We made the point that when measuring bond lengths using these models you needed

Question

We made the point that when measuring bond lengths using these models you needed to measure from center atom to center atom and not the length of the plastic bond. At first sight this seems silly, since the length of the bond would seem to be the length of the piece of plastic that represents the bond! However, there is a good reason fro measuring atom center to atom center. You have not been told this explicitly, it is not in your lab packet notes and you probably can't Google the answer, and so this will seem to be an unfair question, but this question is not worth a lot of points, and the TAs have been told to grade it generously, so try to give a very BRIEF explanation for why this is based on what you know about the positions of electrons in space and the position of nuclei (think about VSEPR)/

Explanation / Answer

Bond length is defined as the distance between the centre of two nucleus in a covallently bonded atoms in a molecule.

According to the definition the distance between the centre of two nucleus is to be considered when calculating the bond length.

According to Bohrs atomic model atom consisit of nucleus and electron, nucleus is concentrated in very small region whereas electrons extend in space around the nucleus. The volume of nucleus is negligible when comparedd to volume of atom.

atomic bond is formed by overlapping of atomic orbitals, if we consider the atoms to be sphere these sphere touch each other in real while they form bond, the above shown model is only hypothetical.

Hence it is necesssary to consider the distance between the centre of two atoms.

VSEPR theory is used to explain geometry of molecules, the repulsion between the valence shell electron pairs make the atoms of the molecule to occupy specific region in space so as to minimise the repulsion, this shows that bonds are not static, they are like spring maintained at equillibrium distance.

There is both repulsive interaction and attractive intraction between two atoms, so equillibrium disatnce is considered as bond length

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