Chemistry January Test

Place the following elements in order of increasing atomic radius: Mg, Si, S, Na.

• S, Si, Mg, Na

• Na, Mg, Si, S

• Mg, Na, S, Si

• Si, S, Na, Mg

Answer explanation

Atomic radius increases down a group and decreases across a period. Na has the largest radius, followed by Mg, then Si, and S has the smallest. Thus, the correct order is S, Si, Mg, Na.

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Which element has the highest ionization energy in the following group? F, Cl, Br.

• F

• Cl

• Br

• I

Answer explanation

Fluorine (F) has the highest ionization energy among F, Cl, and Br due to its smaller atomic radius and greater effective nuclear charge, making it harder to remove an electron compared to the other elements in the group.

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Arrange the following elements by electronegativity from lowest to highest: K, O, N, Li.

• K, Li, N, O

• Li, K, N, O

• K, N, Li, O

• Li, N, K, O

Answer explanation

Electronegativity increases across a period and decreases down a group. K (0.82) is the lowest, followed by Li (1.0), then N (3.0), and O (3.5). Thus, the correct order from lowest to highest is K, Li, N, O.

Compare the atomic radius of Na and K. Which one is larger?

• K

• Na

• Mg

• Li

Answer explanation

Potassium (K) has a larger atomic radius than sodium (Na) because it is located further down the periodic table. As you move down a group, the atomic radius increases due to the addition of electron shells.

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Why is chlorine more reactive than bromine?

• Chlorine has a higher electronegativity

• Chlorine has a larger atomic radius

• Bromine has a higher ionization energy

• Bromine is a better oxidizing agent

Answer explanation

Chlorine is more reactive than bromine because it has a higher electronegativity, which means it can attract electrons more effectively. This increased ability to gain electrons makes chlorine a stronger oxidizing agent than bromine.

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Why is sodium more likely to lose an electron than magnesium?

• Sodium has a lower ionization energy

• Sodium has a higher atomic mass

• Sodium is a transition metal

• Sodium has more protons than magnesium

Answer explanation

Sodium is more likely to lose an electron than magnesium because it has a lower ionization energy. This means it requires less energy to remove an electron, making it easier for sodium to form a positive ion.

Why are noble gases often used in lightbulbs and signs?

• They are non-reactive.

• They are highly reactive.

• They are magnetic.

• They are radioactive.

Answer explanation

Noble gases are non-reactive, which means they do not easily form compounds. This property makes them ideal for use in lightbulbs and signs, as they can safely contain the gas without reacting with the materials.

Why is fluorine often used in toothpaste? _________

• It is highly reactive.

• It tastes sweet.

• It is a natural dye.

• It is a thickening agent.

Answer explanation

Fluorine is highly reactive, which allows it to bond with minerals in teeth, helping to prevent decay and strengthen enamel. This property makes it effective in toothpaste, unlike the other options listed.

What is the ionization energy of Potassium (K) in Group 1?

• Low

• High

• Very High

• Moderate

Answer explanation

Potassium (K) has a low ionization energy because it is in Group 1, where elements readily lose their outermost electron. This makes it easier to ionize compared to elements with higher ionization energies.

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How does understanding periodic trends help us? _________

• It helps predict the properties and behavior of elements.

• It makes elements heavier.

• It changes the atomic number of elements.

• It allows elements to bond with any substance.

Answer explanation

Understanding periodic trends allows us to predict the properties and behavior of elements, such as reactivity and bonding patterns, which is crucial for studying chemistry and materials.

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