Everything from the 3 lessons of this topic on a few pages: the key idea of each lesson, the diagram to remember, the points to learn and the traps examiners set. Read it, cover it, test yourself.
Across Period 3 the nuclear charge rises while electrons enter the same shell, so shielding is almost constant: the atomic radius decreases, and first ionisation energy and electronegativity generally increase. Melting point depends on structure: it rises from Na to Al as metallic bonding strengthens, peaks at silicon (giant covalent), then drops sharply for the simple molecular P4, S8, Cl2 and monatomic Ar. Conductivity rises from Na to Al (more delocalised electrons); Si is a semiconductor and the rest are insulators.
Silicon's high melting point is due to its giant covalent structure, not to being a metal. And the fall from sulfur to chlorine to argon in melting point is about intermolecular forces between small molecules or atoms; no covalent bonds are broken when P, S or Cl2 melt.
Across Period 3 the bonding in the oxides and chlorides changes from ionic (Na, Mg) to covalent (Si, P, S). The oxides go from basic (Na2O, MgO) through amphoteric (Al2O3) to acidic (SiO2, P4O10, SO2, SO3). Ionic chlorides dissolve to give neutral or near-neutral solutions; covalent chlorides are hydrolysed by water, producing HCl and strongly acidic solutions. The highest oxidation number in the oxides and chlorides equals the number of outer electrons.
Aluminium oxide and silicon dioxide are insoluble in water, so they do not change its pH; their acid-base character is shown by their reactions with acids and alkalis. And AlCl3 is not neutral in water: the small, highly charged Al3+ ion polarises water molecules, releasing H+.
The trends seen in Period 3 recur in every period. To place an unknown element, use several clues together: the formulae of its oxide and chloride give its oxidation number and so its group; successive ionisation energies jump after the last outer electron; a very high melting point and non-conducting behaviour point to a giant covalent structure; oxide and chloride behaviour with water (basic, amphoteric, acidic, hydrolysed) shows where it sits between metal and non-metal.
Do not base an identification on a single property. Melting point alone cannot separate a strong metal from a giant covalent solid; combine it with conductivity, oxide behaviour and ionisation energy data. And remember that the dips in first ionisation energy (at Groups 13 and 16) repeat in every period.