Structure of the Atom: Orbitals and Electronic Structure of the Atom

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In today’s class, we will be talking about the structure of the atom. Enjoy the class!

STRUCTURE OF THE ATOM: ORBITALS AND ELECTRONIC STRUCTURE OF THE ATOM

ORBITALS OF THE ATOM

The region in space within which there is a maximum possibility of finding an electron in an atom is called an ATOMIC ORBITAL. We have s, p, d, and f orbitals.

Shapes of s and p orbitals are as follows:             

EVALUATION

1. Define atomic orbital
2. State the shape of (i) S-orbital (ii) P-orbital.

ELECTRONIC STRUCTURE OF THE ATOM

With the knowledge of atomic orbital the spectra of more complex atoms than hydrogen atom can be explained as follows:

1. (a) that within a given principal quantum number or energy level, there are sub energy levels, i.e. energy levels otherwise called K, L, M, N, O, P AND Q shells have sub-energy levels otherwise called s, p, d and f orbitals

(b) The total number of sub-shells within a shell is given by n²

while the total maximum number of electrons is given by 2n² where n is the number of energy levels.

Energy Level                       Number of orbitals            Maximum No of electrons

n = 1(K- shell)                              1² =1                                        2´1² =2

 n =2 (L- shell)                              2² = 4                                       2´2² = 8

n = 3 (M- shell)                           3² = 9                                       2´3² = 18

n = 4 (N- shell)                           4² =16                                       2´ 4² = 32

n = 5 (O- shell)                            5² = 25                                      2´ 5² =50

n = 6 (P-shell)                              6² = 36                                      2´6² =72

n = 7 (Q – shell)                           7²  = 49                                      2´7² = 98

(c) In a given orbital there could be a maximum of only two electrons and electron in all orbitals of the same type within a principal quantum number possess equal energies.

(d) The electrons in the different subshells or orbitals within a principal quantum number do not all have equal energies.

The gradation of energies of orbitals is as follows:

1s< 2s<2p<3s<3p<3d<4s<4p<4d—

EVALUATION

1. State the first five energy levels.
2. Calculate the total no of electrons when n is equal to (i) 2 (ii) 4.

FILLING OF ELECTRONS IN ORBITALS

In filling electrons into the atoms of elements, considerations are given to the conditions laid down by Aufbau Principle, Pauli exclusion principle and Hund’s rule of maximum multiplicity.

• AUFBAU PRINCIPLE: states that electrons go in to fill orbitals of lower energy first before filling orbitals of higher energy and each orbital may hold up to two electrons.
• PAULI EXCLUSION PRINCIPLE: states that no two electrons have identical sets of the four quantum numbers {n, l, m and s in an atom}.
• HUND’S RULE OF MAXIMUM MULTIPLICITY: state that in filling degenerate orbitals with electrons, electrons go in singly first before pairing up occurs.

EVALUATION

State the following principle

{a} Aufbau Principle {b} Hund’s rule.

QUANTUM NUMBERS

Studies show that the energy of an electron may be characterized by four quantum numbers. These are

{1}    The principal quantum number represented by n with integral values of     1,2,3,4 e.t.c.

{2}  The subsidiary or Azimuthal quantum number represented by l with integral values ranging from O to (n-1).

{3}   The magnetic quantum number represented by m with integral values ranging from –l to +l.

{4}    The spin quantum number represented by s with integral values – ¹/₂ and = ¹/₂.

      Element           Atomic Number         Electronic configuration.

1. H                            1                               1S¹
2. He                          2                              1S²
3. Li                            3                              1S² 2S¹
4. Be                          4                              1S² 2S²
5. B                            5                              1S² 2S² 2P¹
6. C                            6                              1S² 2S² 2P²
7. N                            7                              1S² 2S² 2P³
8. O                            8                              1S² 2S² 2P⁴
9. F                             9                              1S² 2S² 2P⁵
10. Ne                         10                              1S² 2S² 2P⁶
11. Na                         11                              1S² 2S² 2P⁶ 3S¹
12. Mg                         12                              1S² 2S² 2P⁶ 3S²
13. Al                           13                             1S² 2S² 2P⁶ 3S² 3P¹
14. Si                            14                             1S² 2S² 2P⁶ 3S² 3P²
15. P                              15                             1S² 2S² 2P⁶3S²³3P³
16. S                              16                             1S² 2S² 2P⁶3S² 3P⁴
17. Cl                            17                             1S² 2S² 2P⁶ 3S² 3P⁵
18. Ar                            18                             1S² 2S² 2P⁶ 3S²3P⁶
19. K                             19                             1S² 2S² 2P⁶ 3S²3P⁶ 4S¹
20. Ca                          20                             1S² 2S² 2P⁶ 3S²3P⁶ 4S²

GENERAL EVALUATION

1. State the four quantum numbers.
2. Write the electronic configuration of the following a) Mg b) S^2- c) Ca²⁺ d) Si

READING ASSIGNMENT

• New School Chemistry By O.Y. Ababio pg 49-54.

WEEKEND ASSIGNMENT

1. Which of the following orbitals is spherical in shape? (a) s (b) p (c) d (d) f

2. Which of the following shells have a maximum of eight electrons? (a) k (b) l (c) m (d) n

3. 1s² 2s² 2p⁶ 3p¹ is the electronic configuration of (a) potassium (b) calcium (c) sodium (d) aluminum.

4. “No two electrons have identical sets of four quantum numbers”. This statement is (a) Aufbau principle (b) Pauli exclusion (c) Hund’s rule (d) Rutherford’s model.

5. Which of the quantum number is represented by L? (a) principal quantum no (b) subsidiary quantum no (c) magnetic quantum (d) spin quantum.

THEORY

1. State the following principle (a) Pauli Exclusion Principle. (b) Aufbau principle.
2. Write the electronic configuration of (a) Oxygen (b) Calcium (c) Chloride ion (Cl^–) (d) Aluminum ion (Al³⁺)

 

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