Chapter 2Chapter 22.4 The Electronic Structure of an Atom

Electron configurationElectron configuration

The elcetron in an atom are arrange in shells around its nuclues.

2.42.4 The Electronic Structure The Electronic Structure of an Atomof an Atom

1. The electron configuration (electron arrangement) of an atom is the arrangement of electrons in shells (orbits) around that atom's nucleus.

2.8.1

2.42.4 The Electronic Structure The Electronic Structure of an Atomof an Atom

2. The electrons in an atom are arranged in shells around the nucleus. The maximum number of electrons which can fill a particular shell is as follows:

Shell Maximum number of electrons1st 22nd 83rd 8 or 184th 36

Perodic TablePerodic Table

2.42.4 The Electronic Structure The Electronic Structure of an Atomof an Atom

3. The electrons in the last shell of an atom are known as valence electrons. They determine the chemical properties of the element.

Valence electron = 5 Valence electron = 1

2.42.4 The Electronic Structure The Electronic Structure of an Atomof an Atom

4. To write the electron arrangement of an atom,

for example, sulphur, the proton number of the element should be known, as in . This means that S has 16 electrons as:

Number of electrons = number of protons.

3216S

2.42.4 The Electronic Structure The Electronic Structure of an Atomof an Atom

The electrons will thus be arranged as follows: 1st shell has 2 electrons 2nd shell has 8 electrons 3rd shell has 6 electrons Total = 16 electrons

The electronic configuration or electron arrangement is then written as 2.8.6.

2.42.4 The Electronic Structure The Electronic Structure of an Atomof an Atom

All elements having the same valence electrons will show the same chemical properties, for example, chlorine and bromine, have 7 valence electrons, will exhibit similar chemical properties.

2.8.7

2.8.18.7

2.42.4 The Electronic Structure The Electronic Structure of an Atomof an Atom

Helium has a complete shell of 2 valence electrons or duplet condition. Similarly, neon and argon also have 8 valence electrons or the octet condition. These elements are monoatomic and are very stable gases.

Helium2

Neon2.8

Argon2.8.8

2.42.4 The Electronic Structure The Electronic Structure of an Atomof an Atom

The atomic structures of the first 20 elements in the Periodic Table of Elements are given in Table 2.4.

Element Proton number

Number of electrons

Number of elements in shell Electron arrangement

Number of valance electrons

1 2 3 4

Hydrogen 1 1 1 1 1

Helium 2 2 2 2 2

Lithium 3 3 2 1 2.1 1

Beryllium 4 4 2 2 2.2 2

Boron 5 5 2 3 2.3 3

Carbon 6 6 2 4 2.4 4

Nitrogen 7 7 2 5 2.5 5

Element Proton number

No. of electrons

Number of elements in shell

Electron arrangement

Number of valance electrons1 2 3 4

Oxygen 8 8 2 6 2.6 6Fluorine 9 9 2 7 2.7 7Neon 10 10 2 8 2.8 8Sodium 11 11 2 8 1 2.8.1 1Magnesium 12 12 2 8 2 2.8.2 2Aluminium 13 13 2 8 3 2.8.3 3Silicon 14 14 2 8 4 2.8.4 4

2.42.4 The Electronic Structure The Electronic Structure of an Atomof an Atom

Element Proton number

Number of electrons

Number of elements in shell

Electron arrangement

No. of valance electrons

1 2 3 4

Phosphorus 15 15 2 8 5 2.8.5 5

Sulphur 16 16 2 8 6 2.8.6 6

Chlorine 17 17 2 8 7 2.8.7 7

Argon 18 18 2 8 8 2.8.8 8

Potassium 19 19 2 8 8 1 2.8.8.1 1

Calcium 20 20 2 8 8 2 2.8.8.2 2

2.42.4 The Electronic Structure The Electronic Structure of an Atomof an Atom

The electron arrangement of an element, for example; Na is constructed by drawing 3 circles around the nucleus to represent each shell, as its electron configuration is 2.8.1. Thus we have

2 8 1

2.42.4 The Electronic Structure The Electronic Structure of an Atomof an Atom

Table shows the electron arrangement of the first 20 elements in the Periodic Table.

Hydrogen(1)

Helium(2)

Lithium(2.1)

Beryllium(2.2)

2.42.4 The Electronic Structure The Electronic Structure of an Atomof an Atom

Table shows the electron arrangement of the first 20 elements in the Periodic Table.

Boron(2.3)

Carbon(2.4)

Nitrogen(2.5)

Oxygen(2.6)

2.42.4 The Electronic Structure The Electronic Structure of an Atomof an Atom

Table shows the electron arrangement of the first 20 elements in the Periodic Table.

Fluorine(2.7)

Neon(2.8)

Sodium(2.8.1)

Magnesium(2.8.2)

2.42.4 The Electronic Structure The Electronic Structure of an Atomof an Atom

Table shows the electron arrangement of the first 20 elements in the Periodic Table.

Aluminium(2.8.3)

Silicon(2.8.4)

Phosphorus(2.8.5)

Sulphur(2.8.6)

2.42.4 The Electronic Structure The Electronic Structure of an Atomof an Atom

Table shows the electron arrangement of the first 20 elements in the Periodic Table.

Chlorine(2.8.7)

Argon(2.8.8) Potassium

(2.8.8.1)Calcium(2.8.8.2)