Chapter 9, Problem 9.119QP

Interpretation Introduction

Interpretation:

Formula of binary hydride for the second period elements from $Li$ to $F$ have to be written.  The change from ionic character to covalent character of these compounds has to be discussed given that beryllium behaves differently from the rest of the group 2A metals.

Concept Introduction:

Ionic bond is the electrostatic force of attraction that binds ions of opposite charges into a stable molecule.  Compounds formed of ions and bound by ionic bond are called ionic compounds.

Covalent bond refers to the bond formed between two atoms by mutual sharing of electrons – that each atom shares equal number of electrons between them and the charge distribution (electron) between the two atoms held by covalent bond is symmetrical.  Such compounds are called covalent compounds.

Polar covalent bond refers to the covalent bond which has polarity caused by unsymmetrical distribution of bonding electrons between the two atoms.  When atoms of moderately different electronegativity bonded by mutual sharing of electrons, the atom having more electronegativity tend to pull the electron cloud towards it.  This leads to unsymmetrical distribution of electrons between the bonded atoms that one end of the molecule develops slight positive charge and another end of the molecule develops slight negative charge.  This is called polarity and such bond is called polar covalent bond.

Electronegativity difference between the atoms must be $1.7$ or nearer to $1.7$ to form polar covalent bond between these atoms.