CHEMICAL
REACTIONS
UNIT 7
PERIODIC TABLE OF ELEMENTS
• The periodic table of chemical elements, often called the periodic table,
organizes all discovered chemical elements in rows (called periods) and
columns (called groups) according to increasing atomic number.
• Scientists use the periodic table to quickly refer to information about an
element, like atomic mass and chemical symbol
• https://ptable.com/?lang=en#Properties
Periodic Table Vocabulary
• Elements: A pure substance composed of a single atom with a unique
atomic number.
• Groups: The vertical column of the periodic table that signifies the number
of valence electrons in an element.
• Periods: The horizontal rows in the periodic table that signify the number of
electron shells in an element.
• Families: Elements that have the same number of valence electrons and
therefore similar properties.
VOCABULARY
• Protons: Positively charged subatomic particles located in the nucleus of an atom.
• Neutrons: Neutrally charged subatomic particles located in the nucleus of an atom.
• Electrons: Negatively charged subatomic particles located in orbitals surrounding
the nucleus.
• Atomic Mass: A weighted average of the number of neutrons and protons present
for all isotopes.
• Atomic Number: Number of protons present in an atom.
• Element: A pure substance that cannot be broken down into a simpler substance by
chemical means
PROTONS, NEUTRONS, ELECTRONS
• The number of protons, neutrons, and electrons in an atom can be determined from a set
of simple rules.
• The number of protons in the nucleus of the atom is equal to the atomic number (Z).
• The number of electrons in a neutral atom is equal to the number of protons.
• The mass number of the atom (M) is equal to the sum of the number of protons and
neutrons in the nucleus.
• The number of neutrons is equal to the difference between the mass number of the atom
(M) and the atomic number (Z).
How to find the Atomic Number
Finding the Number of Protons
• The number of protons in an atom is
equal to the atomic number of the
element. For example, let’s use oxygen.
According to the periodic table,
oxygen has the atomic number eight.
The atomic number is located above
the element’s symbol. Since oxygen has
an atomic number of eight, there must
be eight protons total. Moreover, the
number of protons never changes for
an element.
Finding the Number of Neutrons
• The number of neutrons in an
atom can be calculated by
subtracting the atomic number
from the atomic mass. Both of
these numbers can be found on the
periodic table. The atomic number
is listed above the symbol of the
element whereas the mass number
is placed below.
Finding the Number of Electrons
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• The number of electrons in an atom is
equal to the atomic number of an
element, for neutrally charged species.
This means the number of electrons
and the number of protons in an
element are equal. Therefore, the
number of electrons in oxygen is 8.
Moreover, since these two subatomic
particles, electrons and protons, have
opposite charges, they cancel out and
keep the atom neutral.
VOCABULARY WORDS
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PROPERTY
SUBSTANCE
ATOMS
CHEMICAL REACTION
PRODUCT
• REACTANT
• REARRANGE
• SCALE
CHEMICAL REACTIONS
• A chemical reaction is in which the bonds are broken within reactant molecules,
and new bonds are formed within product molecules in order to form a new
substance
• Chemical reactions occur when chemical bonds between atoms are formed or
broken. A chemical reaction occurs when two or more substances (reactants) are
mixed together and result in one or more new substances (products).
• The substances that go into a chemical reaction are called the reactants, and the
substances produced at the end of the reaction are known as the products.
BASIC CONCEPTS OF CHEMICAL
REACTIONS
• A Chemical Reaction is a process that occurs when two or more molecules
interact to form a new product(s).
• Compounds that interact to produce new compounds are called reactants
whereas the newly formed compounds are called products.
• Chemical reactions play an integral role in different industries, customs and
even in our daily life. They are continuously happening in our general
surroundings; for example, rusting of iron, pottery, fermentation of wine
and so on.
BASIC CONCEPTS OF CHEMICAL
REACTIONS
• In a chemical reaction, a chemical change must occur which is generally
observed with physical changes like precipitation, heat production, colour
change etc.
• A reaction can take place between two atoms or ions or molecules, and they
form a new bond and no atom is destroyed or created but a new product is
formed from reactants.
• The rate of reaction depends on and is affected by factors like pressure,
temperature, the concentration of reactants.
CHEMICAL EQUATIONS
• Due to the vast amounts of chemical reactions happening around us, a
nomenclature was developed to simplify how we express a chemical reaction
in the form of a chemical equation. A chemical equation is nothing but a
mathematical statement which symbolizes the product formation from
reactants while stating certain condition for which how the reaction has been
conducted.
CHEMICAL EQUATIONS
• The reactants are on the left-hand side whereas the products formed are on the right-hand
side. The reactants and products are connected by a one-headed or two-headed arrows. For
example, a reaction
• A+B→C+D
• Here, A and B are the reactants, which react to form the products C and D. In an actual
chemical equation, reactants are denoted by their chemical formula. In order to assure the
law of conservation of mass, a chemical equation must be balanced i.e. the number of
atoms on both sides must be equal. This is the balancing of the equation.
