Intermolecular Forces and States of Matter

Using geometry and polarity, we can determine the forces that allow molecules to be attracted to each other -Without this attraction, there would only be gases for states of matter I. Bond Types (strongest to weakest) A. Network Solids – these are created when atoms have multiple bonds between each atom forming a web of attractions

Examples would be graphite, diamond or quartz 1. these bonds are typically very strong and the substances with these bonds have high melting and boiling points

B. Ionic Solids – these bonds are caused by B. Ionic Solids – these bonds are caused by the electrostatic attraction between a cation (+) and an anion (-) due to the transfer of electrons Examples would be NaCl, MgCl2, Ca3(PO4)2 1. These bonds are very strong, with high melting and boiling points. Substances are very brittle and will conduct electricity only in solution

C. Metallic Solids – formed due to free C. Metallic Solids – formed due to free floating electrons of metals creating electrostatic attractions between the negative electrons and the positive nuclei Examples would be copper, iron, silver 1. These are fairly strong, but allow for malleability, ductile properties and these substances will conduct electricity in their solid form

D. Covalent Compounds – electrostatic D. Covalent Compounds – electrostatic attractions created through the process of sharing of electrons -Three types 1. Hydrogen Bonds – Polar molecules only. Electrostatic attractions created due to uneven sharing of electrons. Must include a Hydrogen atom as well as a Nitrogen, Oxygen or Fluorine -strongest of covalent

2. Dipole – Dipole – Polar molecules only 2. Dipole – Dipole – Polar molecules only. Also created by the uneven sharing of electrons. Less strong than the Hydrogen bond. Examples would be NO2, HCl, CH2O

3. London Forces/Van der Waals –. Nonpolar molecules. Created by 3. London Forces/Van der Waals – Nonpolar molecules. Created by temporary dipoles due to moving electrons. Very weak. Examples would be N2, CO2, NH4+1 -increasing numbers of electrons results in increasing IMF strength

II. Impact of Strength of Bond A. States of Matter 1. Solids-strong bonds. With the exception of Mercury, all ionic compounds, metals and network solids exist in this state at room temperature -atoms are closely packed with little movement. They vibrate in place

2. Liquids – medium strength bonds. Only Mercury is a liquid out of the metallic, ionic or network category. This state of matter comes from covalent compounds -can take shape but not volume of container. Free-flowing, but still has attractions

3. Gases – least strength of all, most covalent compounds fall in this category Particles have very little attraction, thus are able to move freely. Take shape AND volume of container.

B. Melting Point – the stronger the bonds, B. Melting Point – the stronger the bonds, the more heat it takes to break the bonds and turn a solid to a liquid C. Freezing Point – the stronger the bonds, the higher the temperature at which a substance solidifies (freezing doesn’t always mean ‘cold’) D. Boiling Point – the stronger the bonds, the higher the boiling point 1. once liquid reaches boiling, the temperature will no longer change

E. Vapor Pressure – a volatile substance is E. Vapor Pressure – a volatile substance is one that converts from a liquid to a gas very rapidly, increasing the amount of pressure created by the substance. The higher the IMF’s, the lower the vapor pressure due to the large amount of energy needed to break the attractions holding molecules together 1. The easier it is to break the force of attraction, the quicker it can convert to a gas, increasing the vapor pressure

F. Viscosity – “stickiness” of a substance F. Viscosity – “stickiness” of a substance. The more viscous, the slower it moves. Due to attractive forces and structure 1. long structures with branches can get hung up on each other preventing easy movement past each other G. Surface Tension – unbalanced attractions create an inward forces resulting in a kind of skin

III. Phase Changes

A. Triple Point – the temperature and A. Triple Point – the temperature and pressure at which all three states of matter exist at the same time B. Critical Point – point past which a gas will never condense C. Each substance has it’s own diagram, showing each state of matter depending on temperature and pressure

IV. State of Matter Graph A. Energy makes particles move faster, increasing the temperature a – solid B. Energy goes towards breaking bonds, temperature stays constant

b – melting point C. Energy makes particles move faster, increasing temperature c - liquid D. Energy goes towards breaking bonds, temperature stays constant d - gas E. Energy makes particles move faster, increasing temperature *temperature only occurs between phase changes