Home » Ask & Discuss » Chemistry. » Physical Chemistry « Back to Discussion

Physical Chemistry

Blazing goIITian

Joined:	13 Aug 2008
Post:	1313

17 Nov 2008 19:50:33 IST

0 People liked this

266

Doubt on Work Fuction .........

None

What does Work Fuction (W₀ = h.v_o) of a Metal depend on??

{ apart from threshold frequency or Plancks const }

Also, does it follow any trend in the periodic table for metals ??

Pls, explain with reason ...

Share this article on:

Comments (3)

Mirka

Blazing goIITian

Joined: 13 Aug 2008

Posts: 1313

17 Nov 2008 20:06:59 IST

Like 0 people liked this

REPLY !!!!!!!!

Bhimsen Padalkar

Scorching goIITian

Joined: 29 Oct 2008

Posts: 298

17 Nov 2008 21:18:54 IST

Like 1 people liked this

The work function gives minimum energy required to remove an electron from an atom. This enrgy is called as binding energy.

Now, binding energy is different for different metals. So, photoelectric work function is different for different metals.

From this, we can conclude that work function is more for electronegative elements.

Sagar Saxena

Forum Expert

Joined: 8 Oct 2008

Posts: 7221

28 Feb 2011 00:00:32 IST

Like 0 people liked this

Work Function

The minimum amount of energy required to emit electrons from a metal surface is called the work function or threshold energy of that metal.

The number of electrons emitted per second i.e. the rate of emission depends upon

the material of the surface

temperature of the surface

area of the surface

To obtain a good emission of electron the material used must have the following properties:

1) low work function so that the electrons may be emitted at low temperature.

2) High melting point so that the metal does not melt on heating to a high temperature.

Tungsten is a suitable metal, has a melting point of 3655 K but work function is high about 4.52 eV (electron volt-energy unit). It starts emission at 2500 K.

If thoriated tungsten (coated with carbon and thorium) is used work function reduces to 2.6 eV and emission begins at 2000 K.

If tungsten is coated with barium and strontium oxide work function reduces to

1 eV and emission begins at 1000 K and a good supply of electrons is obtained.

A metal contains a large number of free electrons. They move at random within the metal with different velocities. But at ordinary temperatures, they cannot leave the surface due to attractive forces between the electrons and the positive ions. If the metal is heated, the kinetic energy of the electrons increases.

Above a certain temperature, a large number of electrons get energy greater than the work function of the metal and the thermionic emission begins. When a metal surface is coated with oxides of barium, strontium etc., the work function is reduced.

Work Function for Some metals

Metal	Work function in eV
Barium coated tungsten	1.6
Caesium coated tungsten	1.4
Chromium (Cr)	4.37
Platinum (Pt)	6.2
Potassium (K)	2.26
Sodium (Na)	2.3
Tungsten (W)	4.52
Zinc (Zn)	4.24

Quick Reply

Reply

	Some HTML allowed.
	Keep your comments above the belt or risk having them deleted.
	Signup for a avatar to have your pictures show up by your comment
	If Members see a thread that violates the Posting Rules, bring it to the attention of the Moderator Team