Module 3 Chapter 7

He is one of the main chemists credited with the development of the periodic table

He organised elements by atomic mass He placed elements into groups of which they shared similar chemical properties with He left gaps where no known elements fitted with the chemical properties of the group

60 elements ordered by atomic mass groups with similar properties Properties had to fit, elements swapped and gaps left Assumed incorrect atomic masses and some not discovered Predicted properties of missing elements using group trends

118 elements Vertical groups and horizontal periods Elements arranged in increasing atomic number

They are arranged in increasing atomic number

In each group the elements have atoms with the same number of electrons in the outer shell and similar properties.

The number of the period gives the number of electron shells in the atom

The repeating trend of properties across the period

A lot of the chemistry is determined by electron configuration, particularly the highest energy outer shell.

Ionisation energy Structure Melting points

Across period 2: 2S —> 2P Across period 3: 3S —> 3p Across period 4: 4S —> 3D —> 4P

There are 18 groups in the periodic table

The Pnictogens

The Chalcogens

The alkali metals

The alkaline earth metals

The transition metals

The halogens

The noble gases

The reactivity increases as you go down the group

The atomic radius increases, so the force of attraction between the nucleus and electrons in the outer shell is weaker, therefore it looses its electrons to form ions more easily and is therefore more reactive.

It measures how easily and atom can lose electrons to form positive ions

The energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions.

• Atomic radius • Nuclear charge • Electron shielding