Molecular Structure,

Properties and State of Matter

COMPOSITION
OF MATTER
• Chemistry is the study of matter, its properties,
composition, and structure and the changes it
undergoes.
• It is central to our fundamental understanding of many
science-related fields.
Atomic and Molecular Perspective
• Matter - Anything that has mass and occupies space.
• Atom - The smallest stable building block of matter.
• Molecule – groups of atoms held together with a
specific connectivity and shape. (for example O2 )
• Composition – the types of atoms that are present in a
compound and the ratio of these atoms (for example
H2 O, )
• Structure – how atoms are connected (bonded) to
each other, how far apart they are, and the shape of the
molecule.
Methods of Classification of Matter
• State of Matter – physical state is gas, liquid, or solid.
• Composition of Matter - element, compound, or
mixture
 Substances

• Substance: type of matter with a fixed composition

that cannot be separated by physical means.
• Elements – Substance made up of atoms with the
same identity
• Compound – Atoms of two or more elements
combined
• Examples: water (H2O) Carbon Dioxide (CO2)
 Mixture
Mixture: Material made up of two or more substances that
can be separated by physical means
• Heterogeneous – mixture in which different materials
can be easily distinguished.
Examples: Pizza, fruit salad, granite
• Homogeneous – mixture in which two or more
substances are uniformly spread out.
Examples: vinegar, salt water, coffee
 TYPES OF MIXTURES
Solution: Homogeneous mixture of particles so small that
they cannot even be seen with a microscope and will
never settle to the bottom of their container.

Examples: Vinegar, Soda (unopened), Hydrogen

Peroxide
 Types of Mixtures
Colloid: type of mixture with particles that are larger than
those in solution but still too light to settle out.

Example: Milk (Water and Fat), Fog (water and air), Cool
Whip
 Types of Mixtures
Suspension: heterogeneous mixture containing a liquid in
which visible particles settle.

Example: Italian dressing, muddy pond water, chocolate

milk
Separation of Mixtures
PROPERTIES
OF
MATTER
A physical property of matter is one that can be
observed without changing its composition. Gold is a
shiny yellow metal. Lead has a high density. Observations
of these characteristics do not change the composition.

A physical change is a change in the form of matter

without changing its composition. Examples of such
changes are phase changes such as melting, boiling, etc.
A chemical property is one which is observed when
matter undergoes a transformation that results in a change
of composition. Gasoline will burn in air to form products
which are very different from the original material. Iron
will rust in moist air to form a compound called iron
oxide. The fact that gasoline burns and iron rusts are
therefore chemical properties.

A chemical change is one that leads to a change in the

composition of the matter involved. The burning of wood
leads to products very different than the starting material.
Note: Physical changes are quite often reversible. Ice can
be melted to form liquid water; however, water can be
readily reconverted to ice. Chemical changes are usually
irreversible. Gasoline can be burned to produce water and
carbon dioxide, but it is not possible to reconvert these
into the original material.

Even though matter can undergo changes it is important to

realize that in ordinary chemical reactions matter cannot
be created or destroyed. We say that matter is conserved.
This is one of the fundamental conservation laws.
 Properties of Matter
• Intensive Properties:
- independent of the amount of the substance that is
present.
- Density, temperature, melting point, boiling
point, hardness, etc.

• Extensive Properties:
- dependent upon the amount of the substance
present.
- Mass, volume, energy, etc.
 States of Matter
• Gas (vapor) – has no fixed volume or shape,
uniformly expands to fill its container, compressible,
flows readily, diffusion occurs rapidly.
• Liquid – has a distinct volume independent of its
container, assumes the shape of the portion of the
container it occupies, not significantly compressible,
diffusion occurs but slower than a gas.
• Solid - has both a definite shape and definite volume,
not significantly compressible, diffusion occurs
extremely slowly.
• Plasma - Highly energized particles that begin
emitting energy. Florescent lights, Neon lights, and
fire have plasma inside. The Sun is nearly all Plasma
 STATES OF MATTER
Matter can be classified according to its physical state and its
composition.

