Chemistry and Matter
Section 1
Matter is anything that has mass (material with-in) and volume (takes up space). Atoms are known
as the “building blocks” of matter. All matter is made of atoms. Atoms combine to form molecules
and compounds (these will be discussed later) to make the things around us.
An atom is the smallest piece of a substance. 7 million
atoms joined together in a straight line would be about 1mm
long. The middle of the atom is called the nucleus. It
contains protons and neutrons. The protons have a positive
electrical charge while the neutrons have no electrical
charge. All atoms have electrons orbiting around the
nucleus. Electrons have a negative electrical charge. The
number of protons is the same as the number of electrons. If
an atom loses or gains electrons, it is called an ion. Ions are
positively or negatively charged atoms.
Each proton has an electrical charge of +1. Each electron has a charge of -1. The neutron has no
charge so it is considered neutral. An atoms charge is neutral when it has the same number of
protons and electrons.
Particle
Relative Mass Relative Charge
The masses of neutrons and protons are
Proton
1
+1
about the same. An electron is about .054
Neutron
1
0
% the size of a proton. The electrons,
although tiny, take up most of the space in
Electron
.054 %
-1
an atom. This means most of the space of
an atom contains very little mass. Nearly all the mass is centered at the nucleus.
An element is a substance made from only one type of atom. For example, Carbon is made entirely
from Carbon atoms and Sodium is made entirely from Sodium atoms. An element can not be broken
down (chemically) into simpler substance. The Periodic Table shows all known the elements.
The Periodic Table
The Periodic Table came about through attempts by people to group elements according to their
chemical properties. John Newlands (1863) noticed that every eighth element seemed to have
similar properties when arranged in order of increasing atomic mass. He proposed a similarity with
music, where the eighth note is an octave above the first. This became known as Newlands Octaves.
But it did not work for the fourth period with the transition metals. It works for the lighter elements
because eight electrons complete their outer shells.
Dmitri Mendeleev is credited as being the Father of the modern Periodic Table. In 1869 he arranged
the 50 or so known elements in order of atomic mass, putting elements with similar properties in the
same vertical group and leaving gaps for unknown elements that were yet to be discovered. When
the elements were later discovered, they were found to have the properties
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predicted by Mendeleev's table. Knowing nothing of protons, nuclei or atomic numbers, Dmitri
Mendeleev's Periodic Table was mostly correct. In the modern Periodic Table, the elements are
arranged in order of increasing atomic number.
Group 1
Alkali Metals
Group 2
Alkaline Earth Metals
The columns in the Periodic Table are called groups or
Group 3-12
Transition Metals
families. The rows are called periods (hence the name
Group
13
Boron Family
Periodic Table). The groups or families contain elements
Group 14
Carbon Family
with similar chemical properties. Some of the groups have
Group 15
Nitrogen Family
names, here is a list of those names.
Group 16
Oxygen Family
Group 17
Halogens
The groups may also show the number of valence electrons
Group
18
Noble
Gases
that an element has. These groups are sometimes labeled
with Roman Numerals. Group IA has one valence electron, group IIA has two valence electrons and
the number of valence electrons would continue to go up by one. Group O would have eight
valence electrons.
The metal elements are on the left and in the center of the Periodic Table. The nonmetal elements
are on the right. Metals and nonmetals are separated by metalloids. Metalloids have properties of
both metals and nonmetals. They border the “staircase” that separates the metals and nonmetals. All
elements in the same group have the same number of electrons in their outer shells. This is what
gives the element its chemical properties. Chemical properties determine how the element will
react with another element or substance. Chemists use the electron structure of elements to classify
them as metals or nonmetals. As a general rule, elements with three or fewer electrons in the outer
level are considered to be metals. Elements with five or more electrons in the outer level are
considered to be nonmetals. Transition elements have one or two electrons in the outer level so they
show metallic properties.
The number of electron shells an element has, shows the period (row) in which it is found. The first
period contains Hydrogen and Helium. The second period is from Lithium to Neon. The third
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period is from Sodium to Argon etc. Potassium is in Group IA showing it has 1 electron in its outer
shell and since it is in period 4, it has 4 shells. Fluorine in group VIIA showing it has 7 electrons in
its outer shell and since it is in period 2 it has 2 shells.
