till which at no. should we know the at. wt.I hope for others it will be given

Dear Neha Gaur,

It is always good to know the Atomic Weights of the First 30 elements of the Periodic Table.

Here are the Atomic Weights of the first 30 elements of the Periodic Table till Zinc(Z=30)

1  H  - Hydrogen - [1.007 84; 1.008 11]
2  He - Helium - 4.002 602(2)
3  Li - Lithium - [6.938; 6.997]
4  Be - Beryllium - 9.012 182(3)
5  B  - Boron - [10.806; 10.821]
6  C  - Carbon - [12.0096; 12.0116]
7  N  - Nitrogen - [14.006 43; 14.007 28]
8  O  - Oxygen - [15.999 03; 15.999 77]
9  F  - Fluorine - 18.998 4032(5)
10 Ne - Neon - 20.1797(6)
11 Na - Sodium - 22.989 769 28(2)
12 Mg - Magnesium - 24.3050(6)
13 Al - Aluminium - 26.981 5386(8)
14 Si - Silicon - [28.084; 28.086]
15 P  - Phosphorus - 30.973 762(2)
16 S  - Sulfur - [32.059; 32.076]

 17 Cl - Chlorine - [35.446; 35.457]

18 Ar - Argon - 39.948(1)
19 K  - Potassium - 39.0983(1)
20 Ca - Calcium - 40.078(4)
21 Sc - Scandium - 44.955 912(6)
22 Ti - Titanium - 47.867(1)
23 V  - Vanadium - 50.9415(1)
24 Cr - Chromium - 51.9961(6)
25 Mn - Manganese - 54.938 045(5)
26 Fe - Iron - 55.845(2)
27 Co - Cobalt - 58.933 195(5)
28 Ni - Nickel 58.6934(4)
29 Cu - Copper - 63.546(3)
30 Zn - Zinc - 65.38(2)

Also the Atomic Weights of other elements like Mercury(Hg),Cadmium(Cd),Caesium(Cs),Barium(Ba),Lead(Pb) and Auric(Au) are better kept in mind for they are usually in use in IIT-JEE

1.  Hg - Mercury - 200.59(2)

2. Cd - Cadmium - 112.411(8)

3. Cs - Cesium - 132.905 4519(2)

4. Ba - Barium - 137.327(7)

5. Pb - Lead - 207.2(1)

6. Au - Gold - 196.966 569(4)

Hope this helped you immensely..!

All the Very Best & Good Luck to you ..!!

Best Regards,

AskIITians Expert,

Godfrey Classic Prince

IIT-M

Please approve my answer if you liked it by clicking on "Yes" given below..!!

It''s not exactly about "till which number" 

You should know the atmic weights of first 20 elements and besides that, atomic weights of freqeuntly used/important elements. Some of these include Mercury, Lead, Silver, Copper, Chromium etc.

Approve if i helped ;)

I most of the questions you would provided with the at. wt. but it is advisable to learn the whole periodic table.

Otherwise upto at. no. 36 you must know the at. config.

Plz. approve my answer by clicking Yes given below, if u loved it... Plz/....

And best of luck for your preparation!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!