Define the first ionisation energy of an element.
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energy required to remove one mole of electrons; from one mole of gaseous atoms; to form one mole of gaseous +1 ions
Ionisation Energies Orbitals And Electronic Configuration
Write an equation, including state symbols, for the second ionisation energy of magnesium.
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Mg⁺(g) → Mg²⁺(g) + e⁻; correct state symbols on both species
Explain why all ionisation energies are endothermic.
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energy is required to overcome the electrostatic attraction; between the electron being removed and the positive nucleus
State the maximum number of electrons that can occupy a single orbital.
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two
Explain why two electrons in the same orbital must have opposite spins.
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parallel spins would repel each other; opposite spins reduce repulsion and allow pairing
State three factors that affect the size of an ionisation energy.
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nuclear charge / number of protons; shielding by inner electrons; distance of electron from nucleus / sub-shell from which electron is removed
Explain why the first ionisation energy of sodium is lower than that of lithium.
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sodium’s outer electron is in a higher quantum shell / further from the nucleus; there is more shielding by inner electrons in sodium; both factors outweigh the increased nuclear charge in sodium
Explain how successive ionisation energies provide evidence for quantum shells.
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large jumps occur in successive ionisation energy values; each jump corresponds to removing an electron from a shell closer to the nucleus; smaller increases between jumps correspond to electrons in the same shell
The successive ionisation energies of an element show a large jump between the third and fourth electrons removed. Deduce the group of the element and justify your answer.
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Group 3; because three electrons are removed easily before the first large jump, indicating three outer-shell electrons
Explain why the first ionisation energy of aluminium is lower than that of magnesium.
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aluminium’s outer electron is removed from a 3p sub-shell; magnesium’s outer electron is removed from a 3s sub-shell; the 3p sub-shell is at a higher energy so its electron is removed more easily
Explain why the first ionisation energy of sulfur is lower than that of phosphorus.
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sulfur has two electrons paired in one 3p orbital; the paired electrons repel each other; less energy is required to remove one of these paired electrons than to remove an unpaired 3p electron in phosphorus
Describe the shape of an s orbital.
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spherical
Describe the shape and orientation of p orbitals in a p sub-shell.
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dumb-bell shape with two lobes either side of the nucleus; three p orbitals oriented along x, y and z axes at right angles
State the two rules for filling orbitals within a sub-shell.
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each orbital takes a single electron before pairing; paired electrons have opposite spins
Draw the electron-in-boxes arrangement for the 2p sub-shell of a nitrogen atom.
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three boxes drawn side by side; each box contains a single arrow pointing in the same direction
Write the full electronic configuration of a sulfur atom using s, p, d notation.
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1s² 2s² 2p⁶ 3s² 3p⁴
Write the electronic configuration of a Cu²⁺ ion.
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1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁹; (4s electrons removed before 3d)
Explain why the electronic configuration of chromium is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹ rather than 3d⁴ 4s².
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a half-filled 3d sub-shell is more stable; promotion of one 4s electron to 3d gives the lower-energy arrangement
Explain why elements in the same group of the Periodic Table show similar chemical properties.
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they have the same outer-shell electronic configuration; outer electrons determine chemical reactivity and bonding behaviour
Predict, using electronic configuration, the formula of the ion formed by potassium and explain your reasoning.
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K⁺; potassium has electronic configuration ending in 4s¹ and loses this single outer electron to achieve a stable noble-gas configuration