4.1 The ammonium ion (NH4+) is formed when an ammonia molecule (NH3) reacts with a hydrogen ion (H+). Describe the formation of the dative covalent bond in the ammonium ion. Use Lewis diagrams to aid your explanation. (4)

4.2 The hydronium ion (H3O+) is another example of a species containing a dative covalent bond.

a) Draw Lewis structures to show the formation of the hydronium ion from a water molecule and a hydrogen ion. (4)

b) Name the molecule that provides the lone pair for the dative covalent bond in the formation of H3O+. (1)

c) How many covalent bonds are present in a hydronium ion? (1)

QUESTION 5: ELECTRONEGATIVITY & BOND POLARITY (18 MARKS)

Use the table of electronegativity values below to answer the questions that follow:

| Element | Electronegativity (Pauling scale) |
|---|---|
| H | 2.1 |
| C | 2.5 |
| N | 3 |
| O | 3.5 |
| F | 4 |
| Na | 0.9 |
| Cl | 3 |
| Br | 2.8 |

5.1 Define electronegativity. (2)

5.2 What is the difference between a non-polar covalent bond and a polar covalent bond? Refer to the sharing of electrons in your answer. (3)

4.1 The formation of the ammonium ion (NH4+) involves a dative covalent bond, which occurs when a lone pair of electrons from one atom is donated to an electron-deficient species. In this case, the ammonia molecule (NH3) reacts with a hydrogen ion (H+) to form the ammonium ion.
In a Lewis diagram, the ammonia molecule is shown with nitrogen at the center and three hydrogen atoms bonded to it. Nitrogen has a lone pair of electrons. The hydrogen ion (H+) lacks electrons, so it is electron-deficient. The lone pair on nitrogen is donated to the hydrogen ion to form a dative covalent bond, resulting in the ammonium ion (NH4+), which is structurally similar to a tetrahedral shape with formal positive charge.
4.2 a) To form a hydronium ion (H3O+) from a water molecule and a hydrogen ion, start with a water molecule (H2O). Water has two hydrogen atoms and an oxygen atom in the center with two lone pairs of electrons. When a hydrogen ion (H+) approaches, one of the oxygen's lone pairs is donated to the electron-poor hydrogen ion, forming a dative covalent bond.
A Lewis structure for the hydronium ion shows the oxygen in the center bonded to three hydrogen atoms with one lone pair on the oxygen atom. This results in a positive charge on the oxygen atom.
b) In the formation of H3O+, the oxygen atom from the water molecule provides the lone pair for the dative covalent bond.
c) The hydronium ion (H3O+) has three covalent bonds in total.
5.1 Electronegativity is defined as the tendency of an atom to attract a shared pair of electrons towards itself in a chemical bond.
5.2 A non-polar covalent bond is a type of bond where electrons are shared equally between atoms with similar electronegativities. In contrast, a polar covalent bond occurs when electrons are shared unequally between atoms due to a significant difference in electronegativity. This causes a partial positive charge on the less electronegative atom and a partial negative charge on the more electronegative atom.

Answered by LucasMatthewHarris | 2025-07-06

The ammonium ion (NH4+) forms through a dative covalent bond between ammonia (NH3) and a hydrogen ion (H+), where the nitrogen donates a lone pair. The hydronium ion (H3O+) is formed similarly, using a lone pair from a water molecule. Electronegativity measures an atom's ability to attract electrons, with non-polar bonds sharing electrons equally and polar bonds sharing them unequally.
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Answered by LucasMatthewHarris | 2025-08-24