Why do electrons form shells/clouds around nucleus? If electron is negative charge and protons in nucleus are positive they should attract each other and as a end result stick in one place? Second question (an I think it's related) is about ionic bonding. I think this is most popular example:  But why does the electron jump from Na to CL? The octet rule makes very less sense for me, as it says &quot;Atoms try to get 8 electron in outer shell&quot;, and it's rather incomplete and abstract explanation. And more over, why is is sometimes Ionic Bonding and sometimes Covalent Bonding? Edit: Dear members stop voting for duplicate and read the whole thing. This topic answers multiple linked questions, not just one (1st that is similar) and I picked already a solution.
I'm having trouble understanding the simple "planetary" model of the atom that I'm being taught in my basic chemistry course.   In particular,    I can't see how a negatively charged electron can stay in "orbit" around a positively charged nucleus. Even if the electron actually orbits the nucleus, wouldn't that orbit eventually decay?  I can't reconcile the rapidly moving electrons required by the planetary model with the way atoms are described as forming bonds. If electrons are zooming around in orbits, how do they suddenly "stop" to form bonds.     I understand that certain aspects of quantum mechanics  to address these problems, and that there are  of atoms. My question here is whether the planetary model itself addresses these concerns in some way (that I'm missing) and whether I'm right to be uncomfortable with it.
How do I access folders created on Ubuntu with Windows? How to forward X over SSH to run graphics applications remotely? I have a machine running Ubuntu which I SSH to from my Fedora 14 machine. I want to forward X from the Ubuntu machine back to Fedora so I can run graphical programs remotely. Both machines are on a LAN.  I know that the -X option enables X11 forwarding in SSH, but I feel like I am missing some of the steps.  What are the required steps to forward X from a Ubuntu machine to Fedora over SSH? 64 bit enum in C++? Is there a way to have a 64 bit enum in C++?  Whilst refactoring some code I came across bunch of #defines which would be better as an enum, but being greater than 32 bit causes the compiler to error.  For some reason I thought the following might work:  enum MY_ENUM : unsigned __int64   {       LARGE_VALUE = 0x1000000000000000,   }; Why don't C++ compilers define operator== and operator!=? I am a big fan of letting the compiler do as much work for you as possible.  When writing a simple class the compiler can give you the following for 'free':   A default (empty) constructor A copy constructor A destructor An assignment operator (operator=)   But it cannot seem to give you any comparison operators - such as operator== or operator!=.  For example:  class foo { public:     std::string str_;     int n_; };  foo f1;        // Works foo f2(f1);    // Works foo f3; f3 = f2;       // Works  if (f3 == f2)  // Fails { }  if (f3 != f2)  // Fails { }   Is there a good reason for this?  Why would performing a member-by-member comparison be a problem?  Obviously if the class allocates memory then you'd want to be careful, but for a simple class surely the compiler could do this for you? Nowhere monotonic continuous function Does there exist a nowhere monotonic continuous function from some open subset of $\mathbb{R}$ to $\mathbb{R}$? Some nowhere differentiable function sort of object? I have data in an Excel file that I want to join with a shapefile in my project. The Excel file contains values like volumes. The Excel file and the shapefile I want to join it with both contain the same property names.  The problem is, when I join the two, I get too many decimals in the attribute table. I get six, but I only want it to be one.  I tested to change the format of the cells to one decimal, and then I saved the file as *csv. But, somehow I seem to loose data in the process? It should be 42 rows that contains data in the column i am working with, but I end up with only like 10?  Another thing is that my property names contains the letters Å. Ä and Ö, perhaps this complicates things?  I read the question , but it doesn't mention the problem with the data loss.  My question was tagged with , but I didn't write what version I'm using. I use QGIS 2.2.0. Would it help to upgrade to the latest version? Placement of the asterisk in pointer declarations I've recently decided that I just have to finally learn C/C++, and there is one thing I do not really understand about pointers or more precisely, their definition.  