11SCIAB TERM 3 MCQ AY 24-25

The graphs illustrate trends in four physical properties of elements in Period 3, excluding argon. Show the graph with electronegativity on the y-axis. (Na, Mg, Al, Si, P, S, Cl)

During a science project, Feli and Spring were discussing different types of solids. Feli mentioned that sulfur is an example of a solid that has a simple molecular lattice. Which solid are they referring to?

• calcium fluoride

• sulfur

• silicon(IV) oxide

• nickel

Answer explanation

Feli correctly identifies sulfur as a solid with a simple molecular lattice structure. This distinguishes it from the other options, which do not share this characteristic.

During a chemistry experiment, Bryant discovered that a certain semi-conductor, Q, when combined with water, produced white fumes and an acidic solution. Can you identify which Period 3 element Q is?

• magnesium

• aluminium

• silicon

• phosphorus

Answer explanation

Silicon (Si) reacts with water to form silicon dioxide, which can produce white fumes and an acidic solution. Silicon is the only semi-conductor listed among the Period 3 elements, making silicon the correct choice.

Winston and Kath are conducting an experiment in their chemistry lab. Elements X and Y are in Period 3 of the Periodic Table. Element X is either phosphorus or sulfur, while Element Y is either sodium or magnesium. During their experiment, Element X forms an oxide that reacts with water to produce a solution containing the aqueous anion XO₄^2–. They discover that one mole of Element Y reacts with one mole of chlorine molecules. By the end of the reaction, all of Element Y and all of the chlorine molecules have been completely consumed. Can you help Winston and Kath identify elements X and Y?

Answer explanation

Element X is sulfur (S), as it forms sulfate (SO4 2–) when reacting with water. Element Y is Magnesium (Mg), in which 1 mole of Mg reacts with 1 mole of Cl₂, which matches the problem statement.

Hillary and Kiven are studying the first eight successive ionisation energies for two elements of Period 3 of the Periodic Table. They are curious about the formula of the ionic compound that could be formed from these elements. What is the formula of the ionic compound formed from these elements?

• MgCl₂

• CaBr₂

• Na₂S

• K₂Se

Answer explanation

The elements in Period 3 include metals like magnesium (Mg) and nonmetals like chlorine (Cl). Mg forms a +2 ion and Cl forms a -1 ion, leading to the ionic compound MgCl2, which is the correct formula.

During a chemistry lab, Hayden and Louis were discussing the properties of different compounds. Louis claimed, "Aluminium chloride has a giant ionic lattice of Al 3+ and Cl – ions." Meanwhile, Hagra mentioned, "Sodium chloride dissolves in water, forming hydrogen chloride and sodium hydroxide." Faith argued, "The strong covalent bonds in silicon chloride prevent it from reacting with water." Anon added, "When phosphorus(V) chloride is added to water, the resulting solution conducts electricity." Which statement is correct?

• Aluminium chloride has a giant ionic lattice of Al 3+ and Cl – ions.

• Sodium chloride dissolves in water, forming hydrogen chloride and sodium hydroxide.

• The strong covalent bonds in silicon chloride prevent it from reacting with water.

• When phosphorus(V) chloride is added to water, the resulting solution conducts electricity.

Answer explanation

• While aluminum chloride does have ionic bonds, its structure is not a typical "giant ionic lattice" due to a significant degree of covalent character, meaning the ions are not fully separated in the solid state. 

• When sodium chloride dissolves in water, it forms sodium ions (Na+) and chloride ions (Cl-) in solution, not hydrogen chloride and sodium hydroxide. Silicon chloride does have covalent bonds, but they are not strong enough to prevent it from reacting with water. 

• When phosphorus(V) chloride (PCl5) reacts with water, it undergoes a vigorous reaction producing hydrochloric acid (HCl) which readily ionizes in water, making the solution conductive. 

Nadia and Kiven are studying the periodic table in their chemistry class. They notice that as they move from left to right across a period, the atomic radius of the elements decreases. They wonder why this happens. Can you explain the reason behind this trend?

• Increase in the number of electron shells

• Increase in nuclear charge

• Decrease in nuclear charge

• Increase in shielding effect

Answer explanation

As you move from left to right across a period, the number of protons in the nucleus increases, leading to a greater nuclear charge. This stronger attraction pulls the electrons closer, resulting in a decrease in atomic radius.

In a science class, Kenneth and Grace are discussing why the ionic radius of metals decreases across Period 3 from sodium to aluminum. Kenneth believes it is because the increased nuclear charge pulls the electrons more tightly, while Grace thinks that metals lose more electrons, resulting in a larger radius. Hagra chimes in, saying that the atomic number decreases, reducing the ionic size, and Gio adds that electrons occupy higher energy levels, expanding the radius. Who is correct?

• Increased nuclear charge pulls the electrons more tightly.

• Metals lose more electrons, resulting in a larger radius.

• The atomic number decreases, reducing the ionic size.

• Electrons occupy higher energy levels, expanding the radius.

Answer explanation

Kenneth is correct. As you move across Period 3, the increased nuclear charge from more protons pulls the electrons closer, resulting in a smaller ionic radius for metals like sodium to aluminum.

In a science class, Faith and Grace are discussing the trend in atomic radius across Period 3. Faith believes that the number of protons increases, which increases the nuclear charge and pulls electrons closer. Grace thinks that electrons in the outer shell experience increased repulsion, which increases atomic size. Who is correct?

• Electrons in the outer shell experience increased repulsion, increasing atomic size.

• The number of electron shells increases, causing greater shielding.

• The number of protons increases, increasing the nuclear charge and pulling electrons closer.

• Atomic radius remains constant due to balanced nuclear and electron forces.

Answer explanation

Faith is correct. As protons increase across Period 3, the nuclear charge rises, pulling electrons closer and reducing atomic radius. Grace's view on electron repulsion does not outweigh the effect of increased nuclear charge.

During a science experiment, Gio and Spring were discussing why silicon has a much higher melting point than sodium. Spring suggested that sodium forms a molecular structure with weak van der Waals forces, while Gio argued that silicon has a giant covalent structure requiring a large amount of energy to break bonds. Kiven chimed in, saying that silicon forms a metallic lattice with delocalized electrons, and Grace pointed out that sodium has a smaller atomic mass than silicon. Who is correct?

• Sodium forms a molecular structure with weak van der Waals forces.

• Silicon has a giant covalent structure requiring a large amount of energy to break bonds.

• Silicon forms a metallic lattice with delocalized electrons.

• Sodium has a smaller atomic mass than silicon.

Answer explanation

Gio is correct. Silicon has a giant covalent structure, meaning it requires a significant amount of energy to break the strong covalent bonds, resulting in a much higher melting point compared to sodium's weaker molecular structure.