Unit 11: States of Matter

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Unit 11 States of Matter
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Types of Covalent Bonds

• Polar Covalent Bond
• e- are shared unequally
• asymmetrical e- density
• results in partial charges (dipole)

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Types of Covalent Bonds

• Nonpolar Covalent Bond
• e- are shared equally
• symmetrical e- density
• usually identical atoms

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If ?EN is Bond type is
lt 0.4 Nonpolar covalent
0.4 lt ? EN lt 1.7 Polar covalent
gt 1.7 Ionic
Given Electronegativities of these elements H
2.2 C 2.55 N 3.04 O 3.44 F 3.98 Na
0.93 K 0.82 P 2.19 S 2.58 Cl 3.16
Determine bond type for the following bonds H
H __________ H O ___________ H
C __________ Na Cl ___________
Take the absolute value of the difference!
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Intermolecular Forces (IMF)

• Attractive forces between molecules.

• Much weaker than
• chemical bonds
• within molecules (INTRAmolecular forces.

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London Dispersion Forces

• London dispersion forces
• Exist in all atoms and molecules
• Electrons within atoms are constantly moving
  around. Sometimes they are not disbursed evenly
  around the nucleus.
• When atoms are close to each other, they are
  attracted due to the temporary area of partial
  and - charges (temporary dipoles) produced.

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London Dispersion Forces
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Dipole-Dipole Forces

• Attraction between two PERMANENT dipoles
• Polar molecules ONLY.
• Medium strength
• Stronger when molecules are closer together

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Types of IMF

• Dipole-Dipole Forces

View animation online.
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Hydrogen Bonding

• Special kind of dipole-dipole
• Occurs between molecules that have an H bonded to
  either O, N, or F.
• Strongest
• Not chemical bonding

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Hydrogen Bonding
Animation of water molecules being attracted to
each other.
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IMF and Boiling Point

• The stronger the IMF, the higher the boiling
  point.

Molecule IMF (s) present Molar Mass (g/mol) Boiling Point (oC)
CH4 16.05 - 164
HCl 36.46 - 85
H2O 18.02 100
London Disp.
London Disp. Dipole-Dipole
London Disp./Dipole-Dipole/Hydrogen Bonding
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Density
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Compressibility
The more empty space between particles, the
easier it is to compress it. Solids are not
easily compressed, liquids a little bit, gases a
lot.
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Liquid Properties

• Viscosity
• Resistance to flow

Oil
Viscosity Demo
Water
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Liquid Properties

• Surface Tension
• attractive force between particles in a liquid
  that minimizes surface area. Creates a SURFACE
  that keeps the liquid together.

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Detergents/Soap

• Oils dont mix with water.
• Fats/oils are non polar
• Water is polar
• LIKE DISSOLVES LIKE
• Soaps and detergents disrupt the hydrogen bonding
  between the water molecules.
• A micelle is formed. (Detergent wraps around
  grease particle and it can be mixed with water.)

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Cohesion and Adhesion

• Cohesion is the force of attraction between
  identical molecules in a liquid (cohesion is a
  result of intermolecular forces).
• Adhesion is the force of attraction between
  liquid molecules and a solid that is touching
  them.

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Liquid Properties
Meniscus of water in a glass tube is concave
adhesion gt cohesion Meniscus of Hg in a glass
tube is convex cohesion gt adhesion
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PROPERTIES OF SOLIDS

• Density Solids are denser than their liquid
  form.
• EXCEPT wax, cork, ice
• In these solids, the molecules are spaced farther
  apart than in their liquid form so they float.

Ice
cork wax
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Crystalline vs. Amorphous

• A crystalline solid has particles which are
  arranged in an orderly, geometric, 3-D structure.
  
• Brittle, hard structure
• Examples sodium chloride, ice, gems and
  minerals

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Types of Solids
In an amorphous solid, the particles are not
arranged in any particular pattern. Flexible
structure Examples rubber, plastics.
Amorphous (SiO2 - glass)
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Phase Changes
E. QmC?T D. Q mHv

Temperature
Tb ?
B. Q mHf C.
QmC?T Tm ? A. Q mC?T
Thermal Energy (Heat)
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Thermal Energy (heat)

• Phase Changes
• B and D represent phase changes
• Occur at constant temperature
• Temperature Changes
• A,C, and E
• Temp is changing
• Sloping portion of the graph

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Thermal Energy (heat )

• What is happening at each part of the graph
• A. Substance is a solid. Can heat it up or cool
  it down along this line.
• B. Phase change solid-liquid. The temperature
  at B (Tm) is the melting (freezing) point.
• C. Substance is a liquid. Can heat it up or
  cool it down along this line.
• D. Phase change liquid-gas. The temperature
  at D (Tb) is the boiling (condensation) point.
• E. Substance is a gas. Can heat it up or cool
  it down along this line.

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Heat Calculations

• Q m c ? T
• Q heat or thermal energy in Joules (J) or
  calories (cal)
• m mass in grams (g)
• C specific heat in J/(g oC) or cal/(g oC)
• ?T change in temperature in oC

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Heat Calculations

• Q mHf
• Q heat or thermal energy in Joules (J) or
  calories (cal)
• m mass in grams (g)
• Hf Heat of fusion (J/g or cal/g) use for
  liquid-solid phase change

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Heat Calculations

• Q mHv
• Q heat or thermal energy in Joules (J) or
  calories (cal)
• m mass in grams (g)
• Hv Heat of vaporization (J/g or cal/g) use for
  gas-liquid phase change

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Things to remember

• You can move from left to right or right to left
  along the curve.
• If you move left to right
• all the processes are endothermic (heat must be
  supplied).
• Your answer for heat calculations will be
  positive.

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Things to remember

• If you move right to left
• all the processes are exothermic (heat is
  removed/released).
• Your answer for heat calculations will be
  negative. You have to write in the negative, but
  you solve the problem the same way!