Survivorship curves 

#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

#Id: 7750

#Unit 1. Molecules and their Interaction Relevant to Biology

The greater the effective nuclear charge the more tightly an electron is held in by the nucleus because there is less electron shield between the valence electrons and the nucleus, and so, the smaller the radius.

#Id: 7751

#Unit 1. Molecules and their Interaction Relevant to Biology

Ranks the following in increasing atomic radius

S, Mg, Al

S: 16-10 +6

Mg: 12-10 = +2

Al: 13-10 +3

So: S < AlMg

#Id: 7752

#Unit 1. Molecules and their Interaction Relevant to Biology

Electron affinity: The enthalpy change that results from adding an electron to a gaseous atom.

Electron affinity is becoming less negative (less exothermic) and less likely to gain an electron.