this energy in the form of light. what happens to the electrons as the light is released? section 3 review key ideas 1. state two key features of the modern model of the atom. 2. explain what determines how the energy levels in an atom are filled. 3. describe what happens when an electron jumps from one energy level to another. 4. identify how many electrons the third energy level can hold, and explain why this is the case.

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### Question 1: State two key features of the modern model of the atom.
# Brief Explanations:
1. Electrons occupy specific energy levels (orbitals) around the nucleus, and these energy levels have discrete energies.
2. The nucleus contains protons (positively charged) and neutrons (neutral), and the electrons (negatively charged) are in the electron cloud outside the nucleus, with their behavior described by quantum mechanics (e.g., electron probability distributions).
# Answer:
1. Electrons exist in discrete energy levels (orbitals) with specific energy values around the nucleus.
2. The nucleus is composed of protons (positive charge) and neutrons (neutral), and electrons (negative charge) are in a probabilistic electron cloud described by quantum mechanics.

### Question 2: Explain what determines how the energy levels in an atom are filled.
# Brief Explanations:
The filling of energy levels in an atom is determined by three main principles: the Aufbau principle (electrons fill the lowest - energy orbitals first), the Pauli exclusion principle (no two electrons in an atom can have the same set of four quantum numbers, meaning each orbital can hold a maximum of two electrons with opposite spins), and Hund's rule (electrons fill degenerate orbitals singly with parallel spins before pairing up).
# Answer:
The filling of energy levels in an atom is determined by the Aufbau principle (lowest - energy orbitals filled first), the Pauli exclusion principle (max two electrons per orbital with opposite spins), and Hund's rule (single filling of degenerate orbitals before pairing).

### Question 3: Describe what happens when an electron jumps from one energy level to another.
# Brief Explanations:
When an electron jumps from a lower energy level to a higher energy level, it absorbs energy (usually in the form of a photon). Conversely, when an electron jumps from a higher energy level to a lower energy level, it releases energy in the form of a photon (light). The energy of the photon is equal to the difference in energy between the two energy levels ($\Delta E = E_{higher}-E_{lower}$ for emission, and $\Delta E = E_{lower}-E_{higher}$ for absorption, with the sign indicating the direction of energy transfer).
# Answer:
- Absorption: Electron moves from lower to higher energy level, absorbing a photon with energy equal to the energy difference between the levels.
- Emission: Electron moves from higher to lower energy level, releasing a photon with energy equal to the energy difference between the levels.

### Question 4: Identify how many electrons the third energy level can hold, and explain why this is the case.
# Explanation:
## Step 1: Recall the formula for electron capacity of an energy level
The maximum number of electrons that an energy level with principal quantum number $n$ can hold is given by the formula $2n^{2}$.
## Step 2: Calculate for $n = 3$
For the third energy level, $n = 3$. Substitute $n = 3$ into the formula $2n^{2}$. We get $2	imes(3)^{2}=2	imes9 = 18$.
To explain, the third energy level has sub - levels: $s$ (holds 2 electrons), $p$ (holds 6 electrons), and $d$ (holds 10 electrons). The sum of the number of electrons in these sub - levels is $2 + 6+10=18$.
# Answer:
The third energy level can hold 18 electrons. This is because the formula for the maximum number of electrons in an energy level is $2n^{2}$, and for $n = 3$, $2	imes3^{2}=18$. Also, the third energy level has $s$ (2e⁻), $p$ (6e⁻), and $d$ (10e⁻) sub - levels, and their electron capacities sum to 18.

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Explanation:

Question 1: State two key features of the modern model of the atom.

Answer:

Question 2: Explain what determines how the energy levels in an atom are filled.