Ultraviolet irradiation causes dimer formation between adjacent thymines. The dimer blocks replication and transcription. 

#Id: 7744

#Unit 1. Molecules and their Interaction Relevant to Biology

An ionic radius is one-half the distance between the nuclei of two ions in an ionic bond.

#Id: 7745

#Unit 1. Molecules and their Interaction Relevant to Biology

The noble gases are left out of the trends in atomic radii because there is great debate over the experimental values of their atomic radii.

The SI units for measuring atomic radii are the nanometer (nm) and the picometer (pm). 1 nm = 1 X 109 m; 1 pm = 1 X 10-12 m.

#Id: 7746

#Unit 1. Molecules and their Interaction Relevant to Biology

The noble gases are left out of the trends in atomic radii because there is great debate over the experimental values of their atomic radii.

The SI units for measuring atomic radii are the nanometer (nm) and the picometer (pm). 1 nm = 1 X 109 m; 1 pm = 1 X 10-12 m.

#Id: 7747

#Unit 1. Molecules and their Interaction Relevant to Biology

Size of atom or atomic radii can be estimated by effective nuclear charge

#Id: 7748

#Unit 1. Molecules and their Interaction Relevant to Biology

Zeff=Z –S

Chlorine would have a Z value of 17 (the atomic number of Chlorine). Continuing to use Chlorine as an example, the 10 inner electrons (S) would screen out the positive charge of ten protons. Therefore there would be and effective nuclear charge of 17-10 or +7.

#Id: 7749

#Unit 1. Molecules and their Interaction Relevant to Biology