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CHEM 1405:
Introductory Chemistry
Houston Community College
Dr. Laura Jakubowski
Chapter 11 – Liquids and Solids
Textbook “Introductory Chemistry: Concepts and Critical Thinking” Seventh Edition by Charles H. Corwin
© 2014 Pearson Education, Inc.
Properties of Liquids
• Liquids have the following general properties
1. Liquids have a variable shape, but a fixed volume – the shape of a
liquid conforms to shape of container
2. Liquids usually flow readily – liquids flow at different rates
3. Liquids do not compress or expand significantly – the volume of a
liquid varies very little with changes in temperature and pressure
4. Liquids have a high density compared to gases – liquid particles
are much closer together and are ~1000 more dense than gases
5. Liquids that are soluble mix homogeneously – liquids diffuse more
slowly than gases, but liquids that are soluble eventually form a
homogeneous mixture
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The Intermolecular Bond Concept
• The attraction between two separate molecules is known as an
intermolecular bond (as opposed to a bond between two atoms, known
as an intramolecular bond)
• Intramolecular bonds are much stronger than intermolecular bonds
• Intermolecular bonds determine properties such as vapor pressure
• Three types of intermolecular bonds
• Temporary dipole
• Permanent dipole
• Hydrogen bonds
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Temporary Dipole Attraction
• In molecules, positive and negative charges are concentrated in different
regions – caused by an uneven distribution of electrons
• A molecule having regions of positive and negative charge is said to
possess a dipole
• A negative region in one molecule has a weak
attraction for a positive region in another molecule,
known as a dispersion force
• A temporary dipole in one molecule can induce a
temporary dipole in neighboring molecules
• Dispersion forces last for only brief periods of time,
but they occur frequently between molecules
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Permanent Dipole Attraction
• Atoms of different elements vary in their attraction of electrons – in some
molecules this gives rise to permanent positive and negative regions
• Similar to a magnet, the opposite charges are attracted to each other
between molecules
• This is known as a dipole force, and operates continuously
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Hydrogen Bonds
• In molecules where a hydrogen atom is bonded to an oxygen or nitrogen
atom, an especially strong dipole results
• This special type of dipole attraction is called a hydrogen bond
• It is about 10% of the strength of an intramolecular bond
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Vapor Pressure
• At the surface of a liquid, some molecules gain enough energy to
escape the intermolecular attractions of neighboring molecules and
enter the vapor state (known as vaporization)
• The reverse process also occurs, where molecules in the vapor return to
liquid form (known as condensation)
• When the rate of vaporization and condensation are equal, the pressure
exerted by the gas molecules above a liquid is known as the vapor
pressure
• The vapor pressure above a liquid depends on the attraction between
molecules in the liquid – stronger intermolecular attraction means lower
vapor pressure
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Vapor Pressure
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Boiling Point
• When the temperature of a liquid is
increased, its vapor pressure increases
• A liquid begins to boil when the vapor
pressure equals the pressure of the
atmosphere
• The normal boiling point (Bp) is the
pressure at which the vapor pressure
equals standard atmospheric pressure
• Liquids which have high boiling points
have low vapor pressures
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Viscosity
• The resistance of a liquid to flow is a property called viscosity – that is,
a liquid such as water is easier to pour than a liquid such as honey
• Viscosity is affected by intermolecular forces, and the size and shape of
the molecules
• Generally, the greater the intermolecular force, the greater the viscosity
VISCOSITY*
1.00
1.10
2.95
0.35
0.23
*Values are expressed in centipoise, a common unit of viscosity.
