M3 Periodicity Q&A

• Atomic radius decreases • Number of protons increases, or nuclear charge increases • Outer electrons in the same shell so experience the same shielding • Outer electrons are more strongly attracted to nucleus so pulled closer to the nucleus

• Melting point increases • Na, Mg and Al are all giant metallic; metallic bonding is electrostatic attraction between positive ions and delocalised electrons • Ionic charge increases: Na+, Mg2+, Al3+ across the period • (Ions also get smaller so charge density increases) • Number of delocalised electrons increases • Attraction between positive ions and delocalised electrons increases • More heat energy is needed to break the metallic bonds

• Silicon is giant covalent • All strong covalent bonds between atoms • Lots of heat energy needed to break the covalent bonds

• Phosphorus, P4, sulphur, S8, and chlorine, Cl2 are all simple covalent/molecular • They have weak induced dipole-dipole interactions between molecules (intermolecular forces) • All have low melting and boiling points are little heat energy is needed to overcome induced dipole-dipole interactions • S8 has the highest melting/boiling point as it has the most electrons (biggest molecules) so the induced dipole-dipole interactions between molecules are stronger • Cl2 has the lowest melting/boiling point as it has the least electrons (smallest molecules) so the induced dipole-dipole interactions between molecules are weaker • More heat energy needed to overcome intermolecular forces in S8, less energy needed to overcome forces in Cl2 If asked to compare the melting point of a giant covalent substance to a simple covalent substance, you must include the term ‘intermolecular’ for the simple covalent substance.

• Argon is a noble gas with full outer shell of electrons so exists as atoms (monatomic) • Induced dipole-dipole forces between atoms • Ar atoms have least electrons so the induced dipole-dipole interactions are the weakest • Least heat energy needed to overcome the forces