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Author Topic: How do I place electrons evenly along an atom shell?  (Read 1945 times)

April 21, 2018, 01:56:39 PM
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Alexandros81

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Hi,
I want to place lets say 18 electrons in the shell of an atom.
I want to be placed evenly at equal distance among them along the shell.
I have done this by visual inspection.
Is there another more precise way to do this?

I am attaching an atom shell with one electron along the shell.Electrons along a shell.svg
*Electrons along a shell.svg
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April 21, 2018, 02:24:00 PM
Reply #1

drlarrye

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I'm new so there might be an easier way.....Set up a vertical and horizontal guide through your electron.  Duplicate your electron.  Rotate the entire thing 20 degrees.  Snap the center of the bounding box of your duplicate electron to the guides.  Repeat 16 more times.
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April 21, 2018, 07:02:58 PM
Reply #2

brynn

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Welcome Alexandros81!

As we often find with Inkscape, there is more than one way to accomplish a particular goal.  Often, the choice comes down to personal preference.  But other times, the requirements for reaching the goal for the image decides the choice.

You could put 18 tick marks around the circle, sort of like an 18 hour clock face (I think there's an LPE that will do this), and then snap the little circles to the intersection of the tick marks and the large circle.  Or drlarrye's idea is another way to go.  But I think I'll give instructions for yet a 3rd way (and I can even think of a 4th way to do it!).  (Although the 4th way is probably the easiest, it doesn't seem to be working.  Is Object menu > Arrange > Polar Coordinates broken?)

You can start with your existing SVG file, the way it is.  Since you mentioned that you achieved the image visually, without precision, you probably want to snap the little circle to the large circle.  It looks very close.  But for precision, you can configure your snap control bar like in this screenshot (light green buttons are enabled, dark green disabled)

snap-basic.png
*snap-basic.png
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1 -- Grab the circle with the mouse, and really you'll just have to move it a tiny amount to achieve the snap.  You'll see some text pop up to tell you which element was snapped to which target.  You should see something like "rotation center to quadrant point".  Release the mouse when you see the expected text.

2 -- While it's still selected, click a 2nd time on it, to reveal the rotation center.

3 -- It's a little hard to notice the rotation center, which is a small plus sign or crosshair in the center.  But anyway, grab that plus sign with the mouse and drag it straight down.  When it gets near the rotation center of the large circle you'll see it snap, and you'll see the text pop up to confirm that a rotation center is snapped to a rotation center.  (Note that you can't actually see the rotation center of the large circle while you're trying to snap the rotation center of the small circle to it.  So it's a little tricky, but still not hard to do.)

4 -- Next you have a choice whether you want to clone the small circle (group of 2), or just duplicate it.  If you think you might want to edit the group again later, choose clone.  (Editing the parent of clones, edits all the clones at once.)  But if you don't expect to edit them further, use duplicate.  (Both are in the Edit menu, or these buttons on the command bar:  duplicate  :dup:, clone  :cl:, or use Help menu > Key and Mouse Ref to find key shortcuts)

5 -- While the duplicate/clone is still selected, open Object menu > Transform > Rotate, and set for 20°, then click Apply.

6 -- If you decided to duplicate, you can duplicate the last circle, and repeat steps #4 and #5, until you finish.  If you decided to clone, you need to re-select the orginal circle (group) each time, and then either click Apply in the Transform dialog as many times as necessary, to rotate each clone to the proper amount; or change the degrees each time.
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April 22, 2018, 08:12:46 AM
Reply #3

Moini

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If you ever encounter elements where the number of atoms makes the previous way feel tedious, consider doing it this way (e.g. 64 electrons):

https://framadrive.org/s/2bNJz8eDyEtRSdS

(if you wonder about the repeated ungrouping - it seems it grouped the electron a couple of times, when I held down the G key for too long for demo purposes...)

Whenever a step is unclear, check the status line at the bottom for more info, and also check what the mouse/keyboard indicator says.

Edit: Main important info for you starts at 1:51 (I also included making the elements).

