Chemical Change
Learning objectives
• Key Concepts:
– Combination, synthesis, decomposition,
displacement, double displacement,
precipitation, signs of reaction
– reaction, physical property, chemical property,
element, compound, mixture, word equation,
chemical equation,
– Word equation, chemical equation, reactant,
product,
M4 Periodic Table: Chemical Change
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Learning objectives
• Skills:
– Identify diagrammatic representation for
element, compound and mixture
– Distinguish between element, compound and
mixture
– Distinguish between physical change and
chemical change
– Identify a chemical reaction
Learning objectives
– Write word equations for simple combination reactions
between metals and non-metals given the names of the
chemicals involved.
– Write chemical equations for simple combination
reactions given the formula of the compounds
– Balance simple combination reactions given the formula
of the chemicals involved using particle diagrams and
the law of conservation of matter.
– Discuss signs of reaction (the four hints that indicate a
chemical change)
M4 Periodic Table: Chemical Change
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Combination Reaction
• We will next start by considering a few variety of
interactions between elements which produce compounds.
Whenever elements and/or compounds interact, they are
said to have undergone a chemical reaction.
A chemical reaction produces a completely new substance or
substances.
The most simple of these reactions is combination (or
synthesis) reaction.
(When elements and/or compounds are just physical brought
together, they form a mixture of course.)
M4 Periodic Table: Chemical Change
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Practice Question (7)
• Balance the following formulas
– BaCl
– NH4O
– NaS
– AuAg
– Iron III Oxide
Combination Reaction
• Combination reactions are ones where two different
elements chemically combine to produce a single compound.
Element A + Element B  Compound containing A
and B
– A metal can combine with a non-metal to form a compound
Metal + Nonmetal  Compound containing metal &
nonmetal
– Two non-metals can combine to form a compound.
Nonmetal A + Nonmetal B  Compound containing
nonmetal A & B
M4 Periodic Table: Chemical Change
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Combination Reaction
• Two metals cannot combine to form
compounds however. (They do mix to give
alloys, which is a mixture and not a
compound.)
• The physical and chemical properties of
the compound are usually different from
those of the elements it is made from.
Chemical Equation
• You will study several different types of
chemical reactions and learn to represent
them using words or formula of the
substances involved.
The simplest way of representing a reaction is
using the names of the chemical involved
(called word equation).
A chemical equation is a chemical short-hand
for a host of information
M4 Periodic Table: Chemical Change
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Chemical Equation
Sodium + oxygen  Sodium oxide
– Everything to the left of the arrow is referred
to as reactants and everything to the right
product(s)
– “” means produces or yields or gives or
results in
– “+” on the left side means “reacts with” or
“combines with”
– (If “+” appears on the right hand side it means
“and.”)
Representing Reactions
• Here are some more examples of word equations:
Hydrogen + oxygen  Water
Coal (carbon) + oxygen  Carbon dioxide
Zinc + Iodine  Zinc iodide
Aluminum + Iodine  Aluminum iodide
Aluminum + bromine  aluminum bromide
M4 Periodic Table: Chemical Change
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Representing Reactions
• The other method of representing
chemical reactions is to use the formula
of the substances involved.
– 2Na (s) + O2 (g)  2Na2O (s)
• Is this balanced?
– 2H2 (g) + O2 (g)  2H2O (l)
– (Note hydrogen and oxygen and are diatomic
elements)
Representing Reactions
C
(g)
Zn
+ O2
(s)
(g)
 CO2 (g)
+ 2I (s)  ZnI2
(s)
2Al
(s)
+ 6I (s)  2AlI3
2Al
(s)
+ 6Br
(l)
(s)
 2AlBr3 (s)
• The equations above are referred to as
chemical (or symbolic) equations.
M4 Periodic Table: Chemical Change
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Representing Reactions
•
Notice a couple of things that’s different
about a chemical equation compared to
word equation:
– Chemical equation includes symbols in
bracket next to the chemicals involved in the
process
– Coefficients in front of the formula of the
chemicals involved in the chemical process.
State Symbols
•
The symbols in brackets are referred to as the (physical) state
symbol.
The state symbols indicate the physical state of the substances.
– s = Solid
– l = liquid
– g = gas
– aq = aqueous (dissolved in water, in other words in solution)
•
You should by now know the physical states of most of the elements
and be able to supply the state symbol for any element that appears
in an equation.
M4 Periodic Table: Chemical Change
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State Symbols
• As far as compounds go all compounds of metals are solid.
Compounds formed by the combination two non-metals however, can be
solid, liquid or gas.
– However, most of those that you will have to work with and be able to
recognize are gaseous.
– Water of course is liquid.
– But, carbon dioxide (CO2) and carbon monoxide (CO), both oxides of
carbons are gaseous.
– Both sulfur dioxide (SO2) and sulfur trioxide (SO3) are gaseous as well.
– Hydrogen sulfide (H2S) is also gaseous.
– All halides of hydrogen (hydrogen chloride, HCl, hydrogen bromide, HBr,
and hydrogen iodide, HI) are gaseous as well.
M4 Periodic Table: Chemical Change
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Coefficients
• Coefficients in front of the formula are required to
conform to the law of conservation of matter. That
is, since matter cannot be destroyed or created,
atoms and molecules cannot be destroyed or
created in a chemical process. The number of
atoms at the end of a chemical process must be
equal to the number of atoms in the beginning.
For simple combination reaction, you can balance
them by drawing (or imagining) particle diagrams.
M4 Periodic Table: Chemical Change
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Combination Reaction
• So a reaction between sodium and oxygen can be visualized as
follows:
Na
+
O2

