What is Atomic Radius? Periodic Trends

Summary

This video explains the concept of atomic radius and its periodic trends. Atomic radius is defined as the distance between an atom's nucleus and its outermost electron. The video explores how atomic radius decreases across a period from left to right due to increased nuclear attraction, while it increases down a group because of the addition of electron shells and the shielding effect. The script also covers how atomic radius is measured in picometers and answers common conceptual questions to help viewers better understand these trends in the periodic table.

Takeaways

• 😀 Atomic radius is the distance from the nucleus to the outermost electron of an atom.
• 😀 The atomic radius can be demonstrated by looking at different atoms, such as hydrogen and sodium, where hydrogen has a single shell and sodium has three.
• 😀 Atomic radius is measured in picometers (pm), a unit commonly used in atomic scale measurements.
• 😀 As you move across a period (left to right) in the periodic table, the atomic radius decreases.
• 😀 The decrease in atomic radius across a period is due to an increasing number of protons which attract electrons more strongly, pulling them closer to the nucleus.
• 😀 Despite the increase in atomic number, the number of electron shells remains the same across a period, which contributes to the decreasing size of the atom.
• 😀 Atomic radius is smaller in elements like fluorine compared to lithium because fluorine has more protons, creating a stronger pull on electrons.
• 😀 As you move down a group in the periodic table, the atomic radius increases.
• 😀 The increase in atomic radius down a group is due to the addition of electron shells, which increase the distance between the nucleus and the outermost electrons.
• 😀 The shielding effect, which occurs when inner electron shells repel outer electrons, increases as you go down a group, making the nucleus’ attraction weaker on outer electrons.
• 😀 The larger atomic radius of elements like sodium compared to lithium or hydrogen is a result of more electron shells and a greater shielding effect as you move down the group.

Q & A

What is atomic radius?

Atomic radius is the distance between the nucleus of an atom and its outermost electron.

How is atomic radius measured?

Atomic radius is measured in picometers (pm).

What is the atomic radius of a hydrogen atom?

The atomic radius of a hydrogen atom is the distance between its nucleus and its single outer electron.

Why does the atomic radius decrease across a period in the periodic table?

The atomic radius decreases across a period because the number of protons increases, which attracts electrons more strongly, pulling them closer to the nucleus. The number of electron shells remains constant.

How does the atomic radius change across the second period of the periodic table (Li to F)?

As we move from lithium to fluorine across the second period, the atomic number increases, and the atomic radius decreases. This is because the nuclear charge increases, attracting electrons more strongly, and pulling them closer to the nucleus.

Why is the atomic radius of fluorine smaller than lithium?

Fluorine has more protons and electrons than lithium, resulting in a stronger nuclear attraction, which pulls its electrons closer to the nucleus, making its atomic radius smaller.

What happens to the atomic radius as we move down a group in the periodic table?

As we move down a group, the atomic radius increases because the number of electron shells increases. This leads to greater shielding by inner electrons, reducing the attractive force between the outer electrons and the nucleus, allowing the outer electrons to be farther from the nucleus.

What is the shielding effect?

The shielding effect refers to the repulsion between electrons in inner shells and the electrons in outer shells, which reduces the attraction between the outer electrons and the nucleus.

Why is the atomic radius of sodium larger than lithium or hydrogen?

Sodium has more electron shells than lithium and hydrogen, which leads to increased shielding and a larger atomic radius. The outer electrons are farther from the nucleus due to the shielding effect.

How does the atomic radius of elements in Group 1 change as you move from hydrogen to sodium?

As you move down Group 1 from hydrogen to sodium, the atomic radius increases because the number of electron shells increases, and the shielding effect becomes stronger, causing the outer electrons to be farther from the nucleus.