The Periodic Table (Edexcel International A Level (IAL) Chemistry): Flashcards
Exam code: YCH11
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What is the general trend in first ionisation energy across a period, and why does it occur?
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What is the general trend in first ionisation energy across a period, and why does it occur?
First ionisation energy increases across a period. Nuclear charge increases while shielding remains roughly constant and atomic radius decreases, making it progressively harder to remove the outer electron.
Describe the general trend in melting point across Period 3 (Na to Ar).
Melting point increases from Na to Si (which has the highest melting point) then decreases sharply from P to Ar. The trend reflects changes in bonding and structure across the period.
Why is the first ionisation energy of boron lower than that of beryllium, despite boron having a higher nuclear charge?
In boron, the outer electron is in the 2p subshell, which is at a higher energy and further from the nucleus than the 2s subshell of beryllium. This more than offsets the increased nuclear charge, lowering boron's IE1.
Why does the melting point increase from sodium to aluminium across Period 3?
Na, Mg and Al have metallic bonding in a giant lattice. Going from Na to Al, each atom donates more electrons to the delocalised sea (1, 2 and 3 respectively), increasing the electrostatic attraction between the positive ions and the electron sea.
The first ionisation energy of oxygen is lower than that of nitrogen because of .......... in oxygen's 2px orbital.
The first ionisation energy of oxygen is lower than that of nitrogen because of spin-pair repulsion in oxygen's 2px orbital.
Oxygen has two electrons in 2px; the repulsion makes one of them easier to remove.
Silicon has the highest melting point in Period 3 because it has a .......... structure.
Silicon has the highest melting point in Period 3 because it has a giant covalent (giant molecular) structure.
Each Si atom is bonded to four neighbours by strong covalent bonds that require a large amount of energy to break.
True or False?
First ionisation energy decreases down a group in the Periodic Table.
True.
Down a group, atomic radius increases, distance between the nucleus and outer electron increases, and shielding increases. These factors outweigh the increased nuclear charge, making the outer electron easier to remove.
True or False?
Phosphorus, sulfur, chlorine and argon have low melting points because the covalent bonds within their molecules are weak.
False.
The covalent bonds within their molecules are strong. It is the weak instantaneous dipole-induced dipole forces between molecules that require little energy to overcome, giving low melting points.
What is periodicity in the context of ionisation energy?
Periodicity is the repeating pattern of chemical and physical properties (including ionisation energy) observed across successive periods of the Periodic Table.
What is a giant metallic lattice?
A giant metallic lattice is a regular arrangement of positive metal ions held together by a sea of delocalised electrons. The electrostatic attraction between the ions and the electrons gives metals their high melting points.
Give three reasons why ionisation energy decreases down a group.
Atomic radius increases as more electron shells are added.
Distance from the nucleus to the outer electron increases.
Shielding by inner electron shells increases.
All three reduce the effective nuclear attraction on the outer electron.
Why does sulfur have a higher melting point than phosphorus in Period 3?
Sulfur exists as S8 molecules, which are larger than the P4 molecules of phosphorus. Larger molecules have stronger instantaneous dipole-induced dipole forces between them, requiring more energy to overcome.
The slight decrease in first ionisation energy between aluminium and magnesium occurs because aluminium's outer electron is in the .......... subshell.
The slight decrease in first ionisation energy between aluminium and magnesium occurs because aluminium's outer electron is in the 3p subshell.
The 3p subshell is at higher energy and further from the nucleus than the 3s subshell of magnesium.
The delocalised electrons in the metallic lattice of aluminium come from the .......... shell of each Al atom.
The delocalised electrons in the metallic lattice of aluminium come from the valence shell of each Al atom.
Aluminium donates all three of its outer electrons to the electron sea.
True or False?
The decrease in first ionisation energy from phosphorus to sulfur is caused by spin-pair repulsion in sulfur's 3px orbital.
True.
Sulfur has two electrons paired in the 3px orbital. Spin-pair repulsion makes one of these electrons easier to remove than the unpaired 3p electrons in phosphorus.
True or False?
Argon has a higher melting point than chlorine in Period 3.
False.
Argon exists as single atoms (Ar) with only very weak instantaneous dipole-induced dipole forces, giving it a lower melting point than chlorine (Cl2), which has slightly larger molecules and stronger intermolecular forces.
Why does increasing nuclear charge not always lead to increasing ionisation energy across a period?
Two specific cases cause the general trend to dip: when the outer electron moves to a higher-energy subshell (e.g. Be to B, Mg to Al), and when spin-pair repulsion in a half-filled orbital makes removal easier (e.g. N to O, P to S).
Why do the elements from phosphorus to argon have much lower melting points than silicon in Period 3?
Silicon has a giant covalent structure requiring large amounts of energy to break strong covalent bonds. Phosphorus to argon exist as simple molecules held together only by weak instantaneous dipole-induced dipole forces, which are easily overcome.
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