Questions

(1) lifetime of molecule in an excited electronic state is 10 ^ -10 s. The uncertainty in the energy eV approx is

uncertainty in energy can be calculated by using the formula
delta E * delta t > h bar / 2
here h bar = h/2pi
therefore
 uncertainty in energy delta E = h/4 pi delta t
put he values and you will get the answer as 5.275*10^-25 J = 3.29 *10^-6 eV

periodic trends 1

Periodic trends are those properties which change periodically in group or period.

As we know elements are arranged in periodic table according to their atomic weights in ascending order.

Atomic radius - atomic radius decreases in period and increases in group

according to electronic configuration new electron is added to the same orbital in period hence atomic radius decreases
but in group new electron is added to new orbital hence atomic radius increases

effective nuclear charge is the thing to be considered here

as in the period electron is added to same orbital,  positive charge applied by nucleus on electron increases and due to this effect atomic radius decreases

units 2

Smaller microscopic units of length measurements are very useful is solving problems.
These units are expressed in terms of bigger unit 'meter '.

Angstrong
1 A = 10 ^-10 m

nanometer
 1 nm = 10 ^-9 m

micrometer
1 um = 10 ^-6

picometer
1 pm = 10 ^-12 m

Units 1

Units are very important in chemistry as we often have to do conversions.

Mole- This is the SI unit for amount of substance.

Avogadro no  = 6.023 *10^23 mol ^-1

Unit of force - newton N

1 N = 1 kgms^-2
as per my experience units expressed in terms of simple ' kg - m - s ' are very important for deriving equations.

Pressure is force applied per area
Pascal is the unit used for measuring pressure.

1 Pa = 1 Nm^-2 = 1 kgm^-1s^-2

Energy is measured in terms of joule

1 J = 1 Nm = 1 kgm^2s^-2

calorie ( cal) = the amount of heat required to raise temp of 1g of water by 1 degree C

1 cal = 4.184 J
1 atm= 101,325 Pa
760 torr = 1 atm
1 bar= 750 torr

bar stands for barometer which is the unit for measuring pressure.
average barometric pressure near sea level is approx 1 atm.

Periodic table

When you start preparing for such competitive exams related to chemistry, first of all mug up periodic table. Because at the exam many problems are based on periodic table or trends in periodic table and that time you have to know the position of elements in periodic table, their atomic numbers.
While studying periodic table you will come to know that many properties of elements depend on their positions in periodic table, their atomic numbers.
If possible create your own periodic table and make it as simple as possible.

Here is the image of periodic table which we are going to use as a reference for further studies.

Chemistry only

This blog is dedicated to study of chemistry. I am going to solve problems from different exams like SET, CSIR NET, GATE. Also will try to share knowledge I gained during preparation of these exams. If anyone have any problem based on any chemistry related topic you can share with me and all the readers here.
Thanks for stopping by.