3.2.1 Periodicity

Elements in the periodic table are arranged by what number?

Proton number

What are the horizontal rows on the periodic table called?

Periods

What are the vertical columns on the periodic table represent?

Groups

What does the group number indicate about an element?

Number of outer electrons.

What are the four blocks on the periodic table?

s-, p-, d-, f- blocks

What elements are in each block of the periodic table?

s-block = group 1 & 2

p-block = group 3 to 0

d-block = transition metals

f-block = radioactive elements

What is the study of trends within the periodic table called?

Periodicity

True or False?

Atomic radius increases when moving across a period from left to right.

False

Why does atomic radius decrease along a period?

Increased nuclear charge for same number of electron shells.

Means outer electrons pulled closer to nucleus → reduced atomic radius

What is the trend in ionisation energy along a period?

ionisation energy increases.

Why does ionisation energy increase along a period?

Atomic radius decreases, therefore nuclear charge increases.

Means outer electrons more attracted to nucleus, so more energy is needed to remove outer electron.

What does mp of Period 3 elements depend on?

• Structure of the element

• Bond strength

What happens to mp across period 3 between Na & Al?

Na, Mg, Al are all bonded metallically. Mp increase due to greater positive charge of ions. (Na = +1, Mg = +2)

Means more electrons released in the form of free electrons.

Increases attractive electrostatic forces from Na to Al, so more energy required to break them.

Why does mp increase drastically for Si in period 3?

Si has strong covalent structure.

Means more energy is required to break strong covalent bonds.

Why does mp decrease in Period 3 between P & Cl?

P, S, Cl are all simple covalent molecules with weak van der waals forces.

Less energy need to overcome them.

Why does Ar have a lower mp than Cl?

Ar is a noble gas that exists as individual atoms with a full outer shell of electrons.

Makes atom very stable and van der waals forces between them are very weak.

Less energy is needed to overcome them.

Ar → gas at room temp

What is the trend in atomic radius going down a group?

Atomic radius increases

Why does atomic radius increase down a group?

Down the group, more electron shells.

Increases distance between outer electrons and nucleus, reducing power of attraction.

More shells also increases electron shielding, inner shells create a ‘barrier’ that blocks the attractive forces.

Nuclear attraction reduces and atomic radius increases.

What is the trend in ionisation energy going down a group?

Ionisation energy decreases.

Why does ionisation energy decrease going down a group?

Nuclear attraction between nucleus and outer electrons reduces and shielding also increases.

Means less energy is required to remove outer electron.