April 23, 2018, 03:28:27 AM
Reply #4

Alexandros81

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Thanks everyone for your help!
I'll try to make a post of what I have tried out from your suggestions.
Moini's way seems the most quick way, and is also suggested by brynn.
I also tried before Moini's post polar coordinates with no success.
I'll give it a try again using Moini's steps.

Alexandros
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April 23, 2018, 11:54:42 AM
Reply #5

brynn

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I couldn't get Polar Coordinates to work the other day.  But it seems to working now.  I'm  not doing anything different (except I only used 6 little circles today, and I was trying with 18 the other day).
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April 23, 2018, 01:13:59 PM
Reply #6

Moini

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Had the same experience in making the video - my 'no success' meaning that all items ended up in the same position on the circle. After I moved the circle in that situation, the problem disappeared. Next time I opened Inkscape, I couldn't reproduce, so didn't know if it was just a one-time occurrance - and I didn't have the energy to follow up on it for longer yesterday.

Was your problem identical, brynn + Alexandros?

April 23, 2018, 01:30:06 PM
Reply #7

brynn

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Yes, it placed all the little circles at the 3 o'clock position on the big circle!  I didn't think of moving the big circle, but I'll try that if it happens in the future.

Too bad, I don't still have the file where the problem was happening.  But if I see it again, I try to remember to save the file.
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April 24, 2018, 05:08:21 AM
Reply #8

Alexandros81

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Quote (selected)
my 'no success' meaning that all items ended up in the same position on the circle. After I moved the circle in that situation, the problem disappeared.

Quote (selected)
Yes, it placed all the little circles at the 3 o'clock position on the big circle!

Same problem. Fixed by moving the bigger circle!



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April 24, 2018, 08:14:51 AM
Reply #9

Moini

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Could one of you or both investigate further how to reproduce this reliably, so we can make sure devs can reproduce it and try to fix?

It doesn't seem to happen every time, it's a bit weird. Experiment with moving/not moving the circle before and after using the polar arrangement, and maybe with the order in which you do things, maybe also with different numbers of items, and could even change with different settings for saving coordinates in the preferences, who knows (absolute, relative could be tested). I think it might have to do with those ugly transforms again...

April 24, 2018, 12:02:54 PM
Reply #10

brynn

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Well, I have a doc where it's misbehaving.  But I don't know what's causing it.  So far, the only evidence I have, is that I first created the large circle several hours ago, and applied Polar Coordinates.  Coming back to the doc, I deleted the little circles, but I didn't change the large circle, I just tried to re-use it.

But in a different file, where I just created a new large circle, even though I've applied polar coordinates, deleted the little circles, and tried to re-use it with small squares.  But still working properly.  I'll try again in a few hours.  But so far, all I have for sure is a time delay of several hours.'/fd
Should I save that file, for testing?
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April 24, 2018, 03:35:55 PM
Reply #11

Moini

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Yes, please share the file that still has the issue. I couldn't make one, either, but I'd like to have one to start a comparison.

April 24, 2018, 10:26:32 PM
Reply #12

Lazur

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There are many ways of doing so -didn't read all the above, just suggesting an obscure way.

Draw an electron, group it (Ctrl+G), convert it to a marker.

Draw two concentric circles, combine them together (Ctrl+K).
Add a stitch subpaths lpe and the marker to the path.

Done similar before, haven't tested it this time for the details but theoretically this way you can place the same graphic rotated along a path evenly as many times as you type in the stitch subpath's settings. Which setting can be modified for another atom model later.


Downside of the process is it's relying on if the renderer is up to the specs -there may be problems if the output is needed in svg or pdf?
Needs testing.

April 27, 2018, 11:18:09 PM
Reply #13

brynn

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Oh great -- now it's working fine! 

I'll keep it open for some time, since that's the only clue I have.  If it eventually starts to malfunction, I'll upload it.
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April 28, 2018, 06:59:52 AM
Reply #14

Moini

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Thanks, brynn, that would be helpful. Maybe we should make a bug report already, even without a file? After all, all three of us hit the issue. It's definitely real.