When looking at the values of l and ml for a given n, we are dealing with the quantum numbers that describe the properties of electrons in an atom. Specifically, n represents the principal quantum number, l represents the orbital angular momentum quantum number, and ml represents the magnetic quantum number.

The principal quantum number n can take on positive integer values starting from 1. It describes the electron shell or energy level. For our case here, we are fixing n to be 3.

The orbital angular momentum quantum number l ranges from 0 to n-1. Therefore, when n is 3, l can be 0, 1, or 2.

Finally, the magnetic quantum number ml can take on integer values ranging from -l to +l. So when l is 0, ml can only be 0. When l is 1, ml can be -1, 0, or +1. And when l is 2, ml can be -2, -1, 0, +1, +2.

## Possible Values for l and ml When n = 3

Let’s list out the possibilities systematically:

When l = 0:

ml can only be 0

When l = 1:

ml can be -1, 0, or +1

When l = 2:

ml can be -2, -1, 0, +1, +2

So for n = 3, the combinations of l and ml values are:

l | ml |

0 | 0 |

1 | -1 |

1 | 0 |

1 | +1 |

2 | -2 |

2 | -1 |

2 | 0 |

2 | +1 |

2 | +2 |

So when n = 3, there are 9 possible combinations for the l and ml quantum number values.

## Expressing the Number of Combinations as an Integer

Since the question asks us to express the number of possible l and ml combinations as an integer, the answer is simply:

**9**

When the principal quantum number n is equal to 3, there are 9 possible combinations for the orbital angular momentum quantum number l and magnetic quantum number ml.

## Deriving the Number of Combinations

We can also derive the number of l and ml combinations mathematically as follows:

For a given n, l ranges from 0 to n-1

ml ranges from -l to +l

So the number of ml values for a given l is: 2l + 1

When n = 3:

For l = 0, number of ml values is 2(0) + 1 = 1

For l = 1, number of ml values is 2(1) + 1 = 3

For l = 2, number of ml values is 2(2) + 1 = 5

So total number of combinations is:

Number of ml values for l = 0: 1

Number of ml values for l = 1: 3

Number of ml values for l = 2: 5

Total = 1 + 3 + 5 = 9 combinations

This matches our direct enumeration of the l and ml possibilities for n = 3 earlier. Therefore, the total number of combinations can be expressed as: 2(0) + 1 + 2(1) + 1 + 2(2) + 1 = 9

## Significance of Quantum Numbers

The quantum numbers n, l, and ml describe the unique quantum states that electrons can exist in around the atom’s nucleus. Each combination of quantum numbers specifies a unique orbital for the electron.

The principal quantum number n determines the general scale and energy of the orbital. The angular momentum quantum number l determines the orbital shape and orientation in space. Finally, the magnetic quantum number ml determines the orbital orientation relative to standard coordinates.

By understanding the valid quantum numbers for electrons in different energy levels, we gain insight into the possible orbital configurations and how electrons can be distributed in an atom. The Aufbau principle establishes an order in filling electron orbitals that corresponds to the lowest energy arrangement of electrons.

The number of combinations for l and ml grows quickly for larger values of n. This correlates with the increasing number of available electron orbitals at higher principal/energy levels. The quantum numbers allow us to mathematically distinguish between the orbitals as they fill up according to the Aufbau process.

In summary, enumerating the l and ml combinations provides us with the total number of unique orbital states at a given principal quantum number n. This demonstrates the relationship between the quantum numbers and how they determine allowable electron configurations in an atom.

## Example Calculations

Let’s do some example calculations of the number of l and ml combinations for different values of n:

If n = 1

l can only be 0

So ml can only be 0

Total combinations = 1

If n = 2

l can be 0 or 1

When l = 0, ml = 0 (1 combination)

When l = 1, ml = -1, 0, +1 (3 combinations)

Total combinations = 1 + 3 = 4

If n = 3 (our original example)

Total combinations = 1 + 3 + 5 = 9

If n = 4

l can be 0, 1, 2, or 3

Total combinations = 1 + 3 + 5 + 7 = 16

We can see that for larger n, the number of l and ml combinations grows rapidly. This demonstrates the exponential increase in possible electron orbitals at higher principal/energy levels.

## Conclusion

To summarize, when the principal quantum number n is equal to 3, there are 9 possible combinations for the orbital angular momentum quantum number l and magnetic quantum number ml.

This is derived by observing that l ranges from 0 to n-1 (which is 0 to 2 when n=3), and ml ranges from -l to +l. Adding up the number of ml values for each l gives us the total combinations.

Expressed as an integer, the answer to the original question is: 9.

The quantum numbers describe the valid electron orbital states in an atom. Enumerating the l and ml combinations for a given n allows us to determine the number of unique orbitals at a particular principal energy level. This demonstrates the relationship between the quantum numbers and resulting electron configurations.