Main Group Elements: Periodic Trends: Videos & Practice Problems

Periodic trends can be categorized into two groups: Type A and Type B. Type A trends, including Lattice Energy, Ionization Energy, Electron Affinity, and Electronegativity, all increase towards the top right corner of the periodic table, which can be remembered with the phrase "when you lie, you make stuff up." In contrast, Type B trends, such as metallic character and atomic radius, decrease in the same direction. Understanding these trends is crucial for grasping concepts like ionization energy and electron affinity, which are foundational in chemistry.

Periodic Trends

In the study of periodic trends within the periodic table, two distinct categories emerge: Periodic Trends A and Periodic Trends B. Periodic Trends A encompasses Lattice Energy, Ionization Energy, Electron Affinity, and Electronegativity, all of which exhibit an increasing trend as one moves towards the top right corner of the periodic table. A mnemonic to remember these trends is the phrase "when you lie, you make stuff up," where the initial letters correspond to the trends: L for Lattice Energy, I for Ionization Energy, E for Electron Affinity, and E for Electronegativity.

Conversely, Periodic Trends B includes Metallic Character and Atomic Radius, which decrease as one approaches the top right corner. This inverse relationship highlights that as the trends in A increase, those in B must decrease, reinforcing the interconnected nature of these properties. Understanding these trends is crucial, especially for concepts like Ionization Energy and Electron Affinity, which can become complex. Therefore, reviewing these properties is recommended for a comprehensive grasp of periodic trends.

In summary, Periodic Trends A increase towards the top right corner, while Periodic Trends B decrease, illustrating the dynamic nature of elemental properties across the periodic table.

Main Group Elements: Periodic Trends Example

In comparing the properties of group 3A elements to group 1A elements in the periodic table, we observe distinct trends in atomic radii and ionization energies. The atomic radius, which is a measure of the size of an atom, generally decreases as one moves from left to right across a period. This trend indicates that group 3A elements possess smaller atomic radii compared to group 1A elements. On the other hand, ionization energy, the energy required to remove an electron from an atom, exhibits an increasing trend as one moves towards the top right corner of the periodic table. Consequently, group 3A elements have higher ionization energies than their group 1A counterparts. Thus, when evaluating these properties, it is clear that group 3A elements have lower atomic radii and higher ionization energies than group 1A elements, leading to the conclusion that the correct choice reflects these differences.

Rank the following elements in order of increasing lattice energy: S, In, K, Ba and Cl

• A. Ba < In < S < K < Cl
• B. Cl < S < In < K > Ba
• C. Ba < K < In < S < Cl
• D. Cl < In < K < S < Ba
• E. In < Ba < Cl < S < K

Answer: (C)

Which of the following elements will have the lowest electron affinity?

• A. Cl
• B. K
• C. P
• D. Be
• E. O

Answer: (B)

For Group 5A elements, the ionization energy decreases going down a group because:

• A. Their atomic masses increases.
• B. The highest number of their valence orbital shell increases.
• C. Their metallic character decreases.
• D. Their electron affinity increases.
• E. The number of neutrons in their nuclei decreases.

Answer: (B)

Here’s what students ask on this topic:

What are the periodic trends for ionization energy and how do they change across the periodic table?

Ionization energy is the energy required to remove an electron from an atom in its gaseous state. As you move across a period from left to right, ionization energy increases. This is because the nuclear charge increases, making it more difficult to remove an electron. As you move down a group, ionization energy decreases because the electrons are further from the nucleus and are shielded by inner electrons, making them easier to remove. Therefore, ionization energy increases towards the top right corner of the periodic table.

How does electronegativity vary across the periodic table?

Electronegativity is a measure of an atom's ability to attract and hold onto electrons in a chemical bond. As you move across a period from left to right, electronegativity increases due to the increasing nuclear charge, which attracts electrons more strongly. As you move down a group, electronegativity decreases because the additional electron shells reduce the nucleus's pull on the bonding electrons. Therefore, electronegativity increases towards the top right corner of the periodic table, with fluorine being the most electronegative element.

What is the trend for atomic radius across the periodic table?

Atomic radius is the distance from the nucleus to the outermost electron shell. As you move across a period from left to right, atomic radius decreases because the increasing nuclear charge pulls the electron cloud closer to the nucleus. As you move down a group, atomic radius increases due to the addition of electron shells, which outweighs the increase in nuclear charge. Therefore, atomic radius decreases towards the top right corner of the periodic table.

How do lattice energy and electron affinity change across the periodic table?

Lattice energy is the energy released when ions form a crystalline lattice. It increases with the charge of the ions and decreases with the size of the ions. As you move across a period, lattice energy generally increases due to smaller ionic sizes and higher charges. Electron affinity is the energy change when an electron is added to a neutral atom. It becomes more negative (more energy is released) as you move across a period from left to right, indicating a stronger attraction for the added electron. Both lattice energy and electron affinity increase towards the top right corner of the periodic table.

What is the relationship between metallic character and periodic trends?

Metallic character refers to the tendency of an element to lose electrons and form positive ions (cations). As you move across a period from left to right, metallic character decreases because elements become less likely to lose electrons due to increasing ionization energy and electronegativity. As you move down a group, metallic character increases because elements are more likely to lose electrons due to lower ionization energy. Therefore, metallic character decreases towards the top right corner of the periodic table, with elements on the left and bottom being more metallic.