Consider the following substances: MgBr2, NH3, Mn. 4.1 Define a chemical bond. 4.2 Write down a substance from the list above which has: 4.2.1 a covalent bond. 4.2.2 An ionic bond. 4.3 Magnesium reacts with bromine to form magnesium bromide.

The formula for relative atomic mass is:

$$\text{Relative Atomic Mass} = (\text{mass of isotope 1} \times \frac{\text{abundance 1}}{100}) + (\text{mass of isotope 2} \times \frac{\text{abundance 2}}{100})$$

$$63.5 = (63 \times \frac{x}{100}) + (65 \times \frac{100-x}{100})$$ $$6350 = 63x + 65(100-x)$$ $$6350 = 63x + 6500 - 65x$$ $$6350 = 6500 - 2x$$

$$2x = 6500 - 6350$$ $$2x = 150$$ $$x = 75$$

Percentage abundance of $^{63}\text{Cu} = 75\%$.
Percentage abundance of $^{65}\text{Cu} = 100\% - 75\% = 25\%$.
The percentage abundance of $^{63}\text{Cu}$ is $\boxed{75\%}$ and $^{65}\text{Cu}$ is $\boxed{25\%}$.

3.2 Complete the table below.

• Aluminium

  • 3.2.1 Mass Number: For Aluminium (Atomic Number 13), the most common isotope has a mass number of 27.
    • $\boxed{27}$
  • 3.2.2 Number of Neutrons: Mass Number - Atomic Number = $27 - 13 = 14$.
    • $\boxed{14}$
  • 3.2.3 Number of Electrons: For a neutral Aluminium atom, the number of electrons equals the atomic number, which is 13.
    • $\boxed{13}$

• Ion

  • 3.2.4 Element: Given Mass Number = 30 and Number of Neutrons = 16. Atomic Number = Mass Number - Number of Neutrons = $30 - 16 = 14$. The element with atomic number 14 is Silicon (Si).
    • $\boxed{\text{Silicon}}$
  • 3.2.5 Atomic Number: As calculated above, the atomic number is 14.
    • $\boxed{14}$

3.3 Write down:

3.3.1 the name of the compound: $\text{KMnO}_4$
The name of the compound is Potassium permanganate.

3.3.2 the chemical formula for iron (III) chloride.
Iron (III) means $\text{Fe}^{3+}$ and chloride means $\text{Cl}^-$. To balance the charges, three chloride ions are needed for one iron (III) ion.
The chemical formula is $\boxed{\text{FeCl}_3}$.

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QUESTION 4

4.1 Define a chemical bond.
A chemical bond is a strong attractive force that holds atoms together in molecules or compounds, resulting from the electrostatic attraction between oppositely charged ions or between nuclei and shared electrons.

4.2 Write down a substance from the list above which has:
List: $\text{MgBr}_2$; $\text{NH}_3$; $\text{Mn}$

4.2.1 a covalent bond.
$\boxed{\text{NH}_3}$ (Ammonia consists of nitrogen and hydrogen, both non-metals, sharing electrons).

4.2.2 An ionic bond.
$\boxed{\text{MgBr}_2}$ (Magnesium is a metal and bromine is a non-metal, forming bonds by electron transfer).

4.3 Magnesium reacts with bromine to form magnesium bromide.

4.3.1 Using Lewis dot diagrams, show how magnesium reacts with bromine to form magnesium bromide.
Magnesium (Mg) is in Group 2, so it has 2 valence electrons. Bromine (Br) is in Group 17, so it has 7 valence electrons. Magnesium will lose its 2 valence electrons, and each bromine atom will gain 1 electron. Therefore, one magnesium atom reacts with two bromine atoms.

$$\text{Mg} \cdot + 2 \cdot \ddot{\text{Br}}: \longrightarrow [\text{Mg}]^{2+} + 2[:\ddot{\text{Br}}:]^-$$

4.3.2 Draw the Aufbau (orbital box) diagram for the magnesium ion.
Magnesium (Mg) has an atomic number of 12.
Electron configuration of neutral Mg: $1s^2 2s^2 2p^6 3s^2$.
The magnesium ion is $\text{Mg}^{2+}$, meaning it has lost its two outermost electrons (from the $3s$ orbital).
Electron configuration of $\text{Mg}^{2+}$: $1s^2 2s^2 2p^6$.

Orbital box diagram for $\text{Mg}^{2+}$:

$$\begin{array}{c c c c c} \text{1s} & \text{2s} & \multicolumn{3}{c}{\text{2p}} \\ \uparrow\downarrow & \uparrow\downarrow & \uparrow\downarrow & \uparrow\downarrow & \uparrow\downarrow \end{array}$$