Chemistry 513
Mr. Szkolar
Introduction to Chemistry & Matter
(Chapters 1 & 2)
Chemistry is the study of substances in terms of
Composition
what is it made of
Structure
how is it put together
Properties
what characteristics does it have
Reactions and Energies
Physical
how does it change form but stays the same substance – small
energies (joules)
Chemical
how does it behave with other substances and changes to new
substances – larger energies (kilojoules)
Nuclear
how does its nucleus behave – really large energies (megajoules);
these involve transmutations – converting one element into another
Scientific Method

Making observations
o Facts obtained by observing and measuring events in nature

Writing a hypothesis
o A statement that explains the observations

Doing experiments
o Procedures that test the hypothesis
Law:
Theory:
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Activities of Science

Assembling important facts and observations.

Organizing the information and seeking regularities, or patterns, in it.

Trying to explain why the regularities exist – construct models.

Communicating the findings and their explanations to others.
SOME KEY IDEAS
Conservation Laws
initial(i) = final (f)
Mass: mass of reactants = mass of products (Lavoisier)
Energy: energy is neither created or destroyed, only changes form
Charge: electrons lost (oxidation) = electrons gained (reduction)
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MATTER
Matter - anything that occupies space and has mass.
Mass - the quantity of matter possessed by a body or a measure of its inertia; can be
measured two ways:
1) gravitational mass (weight) - the result of mass and the pull of gravity. Mass and
weight are not the same - weight varies as gravitational attraction varies. The terms
are used interchangeably since the earth's gravitational attraction is essentially
constant. Weight is a force due to gravity and is measured with a scale. Mass is an
inherent property of matter and is independent of gravity. Mass is measured using a
balance.
Let’s compare balances and scales on the Earth and the Moon. We will mass/weigh a
5 kilogram ball using each instrument first on Earth and then on the Moon. But first,
what is the numeric equality relating mass (kilograms) and weight (pounds)?
1.0 kg = ______ lb
On Earth:
balance =
scale =
on Moon:
balance =
scale =
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Most of the mass of everyday objects is in protons and neutrons, and a little bit
more in electrons. Identifying the mass of an object basically comes down to saying how
many nucleons are in it. A nucleon is either a proton or a neutron. A person having a
mass of 75 kg has about 50, 000, 000, 000, 000, 000, 000, 000, 000, 000 nucleons. How
would we express this in scientific notation? (Note: don’t confuse this figure with the
national debt you and your children and probably your grandchildren will have to pay).
2) inertial mass - a measure of the resistance to a force that tends to change the motion
of a body. "A body at rest tends to remain at rest. A body in motion tends to continue
moving in a straight line at a constant speed - even when an outside force is pushing or
pulling on it." (Newton's First Law of Motion). All bodies with mass have this
resistance to forces that tend to change their motion. The greater the force needed to
overcome this resistance the greater the mass of the body.
Substance - refers to any particular variety of matter that always has the same properties
and composition, regardless of how and where a sample of it is obtained.
Samples of a substance are said to be homogeneous - the properties and
composition are the same throughout the sample.
Properties - the characteristics by means of which one kind of matter may be
distinguished from any other kind of matter. There are two major types of
properties:
1) physical properties - those characteristics that may be observed without changing the
chemical composition of a substance - e.g. color, taste, odor,
density, melting point.
2) chemical properties - those characteristics that describe how a substance interacts (or
fails to interact) with other substances to produce new
substances - e.g. activity, combustibility.
In addition, there are intensive and extensive properties:
extensive properties – depend on how much of a particular sample is on hand;
examples include volume, weight and mass
intensive properties – properties that do not depend on the size of the sample;
examples include melting point, boiling point and density
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Matter may be classified according to the following scheme:
I)
Elements - substances which cannot be decomposed into simpler substances by
means of an ordinary chemical change; e.g. gold, iron. All atoms of a given
element have the same number of protons (atomic number) in their nucleus.

the elements on the Periodic Table are arranged according to increasing
atomic number.

the Periodic Table consists of 18 vertical columns termed groups or families;
the elements within a group have similar chemical properties (because they
have the same number of electrons in their outermost shell (level) – called
valence electrons.

the Periodic Table consists of 7 horizontal rows called periods. The period
number indicates the level (shell) in which an atom’s valence electrons are
found.

most elements are metals; the metalloids or semimetals occur along the
“steps” separating the metals from the nonmetals – these include B, Si, As,
and Te.