Na2O
+
• What that means is that to form one unit of the compound sodium
oxide, two sodium atoms are needed to combine with one atom of
oxygen.
– Each formula can be made to represent one fundamental particle.
– Na represents 1 atoms of sodium, and O2 represents 1 moleculeof
oxygen (which is 2 atoms).
• Notice, as written, the equation shows the loss/destruction of one
oxygen atom and creation of one sodium atom!
M4 Periodic Table: Chemical Change
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Combination Reaction
• Since oxygen atoms travel around in pairs (Diatomic), we must end up
with two oxygen atoms in the number of units of the compound
produced.
+
• So, in the equation a molecule of oxygen is shown to produce two
units of sodium oxide. Accounting for the number of oxygen atoms
has meant the creation of sodium atoms.
M4 Periodic Table: Chemical Change
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Combination Reaction: Balancing Equation
• The creation of 3 sodium atoms, which we can balance by adding
three more sodium atoms to the left.
+
• Giving us the balanced equation:
4Na
+
O2

2Na2O
• A chemical equation must be balanced so as to not contradict the law
of conservation of matter.
M4 Periodic Table: Chemical Change
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Combination Reaction: Balancing Equation
• A reaction between zinc and iodine can be visualized as follows:
Zn
+
I2

ZnI2
+
• Draw balanced diagrams to represent the following reaction:
Al +
I2
M4 Periodic Table: Chemical Change

AlI3
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Practice Question
• Draw balanced diagrams to represent the following reaction:
Al +
O2
M4 Periodic Table: Chemical Change