The Transition Metals: The transition metals occupy the central block of the Periodic Table. They
are not a group (there is no group number) but are a collection of metals with common properties.
They are sometimes called a family of metals. They do not all have the same number of electrons in
their outer shell.
Atomic Number
The number of protons in the nucleus is called the atomic number. Sodium (Na) has 11 protons so
it is atomic number 11. The atomic number helps you locate the element on the Periodic Table. An
element is matter that contains only one type of atom. For example, Carbon is made entirely from
Carbon atoms and Sodium is made entirely from Sodium atoms. An element cannot be broken
down (chemically) into a more simple substance.
Mass Number
The number of protons plus the number of neutrons is called the mass number.
Sodium has 11 protons and 12 neutrons so the mass number is 23. The mass
number is the total number of particles in the nucleus. The mass number and the
atomic number are written above and below the chemical symbol for the element, as shown. These
numbers may be reversed on some Periodic Tables. The mass number will be the number with the
decimal point on many Periodic Tables.. The chemical symbol is a shorthand way of writing the
element name on the Periodic Table and in chemical formulas.
Atomic number = number of protons or electrons*
Mass number = number of protons + number of neutrons
Number of neutrons = Mass number – Atomic number
*if the atom is an ion, the atomic number is only the number of protons
Atomic
Mass
Element Symbol Number Protons Electrons Neutrons Number
Sodium
Iron
Aluminum
Na
Fe
Al
11
26
13
11
26
13
11
26
13
12
30
14
23
56
27
Isotopes
Atoms of the same element that have different numbers of neutrons are called isotopes. For
example, Chlorine (atomic number 17) may have either 18 or 20 neutrons. The mass number will be
either 35 or 37. Isotopes of the same element will have the same chemical properties, because the
number of protons and electrons will be the same.
Section 2
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Electron Shells (energy levels)
Electrons are arranged in shells (shown as circles around
the nucleus). The shells are also called energy levels or
orbitals. We will use the term shell. Chemists use letters
to name the shells around a nucleus. They use the letters
"k, l, m, n, o, p, and q". The "k" shell is the one closest to
the nucleus and "q" is the farthest away. Not all shells
hold the same number of electrons. The general rule for
calculating the number of electrons for the first four shells
is 2n2 where n represents the shell number. For the first
eighteen elements, there are some easy rules. The “k” shell
only holds two electrons. The “l” shell only holds eight electrons. The “m” shell only holds eight
electrons (for the first eighteen elements). The “m” shell can actually hold up to 18 electrons as you
move farther along the Periodic Table. The maximum number of electrons you will find in any shell
is 32. An atom that has a full outer shell will be stable. Being stable means the atom will not react
with other atoms. The Noble Gases in the right hand column of the Periodic Table are stable
because they have full outer shells. The two inner shells of an atom must be full before the outer
shells get filled. If the outer shell of an atom has less than the maximum number of electrons it will
not be stable so it will react with other atoms forming chemical bonds.
Chemical Reactions and Bonding
All chemical reactions involve atoms trying to get a full outer shell of electrons. When an atom
reacts with another atom, it will either: 1. Lose electrons to form a stable positive ion, 2. Gain
electrons to form a stable negative ion or 3. Share
electrons to form a stable molecule.
Ionic Bonding
An unstable Sodium atom may lose its outer
electron to become stable. Sodium has 1 electron in
its outer shell. Because of this, it is in Group IA of
the Periodic Table. When sodium reacts, it will lose its outer
electron. Its outer shell will then have no electrons. It is as
though the outer shell has vanished. The next shell in is full.
This full shell becomes the new outer shell so the Sodium is
now stable. The Sodium ion still has 11 protons (11 positive
charges), but now only 10 electrons (10 negative charges). So
the Sodium ion has an extra positive charge, shown by a +
sign.
The reaction between Sodium and Chlorine is different from
that of Sodium and Sodium. Chlorine has 7 electrons in its
outer shell so it is in Group VIIA of the Periodic Table. When
an atom of Chlorine reacts with Sodium, it will gain one
electron from the Sodium. The outer shell of Chlorine will
then have 8 electrons and be stable. The stable Chloride ion
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will have an extra electron so it will have an extra negative charge shown as a - sign.
