Ionization Energy

Ionization Energy

High School

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Learning Objectives

• Define ionization energy and its relationship to cations.

• Describe the periodic trends for ionization energy across periods and down groups.

• Explain how atomic radius and nuclear charge influence ionization energy.

Key Vocabulary

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Ionization Energy

The amount of energy required to remove an electron from a gaseous atom.

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Cation

A positively charged ion formed when a neutral atom loses one or more electrons.

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Nuclear Charge

The total positive charge of the nucleus, determined by the number of protons within it.

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Atomic Radius

The distance from the nucleus to the outermost electron shell, a key factor for ionization energy.

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What is Ionization Energy?

Multiple Choice

What is the primary result of an atom absorbing ionization energy?

• The atom gains an electron to form an anion.

• The atom forms a positively charged cation.

• The atom's nucleus splits into smaller parts.

• The atom releases energy and becomes stable.

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Factors Affecting Ionization Energy

• Atomic radius is the main factor affecting ionization energy.

• Small atoms have high ionization energy due to strong electron attraction.

• Large atoms have low ionization energy due to weaker electron attraction.

• A higher nuclear charge increases attraction, raising the ionization energy.

Multiple Choice

Which combination of factors results in the highest ionization energy for an atom?

• A large atomic radius and a low nuclear charge.

• A large atomic radius and a high nuclear charge.

• A small atomic radius and a high nuclear charge.

• A small atomic radius and a low nuclear charge.

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Periodic Trends of Ionization Energy

• Ionization energy increases as you move from left to right across a period.

• ​This is due to an increasing nuclear charge pulling electrons in tighter.

• Ionization energy decreases as you go down a group on the periodic table.

• Electrons are farther from the nucleus, making them easier to remove.

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Solved Example 1
Which has a higher first ionization energy: a sodium atom or a magnesium atom? Explain your answer based on their positions in the periodic table.

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Step 1: Analyze and Sketch the Problem

• Goal: Determine which atom, sodium (Na) or magnesium (Mg), has a higher first ionization energy.

• Knowns: Sodium is in Group 1, and Magnesium is in Group 2. Both are in Period 3.

• Unknown: The atom with the higher first ionization energy.

• Concept: Ionization energy increases from left to right across a period.

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Solved Example 1
Which has a higher first ionization energy: a sodium atom or a magnesium atom? Explain your answer based on their positions in the periodic table.

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Step 2: Solve for the Unknown

• Locate both elements on the periodic table. Sodium (Na) is element 11, and Magnesium (Mg) is element 12.

• They are in the same period (Period 3).

• Magnesium is to the right of Sodium.

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Solved Example 1
Which has a higher first ionization energy: a sodium atom or a magnesium atom? Explain your answer based on their positions in the periodic table.

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Step 3: Evaluate the Answer

• According to the periodic trend, ionization energy increases as you move from left to right across a period.

• Therefore, because magnesium is to the right of sodium, it has a greater nuclear charge and a higher first ionization energy.

Multiple Choice

Why does ionization energy typically increase when moving from left to right across a period?

• The increasing nuclear charge creates a stronger attraction for electrons.

• New energy levels are added, making electrons easier to remove.

• The number of valence electrons decreases.

• The atomic radius increases, weakening the pull on electrons.

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Common Misconceptions about Ionization Energy

Misconception	Correction
Ionization energy is the energy that an atom releases.	Ionization energy is the energy that must be absorbed to remove an electron.
The atom with the most electrons has the lowest ionization energy.	It depends on the outermost electron and the nuclear charge.
Moving across a period adds new electron shells, making electrons easier to remove.	Electrons are added to the same valence shell, increasing the ionization energy.

Multiple Choice

Which of the following sets of elements is arranged correctly in order of increasing ionization energy?

• F, Cl, Br, I

• Ne, C, B, Li

• Cs, K, Na, Li

• Ca, Mg, Be, B

Multiple Choice

Which of these elements would require the least amount of energy to ionize?

• Ca

• K

• P

• S

Multiple Choice

An unknown element has a lower ionization energy than Iodine (I) but a higher ionization energy than Cesium (Cs). Based on periodic trends, which of the following elements is it most likely to be?

• Xenon (Xe)

• Barium (Ba)

• Chlorine (Cl)

• Sodium (Na)

Multiple Choice

If an element has a very low first ionization energy, what can you predict about its characteristics and reactivity?

• It likely has a small atomic radius and does not form ions easily.

• It likely has a large atomic radius and readily forms an anion.

• It likely has a small atomic radius and is chemically inert.

• It likely has a large atomic radius and readily forms a cation.

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Summary

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1

• 2

• 3

• 4