Al2O3
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Combination Reaction: Metal + Nonmetal
• In the lab you observed some dramatic combination reaction, one of
which was that between zinc and iodine.
Zinc + Iodine  Zinc iodide
• When a metal (such as zinc) and non-metal (such as iodine) combine
to form a compound, the name of the compound is derived by writing
the name of the metal first followed by the name of the non-metal
whose last syllable is replaced by an –ide ending.
– Iodine therefore becomes iodide.
• Hence the name of a compound of zinc and iodine is zinc iodide.
You also observed a reaction between aluminum and iodine.
The word equation for that looks like this:
Aluminum + Iodine  Aluminum iodide
M4 Periodic Table: Chemical Change
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Combination Reaction: Metal + Nonmetal
• So, names of all compounds formed by the combination of a metal
and iodine have the format: name of metal followed by iodide.
As a matter of fact, compounds containing iodine and a metal are
referred to as iodides.
– That is, zinc iodide, aluminum iodide, sodium iodide, magnesium iodide
are examples of iodides.
• You also observed some reactions between oxygen and other
elements.
Sodium + oxygen  sodium oxide
Magnesium + oxygen  magnesium oxide
• In other words, compounds of consisting of an element and oxygen
are referred to as oxides.
M4 Periodic Table: Chemical Change
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Combination Reaction: Metal + Nonmetal
• You also observed some reactions between other metals and nonmetals:
zinc + sulfur  zinc sulfide
iron + sulfur  iron sulfide
• In general then:
Metal + non-metal  metal and name of non-metal with –ide ending
M4 Periodic Table: Chemical Change
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Combination Reaction: Metal + Nonmetal
• Hydrogen becomes hydride.
Nitrogen becomes nitride.
Oxygen becomes oxide.
Fluorine becomes fluoride.
Phosphorus becomes phosphide.
Sulfur becomes sulfide.
Chlorine becomes chloride.
Bromine becomes bromide.
M4 Periodic Table: Chemical Change
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Combination Reaction: Non-metal + non-metal
• So what do you call a compound of hydrogen and
oxygen combined together?
Hydrogen + oxygen  hydrogen oxide?
• Not really, though that would make sense.
You all know it’s called water.
M4 Periodic Table: Chemical Change
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Combination Reaction
• The names and the products of a reaction between two non-metals
are not as easy to figure out and determine.
•
hydrogen (gas) + oxygen (gas)

water

carbon dioxide
+
• Other reactions were:
carbon
+
oxgyen
+
– This is the reaction that takes place when coal burns.
M4 Periodic Table: Chemical Change
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Combination Reaction
nitrogen
+
hydrogen

ammonia
+
Nitrogen + oxygen  nitrogen oxide
– This reaction can take place in the engine of a car.
hydrogen
+
fluorine

