AQA Chemistry Past Paper - Periodicity PDF

AS CHEMISTRY 3.2.1 PERIODICITY ORGANISATION OF THE PERIODIC TABLE Periodic Table Facts The elements are placed in order of Atomic Number. Atomic Number = No. of protons in the nucleus (= the number of electrons in...

AS CHEMISTRY 3.2.1 PERIODICITY ORGANISATION OF THE PERIODIC TABLE Periodic Table Facts The elements are placed in order of Atomic Number. Atomic Number = No. of protons in the nucleus (= the number of electrons in the atom) Group Number = No. of electrons in outer energy level Period Number = No. of occupies energy levels “Block” (s, p , d) = the orbital type that the outermost electron occupies s d p s-block p-block All elements’ electronic All elements’ electronic structure ends with an electron structure ends with an electron in an s-orbital in an s-orbital e.g. Na 1s2 2s2 2p6 3s1 e.g. P 1s2 2s2 2p6 3s2 3p3 d-block All elements’ electronic structure ends with an electron in an d-orbital e.g. Fe 1s2 2s2 2p6 3s2 3p6 4s2 These rules and blocks serve as a guide to help you identify elements using electronic structures as well as a system for checking that you have deduced the correct electronic structure for an element. AQA www.chemistrycoach.co.uk © scidekick ltd 2024 AS CHEMISTRY 3.2.1 PERIODICITY PROPERTIES OF PERIOD 3 ELEMENTS The following trends are the most commonly examined. Learn the patterns and the explanations that go with them. Be prepared to compare two elements and explain the differences with respect to these trends. ATOMIC RADIUS DECREASE Across a Period 3 there is a decrease in atomic radius As you move across the period, nuclear charge increases but the number of occupied energy levels (shielding) stays the same. The attraction between the nucleus and outer electrons increases, so the outer electrons are drawn closer to the nucleus. This causes the radius of the atoms to decrease. 1st IONISATION ENERGY DECREASE Across a Period 3 there is a general Increase in 1st I.E. As you move across a period, nuclear charge increases, but the amount of shielding remains the same. This means there is a stronger attraction between the outer electron and the nucleus, so more energy is required to remove its outer electron and the nucleus, so less energy is required to remove it. Watch out for the exceptions though!! See section 3.1.1 AQA www.chemistrycoach.co.uk © scidekick ltd 2024 AS CHEMISTRY 3.2.1 PERIODICITY MELTING POINTS OF PERIOD 3 ELEMENTS Na Mg Al Si P4 S8 Cl2 Ar Metallic Bonding Giant Simple Covalent - Induced Dipole IMF’s Increases with increased charge Covalent Trend varies with the number of electrons on cations, therefore stronger Very in the atoms / molecules. electrostatic attractions strong The greater the number of electrons, the between cations and covalent stronger the induced dipole forces delocalised electrons bonds must be broken in order to melt 1800 1350 900 450 0 AQA www.chemistrycoach.co.uk © scidekick ltd 2024