Here are the dot and cross diagrams and explanations for the type of bonding: a) H$_2$O Step 1: Determine valence electrons. Hydrogen (H) has 1 valence electron. Oxygen (O) has 6 valence electrons. Step 2: Describe the dot and cross diagram. Oxygen is the central atom. Each hydrogen atom shares one electron with the oxygen atom, and the oxygen atom shares one electron with each hydrogen atom, forming two single covalent bonds. The oxygen atom also has two lone pairs of electrons. Using $\times$ for hydrogen's electrons and $\cdot$ for oxygen's electrons: $$ \begin{array}{c} \quad \quad \cdot \cdot \\ \quad \quad \text{O} \\ \quad \quad \cdot \cdot \\ \text{H} \overset{\times}{\cdot} \quad \quad \overset{\cdot}{\times} \text{H} \end{array} $$ Step 3: Explain the type of bonding. The bonding in water ($\text{H}_2\text{O}$) is covalent bonding. This occurs when atoms share electrons to achieve a stable electron configuration. b) NH$_3$ Step 1: Determine valence electrons. Nitrogen (N) has 5 valence electrons. Hydrogen (H) has 1 valence electron. Step 2: Describe the dot and cross diagram. Nitrogen is the central atom. Each hydrogen atom shares one electron with the nitrogen atom, and the nitrogen atom shares one electron with each hydrogen atom, forming three single covalent bonds. The nitrogen atom also has one lone pair of electrons. Using $\times$ for hydrogen's electrons and $\cdot$ for nitrogen's electrons: $$ \begin{array}{c} \quad \quad \cdot \cdot \\ \quad \quad \text{N} \\ \text{H} \overset{\times}{\cdot} \quad \quad \overset{\cdot}{\times} \text{H} \\ \quad \quad \overset{\cdot}{\times} \\ \quad \quad \text{H} \end{array} $$ Step 3: Explain the type of bonding. The bonding in ammonia ($\text{NH}_3$) is covalent bonding. This involves the sharing of electrons between nitrogen and hydrogen atoms. c) Aluminum Step 1: Determine valence electrons. Aluminum (Al) is a metal with 3 valence electrons. Step 2: Describe the bonding. For metals like aluminum, a dot and cross diagram in the traditional sense (showing discrete shared or transferred electrons between two atoms) is not applicable. Instead, metallic bonding is described. Aluminum atoms lose their valence electrons to form positive ions ($\text{Al}^{3+}$). These valence electrons become delocalized and form a "sea" of electrons that are shared among all the positive metal ions in the lattice. Step 3: Explain the type of bonding. The bonding in aluminum is metallic bonding. This involves a lattice of positive metal ions held together by a "sea" of delocalized valence electrons. 3 done, 2 left today. You're making progress.