1 I. STRUCTURE OF SUBSTANCES I.2. Electronic configuration of the atoms Louis de Broglie (France) and Werner Schrödinger (Austria) in the mid 1920s, suggested that like a light, the electron has both wave and particle properties. When Schrödinger carried out a mathematical analysis based on this idea, he obtained a new model for the atom: wave model. In this model the electron has not a well defined orbit. The motion of the electron seems to be rather a vibration. The three-dimensional region of space around the nucleus where we can find the electron is called orbital. In fact, it is a region of probability where the electron is likely to be found.

2 I. STRUCTURE OF SUBSTANCES I.2. Electronic configuration of the atoms The electronic configuration represents the distribution of electrons of an atom in shells, subshells and orbitals. All the electrons which have the same mean path from the nucleus form a main energetic level or main electronic shell. The state of an electron in an atom is completely described by four quantum numbers: principal quantum number, n – correspond to the main energetic shells azimuthal quantum number, l – correspond to the sublevels magnetic quantum number, m – describes the shape of the orbitals spin quantum number, s – describes the rotation of the electron around its own axis. It can take two values: +1/2 or -1/2.

3 I. STRUCTURE OF SUBSTANCES I.2. Electronic configuration of the atoms There are 7 main shells. The first main shell is the closest to the nucleus and it has a minimum energy. It is denoted by K and has the principal quantum number n = 1. Energetic level KLMNOPQ Principal quantum number n n = 1n = 2n = 3n = 4n = 5n = 6n = 7

4 I. STRUCTURE OF SUBSTANCES I.2. Electronic configuration of the atoms Each electronic level is made up of one or more subshells or sublevels, which in turn contain one or more orbitals. There are the following subshells: SubshellAzimuthal quantum number sl = 0 pl = 1 dl = 2 fl = 3 gl = 4

5 I. STRUCTURE OF SUBSTANCES I.2. Electronic configuration of the atoms The orbital is a region of space around the nucleus where there is more likely to found the electrons. There are several types of orbitals: OrbitalShapeMagnetic quantum number s orbital spherical shape m = 0 p orbitaltwo lobesm = -1; 0; +1 d orbitalfour lobesm = -2; -1; 0; +1; +2 f orbital complex shape and symmetry m = -3; -2; -1; 0; +1; +2; +3

6 I. STRUCTURE OF SUBSTANCES I.2. Electronic configuration of the atoms s orbital – has a spherical symmetry and it is characterized by the magnetic quantum number m = 0. z x y

7 I. STRUCTURE OF SUBSTANCES I.2. Electronic configuration of the atoms There are 3 p orbitals, oriented along the coordinate axis x-y-z. The magnetic quantum number takes 3 values (m = -1 ; 0 ; +1) z x y z x y z x y z x y z x y z x y p x orbital p y orbital p z orbital

8 I. STRUCTURE OF SUBSTANCES I.2. Electronic configuration of the atoms There are 5 d orbitals, with the shape of four lobes oriented differently in space. The magnetic quantum number can take 5 values (m = -2 ; -1 ; 0 ; +1 ; +2). There are 7 f orbitals, with complex shape and geometry. The magnetic quantum number can take 7 values (m = -3; -2 ; -1 ; 0 ; +1 ; +2; +3).

9 I. STRUCTURE OF SUBSTANCES I.2. Electronic configuration of the atoms The d orbitals

10 I. STRUCTURE OF SUBSTANCES I.2. Electronic configuration of the atoms The f orbitals

11 K shell (n = 1) consists of 1 sublevel: one s sublevel (l = 0) containing one single s orbital (m = 0) L shell (n = 2) consists of 2 sublevels: one s sublevel (l = 0) containing one single s orbital and (m = 0) one p sublevel (l = 1) containing three p orbitals (m = -1, 0, +1) M shell (n = 3) consists of 3 sublevels: one s sublevel (l = 0) containing one single s orbital and (m = 0) one p sublevel (l = 1) containing three p orbitals (m = -1, 0, +1) one d sublevel (l = 2) containing five d orbitals (m = ±2, ±1, 0) N shel (n = 4) consists of 4 sublevels: one s sublevel (l = 0) containing one single s orbital and (m = 0) one p sublevel (l = 1) containing three p orbitals (m = -1, 0, +1) one d sublevel (l = 2) containing five d orbitals (m = ±2, ±1, 0) one f sublevel (l = 3) containing seven f orbitals f (m = ±3,±2,±1,0) I. STRUCTURE OF SUBSTANCES I.2. Electronic configuration of the atoms

12 I. STRUCTURE OF SUBSTANCES I.2. Electronic configuration of the atoms ShellPrincipal quantum nr Azimuthal quantum nr. Magnetic quantum nr. Kn = 1l = 0m = 0 Ln = 2l = 0 l = 1 m = 0 m = -1 ; 0 ; +1 Mn = 3l = 0 l = 1 l = 2 m = 0 m = -1 ; 0 ; +1 m = -2 ; -1 ; 0 ; +1 ; +2 Nn = 4l = 0 l = 1 l = 2 l = 3 m = 0 m = -1 ; 0 ; +1 m = -2 ; -1 ; 0 ; +1 ; +2 m = -3 ; -2 ; -1 ; 0 ; +1 ; +2 ; +3

13 I. STRUCTURE OF SUBSTANCES I.3. The order of filling orbitals An orbital can be empty or it can contain one or maximum two electrons. If two electrons occupy the same orbital, they must have opposite spins, associated with spin quantum number s, which may be ±1/2. The electron configuration is the arrangement of electrons on shells, subshells and orbitals. Electrons fill low energy orbitals, closer to the nucleus, before they fill higher energy ones. The order of energy levels is not identical to the principal quantum number, due to the interaction between electrons and nucleus.

14 I. STRUCTURE OF SUBSTANCES I.3. The order of filling orbitals The electron configuration is the arrangement of electrons on shells, subshells and orbitals. The electron configuration of an atom can be established according to the following rules: 1) The principle of increasing energy 2) Pauli’s exclusion principle 3) Hund’s rule

15 I. STRUCTURE OF SUBSTANCES I.3. The order of filling orbitals 1) The principle of increasing energy Electrons fill low energy orbitals, closer to the nucleus, before they fill higher energy ones. The order of energy levels is not identical to the principal quantum number, due to the interaction between electrons and nucleus. 1s 2s2p 3s3p3d 4s4p4d4f The order in which electrons occupy orbitals can be established using the minimum (n+l) rule or GOLDANSKI’S chessboard.

16 I. STRUCTURE OF SUBSTANCES I.3. The order of filling orbitals a) Minimum (n+l) rule: the electronic levels and sublevels will be filled in the increasing order of the sum of the principal quantum number and the orbital one. For the same n + l, the low energy corresponds to the orbital with the lower n. The order is: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p n l sspspdspdfspdfgspdfgh n+ln+l

17 I. STRUCTURE OF SUBSTANCES I.3. The order of filling orbitals b) GOLDANSKI’S chessboard

18 I. STRUCTURE OF SUBSTANCES I.3. The order of filling orbitals 2. Pauli’s exclusion principle Two electrons in an atom cannot have all four quantum numbers identical. If two electrons exist in the same orbital (they have identical principal number, orbital and magnetic ones) these electrons must have opposite spins (different spin numbers). Maximum number of electrons in an electronic shell with principal number n is 2.

19 I. STRUCTURE OF SUBSTANCES I.3. The order of filling orbitals 3. Hund’s rule When orbital of identical energy are available, electrons occupy these singly, rather than in pairs. As a result, an atom tends to have as many unpaired electrons as possible.