Periodicity Properties of the elements of the third period This presentation sets out to describe and explain the properties and patterns displayed by the elements of the third period. You will need to use the information presented here, your text books and various websites you have found to complete a task sheet.

The Patterns The patterns are split into two sets: The Physical Properties this presentation – Atomic and ionic radii – Melting/boiling points – Electrical conductivity The Chemical Properties other resources: textbook, websites – Oxidation states – Reactions with oxygen and the properties of the oxides – Reactions with chlorine and the properties of the chlorides

Physical Properties Atomic radii, in nm – NaMgAlSiPSClAr The radii are decreasing (no value for Ar, not found by normal means) Across a period there is an increasing nuclear charge, but no extra shells The atom is therefore smaller NB This uses the idea of effective nuclear charge – the charge experienced by the outer shell electrons, and therefore the pull experienced by the outer shell. From left to right the effective nuclear charge is growing, with no extra shielding, pulling the outer shell closer to the nucleus, shrinking the atom.

Ionic radii, in nm - Na + Mg 2+ Al 3+ Si P 3- S 2- Cl - Ar What do you notice about the ionic radius vs the atomic radius for the sam element? For metals (+ve)? For non-metals (-ve)? smaller larger Why these patterns? Metals lose electrons, becoming +vely charged, and giving the particle a greater effective nuclear charge. Therefore the valence shell experiences a greater pull from the nucleus and the particle shrinks Also as the valence shell is lost the particle must be smaller. Non metals gain electrons, becoming – vely charged. This reduces the effective nuclear charge, reducing the attraction the nucleus has for the outer shell electrons. Thus the ion is bigger than the atom. Also, there is greater repulsion between the valence electrons so they spread out more to compensate.

Melting points, deg C – NaMgAlSiPSClAr What type of structure does each element have and hence justify their melting points. Na, Mg and Al have metallic structures, giving high mpt. Each successive metal donates an extra electron to the delocalised electrons Giving the ion higher charge and providing more attractions Therefore the mpt increases Si has a giant covalent network which requires lots of energy to break up. The mpt is therefore high. S, P and Cl are simple molecules Non polar molecules Weak temporary dipole – induced dipole interactions Low mpt The mpt is controlled by the size of the molecules (P 4, S 8 and Cl 2 ) Ar has a simple atomic structure Non polar atoms Very weak temporary dipole – induced dipole interactions Very low mpt

Electrical conductivity Na, Mg and Al are metals, so their conductivity is good. What is the pattern from Na to Al? Explain. It increases for Na to Al – each successive metal donates more electrons to the delocalised sea of electrons. Therefore conductivity can get better Silicon is a semi-conductor, so it can conduct electricity, but not very well. (You do not need to explain this) S, P and Cl are simple molecules with no free electrons, they cannot conduct electricity Ar has simple atomic structure, so also has not free electrons to conduct electricity.

Graphical Summary of physical properties Which graph refers to each property discussed? Ionic radii Conductivity Melting point Atomic radii

For the chemical properties of the third period elements refer to other resources such as: Your textbook Websites: