CHEM 110 Chapter Notes - Chapter 11: Poise, Atomic Radius, Evaporation
10 May 2018
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Chapter 11
Solid, Liquids and Gases: Molecular Comparison
- Three states of Water
o Gas
▪ 100C
▪ Density of 5.9x10-4
▪ Molar Volume of 31L
o Liquid
▪ 20C
▪ Density of 0.998
▪ Molar Volume of 18mL
o Solid
▪ 0C
▪ Density of 0.917
▪ Molar Volume of 19.6mL
o Major difference between liquid and solids is the freedom of movement of the
constituent molecules
▪ Thermal energy partically overcomes the attractions
▪ Atoms in a solid are locked in their position
▪ Liquids assume the shape of their containers because the atoms are free to
flow
• Not easily compressed because the molecules are already in close
contact
• They cannot be pushed closer together
▪ Molecules in a gas, have a great deal of space between them
• Forced into a smaller volume by increase external pressure
- Properties of the States of Matter
o Solids have a definite shape because the molecules that compose solids are fixed
in place
▪ Like liquids, solids have a definite volume cannot be compressed because
the molecules are composing the are already close
▪ Solid may be crystalline (the atoms or molecules are arranged in a three-
dimensional array)
• Or Amorphous (the atoms that compose them have no long-range
order)
- Changes between States
o We can transform one state of matter by changing the temperature, pressure or
both
o We can induce a transition between the liquid and gas state by changing pressure
▪ Increasing the pressure of a gas sample results in a transition to the liquid
state
▪ Liquified petroleum gas is composed of propan
• It liquifies at pressures above 2.7 bar
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Intermolecular Forces: Hold condensed States Together
- Intermolecular forces originate from the interactions between charges, partial charges and
temporary charges on molecules
o The potential energy of two oppositely charged particles
decreases with increasing magnitude of charge and with
decreasiong separation
▪ Q1 and Q2 are charged particles
▪ E is Potential Energy
▪ R is the increasing magnitude of charge with decreasing separation
• When Q1 and Q2 are opposite in charge, E is negative
o Intermolecular forces are weaker than bonding forces
▪ Weakness of intermolecular forces compared to bondingis also related to
coulombs law
• Bonding forces are the result of large charges
o The charges on protons and electrons interacting at close
distance
• Intermolecular Forces are the result of smaller charges interacting
at a greater distance
▪ The larger distances between molecules, as well as the smaller charges,
result in weaker forces
• To break the bond in water, you must heat the water to a boiling
point of 100C
- Ion-induced Dipole Forces
o When an ion approaches a nonpolar atom it can cause a distortion of the negative
electron in the nonpolar atom
▪ Since electron is distorted to one side of the atom, it has a small dipole
induced by the presence of the ion
▪ Magnitude of ion-induced dipole forces depends on the charge on the ion
and how the electrons can move or polarize in response to the presence of
the ion
▪ The magnitude of the polarizability of an atom is dependent on the size of
the electron cloud
• Polarizability (Capability of electron clouds)
▪ A larger electron cloud results in a dispersion force because the elctrons
are less tightly held by the nucleus and easier to polarize
o Dispersion Force
▪ Result of fluctuations in the electron distribution within atoms in the
absence of an ion
▪ The electron in an atom may be unevenly distributed
▪ Example: Helium
• The left side will have a slightly negative charge
• The right side of the atom, has no electrons, will have a slight
positive charge because of the charge of the nucleus
o This fleeting charge in separation is called temporary
dipole
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▪ The magnitude of the dispersion depends on how easily the electrons can
move or polarize in response to an instantaneous dipole
• A larger electron cloud results in greater dispersion forces because
the electrons are held less tightly by the nucleus and distorted
easily
• As the number of electrons increases, the volume of the electron
cloud increases, and greater dispersion forces result in increasing
boiling points
• To polarize means to form a dipole moment
• The number of electrons alone does not determine the magnitude
of dispersion force
▪ Dispersion forces are the reason we can liquify and freeze rare gases and
hydrocarbons
• Helium and Decane interact through dispersion forces, but boiling
point for helium is 4.2K and that for decane is 446.9K
• Number of electrons can act as a guide when comparing dispersion
forces
o Dipole-Dipole Force
▪ Exist in all molecules that are polar
▪ Polar molecules have permanent dipoles that interact with the permanent
dipoles of neighboring molecules
▪ The positive end of one permanent dipole attracts the negative of another
▪ Polar molecules have dipole-dipole forces
• Raoses melting and boiling points relative to nonpolar molecules
▪ The polarity of molecules composing liquids is important in determining
miscibility
• Ability to mix without separating into two states of liquids
• Polar liquids are miscible with other polar liquids but not with
nonpolar liquids
o Example: Which have dipole-dipole forces
▪ CO2
• Electronegativity of carbon is 2.5 and oxygen is 3.5
• CO2 has polar bonds
• Geometry is linear, and no dipole-dipole forces present
▪ CH2Cl2
• Electronegativity of C is 2.5, H is 2.1, and Cl is 3.0
• CH2Cl2 has two polar bonds and two non-polar bonds
• Geometry is tetrahedral, dipole do not cancel but sum to net dipole
• Dipole-dipole forces
▪ CH4
• Electronegativity of C is 2.5, H is 2.1
• Nearly nonpolar
• Tetrahedral molecule, bonds might have will cancel
• Non-polar with no dipole forces
o Melting points increase as dipole moments decrease
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Document Summary
Changes between states order: we can transform one state of matter by changing the temperature, pressure or both, we can induce a transition between the liquid and gas state by changing pressure. Increasing the pressure of a gas sample results in a transition to the liquid state: liquified petroleum gas is composed of propan. If they were only dipole-dipole interactions, the negative end one water molecule would line up with positive end water molecule: dipole-induced dipole forces. Forces between molecules that have a permanent dipole and an atom that is nonpolar. Ion-dipole forces are the strongest types of intermolecular forces. Increasing in larger molecules that can interact over a greater area and possible become entangled. Increase in viscosity as the number of electrons increase. Increase in length as well: viscosity depends on temperature because thermal energy overcomes the intermolecular forces, allowing molecules to flow past eachother.
