I missed school today so the hw is a bit confusing and I have a quiz on this tmr. For example I have Br which has 35 electrons.

[Ar]_______
and then what do I do? How do I know what to put next?
how would you do Phosphorus?
thanks!

I can't draw these on this board but here is what you do. Write the levels this way.

1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d 6f
7s 7p 7d 7f
8s etc.
Here is a site that show how these are filled. You simply follow the arrows that start at the top and slant downward. When you come to the bottom of the arrow go back to the top with the next arrow down and follow that. So you fill 1s first, (that's the end of the first arrow so go back to the start of the next arrow which starts at 2s. That's the end of the second arrow; go back to the top of the next downward arrow which starts at 2p. Fill 2p then 3s. Continue this until all is filled. There some exceptions to the mnemonic but we won't worry about that right now. For Br, you write [Ar] which gets you to 1s2 2s2 2p6 3s2 3p6.
So you know you must add another 17 electrons so we add them as 3d10 4s2 4p5 so you write [Ar] 3d10 4s2 4p5. If you want to check yourself you can go to webelements.com, click on the element, scroll down to electron configuration and read it from the board. That has all of the elements done that way. Here is the link for Br
http://www.webelements.com/bromine/atoms.html

thank you! I think I kinda understand it now!

To determine the electron configuration of an element, you need to follow the Aufbau principle, which states that electrons fill the orbitals of an atom in order of increasing energy. Here's how you can determine the electron configuration for Br (Bromine) with 35 electrons:

1. Write the noble gas preceding the element: [Ar]. Noble gases have complete electron configurations, so they can be used as a starting point.

2. The atomic number of Bromine is 35, which tells us it has 35 electrons. Start by filling the available orbitals with the first electrons, starting from the lowest energy level.

3. The electron configuration for Bromine can be written as follows:
[Ar] 4s² 3d¹⁰ 4p⁵.

To determine the electron configuration of Phosphorus (P), follow the same steps:

1. The atomic number of Phosphorus is 15, indicating it has 15 electrons.

2. Write the noble gas that comes before Phosphorus, which is [Ne]. It represents the electron configuration up to that point.

3. Fill the remaining orbitals with the electrons for Phosphorus, starting from the lowest energy level.

The electron configuration for Phosphorus would be:
[Ne] 3s² 3p³.

Remember that the brackets represent the noble gas notation, indicating the filled electron shells from the previous noble gas. The numbers and letters outside the brackets indicate the remaining unfilled electron orbitals for the specific element.