down; group 0 unreactive.
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