Name Periodic Trends Worksheet Use the periodic table and your knowledge of periodic trends to answer the following questions. 1. Which atom in each pair has the larger atomic radius? a) Li or K b) Ca or Ni c) Ga or B d) O or C e) Cl or Br f) Be or Ba g) Si or S h) Fe or Au 2. What is the periodic trend for atomic size from top to bottom in a group? from left to right in a period 3. Why do atoms get smaller as you move left to right in a period? 4. Which element in each pair has a larger ionization energy? a) Na or O b) Be or Ba c) Ar or F d) Cu or Ra e) I or Ne f) K or V g) Ca or Fr h) W or Se
The Correct Answer and Explanation is:
Of course. Here are the correct answers to the worksheet, followed by a detailed, book-style explanation of the concepts.
Answer Key
1. Which atom in each pair has the larger atomic radius?
a) K
b) Ca
c) Ga
d) C
e) Br
f) Ba
g) Si
h) Au
2. What is the periodic trend for atomic size from top to bottom in a group? from left to right in a period?
- Top to bottom in a group: Atomic size increases.
- Left to right in a period: Atomic size decreases.
3. Why do atoms get smaller as you move left to right in a period?
As you move from left to right across a period, protons are added to the nucleus, which increases the positive nuclear charge. This stronger positive charge pulls the electrons in the same energy level more tightly toward the nucleus, causing the atom to become smaller.
4. Which element in each pair has a larger ionization energy?
a) O
b) Be
c) F
d) Cu
e) I or Ne -> Ne (Corrected from image)
f) V
g) Ca
h) W or Se -> Se (Corrected from image)
Explanation of Periodic Trends
The properties of chemical elements are not random; they follow predictable patterns, or trends, based on their location in the periodic table. Understanding these trends allows us to predict an element’s behavior. Two of the most fundamental trends are atomic radius and ionization energy.
Atomic Radius
The atomic radius is a measure of the size of an atom, typically defined as half the distance between the nuclei of two identical atoms bonded together. The size of an atom is primarily determined by its electron cloud.
- Trend Down a Group (Increases): As you move down a group in the periodic table, each element has one more principal energy level (or electron shell) than the one above it. This new, outermost shell is significantly farther from the nucleus, causing the atomic radius to increase. While the nuclear charge also increases, the effect of adding a new, distant electron shell is far more dominant. Furthermore, the inner electrons create a “shielding effect,” which blocks some of the nucleus’s positive pull from reaching the outermost electrons, allowing them to remain further away.
- Trend Across a Period (Decreases): When moving from left to right across a period, electrons are added to the same principal energy level. At the same time, protons are added to the nucleus, increasing its positive charge. This increased nuclear charge pulls the entire electron cloud, including the outermost electrons, closer to the nucleus. Because the number of inner, shielding electrons remains constant, the effective nuclear charge experienced by the outer electrons increases, resulting in a smaller atomic radius.
Ionization Energy
Ionization energy is the minimum energy required to remove the most loosely held electron from a neutral gaseous atom. It is a measure of how strongly an atom holds onto its electrons.
- Trend Down a Group (Decreases): As you move down a group, the atomic radius increases. The outermost electron is farther from the nucleus and is more effectively shielded by the inner electron shells. This weakened attraction between the nucleus and the valence electron means that less energy is required to remove it. Therefore, ionization energy decreases down a group.
- Trend Across a Period (Increases): As you move from left to right across a period, the atomic radius decreases and the effective nuclear charge increases. The electrons are held more tightly by the increasingly positive nucleus. Consequently, it takes significantly more energy to overcome this strong attraction and remove an electron. Thus, ionization energy generally increases from left to right across a period. Noble gases (Group 18) have the highest ionization energies in their respective periods because their stable, filled electron shells make them very resistant to losing an electron.
