Question

how does ionization energy change down a group?

1. label your x - axis as atomic number and the y - axis as the ionization energy.
2. go to table s. fill in the table below

element name	atomic number	ionization energy
potassium
cesium
francium

1. plot the data on your graph.

Explanation:

To solve this problem about ionization energy trends down a group (for Group 1 elements: Lithium, Potassium, Cesium, Francium), we follow these steps:

Step 1: Recall Atomic Numbers and Ionization Energies

• Lithium (Li): Atomic number = 3; First ionization energy ≈ 520 kJ/mol (from standard periodic table data).
• Potassium (K): Atomic number = 19; First ionization energy ≈ 419 kJ/mol.
• Cesium (Cs): Atomic number = 55; First ionization energy ≈ 376 kJ/mol.
• Francium (Fr): Atomic number = 87; First ionization energy ≈ 393 kJ/mol (note: Francium is radioactive, and precise values can vary, but the trend is clear).

Step 2: Fill the Table

Using the values above, we fill the table:

Element name	Atomic Number	Ionization energy (kJ/mol)
Potassium	19	419
Cesium	55	376
Francium	87	393 (approximate)

Step 3: Plot the Data

• X - axis (Atomic Number): Mark the atomic numbers 3, 19, 55, 87 on the x - axis.
• Y - axis (Ionization Energy): Use a suitable scale (e.g., from 300 to 600 kJ/mol) and mark the ionization energy values for each element.
• Plot the points (3, 520), (19, 419), (55, 376), (87, 393) on the graph.

Step 4: Analyze the Trend

When we plot the data, we observe that as we move down the group (from Lithium to Cesium, and approximately to Francium), the ionization energy generally decreases (with a small anomaly for Francium, but the overall trend for the first three elements is a clear decrease). This is because as we go down a group, the atomic radius increases. The outermost electrons are further from the nucleus, and the shielding effect (due to inner electron shells) increases. So, the attractive force between the nucleus and the outermost electron decreases, making it easier to remove the electron (lower ionization energy).

If we were to summarize the trend from the plotted data:

1. First, we determine the atomic numbers and ionization energies of Lithium (Li: atomic number 3, ~520 kJ/mol), Potassium (K: atomic number 19, ~419 kJ/mol), Cesium (Cs: atomic number 55, ~376 kJ/mol), and Francium (Fr: atomic number 87, ~393 kJ/mol).
2. Then we fill the table with these values.
3. Next, we plot the points (atomic number, ionization energy) on a graph with atomic number on the x - axis and ionization energy on the y - axis.
4. From the plot, we see that as we move down the group (increasing atomic number), the ionization energy generally decreases (with a small deviation for Francium, but the trend for Li, K, Cs is a decrease). This is due to increasing atomic radius and shielding effect, which weakens the nuclear attraction on the outermost electron.

Answer:

(Trend):
Ionization energy generally decreases as we move down the group (from Lithium to Cesium, and approximately to Francium) in the periodic table. The plotted data shows a downward trend (with a minor exception for Francium) as atomic number increases down the group.