Topic 2 – Bonding and Structure
In order to develop their practical skills, students should be encouraged to carry out a range of practical experiments related to this topic. Possible
experiments include investigating the migration of ions, for example in a U-tube of copper(II) chromate, seeing the effect of a charged rod on a flow
of water. Mathematical skills that could be developed in this topic include representing shapes of molecules with suitable sketches, plotting data to
investigate trends in boiling temperatures of alkanes. Within this topic, students can consider the strengths and weaknesses of the models used to
describe different types of bonding. As part of their study of valence-shell-electron-pair repulsion (VESPR) theory, students can see how chemists can
make generalisations and use them to make predictions.
Topic 2A: Bonding
1. know the definition of an ionic bond
What is an ionic bond? Define the term.
An ionic bond is a strong electrostatic force of attraction between oppositely charged ions (SEFABOCI).
2. understand the effects that ionic radius and ionic charge have on the strength of ionic bonding
The melting temperature of sodium sulfide is higher than that of sodium chloride. Explain this difference.
Sulfide ions have a higher charge than chloride ions (2- vs 1-), therefore there is a greater lattice energy in sodium
sulfide and sodium chloride. This increases the force of attraction between sodium and sulfide ions, meaning it takes
more energy to break these bonds. This makes sodium sulfide’s melting point higher than sodium chloride’s.
Why does lithium fluoride have a higher boiling point than potassium fluoride? Both bond ionically…
Lithium has a smaller ionic radius than potassium, which increases its lattice energy, meaning more energy is
required to break LiF’s bonds than KF’s.
3. understand the formation of ions in terms of electron loss or gain
Describe how sodium (Na) and oxygen (O) form sodium chloride (Na 2O), in terms of electron transfer.
Electrons are transferred from sodium to oxygen. Each sodium atom loses one electron and each oxygen atoms
gains two electrons, forming sodium ions (Na+) and oxide ions (O2-).
4. be able to draw electronic configuration diagrams of cations and anions using dot-and-cross diagrams
Draw the dot-and-cross diagrams for NaCl, MgO, and CaF2.
, 5. understand reasons for trends in ionic radii down a group and for sets of isoelectronic ions, e.g. N 3– to Al3+
Explain the trend in ionic radius of isoelectronic ions as you go across Period 2.
As you go across the period, the nuclear charge increases. This means the electrons feel a greater sense of attraction
from the nucleus, drawing them closer into the atom. This initially reduces the atomic radius across the period (i.e.
Na+ has a bigger radius than Mg2+), but a sudden increase occurs switching from cations to anions as an extra
electron shell is being added. The trend in decreasing ionic radius then continues as you progress across the anions.
6. understand that the physical properties of ionic compounds and the migration of ions provide evidence
for the existence of ions
Describe two reasons why we know the existence of ions is likely true.
Migration of ions – when a voltage is applied to an ionic compound, the ions migrate to their opposite electrodes.
For example, copper (II) chromate (green) separates into copper (II) (blue) and chromate ions (yellow).
Electron density maps – for purely ionic compounds, there are no contours between ions, meaning no electrons are
shared, which is good evidence for the presence of ions.
7. know the definition of a covalent bond
Define the term ‘covalent bond’.
A covalent bond is a strong electrostatic force of attraction between a shared pair of electrons and the nuclei of
bonding atoms (SEFABSPEANBA).
8. be able to draw dot-and-cross diagrams to show electrons in covalent substances, including:
i molecules with single, double and triple bonds
Draw the dot-and-cross diagram for carbon dioxide.
ii species exhibiting dative covalent (coordinate) bonding, including Al 2Cl6 and ammonium ions
Draw the dot-and-cross diagram for carbon monoxide.
Draw the dot-and-cross diagram, and Lewis diagram, for aluminium chloride.
2
In order to develop their practical skills, students should be encouraged to carry out a range of practical experiments related to this topic. Possible
experiments include investigating the migration of ions, for example in a U-tube of copper(II) chromate, seeing the effect of a charged rod on a flow
of water. Mathematical skills that could be developed in this topic include representing shapes of molecules with suitable sketches, plotting data to
investigate trends in boiling temperatures of alkanes. Within this topic, students can consider the strengths and weaknesses of the models used to
describe different types of bonding. As part of their study of valence-shell-electron-pair repulsion (VESPR) theory, students can see how chemists can
make generalisations and use them to make predictions.
Topic 2A: Bonding
1. know the definition of an ionic bond
What is an ionic bond? Define the term.
An ionic bond is a strong electrostatic force of attraction between oppositely charged ions (SEFABOCI).
2. understand the effects that ionic radius and ionic charge have on the strength of ionic bonding
The melting temperature of sodium sulfide is higher than that of sodium chloride. Explain this difference.
Sulfide ions have a higher charge than chloride ions (2- vs 1-), therefore there is a greater lattice energy in sodium
sulfide and sodium chloride. This increases the force of attraction between sodium and sulfide ions, meaning it takes
more energy to break these bonds. This makes sodium sulfide’s melting point higher than sodium chloride’s.
Why does lithium fluoride have a higher boiling point than potassium fluoride? Both bond ionically…
Lithium has a smaller ionic radius than potassium, which increases its lattice energy, meaning more energy is
required to break LiF’s bonds than KF’s.
3. understand the formation of ions in terms of electron loss or gain
Describe how sodium (Na) and oxygen (O) form sodium chloride (Na 2O), in terms of electron transfer.
Electrons are transferred from sodium to oxygen. Each sodium atom loses one electron and each oxygen atoms
gains two electrons, forming sodium ions (Na+) and oxide ions (O2-).
4. be able to draw electronic configuration diagrams of cations and anions using dot-and-cross diagrams
Draw the dot-and-cross diagrams for NaCl, MgO, and CaF2.
, 5. understand reasons for trends in ionic radii down a group and for sets of isoelectronic ions, e.g. N 3– to Al3+
Explain the trend in ionic radius of isoelectronic ions as you go across Period 2.
As you go across the period, the nuclear charge increases. This means the electrons feel a greater sense of attraction
from the nucleus, drawing them closer into the atom. This initially reduces the atomic radius across the period (i.e.
Na+ has a bigger radius than Mg2+), but a sudden increase occurs switching from cations to anions as an extra
electron shell is being added. The trend in decreasing ionic radius then continues as you progress across the anions.
6. understand that the physical properties of ionic compounds and the migration of ions provide evidence
for the existence of ions
Describe two reasons why we know the existence of ions is likely true.
Migration of ions – when a voltage is applied to an ionic compound, the ions migrate to their opposite electrodes.
For example, copper (II) chromate (green) separates into copper (II) (blue) and chromate ions (yellow).
Electron density maps – for purely ionic compounds, there are no contours between ions, meaning no electrons are
shared, which is good evidence for the presence of ions.
7. know the definition of a covalent bond
Define the term ‘covalent bond’.
A covalent bond is a strong electrostatic force of attraction between a shared pair of electrons and the nuclei of
bonding atoms (SEFABSPEANBA).
8. be able to draw dot-and-cross diagrams to show electrons in covalent substances, including:
i molecules with single, double and triple bonds
Draw the dot-and-cross diagram for carbon dioxide.
ii species exhibiting dative covalent (coordinate) bonding, including Al 2Cl6 and ammonium ions
Draw the dot-and-cross diagram for carbon monoxide.
Draw the dot-and-cross diagram, and Lewis diagram, for aluminium chloride.
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