most elements in nature occur as monatomic atoms – that is they occur as
single atoms bonded to each other in a sample of that element; a few exist as
diatomic molecules – two atoms bonded together – these are H2, N2, O2, F2,
Cl2, Br2, and I2; in addition phosphorous occurs as a tetratomic molecule (P4)
and sulfur as an octatomic molecule (S8).
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
most elements occur as solids at room temperature and pressure. The only
two liquids are mercury (Hg) and bromine (Br2); the elements which are gases
include H2, N2, O2, F2, Cl2, and the Noble gases (Group 18 – He, Ne Ar, Kr,
Xe, Ar and So.
II) Compounds - substances made up of two or more elements chemically combined,
e.g. water, carbon dioxide. Compounds can be decomposed by ordinary chemical
means into simpler substances. For example, heating sugar will decompose it to
water and carbon. Another way in which a compound like a salt (consisting of a
metal chemically combined with a nonmetal) can be decomposed is by a process
called electrolysis. If we pass an electric current through a molten (melted) salt, it
will break the compound into the elements that make it up; one element at the
positive electrode (designated the anode) and the other at the negative electrode
(designated the cathode)
Can you write a chemical equation representing this reaction?
The elements in a compound are combined in a definite proportion by mass. This
is a statement of the Law of Constant Composition. To determine the percentage
composition by mass of the elements in a compound, we first determine the mass
of the compound and then the percent of each element is the mass each element
contributes over the total mass times 100. Water, for example has a total mass of
18 amu (atomic mass units). The percentage of hydrogen = 2/18 X 100 = 11.2%
and oxygen = 16/18 X 100 = 88.8%. Another way of saying tis is that in 100.
Grams of water we have 11.2 g of hydrogen and 88.8 g of oxygen.
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Problem: Determine the percentage by mass of each of the elements in any sample
of carbon dioxide:
II)
Mixtures - consist of two or more substances physically combined, each of which
retains its individual properties. Hence, the properties of a mixture are
intermediate between those of its components. Mixtures may be homogeneous i.e. a solution of salt water, or they may be heterogeneous - having nonuniform
composition throughout - e.g. soil, concrete.

the composition of a mixture is not fixed by mass (as in the case of
compounds).

the components of a mixture are held together by physical means; the
elements in a compound are held together as a result of a chemical reaction –
chemical bonds