How about these examples:   int* test; int *test; int * test; int* test,test2; int *test,test2; int * test,test2;   Now, to my understanding, the first three cases are all doing the same: Test is not an int, but a pointer to one.  The second set of examples is a bit more tricky. In case 4, both test and test2 will be pointers to an int, whereas in case 5, only test is a pointer, whereas test2 is a "real" int. What about case 6? Same as case 5? How could I execute a script in Shell when a shortcut key is pressed.   Essentially what I need is when a shortcut key is pressed the script should read from a file and display that content in the terminal. I am carrying out research to look at differences in fish density and fish species richness when using two different underwater visual census methods. My data was originally count data but then typically this is changed to fish density but I have still decided to use a Poisson GLM, which I hope is right.   model1 &lt;- glm(g_den ~ method + site + depth, poisson)   My 3 predictor variables are method, site and depth which I ordered as factors when I input them.   My response variables are grouper species richness, grouper density and the same for other fish groups. I am aware that density is not an integer and it is numerical data e.g 1.34849. I am now however getting this error:      In dpois(y, mu, log = TRUE) : non-integer x = 0.037500   I've been reading up and many people suggest using an offset, is this the most advisable thing to do? I can describe "IMHO" as an acronym for "in my humble opinion."  How can I describe the reverse processes of translating the acronym into the actual phrase?  That is to say, if "IMHO" is the acronym, what do we call "in my humble opinion"? Schengen Visa Refusal: Justification for the purpose and conditions of the intended stay was not provided Schengen refusal formulae can be difficult to understand sometimes.    When an applicant receives a refusal with "Justification for the purpose and conditions of the intended stay was not provided", what does it mean? Why does $1+2+3+\cdots = -\frac{1}{12}$? $\displaystyle\sum_{n=1}^\infty \frac{1}{n^s}$ only converges to $\zeta(s)$ if $\text{Re}(s) &gt; 1$.  Why should analytically continuing to $\zeta(-1)$ give the right answer? Properly bootstrap drupal for standalone PHP file? This is what I have right now:  &lt;?php     define('DRUPAL_ROOT', '/var/www/clients/client1/web15/web');     include_once(DRUPAL_ROOT . '/includes/bootstrap.inc');     drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL); //  drupal_flush_all_caches();        $users = views_get_view_result('userlist', 'uid_list');     $i = 0;     foreach ($users as $user) {         $filename = 'sites/default/files/generated_pdfs/individual_pdf_report_' . $user-&gt;uid . '.pdf';         generate_employee_pdf($user-&gt;uid, $filename);         error_log('Generated ' . $filepath);         $i++;     }     // create object     $zip = new ZipArchive();     // open archive     if ($zip-&gt;open("sites/default/files/generated_zips/individual-reports.zip", ZIPARCHIVE::CREATE) !== TRUE) {         die ("Could not open archive");     }     // initialize an iterator     // pass it the directory to be processed     $iterator = new RecursiveIteratorIterator(new RecursiveDirectoryIterator("sites/default/files/generated_pdfs/"));     // iterate over the directory     // add each file found to the archive     foreach ($iterator as $key=&gt;$value) {         $zip-&gt;addFile(realpath($key), $value-&gt;getFilename()) or die ("ERROR: Could not add file: $key");     }     // close and save archive     $zip-&gt;close(); ?&gt;   I'm getting a bunch of errors from the above when run standalone. Works fine in my module. Some of the errors are:  Warning: Invalid argument supplied for foreach() in drupal_depth_first_search() (line 56 of /var/www/clients/client1/web15/web/includes/graph.inc). Warning: Invalid argument supplied for foreach() in _module_build_dependencies() (line 229 of /var/www/clients/client1/web15/web/includes/module.inc). Warning: include_once(sites/all/modules/views_bulk_operations/actions/archive.action.inc): failed to open stream: No such file or directory in views_bulk_operations_load_action_includes() (line 56 of /var/www/clients/client1/web15/web/sites/all/modules/views_bulk_operations/views_bulk_operations.module). How do I photograph a wedding in the rain? I've shot weddings before, but being in Minnesota they almost always have an indoor venue available due to the long cold winters that we have. I am coming up on a wedding that I will likely be shooting outdoors and in the rain. I'm not as worried about my equipment, I am more concerned with how to capture the shots that I need such as b&amp;g alone, the wedding party, family posed portraits, etc while potentially being stuck in poor weather.   