ELECTRON ARRANGEMENT :
Objectives :
• Express the arrangement of electrons in atoms using electron configurations and Lewis valence electron dot structures
- Helium, neon, argon, krypton, and xenon are all in group 8A of the periodic table.
- These elements are all gases at room temperature and generally do not react with other elements.
- They are also similar in that after atoms of each gas are excited using electricity, they emit light.
- As shown by group 8A, elements in the same group have similar properties, but why is this so? This section will introduce electron configurations and Lewis valence electron dot structures, which will help you better understand (and eventually predict) the properties of elements in certain groups.
Structure of an atom
In this page we are going to discuss about explain the structure of an atom concept .Electrons revolve around the nucleus in different energy levels or shells and each shell is associated with definite energy. The energy of the K shell is the least while those of L, M, N and O shells increases progressively. We also know that any system that has least energy is the most stable.1st energy level is K shell2nd energy level is L shell3rd energy level is M shell4th energy level is N shell and so on
Bohr and Bury Scheme - Important Rules
- Maximum number of electrons that can be accommodated in a shell is given by 2n2 where n = shell number
- For 1st energy level, n = 1Maximum number of electrons in 1st energy level = 2n22 x (1) 2 = 2
- For 2nd energy level n = 2Maximum number of electrons in the 2nd energy level = 2n22 x 22 = 2 x 4 = 8
- For 3rd energy level n = 3Maximum number of electrons in the 3rd energy level = 2n2= 2x(3) 2= 2 x 9 = 18
- For 4th energy level n = 4Maximum number of electrons in the 4th energy level = 2n2= 2x(4) 2= 2x16 = 32
Sl.NoElectron Shell
Maximum Capacity1K Shell2 electrons2L Shell8 electrons3M shell18 electrons4N shell32 electrons
- The outermost shell of an atom cannot accommodate more than 8 electrons, even if it has a capacity to accommodate more electrons. This is a very important rule and is also called the Octet rule. The presence of 8 electrons in the outermost shell makes the atom very stable.
Electronic Configuration of an ElementThe arrangement of electrons in the various shells/orbits/energy levels of an atom of the element is known as electronic
configuration. Keeping the Bohr and Bury rules in mind let us write the electronic configuration of elements.
Electronic Configurations of Some Important Elements
Element Symbol Atomic number Electronic configuration
(or Electron arrangement)
K L M N Hydrogen H 1 1 Helium He 2 2 Lithium Li 3 2,1 Beryllium Be 4 2,2 Boron B 5 2,3 Carbon C 6 2,4 Nitrogen N 7 2,5 Oxygen O 8 2,6 Fluorine F 9 2,7 Neon Ne 10 2,8 Sodium Na 11 2,8,1 Magnesium Mg 12 2,8,2 Aluminium Al 13 2,8,3 Silicon Si 14 2,8,4 Phosphorus P 15 2,8,5 Sulphur S 16 2,8,6 Chlorine Cl 17 2,8,7 Argon Ar 19 2,8,8 Potassium K 19 2,8,8,1 Calcium Ca 20 2,8,8,2
Geometric Representation of Atomic StructureBelow are the examples on Geometric Representation of Atomic Structure
Example: 1
24 Mg 12
Steps:
- The first 2 electrons will go to the 1st shell = K Shell (2n2)
- The next shell L takes a maximum of 8 electrons (2n2)
- In this way 2 + 8 = 10 electrons have been accommodated. The next 2 electrons go to the M Shell.
KLM282Atomic parameters of the first twenty elementsName and SymbolAtomic no.(Z)Mass no.(A)Sub Atomic ParticalsElectronic configurationValencyMetal/Non-metal or Noble gases and Nature of element K L M N Hydrogen (H) 1 1 p = 1
e = 1
n = 0
1 ±1 Metal as well as Non-Metal (Gas) Helium(He) 2 4 p=2
e =2
n =2
2 2 Noblegas (Gas) Lithium (Li) 3 7 p = 3
e =3
n =4
2 1 +1 Metal (Solid) Beryllium (Be) 4 9 p = 4
e=4
n=5
2 2 +2 Metal (Solid) Boron(B) 5 11 p=5
e =5
n = 6
2 3 +3 Metal (Solid) Carbon (C) 6 12 p = 6
e =6
n =6
2 4 4 Non-metal (Solid) Nitrogen (N) 7 14 p = 7
e =7
n =7
2 5 -3 Non-metal (Gas) Oxygen (0) 8 16 p = 8
e =8
n =8
2 6 -2 Non-metal (Gas)Fluorine
(F)919p=9
e=9
n=10
27 -1Non-Metal(Gas)Neon(Ne)1020p=10
e=10
n=10
28 0Noble Gas(Gas) Sodium (Na) 11 23 p = 11
e =11
n = 12
2 8 1 +1 Metal (Solid) Magnesium (Mg) 12 24 p = 12
e =12
n = 12
2 8 2 +2 Metal (Solid) Aluminium (Al) 13 27 p = 13
e =13
n = 14
2 8 3 +3 Metal (Solid) . Silicon (Si) 14 28 p = 14
e =14
n = 14
2 8 4 4 Non- Metal (Solid) Phosphorus (P) 15 31 p = 15
e =15
n = 16
2 8 5 -3 Non- Metal (Solid) Sulphur (S) 16 32 p = 16
e = 16
n = 16
2 8 6 -2 Non- Metal (Solid) Chlorine (Cl) 17 35 p = 17
e = 17
n = 18
2 8 7 -1 Non- Metal (Gas) Argon(Ar) 18 40 p=18
e = 18
n = 22
2 8 8 0 Noblegas (Gas) Potassium (K) 19 39 p = 19
e = 19
n = 20
2 8 8 1 +1 Metal (Solid) Calcium (Ca) 20 40 p = 20
e = 20
n = 20
2 8 8 2 +2 Metal (Solid)
Atomic structures of the First Twenty Elements