Covalent radius, hydrogen

Element Electronegativity Covalent radius, pm Usual coordination number Bond with hydrogen Bond length, pm Bond energy, kj/mot ... 

To accommodate this problem, scientists have come up with several approaches to measuring atomic sizes. A common one is called the covalent radius, which is half the distance between the nuclei of two identical atoms. This technique works well for atoms such as hydrogen or oxygen, both of which readily pair up to form and O2. But how would one determine the covalent radius of a noble gas, which exists only as single atoms ... 

The effectiveness of overlap of bonding orbitals of ihe same symmetry appears to decrease as the principal quantum number increases and as the difference between the principal quantum numbers increases. This is reflected in the bond strengths shown in Table 10, The covalent radius of hydrogen is especially subject to effects of this kind, and has the values 0.3707, 0.362, 0.306. 0.284 and 0.293 A respectively in H2. HF. HCI. HBr and HI. The apparent anomaly of the P-P, S-S. and Cl-Cl bonds being stronger than the N—N. O-O. and F—F bonds has been considered in paragraph (I). 

The hydrogen atom can use its Is orbital to overlap with a valence orbital of another atom to form a covalent bond, as in the molecules listed in Table 11.1.2. The covalent radius of hydrogen is 37 pm. 

The conception of a covalent radius may be tested by considering the hydrides. The covalent radius of the hydrogen atom as measured from molecular hydrogen will be half the bond length, 0 37 A. In Talf/e LIX,... 

Table LIX. Covalent Radius of Hydrogen determined from Hydrides the value of the COValent...

The orbital exponent is related to the atomic covalent radius. In QEq the value of parameter for hydrogen depends on the charge on the H atom, a dependence that makes QEq iterative, unlike EEM. 

For example, in molecule 4-amino-2-hydroxy-but-2-ene (Example V3), the Kupchik vertex degree of vertex 5 (N) is equal to 3.080 because the atomic number Z is 5, the bonded hydrogens are 2 and the covalent radius is equal to 0.75 (the covalent radius of carbon atom is 0.77) the Kupchik vertex degree of vertex 6 (O) is equal to 5.274because the atomic number Z is 6, there is only one bonded hydrogen and the covalent radius is equal to 0.73. 

Bond H—X Molecule Interatomic distance H—X A Half of interatomic distance X—X A Covalent radius of hydrogen A... 

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