Atomic radius trends on periodic table | Periodic table | Chemistry | Khan Academy
TLDRThe video script delves into the concept of atomic size and radius, clarifying misconceptions about electron orbits and introducing the idea of orbitals as probability distributions. It explains that atomic radius is not fixed due to the probabilistic nature of electron locations. The Van der Waals radius and covalent bond measurements are presented as methods to determine atomic size. The script then explores the trends in atomic radii across the periodic table, noting that atoms generally decrease in size from left to right within a period due to increased nuclear charge attracting electrons more strongly. Conversely, as you move down a group in the periodic table, atomic radius increases because additional electron shells are added, which are located further from the nucleus. The smallest atom is helium, and the largest atoms are found at the bottom left of the periodic table, with a general trend of decreasing size from the bottom left to the top right.
Takeaways
- 🧐 The concept of atomic radius is not as straightforward as measuring the radius of a circle because atoms do not have a fixed size due to the probabilistic nature of electron orbitals.
- 🚀 Electrons are not in fixed orbits but exist in orbitals, which are probability distributions of where the electrons can be found.
- 📏 The atomic radius is often defined as half the distance between two unbonded, identical atoms that are at the closest distance where they do not bond, known as the Van der Waals radius.
- 🔬 In a covalent bond, the atomic radius can be considered as half the distance between the nuclei of two bonded atoms, as the electron cloud overlaps.
- 📉 As you move from left to right across a period in the periodic table, the atomic radius generally decreases due to an increase in nuclear charge attracting the electrons more strongly.
- 📌 The atomic radius of an element is smaller when it has more protons in its nucleus because the increased positive charge pulls the electron cloud closer.
- 📚 The smallest atom is not hydrogen but helium, which has a higher nuclear charge that draws its electrons closer, resulting in a smaller atomic radius.
- 📶 When moving down a group in the periodic table, the atomic radius increases because each successive element has an additional electron shell, which is further from the nucleus.
- 🔄 The general trend in the periodic table is that atomic radius increases as you go down a group and decreases as you move across a period from left to right.
- 🏙️ The largest atoms are found at the bottom left of the periodic table, while the smallest are at the top right, reflecting the overall trend of atomic size.
- ⚛️ The atomic radius is influenced by the balance between the positive charge in the nucleus and the negative charge of the electrons, with more positive charge leading to a smaller radius.
Q & A
What is the concept of atomic radius and why might it be misleading to compare it to the radius of a physical circle?
-Atomic radius refers to the size of an atom, but unlike a physical circle, it does not have a well-defined edge. This is because electrons exist in orbitals, which are probability distributions rather than fixed orbits, making it challenging to pinpoint a specific radius.
How do electrons' orbitals differ from the orbits of planets around the sun?
-Electrons exist in orbitals, which are probability distributions that describe where an electron is likely to be found. This contrasts with the orbits of planets, which are well-defined paths around the sun.
What is the Van der Waals radius and how is it determined?
-The Van der Waals radius is a measure of the size of an atom. It is determined by finding the closest distance at which two identical atoms can approach each other without bonding and then taking half of that distance.
How is the atomic radius defined when two atoms are bonded through a covalent bond?
-In a covalent bond, the atomic radius can be defined as half the distance between the two nuclei since the electron clouds of the bonded atoms overlap, allowing electrons to spend time around both nuclei.
What is the general trend for atomic radii as you move from left to right across a period in the periodic table?
-As you move from left to right across a period, the atomic radius generally decreases. This is due to an increase in the positive charge in the nucleus, which pulls the outer electron shell inward, reducing the atomic size.
Why is helium considered smaller than hydrogen in terms of atomic radius?
-Helium is considered smaller than hydrogen because it has a higher positive charge in the nucleus (+2 compared to hydrogen's +1), which results in a stronger attraction to the electrons, pulling them closer and reducing the atomic radius.
What happens to atomic size as you move down a group in the periodic table?
-As you move down a group in the periodic table, the atomic size increases. This is because each successive element adds a new electron shell, which is further from the nucleus, increasing the overall atomic radius.
What is the general trend for atomic radii as you move up a group in the periodic table?
