Atomic Radius Worksheet Answers: Periodic Trends Explained

Understanding Atomic Radius and Periodic Trends

Atomic radius is a fundamental concept in chemistry that helps us understand the size of atoms and their relationships with other elements. It is defined as the distance from the nucleus of an atom to the outermost electron in its ground state. Understanding atomic radius is crucial in predicting the physical and chemical properties of elements. In this worksheet, we will explore the periodic trends of atomic radius and provide answers to common questions.

What is Atomic Radius?

Atomic radius is a measure of the size of an atom, typically measured in picometers (pm). It is the distance from the nucleus of an atom to the outermost electron in its ground state. The atomic radius of an element is influenced by the number of protons and electrons in its atomic structure.

Factors Affecting Atomic Radius

Several factors affect the atomic radius of an element:

• Effective Nuclear Charge: The effective nuclear charge is the net positive charge experienced by an electron in an atom. As the effective nuclear charge increases, the atomic radius decreases.
• Electron Shielding: Electron shielding occurs when inner electrons shield the outer electrons from the nuclear charge. This reduces the effective nuclear charge and increases the atomic radius.
• Electron Configuration: The electron configuration of an atom determines the number of electrons in each energy level. As the number of electrons in an energy level increases, the atomic radius decreases.

Periodic Trends of Atomic Radius

The atomic radius of elements exhibits periodic trends across the periodic table. These trends can be explained by the factors mentioned earlier.

• Atomic Radius Decreases from Left to Right: As we move from left to right across a period, the effective nuclear charge increases, and the atomic radius decreases. This is because the number of protons in the nucleus increases, pulling the electrons closer to the nucleus.
• Atomic Radius Increases Down a Group: As we move down a group, the atomic radius increases. This is because the number of energy levels increases, and the outermost electrons are farther away from the nucleus.

Exceptions to Periodic Trends

There are some exceptions to the periodic trends of atomic radius. These exceptions occur due to the following reasons:

• Lanthanoid Contraction: The lanthanoid contraction is a phenomenon where the atomic radius of elements in the lanthanoid series (La-Lu) decreases. This is due to the poor shielding of electrons by the 4f electrons.
• Actinoid Contraction: The actinoid contraction is a phenomenon where the atomic radius of elements in the actinoid series (Ac-Lr) decreases. This is due to the poor shielding of electrons by the 5f electrons.

Worksheet Answers

Here are the answers to common questions about atomic radius and periodic trends:

• What is the atomic radius of hydrogen?: The atomic radius of hydrogen is 37 pm.
• Which element has the largest atomic radius?: The element with the largest atomic radius is francium (Fr), with an atomic radius of 348 pm.
• Which element has the smallest atomic radius?: The element with the smallest atomic radius is helium (He), with an atomic radius of 31 pm.
• What is the trend of atomic radius across a period?: The atomic radius decreases from left to right across a period.
• What is the trend of atomic radius down a group?: The atomic radius increases down a group.

💡 Note: The atomic radius values mentioned above are approximate and may vary slightly depending on the source.

In conclusion, understanding atomic radius and periodic trends is crucial in predicting the physical and chemical properties of elements. By analyzing the factors that affect atomic radius and identifying periodic trends, we can better understand the behavior of elements and their relationships with other elements.

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