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8.1 Molecular Compounds >8.1 Molecular Compounds >
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Chapter 8Covalent Bonding
8.1 Molecular Compounds
8.2 The Nature of Covalent Bonding8.3 Bonding Theories8.4 Polar Bonds and Molecules
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Although the types of pieces are limited, you can make many different toy models depending on how many pieces you use and how they are arranged.
CHEMISTRY & YOUCHEMISTRY & YOU
How are atoms joined together to make compounds with different structures?
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Molecules and Molecular Compounds
What information does a molecular formula provide?
Molecules and Molecules and Molecular CompoundsMolecular Compounds
8.1 Molecular Compounds >8.1 Molecular Compounds >
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In nature, only the noble gas elements, such as helium and neon, exist as uncombined atoms.
Molecules and Molecules and Molecular CompoundsMolecular Compounds
• They are monatomic; so they consist of single atoms.
• But not all elements are monatomic. Oxygen exists in molecules as O2.
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Molecules and Molecules and Molecular CompoundsMolecular Compounds
Ionic compounds are generally crystalline solids with high melting points. Other compounds, however, have very different properties.
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Molecules and Molecules and Molecular CompoundsMolecular Compounds
Ionic compounds are generally crystalline solids with high melting points. Other compounds, however, have very different properties.
• Water (H2O) is a liquid at room temperature.
• Carbon dioxide (CO2) and nitrous oxide (N2O) are both gases at room temperature.
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• These bonds do not involve the transfer of electrons.
• Another way that atoms can combine is by sharing electrons.
Molecules and Molecules and Molecular CompoundsMolecular Compounds
The attractions that hold together the atoms in O2, H2O, CO2, and N2O cannot be explained by ionic bonding.
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• Remember that ionic bonds form when the combining atoms give up or accept electrons.
Molecules and Molecules and Molecular CompoundsMolecular Compounds
Sharing Electrons
– Atoms that are held together by sharing electrons are joined by a covalent bond.
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Sharing Electrons
Molecules and Molecules and Molecular CompoundsMolecular Compounds
A molecule is a neutral group of atoms joined together by covalent bonds.
• An oxygen molecule is an example of a diatomic molecule—a molecule that contains two atoms, like oxygen, O2.
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• A compound composed of molecules is called a molecular compound.
H2O is an example of a molecular compound.
A molecular formula is the chemical formula of a molecular compound.
Molecules and Molecules and Molecular CompoundsMolecular Compounds
Sharing Electrons
Molecules can also be made of atoms of different elements.
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A molecular formula shows how many atoms of each element a substance contains.
The molecular formula of carbon dioxide is CO2.
• The subscript written after an element’s symbol shows the number of atoms of each element in the molecule.
Molecules and Molecules and Molecular CompoundsMolecular Compounds
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• Butane is used in lighters and household torches.
• The molecular formula for butane is C4H10.
• According to this formula, one molecule of butane contains four C atoms and ten H atoms.
Molecules and Molecules and Molecular CompoundsMolecular Compounds
Representing Molecules
Butane is another a molecular compound.
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Molecules and Molecules and Molecular CompoundsMolecular Compounds
Representing Molecules
A molecular formula does not tell you how the atoms are arranged in space or which atoms are bonded to one another structure.
• The arrangement of atoms within a molecule is called its molecular structure.
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• The molecular structure of CO2 shows how the 3 atoms are arranged in a row.
• It also shows how the C atom is in the middle between the two oxygen atoms.
Molecules and Molecules and Molecular CompoundsMolecular Compounds
Representing Molecules
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• The molecular structure of ethanol (C2H6O) is more complicated.
• Each C is bonded to four atoms, each H is bonded to one atom, and the one oxygen is bonded to two atoms.
Molecules and Molecules and Molecular CompoundsMolecular Compounds
Representing Molecules
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Comparing Molecular and Ionic Compounds
What representative units define molecular compounds and ionic compounds?
• The representative unit of a molecular compound is a molecule. For an ionic compound, the smallest representative unit is a formula unit.
Comparing Molecular and Comparing Molecular and Ionic CompoundsIonic Compounds
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• Many molecular compounds are gases or liquids at room temperature.
Comparing Molecular and Comparing Molecular and Ionic CompoundsIonic Compounds
Molecular compounds tend to have relatively lower melting and boiling points than ionic compounds.
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• Many molecular compounds are gases or liquids at room temperature.
• Most molecular compounds are composed of atoms of two or more nonmetals.
Comparing Molecular and Comparing Molecular and Ionic CompoundsIonic Compounds
Molecular compounds tend to have relatively lower melting and boiling points than ionic compounds.
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Water, which is a molecular compound, and sodium chloride, which is an ionic compound, are compared here.
Comparing Molecular and Comparing Molecular and Ionic CompoundsIonic Compounds
Collection of water molecules
Molecule of water
Chemical formula H2O
Array of sodium ions and
chloride ions
Formula unit ofsodium chloride
Chemical formulaNaCl
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How is the formula unit of an ionic compound different from a molecule?
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How is the formula unit of an ionic compound different from a molecule?
A molecule is made up of two or more atoms that act as a unit. No such discrete units exist in an ionic compound, which exists as an array of ions.
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A molecular formula shows how many atoms of each element a substance contains.
The representative unit of a molecular compound is a molecule. For an ionic compound, the smallest representative unit is a formula unit.
Key ConceptsKey Concepts
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• covalent bond: a bond formed by the sharing of electrons between atoms
• molecule: a neutral group of atoms joined by covalent bonds
• diatomic molecule: a molecule consisting of two atoms
Glossary TermsGlossary Terms
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• molecular compound: a compound that is composed of molecules
• molecular formula: a chemical formula of a molecular compound that shows the kinds and numbers of atoms present in a molecule of a compound
Glossary TermsGlossary Terms
8.1 Molecular Compounds >8.1 Molecular Compounds >
25
Questions
1.What is a covalent bond?
2.List three examples of covalent bonding.
3. What is a molecule?
4. What is a molecular formula?
5. What is the representative unit in a molecular
compound?
6. List two ways that molecular compounds are different
from ionic compounds.
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