The force of attraction between the oppositely charged ions is called an ionic bond. Sometimes they
are shown as dots and crosses. The chemical equation for the above reaction is: Sodium (solid) +
Chlorine (gas) = Sodium Chloride (solid).
Na(s) + Cl(g) = NaCl(s)
Metals and Nonmetals
Metals are malleable meaning they can be pressed or beaten into thin sheets. Metals can conduct
heat and electricity. Metals have high melting and boiling points. They are all solid at room
temperature except for Mercury which is liquid. Nonmetals have properties different than metals.
Nonmetals are generally gases or brittle solids. Their surfaces are dull and they are insulators.
When a metal reacts with a non-metal, the metal will lose electrons to form a positive ion while the
non-metal will gain electrons forming a negative ion. Together they form an ionic compound.
This is the reaction between Magnesium and Oxygen.
Magnesium is in Group IIA. A Magnesium atom will lose 2
electrons to form a stable ion. Oxygen is in Group VIA. An
Oxygen atom will gain 2 electrons to form a stable ion. In
this example, the electrons are shown as dots and crosses.
The ionic bond between Magnesium and Oxygen is stronger
than the ionic bond between Sodium and Chlorine because of
the greater charge on the ions. Magnesium Oxide has a
higher melting point because of the stronger bond.
The Noble Gases are in Group 18 or Group O of the Periodic
Table. They have full outer shells of electrons. They are
stable and will not react with other atoms. Atoms that have
lost or gained electrons to form ions will have a full outer shell. Stable ions are said to have
achieved a Noble Gas electron structure.
Properties of Ionic Compounds
When metals react with non-metals they form an ionic compound. A compound is a type of matter
that has properties different from the properties of each of the elements in it. Ions have a charge
because electrons are lost or gained in forming an ionic bond. Ionic bonds are strong. Ionic bonds
can only be separated by a chemical change. All ionic compounds are solid at room temperature.
Solid ionic compounds do not conduct electricity because the ions are not free to move. If the solid
is heated until it melts, the liquid will conduct electricity because the ions can move.
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Covalent Bonding
When non-metals react with non-metals, they share electrons to form a covalent bond. Covalent
means sharing. (If you do not know whether an element is a metal or a non-metal, check the
Periodic Table). Covalently bonded compounds
containing a small number of atoms are called simple
molecules. A molecule is the smallest particle of a
compound that still retains all of the properties of the
compound. Two Chlorine atoms will share one electron
each to form a stable Cl2 molecule. Each Chlorine atom
in the molecule has 8 electrons in its outer shell by
sharing the two electrons between them. The outer shell
is now stable and the Cl2 molecule will not react further
with chlorine. There are no ions present (no + or charges) because the
electrons are shared, not
transferred from one atom to another.
These pictures are simple covalent molecules. Count the electrons in
the outer shell of each atom, to see that they add up to 8 for the
Nitrogen and Chlorine or 2 for Hydrogen.
Note the 3 pairs (6 electrons) shared between the atoms. Nitrogen
has a triple bond. Each electron pair is one bond. This is what
makes nitrogen so stable and unwilling to react with other atoms.
Note the 2 pairs (4 electrons) shared between the atoms. Oxygen
has a double bond. Each electron pair is one bond.
Note the shape of the water
molecule, with both
Hydrogen atoms on the
same side of the oxygen
atom. This “polarizes” the
molecule making it seem as
though it has a negative
end (Oxygen) and a
positive end (Hydrogen).
Properties of Molecules
When a non-metal reacts with a non-metal, they form a covalently bonded molecule. Covalent
bonds are strong but only exist between the atoms of the molecule. The force of attraction between
molecules (called the intermolecular force) is very weak. The weak force between molecules means
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that very little energy is required to separate them. Many molecular compounds are liquid or gas at
room temperature. They have low melting and boiling points.
When a molecular compound melts or boils molecules separate from each other but the covalent
bond between the atoms of the molecule does not break. The molecule is the same molecule in the
solid, liquid or gas state. The molecule is said to decompose (break-up) if the covalent bond breaks
between its atoms.
Molecules do not have a charge (no ions) because the electrons are shared between atoms to form a
covalent bond. Molecular compounds will therefore not conduct electricity (with the exception of
Graphite).
Chemical Formulas
Chemicals are represented by formulas. Each chemical has its own unique chemical formula. The
formula is shown by element symbols with small numbers, (subscripts), written after the symbols.