Should I come prepared with 10 umbrellas? Should I make all possible attempts to find a sheltered area for the posed portraits? Do I have an assistant hold an umbrella out of the frame to protect the b&amp;g during alone shots? Just some ideas I've had, but I've never actually shot an outdoor ceremony during the rain. UK visa requirement: Residence or citizenship? On gov.uk's  it is indicated      Check if you need this visa if you’re visiting from outside the European Economic Area (EEA) or Switzerland"   “Visiting from” makes you understand that the country you regularly live in is relevant, thus you can avoid applying for a visa if you are visiting from Italy (as country of regular residency).  As a matter of fact, if you proceed to make the check, the question to answer is "What passport or travel document do you have?", not really consistent with the indication previously given.  So, what is relevant: the country you live in with regular documents (and where you leave from to visit UK) or the country of origin which issued the passport?  To be practical, a Moldovan who is an Italian resident with regular resident card and Italian ID card (but with the note "not valid for expatriation") can avoid applying for a visa if he wants to spend a week-end in London (thus visiting from inside EEA)? This occurs in the  released recently to the public. When someone posts a code block in their question or answer, the code block is cut off on the right hand side, and I can't scroll to the right to view the rest of it. How can I view these code blocks? How to modify the space between the numbers and text of sectioning titles in the table of contents? How can I display additional boot and shutdown information on the Windows 7 welcome screen? There is a small tweak, I believe it is a registry key, that allows to display additional information on the Welcome and Shutting down screens of Windows 7 (and most likely Vista, too). I have activated this tweak on one of my systems; unfortunately I forgot how I did it, and I can't seem to find the website that originally gave me that information.  Usually, the Windows 7 welcome screen will just display "Welcome" when logging in. With the tweak activated, my Welcome screen gives status information such as "Loading user settings" or "Preparing desktop". When shutting down, the default screen simply says "Shutting down". With the tweak activated, it gives additional status information such as "Stopping Windows services". This appears the same way that Windows gives information when updates are installed or configured during the startup or shutdown procedure, and I find them quite helpful in getting a feel for what task takes how long during that process.  The only setting I was able to find is the Boot log checkbox on the Boot tab of the msconfig application. However, this results in Windows displaying console logs of drivers it is loading, etc., instead of the animated Windows title. This is NOT the setting I am looking for. The "additional boot information" setting that I have activated on this system still displays the regular animated Windows logo, and only replaces the strings displayed on the blue Welcome and Shutdown screens.  Could someone direct me to the registry key (or whatever setting) that is used to get this behaviour?  Edit: Here are a few pictures of the enhanced Welcome and Shutdown screens taken with my mobile phone—they're in German though.   Login screen "Waiting for User Profile Service"   Login screen "Preparing desktop"   Logout screen "Stopping Windows services": I installed ubuntu 13.04 on my new notebook (that came with windows 8 installed) and now when I try to load windows 8 appear the error:  impossible to find command 'drivemap'. (this is in portuguese, I'm not sure if I translated it right invalid EFI file path.  ubuntu is working OK. someone knows what can I do to solve this and have both SO running? I have searched on the internet but couldn't find anything I could understand. can someone help me? Do indexes work with "IN" clause If I have a query like:  Select EmployeeId  From Employee  Where EmployeeTypeId IN (1,2,3)   and I have an index on the EmployeeTypeId field, does SQL server still use that index?