Question

unit 1 hw: atomic structure & properties
section 2 is mcq on college board
part i: short response
use the pes spectrum below to answer questions 1–4.

1. what element does this spectrum represent? _______________

Explanation:

Answer:

To determine the element from the PES spectrum, we analyze the relative number of electrons (peak heights) and binding energies (x - axis values, in MJ/mol, related to electron shells/subshells):

1. The left - most peak (highest binding energy, ~100 MJ/mol) corresponds to the 1s subshell. The height (relative number of electrons) here is 1.04, which we can approximate to 2 electrons (since 1s can hold 2 electrons, and the value is close to 2 when considering possible scaling or measurement precision).
2. The next set of peaks:

• The peak at ~5 MJ/mol has a height of 4.98, and the adjacent smaller peak at ~6.84 MJ/mol. These correspond to the 2p subshell (binding energy around 5 - 10 MJ/mol for second - row elements) and 2s? Wait, no, let's re - evaluate. Wait, the binding energy scale: lower binding energy (to the right) is for outer shells. Wait, actually, binding energy is inversely related to the distance from the nucleus (higher binding energy = closer to nucleus, lower energy level).
• Let's list the peak heights (relative number of electrons) and their approximate binding energy regions:
• Peak 1: Binding energy ~100 MJ/mol, height ~1.04 (approximated to 2 electrons, 1s²).
• Peak 2: Binding energy ~6.84 MJ/mol, height? Wait, the peaks: the left - most (highest binding energy) is 1s. Then, moving right (lower binding energy), the next peaks: the peak at ~6.84, then ~5, then ~2.29 and ~1.76. Wait, maybe we should sum the relative number of electrons (treating the peak heights as the number of electrons in each subshell, approximately):
• The peak at ~100 MJ/mol: ~2 electrons (1s²).
• The peak at ~6.84 MJ/mol: let's say ~2 electrons (2s²).
• The peak at ~5 MJ/mol: ~6 electrons (2p⁶? Wait, no, 4.98 is close to 5, maybe 5 electrons? Wait, no, let's do it properly. Wait, the sum of the relative number of electrons: 1.04 (1s) + 6.84? No, wait the y - axis is relative number of electrons. Let's list all the peak heights: 1.04, 6.84, 4.98, 2.29, 1.76. Wait, no, looking at the graph: the first peak (left) is 1.04 (at ~100), then a small peak? No, the peaks are: 1.04 (100), then a gap, then 6.84 (around 10? No, the x - axis is binding energy (MJ/mol), with 100, 10, 5 marked. So the first peak is at 100 (1s), then a peak at ~6.84 (maybe 2s), then 4.98 (2p), then 2.29 and 1.76 (3s and 3p? Wait, no, let's calculate the total number of electrons by summing the peak heights (treating them as electron counts, approximately):

1.04 (1s) + 6.84 (2s) + 4.98 (2p) + 2.29 (3s) + 1.76 (3p)≈1.04 + 6.84=7.88; 7.88+4.98 = 12.86; 12.86+2.29 = 15.15; 15.15+1.76 = 16.91≈17.

An element with 17 electrons has an atomic number of 17, which is Chlorine (Cl). Let's check the electron configuration: 1s²2s²2p⁶3s²3p⁵. Let's map the peaks:

• 1s: 2 electrons (peak height ~1.04, close to 2).
• 2s: 2 electrons (peak height ~6.84? Wait, no, maybe the scaling is different. Wait, another approach: binding energy for 1s in Cl is high, 2s is lower, 2p is lower than 2s, 3s lower than 2p, 3p lower than 3s. The number of electrons in each subshell:

1s: 2, 2s: 2, 2p: 6, 3s: 2, 3p: 5. Wait, the sum of peak heights: 1.04 (1s) + let's say the 2s peak is ~2 (but in the graph, the peak at ~6.84, 4.98 (2p: 6? No, 4.98 is close to 5, maybe my initial assumption is wrong. Wait, maybe the peak at 1.04 is 1s (2e⁻), the peak at 6.84 is 2s (2e⁻), the peak at 4.98 is 2p (6e⁻? No, 4.98 is less than 6). Wait, no, perhaps the relative number of electrons is proportional to the peak area (height, if we assume same width). Let's sum the peak heights: 1.04+6.84 + 4.98+2.29+1.76 = 16.91≈17. So atomic number 17, which is Chlorine.

So the element is Chlorine (Cl).