Physical State:
Solid
Liquid
Gas

Classification into different states based upon:

Particle arrangement
Energy of particles
Distance between particles •

State of matter is dependent on temperature and pressure of the

surroundings
 SOLIDS
• Has a definite shape and volume
• True solids have very rigid, ordered structures, in
fixed positions i.e. high density
• Atoms held tightly together, therefore incompressible
• Atoms move through vibration only, therefore small
thermal expansion
 Liquid
• Has a definite volume, atoms are not widely separated,
therefore high density and small compressibility
• No definite shape i.e. follows the shape of its container
• Atoms move rapidly enough to slide over one another
i.e. ability to flow
• Small thermal expansion
 GASES
• Also known as vapour
• No fixed volume or shape, conforms to the volume
and shape of its container
• Atoms far apart i.e. low density and can be
compressed
• Moving at high speeds, colliding with container,
moderate thermal expansion
 CHANGES IN MATTER

All matter can undergo physical and chemical changes

• Physical change – occurs when a substance alters its
state (phase change), but does not change its chemical
composition – E.g. Grinding, cutting
• Phase change – transition of a substance from one
state to another – Depend on temperature and pressure
– E.g. Boiling, freezing, melting, and condensing.

• Physical changes can be classified as reversible or

irreversible.
 PHASE CHANGES
Depend on Temperature and Pressure
• Affects:
➢ Particle arrangement
➢ Energy of particles
➢ Distance between particles
• Phase change is either an exothermic or endothermic
process
➢ Exothermic – heat is given off i.e. Removal of E
➢ Endothermic – absorption of heat i.e. Input of E
• Phase changes include:
➢ melting, evaporation/ boiling, condensation, freezing,
sublimation and reverse sublimation
 CHANGES OF STATE

• Melting - solid to liquid

• Freezing - liquid to solid
• Evaporation/ boiling - liquid to gas
• Condensation - gas to liquid
• Sublimation – solid to gas
• Reverse Sublimation – gas to solid
 CHANGES IN MATTER
Chemical change – occurs when a substance is converted
into a new or different substance i.e. Change in the
composition of a substance
• Also referred to as a chemical reaction
• Chemical reaction consists of reactants and products
• reactants – starting substances
• products – substances which are form/produce
 Law of Conservation of Mass

The law of the conservation of mass applies to chemical

reactions
• Mass is neither created nor destroyed during a
chemical reaction
• Mass is conserved!

Massreactants = Massproducts
 Elements, Compounds & Mixtures
• Pure Substance Matter that has a fixed composition
and distinct properties. All pure substances are either
elements or compounds.
• Elements. All atoms are the same kind, elements have
only one type of atom. e.g. Oxygen, Gold, Silicon, and
Diamond.
• Compounds Contains more than one type of atom, but
all molecules (or repeat units) are the same, e.g. water,
ethanol, quartz, sodium chloride.
• Mixture. Have variable composition and can be
separated into component parts by physical methods.
Mixtures contain more than one kind of molecule, and
their properties depend on the relative amount of each
component present in the mixture.
Homogeneous & Heterogeneous Mixtures
The composition is variable for both heterogeneous and
homogenous mixtures.

Heterogeneous Mixture - non-uniform.

• Chocolate Chip Cookie – chocolate, dough etc.
• Concrete – cement, rocks, etc.
• Nachos – chips, cheese, salsa, eyc.

