Chemistry: Periodic Trends: Atomic Radius, Ionization Energy Worksheet

Question 1

Define atomic radius and explain the general trend in atomic radius as you move from left to right across a period.

Accepted Answer

Atomic radius is a measure of the size of an atom, often described as half the distance between the nuclei of two bonded identical atoms. Atomic radius generally decreases from left to right across a period because the number of protons increases while electrons are added to the same energy level, so the nucleus pulls the electrons closer.

Question 2

Define first ionization energy and explain the general trend in first ionization energy as you move from left to right across a period.

Accepted Answer

First ionization energy is the energy required to remove the outermost electron from one mole of gaseous atoms. It generally increases from left to right across a period because the nucleus has a stronger pull on the valence electrons, making them harder to remove.

Question 3

Rank the following atoms from smallest atomic radius to largest atomic radius: Na, Mg, Al, Si.

Accepted Answer

The order from smallest to largest atomic radius is Si, Al, Mg, Na. These elements are all in Period 3, and atomic radius decreases from left to right across a period.

Question 4

Rank the following atoms from lowest first ionization energy to highest first ionization energy: K, Li, Na, Rb.

Accepted Answer

The order from lowest to highest first ionization energy is Rb, K, Na, Li. These elements are all in Group 1, and first ionization energy decreases as you move down a group.

Question 5

Explain why atomic radius generally increases as you move down a group on the periodic table.

Accepted Answer

Atomic radius generally increases down a group because each lower element has an additional principal energy level. The added electron shell places valence electrons farther from the nucleus, and inner electrons shield the valence electrons from the full nuclear charge.

Question 6

Which atom has the larger atomic radius, chlorine or bromine? Explain your answer.

Accepted Answer

Bromine has the larger atomic radius. Bromine is below chlorine in Group 17, so it has more occupied energy levels and a larger electron cloud.

Question 7

Which atom has the higher first ionization energy, sulfur or chlorine? Explain your answer.

Accepted Answer

Chlorine has the higher first ionization energy. Chlorine is to the right of sulfur in the same period, so its valence electrons experience a stronger effective nuclear charge and are harder to remove.

Question 8

Use the concept of effective nuclear charge to explain why sodium has a larger atomic radius than magnesium.

Accepted Answer

Sodium has a larger atomic radius than magnesium because magnesium has one more proton in its nucleus while its valence electrons are in the same principal energy level as sodium's. The greater effective nuclear charge in magnesium pulls its electrons closer, making magnesium smaller.

Question 9

Arrange these elements in order of increasing atomic radius: F, O, N, C.

Accepted Answer

The order of increasing atomic radius is F, O, N, C. These elements are in Period 2, and atomic radius decreases from left to right, so the element farthest right is the smallest.

Question 10

Arrange these elements in order of increasing first ionization energy: Al, Mg, Si, P. Note that small exceptions can occur in the trend.

Accepted Answer

A reasonable order of increasing first ionization energy is Al, Mg, Si, P. Although ionization energy usually increases across Period 3, aluminum is lower than magnesium because aluminum's first electron removed is from a higher energy 3p orbital, while magnesium's is from a filled 3s orbital.

Question 11

A student says, "Potassium has a higher first ionization energy than sodium because potassium has more protons." Correct the student's reasoning.

Accepted Answer

The student's conclusion is incorrect. Potassium has a lower first ionization energy than sodium because potassium's valence electron is in a higher energy level farther from the nucleus and is more shielded by inner electrons, so it is easier to remove despite potassium having more protons.

Question 12

Compare the size of a neutral sodium atom, Na, with a sodium ion, Na+. Which is smaller, and why?

Accepted Answer

Na+ is smaller than neutral Na. When sodium loses its valence electron, it loses its outer energy level, and the remaining electrons are pulled closer to the nucleus.

Question 13

Compare the size of a neutral chlorine atom, Cl, with a chloride ion, Cl-. Which is larger, and why?

Accepted Answer

Cl- is larger than neutral Cl. When chlorine gains an electron, increased electron-electron repulsion expands the electron cloud, making the anion larger than the neutral atom.

Question 14

The first ionization energies for three Period 3 elements are about 496 kJ/mol, 738 kJ/mol, and 786 kJ/mol. These values belong to Na, Mg, and Si. Match each value to the correct element and explain your reasoning.

Accepted Answer

Na is 496 kJ/mol, Mg is 738 kJ/mol, and Si is 786 kJ/mol. First ionization energy generally increases from left to right across Period 3, so sodium is the lowest, magnesium is higher, and silicon is higher still.

Question 15

Write a short explanation connecting atomic radius and first ionization energy. Why do they often show opposite trends on the periodic table?

Accepted Answer

Atomic radius and first ionization energy often show opposite trends because electrons in smaller atoms are usually held more tightly by the nucleus. Across a period, atomic radius decreases while ionization energy increases. Down a group, atomic radius increases while ionization energy decreases because valence electrons are farther from the nucleus and more shielded.

Chemistry: Periodic Trends: Atomic Radius, Ionization Energy

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