Dot-and-cross diagrams
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Draw a dot-and-cross diagram for sodium chloride (NaCl), clearly showing the charges on the ions.
Na has 1 valence electron, which it donates to Cl (7 valence electrons) to form Na⁺ (full outer shell) and Cl⁻ (full outer shell). The diagram should show the transfer of the electron and the resulting charges on each ion.
Draw a dot-and-cross diagram for carbon dioxide (CO₂), showing only the outer shell electrons.
Carbon shares two electrons with each oxygen atom forming two double covalent bonds. The diagram should show each oxygen with 8 electrons in its outer shell and carbon with 8 electrons in its outer shell.
Explain, in terms of molecular collisions, how the pressure of a gas arises.
Gas pressure is caused by the continuous random motion of gas molecules colliding with the walls of the container. Each collision exerts a small force; the cumulative force over the area of the container walls is the pressure.
State the two main assumptions of the kinetic theory of gases that are not valid for real gases.
Ideal gases are assumed to have zero particle volume, meaning the volume of the gas particles themselves is negligible compared to the volume of the container. Ideal gases also have no intermolecular forces of attraction between the gas particles.
State the Ideal Gas Equation, defining each term.
The ideal gas equation is pV = nRT, where p is pressure (Pa), V is volume (m³), n is the number of moles, R is the ideal gas constant (8.31 J K⁻¹ mol⁻¹), and T is temperature (K).
A gas occupies 10.0 dm³ at 27 °C and 100 kPa. Calculate the number of moles of gas present (R = 8.31 J K⁻¹ mol⁻¹).
Using pV = nRT, first convert to SI units: V = 0.010 m³, T = 300 K. Rearrange to n = pV/RT = (100000 x 0.010) / (8.31 x 300) = 0.401 mol.
Draw a dot-and-cross diagram for the ammonium ion (NH₄⁺), showing only outer shell electrons and indicating the coordinate bond.
Nitrogen shares electrons with three hydrogen atoms (covalent bonds). The nitrogen atom donates its lone pair to another hydrogen ion (H⁺) forming a coordinate bond, creating the NH₄⁺ ion with a +1 charge.
Define a coordinate bond and how it differs from a covalent bond.
A coordinate bond (also called a dative covalent bond) is formed when one atom provides both of the electrons for the shared pair in the bond. In a regular covalent bond, each atom provides one electron to be shared.
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