Sunday, April 24, 2011

Electronic Structure of the Atom

-         The Electronic Configuration of an atom =
o       A notation - describing the orbitals in which the electrons occupy
                                 - Describes the total number of electrons in each orbital.
               * This helps us understand the structure of the periodic table!

-         Bohr proposed- electrons exist in specific energy states
- when these electrons absorb or emit energy they moves from one orbital to another.

-         Energy level = amount of energy which an electron in an atom can possess
o       n is the number of the energy level

-         Quantum of energy = the energy difference between 2 particular energy levels
-         Ground State = when all electrons of an atom are in their lowest possible energy levels
-         Excited State= when one or more of an atom’s electrons are in energy levels other than the lowest available level
-         An Orbital = the actual region of space occupied by an electron in a particular energy level
-         Shell = the set of all orbitals having the same n value.
-         Subshell = a set of orbitals of the same type.

The letters s, p, d, f refer to 4 different types of orbitals

-         a maximum of 2 electrons can be placed in each orbit.

Order of orbitals

The order in which orbitals are filled is 1s, 2s, 2p, 3s, 3p…

Writing Electron Configuration for Neutral Atoms

o       always start at lowest energy level first

1)      Figure out how many electrons you have
2)      Start at lowest energy level (1s) and keep adding electrons until you have none left
Each electron has an opposite spin represented by:  ↑ and ↓

Example: Lithium is written 1s22s2

Writing Electron Configuration for Ions

For a negative ion- add electrons to last unfilled subshell
For a positive ion- take away electrons (in the order you put them there)

Example: Sulphur 2-
        Sulphur has 16 electrons à Sulphur 2- has 18 electrons

Core Notation

-         Core = the core of an atom is the set of electrons with the configuration of the nearest noble gas that comes before it.
-         Outer  = consist of all electrons outside the core. Core electrons normally take part in chemical reactions.

1)      Locate the atom à note the noble gas before the element
2)      Replace the part of the electron configuration corresponding to the configuration of the noble gas with the symbol for the noble gas in square brackets.

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