## What are the number of elctrons around the central atoms?

Draw the best Lewis structure for each molecule. Then select the number of electrons around the central atom from the list; the choices are 2, 4, 6, 8, 10, 12, or 14 electrons.

XeO2F2

HNO3

H3PO4

ClO41−

H2SO4

BCl3

I just need to know the total number of electrons around the central atoms.

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### The total number of

The total number of electrons around a neutral atom equals its atomic number; these are filled according to the quantum numbers. Oxygen is 8 so there are 8 electrons; 2 completely fill the 1s level; another 2 completely fill the 2s sublevel; the remaining 4 partially fill the 2p sublevel, leaving space for another 2 electrons if they can find a positive charge to balance them out. H (atomic number 1) just happens to have such an electron and needs another electron to fill its 1s level, so if O can find 2 wandering H's it can negotiate joint custody and both parties will be happy; hence H:O:H or H2O. Carbon is 6 so it completely fills the 1s and 2s levels, with 2 in the 2p awaiting 4 more, so it can negotitate any number of arrangements, which makes life enjoyable. It can get those 4 lectrons by sharing 2 each from a friendly O atom (hence CO2 , hence O:C:O or loaning 1 each to four Cl atoms who are only 1 short of filling their 3p sublevels to be content, hence
----------------------Cl
----------------------..
-------------------Cl:C:Cl or CCl4.
----------------------..
----------------------Cl
Neon is 10 so it completely fills 2 in the 1s level, 2 in the 2s sublevel and the remaining 6 will completely fill the 2p level making Ne disinclined to look for any more electrons; hence it is monatomic and a noble gas.

WebElements: the periodic table on the WWW [http://www.webelements.com/]