the components of a mixture can be separated by means; those of a compound
require chemical methods
Physical methods of separation (based on differences in physical properties) include:
distillation – separation on the basis of difference in boiling points.
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filtration –separation of a liquid from a solid (on basis of size)
centrifugation - separation on the basis of difference in density
extraction – separation based on difference in solubility
chromatography – separation on the basis of adherence to a mobile vs stationary phase
in illustration on the next page, for example, component A has a greater adherence for the
stationary column while component B has a greater adherence to the mobile solvent
Matter can undergo two kinds of changes:
1) physical changes - those that produce new physical properties without altering the
chemical properties - no new substance is formed; e.g. melt ice, magnetize iron.
Note that for most substances, the solid phase is the densest phase. The particles
making up the substance are held together by “electrostatic” (meaning plus –
minus attractions) forces of attraction in a crystalline arrangement. This means the
particles can only move (i.e. vibrate) in fixed positions in the crystal. In the liquid
phase the forces of attraction are a little weakened and the substance is a little less
dense. The particles are still hold to each other but now they can “move” around
each other (i.e. they can also rotate). In the gas phase the forces of attraction are
not effective and the particles are separated and fly around randomly. The gas
phase is the least dense. Can you think of any exceptions to the phase-density
relation described here?
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Particle diagram models
H2 and O2 gases
Key:
H2O gas
H2O liquid
hydrogen
oxygen
2)
chemical changes - those that produce new substances that differ in chemical
properties and composition from the original substances, e.g. iron rusts, milk sours,
paper burns.
The Nitrogen Cycle
Nitrogen is an essential component of proteins and the genetic material that makes
up DNA (deoxyribonucleic acid), and a constant supply is vital for all living organisms.
Although 78% of the earth’s atmosphere is composed of nitrogen gas (N2), plants and
animals cannot use this nitrogen directly. Atmospheric nitrogen must be converted to
other nitrogen compounds before it can be absorbed through the roots of plants. This
change is achieved by nitrogen fixation, a process carried out by specialized bacteria
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that have the ability to transform atmospheric nitrogen into ammonia (NH3). Some
nitrogen-fixing bacteria live in soil. Others live in nodules on the roots of leguminous
plants such as peas, beans, clover, and alfalfa. The ammonia produced in root nodules is
converted into a variety of nitrogen compounds that are then transported through the
plant as needed.
Another means by which atmospheric nitrogen is converted to a usable form is
lightning. The electric discharges in lightning cause nitrogen and oxygen in the
atmosphere to combine and form oxides of nitrogen, which in turn react with water in the
atmosphere to form nitric acid (HNO3).
The nitric acid, which reaches the earth’s
surface dissolved in rainwater, reacts with substances in soil and water to form nitrates
(NO3-) which are directly absorbed through plant roots. Compared to biological fixation,
lightning accounts for only a small fraction of the usable nitrogen in soil.
Although some trees and grasses can absorb ammonia produced by nitrogen-fixing
bacteria directly from the soil, most plants can only use nitrogen that is in the form of
nitrates. The transformation of ammonia into nitrates is carried out by specialized soil
bacteria in a process known as nitrification.
Plants convert ammonia or nitrates that they get from the soil or root nodules into
proteins and other essential nitrogen-containing compounds. Animals get their essential
nitrogen supplies by eating plants. When plants and animals die and decompose, the
nitrogen-containing compounds in their tissue are broken down by decomposers;
ammonia is eventually formed and returned to the soil. Nitrogen is also returned to the
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soil in animal wastes. Both urine and feces have a high content of nitrogen-containing
compounds. In this way, nitrogen is continually cycled through food chains.
Not all the ammonia and nitrates that are formed in soil by the process just described
become available for plants. Both ammonia and nitrates are very soluble in water. As
rainwater percolates downward through the ground, these compounds are leached out of
the topsoil. They are often carried away in runoff into nearby streams, rivers, and lakes,
where they are recycled through aquatic food chains. Another process that removes
nitrates from the soil is denitrification, in which bacteria carry out a series of reactions
that convert nitrates back to nitrogen gas.
In a few locations around the world, nitrates have accumulated in large mineral
deposits. In Chile, for example, as mountain streams originating in the Andes Mountains
flowed across dry, hot desert toward the sea over thousands of years, much of the water
evaporated, leaving behind huge deposits of sodium nitrate. Sodium nitrate is called
saltpeter and countries have fought wars over it.
In the natural environment, a balance is maintained between the amount of nitrogen
removed from the atmosphere and the amount returned. However, because most soils
contain an insufficient amount of nitrogen for maximum plant growth, farmers frequently
apply synthetic inorganic fertilizers containing ammonia and nitrates. As a result of
runoff from fertilized farmland, the extra nitrogen-containing compounds reaching rivers
and lakes may upset natural balance, sometimes with damaging consequences for the
environment. The production of these fertilizers is one of the most important chemical
processes in history and will be discussed later in the year as well as the water pollution
resulting from fertilizer runoff.
An alternative to the use of synthetic fertilizer for replenishing nitrogen in the soil is
to plant a nitrogen-fixing crop, such as clover, and plow it back into the soil. Another
method is to spread manure and allow the natural soil bacteria to degrade it and release
nitrogen-containing compounds that plants can absorb.
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Demonstration
Hydrogen
Symbol:
H
Atomic number:
1
Atomic mass:
1.00795
Oxidation states:
1, -1
Electron Configuration:
Boiling point (K):
Melting point (K):
Density:
1s1
20.4
13.4
0.0899 g/L
Of every 1,000 atoms in the Earth’s crust, about 150 are hydrogen. Because of its low
atomic mass, hydrogen constitutes less than one percent of the mass of the Earth’s crust.
However, it appears to be the most abundant element in the universe. More than eightyeight percent of all atoms in the universe are hydrogen, and about ninety percent of the
mass of the Sun is hydrogen. On Earth, hydrogen occurs in thousands of compounds,
from water and hydrocarbons to acids and proteins.
Hydrogen is almost nonexistent in the elemental form in nature. Because of its low
density, hydrogen molecules do not remain in the atmosphere for very long – they simply
rise and drift into space. Any unreacted hydrogen produced in the laboratory today may
be thousands of miles away by tomorrow.
Its small size and mass make hydrogen unique among the elements in properties and
reactions. Hydrogen was discovered in 1776 by Henry Cavendish when he treated active
metals with dilute nonoxidizing acids. Other chemists soon began experimenting with
hydrogen and amazed themselves and others with its properties. Pilatro de Rozier filled
his lungs with hydrogen and set fire to the gas coming out of his mouth. When he
repeated the experiment with a mixture of air and hydrogen, an explosion resulted.
Cavallo, a Frenchmen, filled soap bubbles with hydrogen and ignited them. Joseph
Black, Chair of Chemistry at Edinburgh, astounded his dinner guests by filling a calf’s
bladder with hydrogen and allowing it to float to the ceiling.
Reaction:
Symbols:
Names:
Masses:
Chemical or physical reaction?
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Substance
Physical Properties
Chemical Properties
Zn(s)
HCl(aq)
H2(g)
ZnCl2(aq)
Reaction of hydrogen gas in “air”:
Is this a physical or chemical change? Explain.
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Identify all square(s) that represent:
1. elements:
2. compounds:
3. mixtures:
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