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Surface Tension
• Small insects are able to float on water – for a dense object to sink in a
liquid, it has to break through the surface
• Molecules on the surface resist being pushed apart, the attraction
between the surface molecules in a liquid is called surface tension –
and generally, the greater the intermolecular attraction, the greater the
surface tension
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Physical Property Predictions
• For a liquid with a strong intermolecular attraction, state whether each
property is high or low:
•
•
•
•
vapor pressure
boiling point
viscosity
surface tension
• The intermolecular attraction is greater in isopropyl alcohol (C3H7OH)
than in pentane (C5H12). Predict which liquid has the higher value for
each of the following:
•
•
•
•
vapor pressure
boiling point
viscosity
surface tension
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Physical Property Predictions
• For a liquid with a strong intermolecular attraction, state whether each
property is high or low:
•
•
•
•
vapor pressure – low
boiling point – high
viscosity – high
surface tension – high
• The intermolecular attraction is greater in isopropyl alcohol (C3H7OH)
than in pentane (C5H12). Predict which liquid has the higher value for
each of the following:
•
•
•
•
vapor pressure – pentane
boiling point – isopropyl alcohol
viscosity – isopropyl alcohol
surface tension – isopropyl alcohol
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Properties of Solids
• Solids have the following general properties
1. Solids have a fixed shape and a fixed volume – solids are rigid
2. Solids are either crystalline or noncrystalline – a crystalline solid
contains particles arranged in a regular repeating pattern
3. Solids do not compress or expand to any degree – temperature
and pressure have a negligible effect on the volume of a solid
4. Solids have a slightly higher density than their corresponding
liquids – solid iron sinks in molten iron (ice/water is an exception)
5. Solids do not mix by diffusion – solid particles are not free to diffuse
and will not mix uniformly (a metal alloy is mixed in the molten liquid
state before cooling to a solid)
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Crystalline Solids
• There are three types of crystalline solids
• Ionic solids
• Molecular solids
• Metallic solids
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Ionic Solids
• A crystalline ionic solid is composed of positive
and negative ions
• The ions are arranged in a regular, repeating
pattern to form a three-dimensional structure
known as a crystal lattice
• In table salt, NaCl, sodium ions (Na+) and
chloride ions (Cl-) are arranged as shown in the
image, and crystals generally take a cubic shape
• Other ionic compounds (such as NaF, CaF2, and
CaCO3) will have different crystal lattices and will
form different geometric shapes
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Molecular Solids
• A crystalline molecular solid has molecules
arranged in a particular configuration
• Sucrose, C12H22O11 (table sugar) molecules are
arranged in a regular order that allows light to
pass through the crystal
• Sulfur crystals are made from S8 molecules (held
together by intramolecular bonds) and are
arranged in a regular, 3-D structure
• Diamond is a unique type of molecular solid – it
is a network solid, where all carbon atoms are
connected through intramolecular bonds
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Metallic Solids
• A crystalline metallic solid has atoms of metals
arranged in a definite pattern
• A metallic crystal, such as gold (Au), is made up of
positive metal ions surrounded by valence electrons
which are free to move about the crystal
• Metals good conductors of electricity due to this
property
• This arrangement of atoms and freely moving
electrons is referred to as the “electron sea” model
• The flow of electricity is associated with the
movement of electrons through a metal
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Changes of Physical State
• Remember that specific heat is the amount of energy required to raise
one gram of substance one degree Celcius (units cal/(g×°C)) – for water,
the specific heat is 1.00 cal/(g×°C)
• The amount of heat required to melt 1.00 g of substance at its melting
point is called the heat of fusion (Hfusion) – for water, the heat of fusion is
80.0 cal/g; the reverse process, known as the heat of solidification
(Hsolid) is also 80.0 cal/g
• The amount of heat required to vaporize 1.00 g of a substance at its
boiling point is called the heat of vaporization (Hvapor) – for water, the
heat of vaporization is 540 cal/g; the reverse process, known as the
heat of condensation (Hcond) is also 540 cal/g
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Changes of Physical State
• A temperature-energy curve, or heating curve for water:
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Changes of Physical State
• Calculate the amount of energy required to turn 25.5 g of ice at -5.0 °C
to steam at 100.0 °C
(specific heat of ice: 0.5 cal/(g×°C), of water: 1.00 cal/(g×°C); Hfusion: 80 cal/g; Hvapor: 540 cal/g)
• Break the problem up to solve:
from ice at -5.0 °C to 0.0 °C:
25.5 g × 0.5 cal/(g×°C) × (0.0 °C - (-5.0 °C)) = 63.8 cal
from ice at 0.0 °C to water at 0.0 °C:
25.5 g × 80.0 cal/g = 2,040 cal
from water at 0.0 °C to water at 100.0 °C:
25.5 g × 1.00 cal/(g×°C) × (100.0 °C - 0.0 °C) = 2,550 cal
from water at 100.0 °C to steam at 100.0 °C:
25.5 g × 540.0 cal/g = 13,800 cal
• Add together
63.8 cal + 2,040 cal + 2,550 cal + 13,800 cal = 18,500 cal
