Atoms are made up of three types of smaller particles, namely protons, neutrons and electrons. These particles are known as subatomic particles.

SUBATOMIC PARTICLE

SYMBOL RELATIVE MASS

RELATIVE ELECTRIC CHARGE

PROTON P 1 +1NEUTRON n 1 0ELECTRON e 0 (almost) -1

Protons and neutrons are found in the nucleus of an atom while electrons surround the nucleus.

Each element is given a name and a symbol. Some examples of elements and their symbols are shown below.

ELEMENT SYMBOL ELEMENT SYMBOLHydrogen H Sodium Na

Helium He Magnesium MgLithium Li Aluminium Al

Beryllium Be Silicon SiBoron B Phosphorus P

Carbon C Sulphur SNitrogen N Chlorine Cl

Proton number

Nucleon number

Proton number = An elements is the number of protons in its atom.

Since atoms are neutral, the proton number is also the number of electrons in the atom.

Each elements has its own proton number.

Proton number = electron number

The nucleon number is also known as the mass number.

The relative mass of an atom is almost the same as its nucleon number.

Protons and neutrons are collectively called nucleons because protons and neutrons occupy the nucleus.

Nucleon number: total number of protons and total number of neutrons in its atom.

From definition,

or

Nucleon number = number of proton + number of neutrons

Number of neutrons = nucleon number – number of proton

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.

Isotopes of an element have the same:

(a) number of protons in an atom.(b) number of electrons in an atom.(c) electron arrangement.(d) chemical properties because they have the same electron arrangement.

Isotopes of an element have different: (a) nucleon number.

(b) number of neutrons in an atom.(c) physical properties (such as density, melting point and boiling point), though these different are very small.

Eg: 3He, 4He, 12C, 14C, 235U, and 239U, respectively)

ElementNumber of

ProtonsNumber of Neutrons

Number of Electrons

Atomic Mass

Atomic Number

lithium

carbon

chlorine

silver

lead

calcium

Atomic Structure Worksheet

Fill in the blanks for the elements in this chart. For the purposes of this chart, round all atomic masses to the nearest whole number.

ElementNumber of

ProtonsNumber of Neutrons

Number of Electrons

Atomic Mass

Atomic Number

lithium 3 4 3 7 3

carbon 6 6 6 12 6

chlorine 17 18 17 35 17

silver 47 61 47 108 47

lead 82 125 82 207 82

calcium 20 20 20 40 20

ANSWER

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

ExampleSODIUM Proton number = 11Electron number = 11Electron configuration = 2.8.1

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

Electron configuration = 2.7Valence electron = 7

Electron configuration = 2.4Valence electron = 4

Electron configuration = 2.8.4Valence electron = 4

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

Number of shells = Period in Periodic Table Valence electron (1 and 2) = Group in Periodic

Table Valence electron (3 – 8) = Valence electron + 10

= Group in P.Table

eg: Valence electron =7So, Group 17

28

1

SODIUM Proton number = 11Electron number = 11Electron configuration = 2.8.1

Position in Periodic Table Period: 3Group : 1

Element Proton number

Number of electrons

Number of elements in shell Electron arrangement

Number of valance electrons

1 2 3 4

Oxygen 8 8 2 6 2.6 6

Fluorine 9 9 2 7 2.7 7

Neon 10 10 2 8 2.8 8

Sodium 11 11 2 8 1 2.8.1 1

Magnesium 12 12 2 8 2 2.8.2 2

Aluminium 13 13 2 8 3 2.8.3 3

Silicon 14 14 2 8 4 2.8.4 4

1. Draw electron arrangement for element Na, Ar, Mg, Al, Cl, O, C, N.

2. State the valence electron for each elements

3. State the position in Periodic Table