TYPES OF CHEMICAL REACTIONS
• The basis for different types of reactions is the product formed, the changes that
occur, the reactants involved and so on. Different types of reactions are:
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Combustion reaction
Decomposition reaction
Neutralization reaction
Precipitation or Double-Displacement Reaction
Synthesis reaction
Combustion Reaction
• A combustion reaction is a reaction with a
combustible material with an oxidizer to give an
oxidized product. An oxidizer is a chemical a fuel
requires to burn, generally oxygen. Consider the
example of combustion of magnesium metal.
Decomposition Reaction
• A Decomposition reaction is a reaction in which a
single component breaks down into multiple
products. Certain changes in energy in the
environment have to be made like heat, light or
electricity breaking bonds of the compound.
Neutralization Reaction
• A Neutralization reaction is basically the reaction
between an acid and a base giving salt and water as the
products. The water molecule formed is by the
combination of OH– ions and H+ ions. The overall pH
of the products when a strong acid and a strong base
undergo a neutralization reaction will be 7
Precipitation or Double-Displacement Reaction
• It is a type of displacement reaction in which two compounds react and
consequently, their anions and cations switch places forming two new
products.
Synthesis Reaction
• A Synthesis reaction is one of the most basic types
of reaction wherein multiple simple compounds
combine under certain physical conditions giving
out a complex product. The product will always be
a compound.
IMPORTANT POINTS TO REMEMBER
• In a chemical change, a new compound is formed but in a physical change,
the substance changes its state of existence.
• Atoms or ions or molecules which react to form a new substance are called
reactants; the new atoms or molecules formed are products.
• A chemical reaction follows the law of conservation of mass. That is no
atom is destroyed or created but only a new product is formed from
reactants.
CHEMICAL VS PHYSICAL CHANGES
• In a physical change, a compound’s shape may change, but its chemical identity
will not. For example, freezing or boiling water is a physical change. Once melted or
boiled, the water may be in a different form (solid ice or gaseous water vapor), but it
is still water, H2O, and it still has the same chemical composition.
• A chemical change happens when a substance’s chemical identity changes. An
example of this is rusting. When an iron nail comes into contact with water and is
then exposed to the air, it rusts, forming a brown-red substance. This process
changes the chemical composition of the original substance.
• While some physical changes are easily reversible, such as re-freezing melted ice,
reversing a chemical change requires another chemical reaction.
INDICATIONS OF A CHEMICAL
REACTION
• Based on its definition, a chemical reaction occurs when a substance undergoes a chemical
change. So how can we tell if a chemical change has occurred?
• 1. Heat or Light Emissions
• If a reaction emits heat or light, that is an indication that energy has been released from the
reaction. One example of this is a fire or spark, which is evidence of combustion. Because
many physical changes also involve heat or light, this is not concrete, definitive evidence of a
reaction. But it is a strong argument that one has occurred.
• 2. Change in Color
• A change in color is a possible indication of a chemical reaction.
INDICATIONS OF A CHEMICAL
REACTION
• 3. Gas Formation
• When substances react and bubbles or a vapor appears, this is an indication that a
chemical reaction is occurring. An example of this is when baking soda and vinegar
react violently to produce carbon dioxide gas in the famous volcano experiment.
• 4. Precipitate Formation
• A precipitate is a solid product that forms as a result of a chemical reaction between
liquid reactants. An example of a precipitate is yellow cadmium sulfide, which is
produced when water solutions of ammonium sulfide and cadmium nitrate are
combined.
Chemical Change Examples
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Combustion
Oxidation (rusting)
Biological decomposition or fermentation
Cooking an egg
Photosynthesis
Chemical decomposition
Reacting acids and bases together
Chemical batteries
Digestion
Fireworks
Paper Burning
CHEMICAL REACTION EXAMPLES
• Electrolysis (separating water into its elements, hydrogen and oxygen, using an electric
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current)
Oxidation (the rusting of iron metal when exposed to moisture and oxygen in the air)
Photosynthesis (the process by which plants convert carbon dioxide and water into glucose
and oxygen using energy from sunlight)
Soft drinks going flat (carbonic acid in soft drinks decomposes into its elements, carbon
dioxide and water)
Table salt formation (combination of sodium and chlorine to form table salt)
Cellular respiration (the process by which organisms convert oxygen and food molecules
into carbon dioxide and energy)
CHEMICAL REACTION EXAMPLES
• Driving (the combustion of gasoline and oxygen in engines to produce carbon
dioxide, water vapor, and energy)
• Digestion (hydrochloric acid and enzymes break down proteins in organisms’
stomachs)
• Baking soda – vinegar volcano experiment (combining baking soda and vinegar to
produce sodium acetate, carbon dioxide, and water)
• Batteries (a galvanic cell converting chemical energy into electrical energy)
• Cooking a steak on the grill (new compounds are formed from the intense heat)
PHYSICAL CHANGE EXAMPLES
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Ice melting (water changing phases)
Salt dissolving in water (the compound is simply going into solution)
Breaking a glass into fragments
Cutting paper into pieces
Sugar crystallizing out of solution as the water evaporates
Water evaporating into the air
Mixing oil and water
Melting sulfur (even though the color changes)
Melting wax