1.2.2 Periodicity across periods 2 and 3 Quiz: Pearson Edexcel Chemistry, Unit 1

The 20 questions

1. Which element in Period 3 has the lowest melting temperature?

   • Argon
   • Silicon
   • Phosphorus
   • Sodium

2. Which element in Period 3 has the highest melting temperature?

   • Silicon
   • Sulfur
   • Sodium
   • Aluminium

3. What type of structure does silicon have?

   • Giant metallic
   • Giant covalent
   • Simple molecular
   • Giant ionic

4. Why does silicon have a much higher melting temperature than phosphorus?

   • Silicon has more delocalised electrons per atom than phosphorus, which strengthens its structure greatly
   • Phosphorus is ionic, so its ions are less strongly attracted to each other than silicon's atoms are
   • Silicon has strong covalent bonds throughout a giant lattice, while phosphorus has weak London forces between P4 molecules
   • Phosphorus has weaker metallic bonds between its atoms than the silicon lattice has, so it melts far lower

5. Which statement explains the general increase in first ionisation energy across Period 3?

   • Nuclear charge increases while shielding stays roughly constant, so outer electrons are held more strongly
   • Shielding increases across the period as more inner shells fill, so the outer electrons are held less tightly
   • Electrons are added to a new shell at each element, which moves the outer electron further away from the nucleus
   • Atomic radius increases across the period as each new element adds another electron shell to the atom

6. Why is the first ionisation energy of aluminium lower than that of magnesium?

   • Aluminium's outer electron is in a 3p sub-shell, which is higher in energy than the paired 3s electrons of magnesium
   • Aluminium's outer electron is in the 2p sub-shell, which lies closer to the nucleus than magnesium's 3s electrons
   • Aluminium has a smaller nuclear charge than magnesium, so its outer electron is held more weakly overall in the atom
   • Magnesium's 3s electrons are less shielded than aluminium's 3p electrons, so they are held more tightly by the nucleus

7. Which element in Period 2 has the largest atomic radius?

   • Boron
   • Nitrogen
   • Fluorine
   • Lithium

8. Why is the melting temperature of magnesium higher than that of sodium?

   • Magnesium has more neutrons than sodium, which pull the metal ions closer together in the metallic lattice
   • Magnesium has covalent bonds between its atoms, which are much stronger than the metallic bonds that hold sodium
   • Mg2+ ions are smaller with a higher charge, and each atom contributes two delocalised electrons, giving stronger metallic bonding
   • Sodium has delocalised electrons that repel each other more strongly than those in magnesium do in its lattice

9. Which Period 3 element has the highest first ionisation energy among sodium, magnesium, aluminium and silicon?

   • Magnesium
   • Aluminium
   • Silicon
   • Sodium

10. Why is the first ionisation energy of sulfur lower than that of phosphorus?

    • Sulfur's removed electron comes from a paired 3p orbital, so electron-electron repulsion makes it easier to remove
    • Phosphorus has a paired 3p orbital, which makes its outer electrons easier to remove from the atom
    • Sulfur's outer electron is in a 3s sub-shell, which is higher in energy than the 3p sub-shell of phosphorus
    • Sulfur has fewer protons than phosphorus, so its nucleus attracts the outer electrons less strongly overall

11. Which Period 2 element has the highest melting temperature?

    • Neon
    • Lithium
    • Nitrogen
    • Carbon

12. Which Period 2 element has the lowest first ionisation energy?

    • Beryllium
    • Lithium
    • Boron
    • Neon

13. Which Period 3 element exists as P4 tetrahedra in its standard state?

    • Chlorine, which exists as diatomic molecules that are gases at room temperature and pressure
    • Sulfur, which forms rings of eight atoms in its most stable solid form at room temperature
    • Argon, which exists as single atoms that do not bond to one another under any normal conditions
    • Phosphorus

14. Which statement about the trend in melting temperature across Period 3 is correct?

    • It falls steadily from sodium to argon, because the metallic bonding weakens steadily across the period
    • It is highest at argon and lowest at silicon, because the noble gas has the most electrons per atom
    • It rises steadily from sodium to argon, because the number of electrons per atom increases across it
    • It rises from sodium to silicon, then falls sharply to phosphorus, sulfur and argon, which are simple molecular

15. Which trend in atomic radius across Period 3 is correct?

    • It decreases from sodium to chlorine because nuclear charge increases with similar shielding
    • It increases from sodium to chlorine, because more electron shells are added as the atomic number rises
    • It decreases because a new electron shell is added at each element and pulls the atoms inwards
    • It stays the same across the period, because the extra protons are balanced by the extra shielding

16. Explain why the melting temperature of argon is much lower than that of chlorine.

    • Chlorine has ionic bonding between its atoms, which is much stronger than the forces holding argon together
    • Argon has a smaller nuclear charge than chlorine, so its electrons repel one another more strongly
    • Argon is a giant lattice held together by weak covalent bonds between its neighbouring atoms in the solid
    • Argon is monatomic with only weak London forces between atoms, whereas chlorine forms Cl2 molecules with stronger London forces

17. Predict which has the higher boiling temperature: silicon or phosphorus. Justify using structure and bonding.

    • Silicon, because its delocalised electrons move freely between the atoms and carry the attraction across the whole solid
    • Phosphorus, because the P4 molecules are joined in the solid by strong covalent bonds that must be broken before it can boil
    • Silicon, because it is giant covalent with strong bonds throughout, whereas phosphorus is simple molecular with weak London forces
    • Phosphorus, because it has a giant metallic structure whose delocalised electrons hold the positive ions together strongly

18. A student says that periodicity means each element has identical properties to the one before it. Which correction is best?

    • Properties recur at regular intervals linked to electron configuration, so elements in the same group show similar patterns
    • Periodicity arises from the number of neutrons in each nucleus, which repeats in a regular cycle across each period
    • Periodicity only applies to melting temperatures and not to other properties, which vary without any repeating pattern at all
    • Periodicity means that properties repeat exactly across every period of the table, so each element matches the one before it

19. Explain why the first ionisation energy of an element in Period 3 can be used to show evidence for sub-shells.

    • A small drop occurs when the electron removed is from a new sub-shell of higher energy, such as Mg to Al
    • The values are equal for every element in Period 3 because they all share the same third shell and its energy
    • The drop shows that all electrons in the same shell have identical energies, so removing any one costs the same energy
    • A rise occurs at each element because the nucleus gains a proton, so the outer electrons are held more tightly each step

20. Which Period 3 element is a semiconductor with a giant covalent structure?

    • Phosphorus
    • Sulfur
    • Silicon
    • Chlorine

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