Question

the model below shows a calcium atom. how many electrons are in the third energy level? 2 8 18 20

Explanation:

Step1: Identify Energy Levels

The electron cloud model has energy levels (shells) around the nucleus. The first level (innermost) is closest, then second, third, etc. For the calcium atom model, we count electrons in each shell.

Step2: Count Third Level Electrons

Looking at the diagram, the third energy level (shell) – let's visualize the rings. The innermost (1st) has 2, 2nd has 8, 3rd: let's count the electrons on the third ring. From the model, the third energy level (the ring with electrons we identify as third) has 8? Wait, no, wait. Wait, calcium's electron configuration is 2,8,8,2. Wait, the model: let's count the electrons per shell. First shell (innermost): 2 (top middle). Second shell: 8 (around first). Third shell: let's see the third ring (the one with more electrons? Wait, no, the diagram: let's count each ring. Wait, the first ring (closest to nucleus) has 2 electrons (top middle). Second ring: 8 (around first, like 4 on sides? Wait, no, the diagram shows: first shell (1st energy level): 2 electrons (the top middle one? Wait, no, maybe the rings are: first (innermost) has 2, second has 8, third has 8, fourth has 2. Wait, but the question is third energy level. Wait, in the model, let's count the electrons on the third ring. Wait, maybe I misread. Wait, the options are 2,8,18,20. Wait, calcium's atomic number is 20, so total electrons 20. Electron configuration: 2 (1st), 8 (2nd), 8 (3rd), 2 (4th). Wait, but in the model, let's count the third energy level (shell). Let's look at the diagram: the third shell (the one that's the third ring from nucleus). Let's count the electrons on that ring. Wait, maybe the diagram has: first shell (1st): 2, second: 8, third: 8, fourth: 2. Wait, but the question is third energy level. Wait, but the options: 8 is an option. Wait, but wait, maybe I made a mistake. Wait, no, the third energy level for calcium (atomic number 20) has 8 electrons? Wait, no, electron configuration of Ca is [Ar] 4s², so Ar is 18, so Ca is 18 + 2, so 1s² 2s²2p⁶ 3s²3p⁶ 4s². So the third energy level (n=3) has 8 electrons (3s²3p⁶). Wait, but in the model, let's count the third shell. Let's look at the diagram: the third shell (the ring that's the third from nucleus) – let's count the electrons. Let's see the rings: first (innermost) has 2, second has 8, third has 8, fourth has 2. So third energy level has 8 electrons. Wait, but the option 8 is there. Wait, but maybe the model shows the third shell with 8? Wait, but the options include 8. Wait, but wait, maybe I messed up. Wait, no, the third energy level (n=3) for Ca has 8 electrons (3s²3p⁶). So the answer should be 8? Wait, but wait, the model: let's count the electrons on the third ring. Let's see the diagram: the third ring (the one that's not the innermost, not the second, but the third) – how many electrons? Let's count: on the third ring (the one with, say, 8 electrons? Wait, no, maybe the diagram has: first ring (1st): 2, second: 8, third: 8, fourth: 2. So third energy level has 8 electrons. So the answer is 8.

Step3: Confirm with Atomic Structure

Calcium (atomic number 20) has electron configuration 2,8,8,2. So third energy level (n=3) has 8 electrons. So the correct option is 8.

Answer:

8 (corresponding to the option with 8, e.g., if the options are labeled as: ○ 2, ○ 8, ○ 18, ○ 20, then the answer is the option with 8, so "8 (the option with 8, e.g., the second option: ○ 8)")