Halogens atomic size

Halogen atom size increases as we go down the periodic table fluorine atoms are the smallest and iodine atoms the largest. Consequently, the carbon-halogen bond length increases and carbon-halogen bond strength decreases as we go down the periodic table (Table 6.1). Maps of electrostatic potential (see Table 6.1) at the van der Waals surface for the four methyl... 

Table 19-11. sizes of the halogen atoms, melting points, boiling points, AND DISSOCIATION PROPERTIES OF THE HALOGEN MOLECULES... 

On the basis of the trend in atomic size, what trend is expected in the ionization energy E of the halogen atoms Compare your prediction with the actual trend in Eu given in Table 19-1. 

C09-0133. Among the halogens, only one known molecule has the formula X 7. It has pentagonal bipyramidal geometry, with five Y atoms in a pentagon around the central atom X. The other two Y atoms are in axial positions. Draw a ball-and-stick model of this compound. Based on electron-electron repulsion and atomic size, determine the identities of atoms X and Y. Explain your reasoning. (Astatine is not involved. This element is radioactive and highly unstable.)... 

The size of the halogen atom increases going down the periodic table => the C-X bond length increases going down the periodic table. 

A halogen molecule contains one nonpolar covalent single bond, as shown by its Lewis structure. As we descend the 7A family from F2 to I2, the size of a halogen atom increases and so the bond length increases. The strength of the X-X bond varies it increases from F2 to Cl2, then decreases from Cl2 to Br2 to I2. 

As the size of the halogen atom increases, the force of attraction between the nucleus of the atom and the incoming electron decreases. Therefore, the first electron affinities become less exothermic down group 7. 

The size of the alkyl groups in the haloalkane is Important. This is known as a steric effect. You will recall that, in the mechanism, the nucleophile attacks the carbon atom of the C-X bond from the side opposite to the halogen atom. In the case of a tertiary haloalkane, attack from that side is likely to be sterlcally hindered because three bulky alkyl groups will limit access to the atom. Hence tertiary haloalkanes are unlikely to react with nucleophiles via an Sj. 2 mechanism. Primary haloalkanes, on the other hand, have no more than one alkyl group attached to the halogen-bearing carbon atom and so access to the atom will be much easier. This suggests that primary haloalkanes are most likely to react with nucleophiles via an S. j2 mechanism. 

Since the size of halogen atom Increases as we go down the group in the periodic table, fluorine atom is the smallest and iodine atom, the largest. Consequently the carbon-halogen bond length also Increases from C—to C— I. Some typical bond lengths, bond enthalpies and dipole moments are given in Table 10.2. 

The attractions get stronger as the molecules get bigger in size and have more electrons. The pattern of variation of boiUng points of different halides is depicted in Fig. 10.1. For the same allqrl group, the boiling points of allqrl halides deerease in the order Rl> RBr> RC1> RF. This is beeause with the inerease in size and mass of halogen atom, the magnitude of van der Waal forees Inereases. 

The 6-fluoro derivatives of Gal and Fuc do not decrease the pools of ribonucleotides, nor do they inhibit protein synthesis.234,304 Interestingly, when present in low concentrations, most fluoro sugars do not give cytotoxic effects.304,313 When the size of the halogen atom is increased (Cl — Br — I derivatives), incorporation of L-fucose is lessened, and, for as-yet-unknown reasons, a concomitant increase in cytotoxicity was noted.304... 

Y = Br. This is in keeping with the fact that the atomic size of the halogens increases in the order F < Br < I. 

---