Periodicity

Slide 1

• The periodic table
• -Groups are columns
• -Elements in the same group have the same number of electrons in the outer shell.
• -Periods are rows.
• Elements in the same period have the same number of electron shells.
• -First 2 columns, H and He are S block elements.
• -P block elements are on the right side.
• -Elements in the same group have similar properties, e.g. group 1 elements react with water with increasing vigour as we go DOWN the group.
• -The group number relates to the number of electrons in the outer shell, e.g. Group 2 elements have 2 electrons in their outer shell.

Slide 2

• Atomic Radii
• As we go across period 3, the atomic radius decreases.
• There is an increased nuclear charge as there is an increasing number of protons.
• This pulls the outer shell of electrons further in towards the nucleus.
• Crucially, the extra electrons that elements gain across the period go into the same shell. The shielding effect is similar [in each period].
• Atomic radius increases down groups due to extra electron shells added for each element down the group.

Slide 3

• Melting Points
• First 3 elements in period 3 (Na, Mg, Al) are metals. They have metallic bonding.
• There is a general increase in melting points as metal ions have an increasing positive charge, increasing the number of delocalised electrons and smaller ionic radius. This means a stronger metallic bond.

Slide 4

• Melting points
• Silicon has the highest melting point in period 3. It has a giant covalent [macromolecular] structure.
• Many, strong covalent bonds hold the silicon atoms together. A large amount of energy is needed to overcome these strong covalent bonds.

Slide 5

• Melting points
• Phosphorus has the formula P4. It has a lower melting point than Silicon due to a weaker simple molecular structure. Melting point is determined by weaker van der Waals forces.
• Sulphur has the formula S8. It has a higher melting point that Phosphorus due to a larger simple molecular structure. It has larger vdW forces and therefore a higher melting point.

Slide 6

• Melting Points.
• Chlorine has the formula Cl2. It has a lower melting point than Phosphorus and Sulphur due to a smaller simple molecular structure.It has smaller vdw forces and therefore a lower melting point.
• Argon has the formula Ar. It has a lower melting point than the rest of the elements in period 3 due to it only existing as individual atoms. It has smaller vdw forces and therefore a lower melting point.

Slide 7

• Ionisation
• Ionisation energy is the minimum amount of energy required to remove 1 mole of electrons from 1 mole of atoms in the gaseous state.
• Na (g) --> Na+ (g) + e- 1st IE energy = + 495.8 KJmol-1
• Ionisation requires energy, so they are always endothermic processes and have a positive value,
• Always include state symbols.
• Shielding- The more electron shells between the positive nucleus and negative electron that is being removed, the less energy is required. There is a weaker attraction.
• Nuclear Charge- The more protons in the nucleus, the bigger the attraction between the nucleus and the outer electrons. This means more energy is required to remove the electron.
• Atomic SIze-The bigger the atom, the further away the outer electrons are from the nucleus. The attractive force between the nucleus and the outer electrons is reduced so it is easier to remove electrons.