N o r t h E a st I n d ep en d e nt S c h o o l D i st ri c t
Chemistry
Unit 3: Bonding, Formulas, Reactions
Clarifying Statements
May, 2006
In this unit students will explore chemical bonding by comparing and contrasting
ionic and covalent bonding. They will identify the “chemical and physical properties
of ionic and covalent compounds” (TEKS 8.B) and compare the “arrangement of
atoms in molecules, ionic crystals, polymers, and metallic substances” (TEKS 8.C).
Determining Ionic and Covalent – A Brief Comparison
A covalent bond results from the sharing of electron pairs between two atoms
while an ionic bond results from the attraction of a cation and an anion. Students
must be able to analyze the electronegativities of elements in order to determine
whether they form a covalent or an ionic bond. If a covalent bond is formed, they
should be able to then determine if it is polar or nonpolar.
Ionic Bonding
Ionically bonded compounds are “composed of positive and negative ions that are
combined so that the numbers of positive and negative charges are equal” (Modern
Chemistry HRW, p. 176.) The positive ions (cations) result from metals, and the
negative ions (anions) result from nonmetals. When ionic compounds are formed,
valence electrons are transferred from the cations to the anions so that each
atom obtains eight valence electrons, known as an octet. Using electron dot
notations such as the one below will help students visualize how valence electrons
are transferred. Students should then be able to predict the ionic formula unit of
a compound and draw its structure.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for instructional
design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r t h E a st I n d ep en d e nt S c h o o l D i st ri c t
Chemistry
Unit 3: Bonding, Formulas, Reactions
Clarifying Statements
May, 2006
Students will also learn to name and write balanced formulas for ionic compounds.
In order to accomplish this, they must be able to name monatomic and polyatomic
ions. It is recommended that students commit polyatomic ions to memory. On
major assessments, students will be provided appropriate reference materials,
including the Periodic Table and a polyatomic ion list.
Students must understand that a formula unit is the simplest collection of atoms
and that ionic compounds are crystalline structures made up of many, many
organized ions (as in the following diagram).
Covalent Bonding
Covalently bonded compounds are called molecules. Teachers may choose to use
simple organic or inorganic compounds to exemplify the characteristics of covalent
molecules. Drawing Lewis structures that illustrate the octet rule, such as the
figure below, will help students visualize the structure of molecules. Students
should be able to draw molecules such as water, which contain single bonds
representing lone pairs of electrons. It is appropriate to introduce students to
double and triple bonds as well.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for instructional
design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r t h E a st I n d ep en d e nt S c h o o l D i st ri c t
Chemistry
Unit 3: Bonding, Formulas, Reactions
Clarifying Statements
May, 2006
Students must also be able to use the appropriate prefixes (including the seven
diatomic molecules) to name and write formulas for covalent molecules, as in the
following.
Molecular Shapes
Students will further investigate covalent bonds by studying intermolecular
forces. They must understand the influence of valence electrons on the geometry
and structure of molecules. Students will be able to identify the geometry of
molecules, including bent and linear. If time allows, students may also be
introduced to trigonal planar, trigonal pyramidal, and tetrahedral molecules such as
the ones below.
Once students are familiar with the basic geometric shapes, they should be
prepared to study polarity and hydrogen-bonding.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for instructional
design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
3
N o r t h E a st I n d ep en d e nt S c h o o l D i st ri c t
Chemistry
Unit 3: Bonding, Formulas, Reactions
Clarifying Statements
May, 2006
Induced dipoles and London forces are also introduced at this point. Students will
learn that these intermolecular forces influence many of the chemical and physical
properties of molecules. These properties will be expanded upon in future units
and intermolecular forces will be referred to again, particularly in reference to
water. It is a good practice for teachers to use sigma notation and arrows to
indicate the direction of charge while teaching, as shown in the following diagram.
Metallic Bonding
A metallic bond is a chemical bond that results from the “attraction between
metal atoms and the surrounding sea of electrons” (Modern Chemistry HRW, p.
181). Students must know that metallic properties such as conductivity, shiny
appearance, malleability, and ductility result from the behavior of the electrons in
metallic bonds.
Introduction to Writing and Balancing Equations
Teachers may wish to have students begin to write balanced chemical equations
and determine molar masses of compounds in preparation for the next unit.
Students can also be introduced to empirical and molecular formulas; as well as
percent composition by mass. These concepts are necessary to conduct
appropriate laboratory analysis of molecules.
In this unit, students will begin writing balanced reactions from word equations. If
time permits at the end of the semester, students can begin to classify these
reactions as single replacement, double replacement, decomposition, synthesis, or
combustion.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for instructional
design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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