Liquids and Solids Introduction l Chemical bonds hold

Liquids and Solids

Introduction l Chemical bonds hold atoms together in a molecule. Intermolecular forces hold molecules together, making them solids, liquids and gases

Types of molecular forces l l l Dipole-dipole forces London Forces Hydrogen bond

Dipole-dipole forces l l l Molecules with polar bonds exhibit dipole moments Positive and negative charges of a polar molecules are attracted to each other Ex: HCl, H 2 O, NH 3

London Forces l l Named after Fritz London Very weak intermolecular force A force between nonpolar molecules that has temporary polarity due to the constant moving electrons in a molecule These weak forces explains the low boiling point of nonpolar substance

Hydrogen Bond l l Special kind of dipole - dipole attraction It involves molecules with a H atom bonded to a very electronegative element ( N, O, F)

Properties of Liquids l l l Surface Tension Capillary Action Viscosity

1. Surface Tension l l Water drops are spherical because of intermolecular forces of attraction between molecules Property that tends to draw the surface molecules into the body of the liquid and reduces the surface to a minimum

2. Capillary Action Spontaneous rising of liquid in a narrow tube is due to Adhesive forces l attraction of liquids for molecules of the tube if the tube has bonds of the same polarity as the liquid Cohesive forces attraction of liquid molecules for each other

Meniscus ( Capillary Action) Concave meniscus Is produced if adhesive forces is greater than the cohesive forces l Convex Meniscus Is produced if cohesive forces is greater than the adhesive forces l

3. Viscosity A measure of liquid’s resistance to flow l Note Liquids with large intermolecular forces have high viscosity Ex: syrup has higher viscosity than water l

Solids Types of Solids AMORPHOUS CRSTALLINE

Amorphous Solid l l l Solids that do not have definite melting points Solids that do not have an orderly arrangement; their arrangement is random similar to that in liquid Ex: Gum, Paraffin and glass

Crystalline Solid l l l Solids that have definite melting points Solids that have an orderly arrangement of particles that gives a crystal a recognizable shape Ex: Sodium Chloride and Sugar

Examples of Crystalline Solid l Atomic Crystalline solid Diamond structure and graphite structure. Both are crystalline structures of carbon atoms, both pure carbon but they have very different properties due to their different crystal structures l Ionic Crystalline Solid Na. Cl ( simple cubit unit cell) l Molecular crystalline solid H 2 O ( ice)

Allotropes l l Crystalline solid that can exist in various forms Ex: Carbon – which can exist as diamond and graphite

Bonding in Solids Covalent Particles that occupies the lattice site Atoms Ionic Metallic Molecular Positive and negative ions Metal atoms Molecules Nature of Bonding Electron Sharing Electron static attraction Electrical attraction between the electrons and nucleus Vander Waals forces Properties Hard, nonvolatile and high boiling point Quite hard and brittle, good insulators Variable melting points and hardness Good conductors generally soft and have low melting point Examples Diamond, carborundum, quartz Sodium chloride, potassium nitrate Sodium sulfate Copper, iron , aluminum Ice, dry ice