-As you move up a group in the periodic table, the atomic size decreases. This is due to the increasing positive charge in the nucleus relative to the number of electron shells, which pulls the electrons closer and reduces the atomic radius.
Which elements are expected to have the largest atomic radii in the periodic table?
-The elements at the bottom left of the periodic table, which are the heavier elements in the p-block, are expected to have the largest atomic radii due to the increased number of electron shells.
Which elements are expected to have the smallest atomic radii in the periodic table?
-The elements at the top right of the periodic table, which are the noble gases, tend to have the smallest atomic radii due to the higher effective nuclear charge and fewer electron shells.
How does the number of protons in an atom's nucleus affect its atomic radius?
-The number of protons in an atom's nucleus increases the positive charge, which leads to a stronger attraction to the electrons. This stronger electrostatic force pulls the electron cloud closer to the nucleus, resulting in a smaller atomic radius.
What is the significance of the atomic radius in chemical bonding and the formation of molecules?
-The atomic radius is significant in chemical bonding as it helps determine the distance between bonding atoms and the nature of the bond (covalent, ionic, or metallic). It also influences the types of molecules that can form and their overall shape and size.
Outlines
🤔 Understanding Atomic Radius
The paragraph discusses the concept of atomic size and radius. It clarifies that the traditional idea of radius as the distance from the center to the edge of a circular object doesn't directly apply to atoms. The narrator explains that electrons are not in fixed orbits but exist in orbitals, which are probability distributions of where they might be found. The atomic radius is not a simple measurement because electrons don't have a defined edge. Several techniques are introduced to conceptualize atomic size, including the Van der Waals radius and the radius derived from covalent bonds. The paragraph concludes with an invitation to consider the trends in atomic size across the periodic table.
📊 Trends in Atomic Radii
This paragraph explores the trends in atomic radii within the periodic table. It focuses on the changes in atomic radius as one moves across a period (from left to right) and down a group (from top to bottom) in the periodic table. The narrator explains that as one moves from potassium to krypton in the fourth period, the atomic radius decreases due to an increase in the positive charge in the nucleus, which pulls the outer shell electrons closer. This results in a general trend of decreasing atomic size as one moves right across a period. Conversely, as one moves down a group, the atomic radius increases because additional electron shells are added, which are further from the nucleus. The overall trend is that atoms get smaller moving from the bottom left to the top right of the periodic table, with the smallest atoms found at the top right and the largest at the bottom left.
Mindmap
Keywords
💡Atomic Radius
💡Orbitals
💡Van der Waals Radius
💡Covalent Bond
💡Periodic Table
💡Electron Cloud
💡Coulomb's Law
💡Shells
💡Trends in Atomic Size
💡Helium
💡Isotopes
Highlights
The concept of atomic size or atomic radius is not as straightforward as calculating the radius of a circular object.
People often visualize atoms with a positive nucleus and electrons in fixed orbits, but this is an outdated model.
Electrons exist in orbitals, which are probability distributions rather than fixed paths.
The lack of a hard edge in electron orbitals makes defining atomic size challenging.
The Van der Waals radius is a technique for determining the size of an atom when two of the same atoms are not bonded.
Covalent bonds involve overlapping electron clouds, which can be used to estimate atomic radius.
Atomic radii generally decrease from left to right across a period in the periodic table due to increasing nuclear charge.
Helium has a smaller atomic radius than hydrogen, despite being to the right in the periodic table.
The atomic radius increases as you go down a group in the periodic table because additional electron shells are added.
The general trend in the periodic table is that atomic size decreases from the bottom left to the top right.
The atomic radius is influenced by the balance between the positive charge in the nucleus and the negative charge of the electrons.
As more protons are added to the nucleus, the increased positive charge pulls the electron cloud inward, reducing the atomic radius.
The concept of atomic size is complex and requires understanding the distribution of electrons around the nucleus.
Different methods of measuring atomic size can yield different results, such as the use of Van der Waals radius versus covalent bond lengths.
The atomic radius is not a fixed value and can vary depending on the element's chemical environment.
Understanding atomic size is crucial for predicting chemical behavior and the structure of molecules.
The atomic radius trends in the periodic table are essential for understanding the periodic properties of elements.
Transcripts
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