U2L6 - Interactions of Atoms

Unit 2 Lesson 6 Interactions of Atoms
Copyright © Houghton Mifflin Harcourt Publishing Company

Indiana Standards
• 8.1.3 Explain how the arrangement of atoms and
molecules determines chemical properties of
substances.
• 8.1.4 Describe the structure of an atom and relate
the arrangement of electrons to how that atom
interacts with other atoms.
• 8.1.5 Explain that atoms join together to form
molecules and compounds and illustrate with
diagrams the relationship between atoms and
compounds and/or molecules.

Indiana Standards
• 8.1.7 Explain that chemical changes occur when
substances react and form one or more different
products, whose physical and chemical properties
are different from those of the reactants.
• 8.1.8 Demonstrate that in a chemical change, the
total numbers of each kind of atom in the product
are the same as in the reactants and that the total
mass of the reacting system is conserved.

Breaking Up and Making Up
What happens to atoms during a
chemical change?
• During a chemical change, atoms are not created
or destroyed. Instead, the atoms are simply
rearranged.
• The atoms that make up a substance are joined
by chemical bonds. During a chemical change,
chemical bonds are formed and broken. The result
of a chemical change is different combinations of
atoms joined by bonds.

What happens to atoms during a
chemical change?
• When the atoms in a substance are rearranged,
the identity of the substance changes. The new
substance has different chemical properties.
• A molecule is a distinct group of atoms held
together by chemical bonds. Different molecules
have different chemical properties.

How are chemical changes described?
• A chemical equation can be used to describe a
chemical change, or reaction.
• A chemical equation uses symbols to represent
the various substances that interact during a
reaction.

• In a chemical equation, each substance is
represented by a chemical formula that
describes the substance’s makeup in a shorthand
way.
• The chemical formula for carbon dioxide is CO2.
The letters C and O represent the elements carbon
and oxygen. The 2 is a subscript that tells you
that there are two oxygen atoms in a molecule of
CO2.

C + O2 CO2
• In a chemical equation, the starting materials, or
reactants, appear on the left side of the arrow.
• The substances formed in the reaction, the
products, appear on the right side of the arrow.
• What are the reactants and products in this
chemical equation?

A Balancing Act
How do chemical equations show the
law of conservation of mass?
• The law of conservation of mass states that
matter is neither created nor destroyed in
ordinary physical and chemical changes.
• A balanced chemical equation shows the same
numbers and kinds of atoms on both sides of the
equation.

How do chemical equations show the
law of conservation of mass?
2C + O2 2CO
• Coefficients are numbers placed in front of
chemical formulas in order to balance an equation.
• In this balanced chemical equation, a coefficient of
2 appears in front of the C and the CO.
• This chemical equation shows two carbon atoms
and two oxygen atoms on each side of the arrow.

Let’s Get Together
How is chemical bonding modeled?
• There are different ways of modeling an atom. The
model you choose depends on how you will use
the model.

• A type of atom model called a Bohr model shows
electrons as dots arranged in rings around the
nucleus.

• Bohr models are useful for making predictions
about how atoms form and break bonds during
chemical reactions.
• The rings in a Bohr model represent different
energy levels. Each energy level can hold a
different number of electrons.
• The first, innermost energy level can hold up to
two electrons. The second energy level can hold
up to eight electrons.

• The electrons in the outermost energy level of an
atom are called valence electrons.
• Only valence electrons participate in chemical
bonding. Other electrons in an atom do not.

• How many valence electrons are in this lithium
atom?

• When an energy level of an atom contains the
maximum number of electrons, the energy level is
full.
• An atom with a full outermost energy level is
stable and usually does not form bonds. This kind
of atom is usually not reactive.

• An atom that does not have a full outermost
energy level can form bonds in order to achieve a
full outermost energy level.
• This kind of atom can form bonds by sharing
electrons with other atoms or by transferring
electrons between atoms.

U2L6 - Interactions of Atoms

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