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Structure of Water
• The boiling point and surface tension of water are unusually high, water
also has a strong intermolecular attraction because of hydrogen bonding
• The angle between the two hydrogen atoms,
or the bond angle, is 104.5°
• Each of the bonds is a dipole, O has a slight
negative charge (δ-) and H has a slight
positive charge (δ+)
• A water molecule has two dipoles, these two
δ+ δdipoles average to create a single dipole
104.5°
passing through the center of the molecule,
known as the net dipole
δ+
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Physical Properties of Water
• When water freezes to ice, the hydrogen bonds
produce a crystal lattice which has holes –
these holes create a volume for ice which is
greater than for an equal mass of water, which
is why ice is less dense than water
• Water has an unusually high melting and
boiling point for a molecule its size – again
hydrogen bonding produces a strong
intermolecular attraction that resists the
movement of molecules, therefore a higher
temperature is needed to melt ice and boil
water
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Chemical Properties of Water
• Water is usually a solvent for chemical reactions, although water can be
a reactant or product
Water decomposes to H2 and O2 gases through electrolysis
Water reacts with an active metal to give a metal hydroxide and H2 gas
A metal oxide reacts with water to give a metal hydroxide
A nonmetal oxide reacts with water to give an acid
Water can be formed by igniting H2 gas and O2 gas together
Certain organic compounds combust to form CO2 gas and water vapor
Neutralization reactions produce water and salt as the products
The decomposition of a hydrate also produces water
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Hydrates
• A hydrate is a crystalline compound containing a specific number of
water molecules as part of its structure
• Heating a hydrate drives off the water and produces an anhydrous
compound
CuSO4 • 5H2O(s) ∆ CuSO4(s) + 5 H2O(g)
• The water molecules in a hydrate are referred to as the water of
hydration – the water of hydration for CuSO4 • 5H2O(s) is 5
• According to IUPAC rules, Greek prefixes are used to name hydrates
• CuSO4 • 5H2O(s) is copper(II) sulfate pentahydrate
• Na2CrO4 • 4H2O(s) is sodium chromate tetrahydrate
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Percent Water in a Hydrate
• The percent water in a hydrate is the ratio of the mass of water in the
hydrate to the mass of the hydrate, multiplied by 100%:
mass of water
× 100% = % H2O
mass of hydrate
• Find the percentage of water in gypsum, CaSO4 • 2H2O(s)
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Percent Water in a Hydrate
• The percent water in a hydrate is the ratio of the mass of water in the
hydrate to the mass of the hydrate, multiplied by 100%:
mass of water
× 100% = % H2O
mass of hydrate
• Find the percentage of water in gypsum, CaSO4 • 2H2O(s)
molar mass of H2O is 18.02 g/mol
molar mass of CaSO4 is 136.15 g/mol
molar mass of CaSO4 • 2H2O(s) is 136.15 g/mol + (2 × 18.02 g/mol)
2 × 18.02 g
× 100% = 20.93% H2O
136.15 g + (2 × 18.02 g)
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Determining the Chemical Formula of a Hydrate
• Similar to the empirical formula of a compound, the empirical formula of
a hydrate is the simplest whole number ratio of water molecules to the
anhydrous compound
• The compound Na3PO4 • XH2O(s) is 52.3% water, what is the chemical
formula for the hydrate (what is X)?
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Determining the Chemical Formula of a Hydrate
• Similar to the empirical formula of a compound, the empirical formula of
a hydrate is the simplest whole number ratio of water molecules to the
anhydrous compound
• The compound Na3PO4 • XH2O(s) is 52.3% water, what is the chemical
formula for the hydrate (what is X)?
Assuming a 100.0-g sample, the compound contains 52.3 g water and 47.7 g Na3PO4
1 mol H2O
52.3 g H2O ×
= 2.90 mol H2O
18.02 g H2O
1 mol Na3PO4
47.7 g Na3PO4 ×
= 0.291 mol Na3PO4
163.94 g Na3PO4
Na3PO4 • (2.90/0.291)H2O  Na3PO4 • 10H2O
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Summary
• Five observed properties of a liquid
• Three types of intermolecular interactions: dispersion force, dipole force,
hydrogen bond
• Properties of liquids include vapor pressure, boiling point, viscosity, and
surface tension
• Five observed properties of a solid
• Three types of crystalline solids: ionic solids, molecular solids, metallic
solids
• The heat energy required to change from the solid state to the liquid
state is the heat of fusion and to change from the liquid state to the gas
state is the heat of vaporization
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Summary
• The bond angle of a water molecule is 104.5; the oxygen atom has a
partial negative charge and the hydrogen atoms have a partial positive
charge to create an overall net dipole for the molecule
• Hydrogen bonding between water molecules explain many of the unique
properties of water
• Water undergoes many type of chemical reactions
• Certain inorganic compounds form hydrates with water – the percent
water and chemical formula can be calculated given certain information
Key terms: dispersion force, dipole force, hydrogen bond, vapor
pressure, boiling point, viscosity, surface tension, crystalline solid,
ionic solid, molecular solid, metallic solid, specific heat, heat of fusion,
heat of vaporization, bond angle, net dipole, electrolysis, metal oxide,
nonmetal oxide, anhydrous compound, water of hydration
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