KCl represents one Potassium atom bonded to one Chlorine atom. The formula is not written,
K1Cl1. Na2O means two Sodium atoms are bonded with one Oxygen atom. Al2O3 means two
Aluminum atoms are bonded to three Oxygen atoms. A big number in front of a formula multiplies
the number of elements that follow it in the formula. 2K means two separate potassium atoms. 2Cl2
represents 2 Cl2 molecules equaling four chlorine atoms total. 2KCl represents 2 KCl molecules
equaling two
Total Number of
Potassium
Number of
Names of
Number of Atoms Atoms in One
atoms and two
Name
Formula Elements
Elements
for Each Element
Molecule
Chlorine
Hydrogen
2
3
Water
H2O
2
Oxygen
1
atoms total.
Ammonia
NH3
2
Methane
2CH4
2
Nitrogen
Hydrogen
Carbon
Hydrogen
1
3
2
8
4
5
Elements, Compounds and Mixtures
Elements: An element is a substance made from only one type of atom. For example, Carbon is
made entirely from Carbon atoms and Sodium is made entirely from Sodium atoms. An element can
not be broken down (chemically) into simpler substance. The Periodic Table shows all known the
elements.
A compound is a substance made from two or more elements that have reacted chemically with
each other. Molecules may make-up compounds. A molecule is the smallest particle of a compound
that still retains all of the properties of the compound. A compound is a completely new material
that will often have totally different properties from the elements that made it. For example, the
element Sodium is a highly reactive metal. The element Chlorine is a yellow-green poisonous gas
(non-metal). When the two react together, they form a compound called Sodium Chloride. Sodium
Chloride is common salt, which you eat with food. (You wouldn't want to eat either element
separately). You cannot separate the elements of a compound by physical methods. It can only be
done by using chemical reactions or by passing electricity through it (if it conducts electricity).
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Mixtures: A mixture contains two or more substances that have not reacted chemically with each
other. They are made of little bits of each substance mixed together. A mixture can be separated by
physical methods. For example, a mixture of Iron filings and Sulfur can be separated by using a
magnet to attract the Iron separating it from the Sulfur. The compound Iron Sulfide cannot be
separated in this way.
Separation Techniques include filtration and distillation. Filtration can only
be used with solids that cannot be dissolved in a liquid. A solid that has not
dissolved in a liquid can be separated by filtration. An example would be
water and sand.
Distillation is the process of boiling a liquid to separate the solute from the
solvent. The liquid will evaporate and can be collected and then condensed
into a liquid leaving the solute in the boiling container. The solvent is the liquid in the mixture. The
solute is the solid that is dissolved in the mixture. For example: if saltwater is boiled, the solute is
the salt and water is the solvent. The solid salt will be left behind in the container while the
evaporated water can be condensed to form purified, distilled water.
Section 3
Matter
Matter is anything that has mass (material with-in) and volume (takes up space). The states of
matter are solid, liquid, gas and plasma. These states of matter are also known as phases of
matter. A phase describes a physical state of matter. Phases may change if energy is added or
removed, by increasing or decreasing the temperature and/or pressure or by adding an electrical
charge.
Any substance may exist as solid, liquid or gas. If a solid is heated, it will melt to become a liquid.
The temperature at which it melts is called its melting point. If the liquid is then cooled, it will
freeze to become a solid again. The temperature at which it freezes is called its freezing point. The
melting point and the freezing point are the same for the same substance. Similarly, if a liquid is
heated it will boil to become a gas. The temperature at which it boils is called its boiling point. If
the gas is then cooled, it will condense to become a liquid again. A gas will condense at its boiling
point. Certain solids can become gases without going through the liquid phase when they are
heated. This phase change is called sublimation. Examples of solids that sublime are Iodine and
solid Carbon Dioxide (dry ice).
Phase Change Information
-Freezing is a liquid changing to a solid. Example: water to ice
-Melting is a solid changing to a liquid. Example: ice to water
-Evaporation is a liquid changing to a gas. Example: water to water vapor
-Condensation is a gas changing to a liquid. Example: water vapor to dew on the grass
-Sublimation is a solid changing to a gas without going through the liquid phase.