hydrogen fluoride
+
M4 Periodic Table: Chemical Change
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Combination Reaction
hydrogen + chlorine  hydrogen chloride
hydrogen + bromine  hydrogen bromide
hydrogen + iodine  hydrogen iodide
sulfur + oxygen  sulfur dioxide
• But notice that as long as the compound is
made of two different elements, their
names end in –ide.
M4 Periodic Table: Chemical Change
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Combination Reaction
• A compound is different from a mixture in
that the atoms in a compound are
chemically bonded together, and that’s
why the physical and chemical properties
of the compound is markedly different from
the elements from which it is made.
• In the next several slides we will look at
properties of some elements and the
compounds they form.
Practice Problem (33)
• The next few slides show how compounds
have different properties then the
elements the are made of, they are
examples, you do not need to learn them
• Write the balanced chemical equation for
each in one box on your assignment sheet
Formation of Water
• Element: Hydrogen, symbol: H,
formula: H2
Element: Oxygen, symbol: O; formula:
O2
Properties:
Properties:
• an odorless molecular gas room
temperature
• an odorless molecular gas at
room temperature
• transparent, clear, light passes
through it
• transparent, clear, light passes
through it
• chemically reactive - very reactive
when a small spark is provided
• chemically reactive - very
reactive when heated
Compound: Water, H2O
Properties:
M4 Periodic Table: Chemical Change
•
An odorless liquid at room temperature
•
transparent, clear, light passes through it
•
not very chemically reactive, the compound is stable
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Formation of Ammonia
• Element: Hydrogen, H; symbol:
H, formula: H2
Properties:
Element: Nitrogen, N; symbol: N,
formula: N2
Properties:
• an odorless molecular gas room
temperature
• transparent, clear, light passes
through it
• chemically reactive - very reactive
when a small spark is provided
• A odorless molecular gas at
room temperature
• transparent, clear, light passes
through it
• chemically reactive - very
reactive when heated
Compound: Ammonia, NH3
Properties:
•
a characteristic pungent smelling gas at room temperature
•
transparent, clear, light passes through it
•
A relatively reactive compound
M4 Periodic Table: Chemical Change
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Carbon dioxide
• Element: Carbon, symbol: C;
formula: C.
Element: Oxygen, O; symbol: O;
formula: O2
Properties:
Properties:
• a solid (powder) at room
temperature
• black coloured, absorbs all light,
none passes through
• chemically reactive when heated
slightly
• a gas at room temperature
• transparent, clear, light passes
through it
• chemically reactive - very
reactive when heated
Compound: Carbon dioxide, CO2
Properties:
M4 Periodic Table: Chemical Change
•
a gas at room temperature
•
transparent, clear, light passes through it
•
not very chemically reactive, the compound is stable
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Sulfur Dioxide
• Element: Sulfur, symbol: S;
formula: S.
Element: Oxygen, O; symbol: O;
formula: O2
Properties:
Properties:
– a solid at room temperature
• a gas at room temperature
– yellow coloured
• transparent, clear, light passes
through it
– insoluble in water
– chemically reactive when heated
slightly
• chemically reactive - very
reactive when heated
Compound: Sulfur dioxide, SO2
Properties:
M4 Periodic Table: Chemical Change
•
a gas at room temperature
•
transparent, clear, light passes through it
•
readily dissolves in water
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Sodium oxide
• Element: Sodium, symbol:
Na; formula: Na.
Element: Oxygen, O; symbol: O;
formula: O2
Properties:
Properties:
– a solid at room temperature
• a gas at room temperature
– silver coloured
• transparent, clear, light passes
through it
– very reactive (hence stored
under oil)
• chemically reactive - very
reactive when heated
Compound: Sodium oxide, Na2O
Properties:
•
a gray solid at room temperature
•
hygroscopic
•
readily dissolves in water
M4 Periodic Table: Chemical Change
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Compound and mixture
• A mixture on the other hand retains the properties of the
elements and/or compound it is made of.
– For example sea water is a mixture and it retains the
saltiness of salt and fluidity of water.
– Vinegar is a mixture of acetic acid and water
– Air is a mixture of different gases (nitrogen, oxygen,
argon and a few others).
– Alloys are mixtures of two or more metals. Steel is an
alloy of iron, chromium and nickel; bronze: copper & tin
etc.
M4 Periodic Table: Chemical Change
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Signs of reaction
• When you observed combination reactions, you would have noted the
following signs of reaction
– change in color and/or
– production of a solid where there was no solid or a
different colored solid from that already present in the
mixture, and/or
– Bubbling or evolution of a gas that is colored or has an
odor, and/or
– Change in energy--either production of energy in the
form of sound energy (explosion) or generating heat
energy (increasing temperature) or using up heat
energy (decreasing temperature).
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Why do elements react with one another?
• Elements react with each other because they are
energetically unstable.
Atoms of noble gases are energetically stable while the
rest of the elements in the periodic table are not.
– Atoms of noble gases are energetically stable because
their valence shells contain the maximum number of
electrons that they can accommodate.
• So, atoms of other elements try to attain a similar
electronic structure as those of noble gases and
they do so by reacting with other elements.
Atoms of other elements achieve the same electronic
structure as a noble gas by either losing electrons,
or gaining electrons or sharing electrons between
themselves.
M4 Periodic Table: Chemical Change
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Metal atoms lose electrons
• Metal atoms in general achieve noble gas structure by losing their
valence electrons.
Na
Sodium atom
Mg
Magnesium atom
M4 Periodic Table: Chemical Change
Na
Sodium atom after
losing 1 electron
Mg
Magnesium atom after
losing 2 electrons
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Nonmetal atoms either gains electrons
• Non-metal atoms when reacting with metals achieve noble gas
structure by gaining electrons.
F
Fluorine atom
O
Oxygen atom
M4 Periodic Table: Chemical Change
F
Fluorine atom after
gaining 1 electron
O
Oxygen atom after
gaining 2 electrons
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…or share electrons
• Non-metal atoms when reacting with other non-metal atoms, they
achieve noble gas structure by sharing electrons between themselves.
H
+
Hydrogen atom
Cl
Chlorine atom
H
Cl
Hydrogen & chlorine atoms sharing
2 electrons between them.
• We will have more to say about metals losing electrons, non-metals
either gaining electrons or sharing electron when we look at other
chemical reactions and bonding.
M4 Periodic Table: Chemical Change
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