M3 Groups 2 and 7 Q&A
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State and explain the trend in melting and boiling points down Group 7
• Melting and boiling points increase • Atomic radius increases • Number of electrons increases, as size of molecules increases • Stronger induced dipole-dipole interactions between molecules (intermolecular forces) • More heat energy needed to overcome forces
State and explain the trend in reactivity (or oxidising power) down Group 7.
• Reactivity decreases • Element gains 1 electron to become 1- ion • Atomic radius increases • Outer electrons further from nucleus/ in a different shell • Outer electrons experience more shielding • (Increased shielding outweighs increased nuclear charge) • Outer electrons less strongly attracted to nucleus so are less easily gained • (less energy released when electron is gained – you should not need to say this)
State and explain the trend in atomic radius down Group 2 (true for any group).
• Atomic radius increases • Electrons are added to new shell • Outer electrons experience more shielding • (Increased shielding outweighs increased nuclear charge) • Outer electrons are less strongly attracted to nucleus so are further from nucleus
State and explain the trend in reactivity down Group 2
• Reactivity increases • Element loses 2 electrons to become 2+ ion • Atomic radius increases • Outer electrons are in different shell further from nucleus • Outer electrons experience more shielding • (Increased shielding outweighs increased nuclear charge) • The 2 outer electrons less strongly attracted to nucleus • Less energy needed to lose the electrons