Homogeneous Mixture – uniform throughout, also called

a solution.
Air – principle components include Carbon dioxide.
Vodka – principle components are ethanol and water
Brass - solid solution of Cu (copper) and Zn (Zinc)
Ruby – solid solution of Al2 O3 and Cr2 O3 .
• Elements can interact with other elements to form
compounds, and compounds can be decomposed
into elements.
• The elemental composition of a compound is
always the same, which is known as the Law of
Constant Composition (or Law of Definite
Proportions)
1. Binding forces between molecules
• In order for molecules to exist in aggregates in gases,
liquids, and solids, intermolecular forces must exist.
• An understanding of intermolecular forces is
important in the study of pharmaceutical systems and
follows logically from a detailed discussion of
intramolecular bonding energies.
• Cohesion, or the attraction of like molecules, and
adhesion, or the attraction of unlike molecules, are
manifestations of intermolecular forces.
 1. Binding forces between
molecules
• Repulsive and attractive forces
• Van der Waals forces
• Ion-Dipole and Ion-Induced Dipole forces
• Hydrogen bonds
 Repulsive and attractive
forces
• When molecules interact, both repulsive and attractive forces
operate.
• As two molecules are brought close together, the opposite charges in
the two molecules are closer together than the like charges and cause
the molecules to attract one another.
• When the molecules are brought so close that the outer charge
clouds touch, the molecules repel each other like rigid elastic bodies.
• Thus attractive forces are necessary in order that molecules cohere;
repulsive forces are necessary in order that the molecules do not
interpenetrate and annihilate one another.
• Repulsive is due to the interpenetration of the electronic clouds of
molecules and increase exponentially with a decrease in distance
between the molecules.
 Van der Waals Forces
• Dipolar molecules frequently tend to align themselves with
their neighbors, so that the negative pole of one molecule
points towards the positive pole of the next.
• Thus, large groups of molecules may be associated through
weak attractions known as dipole-dipole or Keesom froces.
• Permanent dipoles are capable of inducig an electric dipole
in nonpolar molecules (which are easily polarizable) in
order to produce dipole-induced dipole, or Debye,
interactions, and nonpolar molecules can induce polarity in
one another by induced dipole-induced dipole,or London,
attractions.
 Ion-Dipole and Ion-
Induced Dipole Forces
• These types of interactions account in part for the
solubility of ionic crystalline substances in water, the
cation for example attracting the relatively negative
oxygen atom of water and the anion attracting the
hydrogen atoms of the dipolar water molecules.
• Ion-induced dipole forces are presumably involved in
the formation of the iodide complex.
 Hydrogen Bonds
• The interaction between a molecule containing a
hydrogen atom and a strongly electronegative atom
such as fluorine, oxygen, or nitrogen is of particular
interest.
• Because of the small size of a hydrogen atom and its
large electrostatic field, it can move in close to the
electronegative atom and form an electrostatic type of
union known as a hydrogen bond or hydrogen bridge.
 2. Gas/Gaseous State
• Owing to vigorous and rapid motion, gas molecules travel in
random paths, frequently colliding with one another and
with the walls of the container in which they are confined.
Hence, they exert a pressure - a force per unit are -
expressed in dynes per cm2.
• Pressure is also recorded in atmospheres or in millimeters of
mercury because of the use of the barometer in pressure
measurement.
• Another important characteristic of a gas, its volume, is
usually expressed in liters or cubic centimeters.
• The temperature involved in gas equations is given in
absolute or Kelvin degrees (0K).
2. Gas/Gaseous State
 2. Liquid States
• When a gas is cooled, it loses some of its kinetic energy
in the form of heat, and the velocity of the molecules
decreases.
• If pressure is applied to the gas, the molecules are
brought within the sphere of the Van der Waals
interaction forces and pass into the liquid state.
• Because of these forces, liquids are considerably
denser than gases and occupy a definite volume.
• The transitions from a gas to a liquid and form a liquid
to a solid depend not only on the temperature, but also
on the pressure to which the substance is subjected.
2. Liquid States
 3. Solid State
• The structural units of crystalline solids, such as ice,
sodium chloride, and menthol, are arranged in fixed
geometric patterns or lattices.
• Crystalline solids, unlike liquids and gases, have
definite shapes and an orderly arrangement of units.
• Gases are easily compressed, whereas solids, like
liquids, are practically incompressible.
• Crystalline solids show definite melting points,
passing rather sharply from the solid to the liquid
state.
3. Solid State
 4. Liquid crystalline state
• A forth state of matter is the liquid crystalline state or
mesophase.
• The term liquid crystal is an apparent contradiction,
but it is useful in a descriptive sense since materials
in this state are in many ways intermediate between
the liquid and solid states
• Certain molecules frequently exhibit a fourth phase,
more properly termed as mesophase, which lies
between the liquid and crystalline states.
• This so called liquid crystalline state.
4. Liquid crystalline state
 Phase rule
• The phase rule a useful device for relating the effect of
the least number of independent variables (e.g.
temperature, pressure and concentration) upon the various
phases (solid, liquid, and gaseous) that can exist in an
equilibrium system containing a given number of
components.
• The phase rule is expressed as follows:
F=C–P+2
• In which F is the number of degrees of freedom in the
system, C the number of components, and P the number
of phases present.
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