Example: solid dry ice (Carbon Dioxide) changing to gas
Water freezes at 00C or 320F
Water boils at 1000C or 2120F
Water is unique because it can exist as a solid, liquid and gas naturally on Earth at the same
place at the same time. (Think about a frozen lake on a spring morning.)
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Even though plasma is the most abundant matter in the universe, it is the least common on Earth.
The Sun and the stars are made of plasma. They are made of electrically charged gases. Plasma is
found in fluorescent lights, lightning and produced when an electric motor is running.
This figure shows how to convert from one phase to another
by heating or cooling. Arrows with (x) involve heating. The
other arrows involve cooling.
Endothermic means the material absorbs heat (thermal
energy). The heat enters the material.
Exothermic means the material releases heat (thermal
energy). The heat exits the material.
Particle Motion
In a solid, the particles can vibrate but
they cannot move from one place to
another. As the solid is heated, the
particles vibrate more and more until the force of attraction between them is overcome. The
temperature at which this happens is the melting point. Beyond this temperature, the solid becomes
a liquid. In a liquid, the force of attraction between the particles is weaker than in the solid. The
attraction is still strong enough that the particles are held close to each other but they are now free to
move. As the liquid is heated the particles move faster and faster until they overcome the force of
attraction between them. This happens at the boiling point. At the boiling point the liquid becomes a
gas. The gas requires a greater volume than the liquid it came from. This increase in space is called
expansion. In a gas, the particles move fast in random directions. There is very little force of
attraction between gas molecules.
Structure and Properties
A solid has a regular arrangement of
atoms or molecules. They are close
together and cannot move. The shape and
volume of a solid is fixed. Solids may be
compressed. Liquids have their particles close
together. They are free to move. A liquid will
flow to take the shape of its container. Liquid
volumes are fixed and can not be compressed.
This is the basic principle behind a hydraulic
system. Gas particles are arranged at random.
Gases appear to fill the volume of their container.
Gases are easily compressed.
This graph shows how the temperature changes
with time as a substance is heated at a constant rate. There are obvious flat sections of the graph at
the melting and boiling point.
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Although the substance is still being heated at the melting point, there is a time when the
temperature does not change. During this time, all the extra heat that is being added goes to
overcome the force of attraction (the bonds) between the particles of the solid as it turns into a
liquid. The temperature of a solid can never be raised above its melting point at atmospheric
pressure. When the solid has completely melted, then the temperature of the liquid will start to rise.
Similarly at the boiling point, the temperature of the liquid does not change until all the liquid has
boiled and has become a gas. During this time, the extra heat energy goes into overcoming the force
of attraction between the particles of the liquid. The temperature of a liquid cannot be raised above
its boiling point at atmospheric pressure. The same graph occurs on cooling a gas to a liquid, or a
liquid to a solid. The processes of melting and boiling require an addition of energy so they are
endothermic processes. The processes of freezing and condensing release energy so they are
exothermic processes.
Observation and study of Matter
There are many characteristics of matter that may be observed and studied. You may study or
observe the chemical properties or physical properties of the matter. Chemical properties describe
the way that an element or compound reacts chemically with other substances. The chemical
properties are determined by the number of electrons in the outer shell of the atom. The number of
electrons in the outer shell of an atom is the same as the atoms element group number on the
periodic table. The Periodic Table will be discussed shortly.
The physical properties of an element or compound include: melting and boiling point,
density, conduction of electricity, color, mass, weight, flexibility, the size of an atom, hardness, etc.
Physical properties are properties that can be measured and/or observed.
Density can be used to identify an unknown substance. Density is defined as the objects mass
divided by the objects volume. Density can be calculated mathematically by the formula: Density =
Mass/Volume. Possible unit labels will be g/cm3 for solids or g/ml for liquids. The proper label
helps to determine whether the substance is a solid or liquid. Changing the mass or volume of an
object can change its density. If the volume increases and the mass remains the same, the object will
become less dense. If the mass
increases, and the volume remains the
same, the density increases.
Relative density is determined by
comparing substances. The density of
objects is often compared to water which
has a density of 1 g/ml or 1g/cm3. If the
object floats, it has a density less than 1
g/cm3. If the object sinks, it has a
density greater than 1 g/cm3. Densities
of liquids can be determined this way as
well. Oil floats on water because it has a
density less than 1 g/ml.
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