Primary Bonding Solid State- Strength TThe strength of the solid depends on the molecular forces that hold the solid together monic interactions are strong because the opposite charges resist breaking of the intermolecular bonds. For I example, the melting temperature of salts is very high Covalent typically400to800°C a Some molecular interactions are strong because of the 3 ngement of the atoms. For example, diamonds ar atoms. The bonds are molecular not ion Metallic Types of Non Bonded (intermolecular, van der waals)Interactions Ion-dipole interactions Dipole-dipole lon-dipole Induced dipole Dispersion Hydroger When polar molecules e er ions he positive end of the dipole is attracted to negative ions and vice versa. hen two polar molecules with net dipoles 甲 es to be present, one to provide ions &HH closer, one end of the dipole in one lin the second molecule than ion ion interactions in io Q o (b). These forces decrease with distance as Dispersion or London forces In non-polar molecules, electrons are distributed Noble gases are atomic gases and do not have dipole metrically. This symmetry can be distorted by an liquefied suggests that forces of attraction exist between These forces are weak and are of short range. atoms of a noble gas. These forces are called Dispersio cThe distribution of electrons in an atom/ molecule uctuate over time. These fluctuations set up temporary forces. These forces exist between all atoms and molecules electrons in atoms/molecules. "Dispersion force ncre group. Thus, forr down a g ases, dispersion forces ase as Xe> Kr> Ar> Ne He2 Primary Bonding e + Na+ e e e e e e e e e e + e e e e e e e e e F- Ionic + + e e Covalent e + + + + + + + + + e e e e e e e e Metallic Solid State ¾ Strength The strength of the solid depends on the molecular forces that hold the solid together. Ionic interactions are strong because the opposite charges resist breaking of the intermolecular bonds. For example, the melting temperature of salts is very high, typically 400 to 800°C. Some molecular interactions are strong because of the 3- D arrangement of the atoms. For example, diamonds are exceptionally hard because the solid state forms, a 3-D network such that each carbon is held close to 4 other atoms. The bonds are molecular, not ionic. Types of Non-Bonded (intermolecular, van der Waals) Interactions Dipole-dipole Ion-dipole Induced dipole Dispersion or London Hydrogen bonding H Cl + - H + Cl - Dipole-dipole interactions: when two polar molecules with net dipoles come closer, one end of the dipole in one molecule will be attracted to the opposite end in the second molecule. (a). These forces are strong, but are weaker than ion-ion interactions in ionic compounds. (b). These forces decrease with distance as 3 r 1 Ion-dipole interactions: When polar molecules encounter ions, the positive end of the dipole is attracted to negative ions and vice versa. The ion-dipole interactions require two species to be present, one to provide ions and another to provide dipoles. O H H d+ d+ d- Na+ Cl￾Induced dipole interactions: In non-polar molecules, electrons are distributed symmetrically. This symmetry can be distorted by an ion/dipole, by inducing dipole in non-polar molecule. These forces are weak and are of short range. e e e e e e + e e e e e e + e e Dispersion or London forces: Noble gases are atomic gases and do not have dipole moments or net charges. The fact that they can be liquefied suggests that forces of attraction exist between atoms of a noble gas. These forces are called Dispersion or London forces. The distribution of electrons in an atom/molecule fluctuate over time. These fluctuations set up temporary dipoles which induce dipoles in others. The attraction between temporary dipoles is responsible for dispersion forces. These forces exist between all atoms and molecules. Strength of dispersion forces increases with number of electrons in atoms/molecules. “Dispersion force increases down a group”. Thus, for rare gases, dispersion forces increase as Xe > Kr > Ar > Ne > He