# 6.4 Electronic structure of atoms (electron configurations)  (Page 2/15)

 Page 2 / 15

The arrangement of electrons in the orbitals of an atom is called the electron configuration    of the atom. We describe an electron configuration with a symbol that contains three pieces of information ( [link] ):

1. The number of the principal quantum shell, n ,
2. The letter that designates the orbital type (the subshell, l ), and
3. A superscript number that designates the number of electrons in that particular subshell.

For example, the notation 2 p 4 (read "two–p–four") indicates four electrons in a p subshell ( l = 1) with a principal quantum number ( n ) of 2. The notation 3 d 8 (read "three–d–eight") indicates eight electrons in the d subshell (i.e., l = 2) of the principal shell for which n = 3.

## The aufbau principle

To determine the electron configuration for any particular atom, we can “build” the structures in the order of atomic numbers. Beginning with hydrogen, and continuing across the periods of the periodic table, we add one proton at a time to the nucleus and one electron to the proper subshell until we have described the electron configurations of all the elements. This procedure is called the Aufbau principle    , from the German word Aufbau (“to build up”). Each added electron occupies the subshell of lowest energy available (in the order shown in [link] ), subject to the limitations imposed by the allowed quantum numbers according to the Pauli exclusion principle. Electrons enter higher-energy subshells only after lower-energy subshells have been filled to capacity. [link] illustrates the traditional way to remember the filling order for atomic orbitals. Since the arrangement of the periodic table is based on the electron configurations, [link] provides an alternative method for determining the electron configuration. The filling order simply begins at hydrogen and includes each subshell as you proceed in increasing Z order. For example, after filling the 3 p block up to Ar, we see the orbital will be 4s (K, Ca), followed by the 3 d orbitals.

We will now construct the ground-state electron configuration and orbital diagram for a selection of atoms in the first and second periods of the periodic table. Orbital diagrams are pictorial representations of the electron configuration, showing the individual orbitals and the pairing arrangement of electrons. We start with a single hydrogen atom (atomic number 1), which consists of one proton and one electron. Referring to [link] or [link] , we would expect to find the electron in the 1 s orbital. By convention, the ${m}_{s}=+\frac{1}{2}$ value is usually filled first. The electron configuration and the orbital diagram are:

Why phosphurs in solid state have one atom but in gas state have four atoms
Are nuclear reactions both exothermic reactions and endothermic reactions or what?
to what volume must 8.32 NaOH be diluted to its analytical concentration 0.20 M
weight in mg 1.76 mole of I
Sheriza
the types of hydrocarbons
u are mad go and open textbook
Emmanuel
hahahahahahahahahahahahaha
Jessica
aliphatic and aromatic hydrocarbons
Osakue
I don't use to see the messages
how can you determine the electronegativity of a compound or in molecules
when u move from left to right in a periodic table the negativity increases
reeza
Are you trying to say that the elctronegativity increases down the group and decreases across the period?
Ohanaka
yes and also increases across the period
reeza
for instance when you look at one group of elements in a periodic table electronegativity decreases when you go across the table electronegativity increases. hydrogen is more electronegative than sodium, potassium of that group. oxygen is more electronegative than carbon.
reeza
i hope we all know that organic compounds have carbon as their back bone
OK,Thank you so much for the answer. I am happy now
can I ask you a question now
Osakue
yes
hanna
what is the oxidation number of nitrogen, oxygen and sulphur
Osakue
5, -2 & -2
hanna
What is an atom?
is a smallest particle of a chemical element that can exist
Osakue
Osakue
it is a substance that cannot be broken down into simpler units by any chemical reaction
An atom is the smallest part of an element dat can take part in chemical reaction.
Idris
an atom is the smallest part of an element that can take part in a chemical reaction nd still retain it chemical properties
Precious
Is the smallest particles of an element that take part in chemical reaction without been change
John
what are the branches of an atomic mass
Still waiting for answers for a very long time now
that question is very strong oooo
Osakue
most of the questions I asked wasn't answered what's the problem guys?
hi, there is no problems ooo
Osakue
between H2SO4 and HCL which is the strongest dehydrating agent ?
Ibirogba
HCl is the strongest dehydrating agent
Osakue
ᴡʜᴀᴛ ᴡɪʟʟ ᴏʙsᴇʀᴠᴇᴅ ɪғ ʟᴇᴀᴅ(ɪɪ)ɴɪᴛʀᴀᴛᴇs ɪs ᴀᴅᴅᴇᴅ ᴏɴ ᴛᴏ sᴏᴅɪᴜᴍ ɪᴏᴅɪᴅᴇ sᴏʟᴜᴛɪᴏɴ
what is the functional group of alkanals
can someone explain salt analysis properly
Frankyx
Find the number of calcium atoms present in a sample weighing 2.0*10 raise to the power of -3g
what is chemistry?
Is a branch of science that deals with matter in relation to energy
Kata