Covalent Bonds (And Metallic Bonds) COVALENT BOND bond formed by the sharing of electrons.
New No Slide Title · 2015. 8. 11. · Covalent Bonds, continued • Atoms may share more than one...
Transcript of New No Slide Title · 2015. 8. 11. · Covalent Bonds, continued • Atoms may share more than one...
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The Structure of Matter Section 1
Chemical Bonds
〉What holds a compound together?
〉The forces that hold atoms or ions together in a
compound are called chemical bonds.
• chemical bond: the attractive force that holds
atoms or ions together
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The Structure of Matter Section 1
Chemical Structure
〉How can the structure of chemical compounds be shown?
〉The structure of chemical compounds can be shown by various models. Different models show different aspects of compounds.
• chemical structure: the arrangement of atoms in a substance
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The Structure of Matter Section 1
Chemical Structure, continued
• Some models represent bond lengths and angles.
• bond length: the average distance between the
nuclei of two bonded atoms
• bond angle: the angle formed by two bonds
to the same atom
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The Structure of Matter Section 1
Visual Concept: Bond Length
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The Structure of Matter Section 1
Chemical Structure, continued • In a ball-and-stick model, atoms
are represented by balls. The bonds that hold the atoms together are represented by sticks.
• In structural formulas, chemical
symbols are used to represent the atoms.
• Space-filling models show the space occupied by atoms.
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The Structure of Matter Section 1
Chemical Structure, continued • Bonds can bend, stretch, and rotate without breaking.
– Bonds can be represented by flexible springs. – Most reported bond lengths are average distances.
– Bonds hold atoms together tightly.
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The Structure of Matter Section 1
How Does Structure Affect Properties?
〉What determines the properties of a compound?
〉The chemical structure of a compound
determines the properties of that compound.
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The Structure of Matter Section 1
How Does Structure Affect Properties?
continued
• Compounds with network structures are
strong solids.
– Example: Quartz, SiO2 is made of silicon
and oxygen atoms.
– The atoms are bonded in a strong, rigid
structure.
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The Structure of Matter Section 1
How Does Structure Affect Properties?
continued
• Some networks are made of bonded ions.
– The strong attractions between the oppositely
charged ions give ionic compounds high melting
points and high boiling points.
– Example: Table salt—sodium chloride—is made
of a tightly packed repeating network of positive
sodium ions and negative chlorine ions.
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The Structure of Matter Section 1
How Does Structure Affect Properties?
continued
• Some compounds are made of molecules. – Some compounds made of molecules are solids,
others are liquids, others are gases.
– The strength of attractions between molecules varies.
– Attractions between water molecules are called hydrogen bonds.
• Hydrogen bonds are not as strong as the bonds holding oxygen and hydrogen atoms together within a molecule.
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The Structure of Matter Section 1
Water Bonding
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The Structure of Matter Section 2
Why Do Chemical Bonds Form?
〉Why do atoms form bonds?
〉Generally, atoms join to form bonds so
that each atom has a stable electron
configuration.
• There are two basic kinds of chemical bonding:
– ionic bonding
– covalent bonding
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The Structure of Matter Section 2
Comparing Ionic and Covalent Bonds
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The Structure of Matter Section 2
Ionic Bonds 〉How do ionic bonds form?
〉Ionic bonds form from the attractions between oppositely charged ions.
• ionic bonds: the attractive force between oppositely
charged ions, which form when electrons are transferred from one atom to another
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The Structure of Matter Section 2
Ionic Bonds, continued • Ionic bonds are formed by the transfer of electrons.
– Two atoms tend to form an ionic bond when one atom
has more attraction for electrons than the other.
• Ionic compounds are in the form of networks, not
molecules.
– A formula unit is the smallest ratio of ions in ionic
compounds.
• When melted or dissolved in water, ionic compounds
conduct electricity.
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The Structure of Matter Section 2
Ionic Bonds, continued
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The Structure of Matter Section 2
Ionic Bonds, continued
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The Structure of Matter Section 2
Covalent Bonds 〉What do atoms joined by covalent bonds share?
〉Atoms joined by covalent bonds share electrons.
• covalent bond: a bond formed when atoms share one or more pairs of electrons.
– Compounds that are networks of bonded atoms, such as silicon dioxide, are also covalently bonded.
– Covalent bonds usually form between nonmetal atoms.
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The Structure of Matter Section 2
Covalent Bonds, continued • Covalent compounds can be solids, liquids,
or gases.
– In a chlorine molecule, Cl2, the atoms share two
electrons.
– They are joined by one covalent bond.
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The Structure of Matter Section 2
Covalent Bonds, continued • Atoms may share more than one pair of electrons.
– Two pairs of shared electrons (4 electrons) form a double covalent bond.
– Three pairs of shared electrons (6 electrons) form a triple covalent bond.
– Double bonds are stronger than single bonds.
– Triple bonds are stronger than double bonds.
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The Structure of Matter Section 2
Multiple Bonds
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The Structure of Matter Section 2
Covalent Bonds, continued • Atoms do not always share electrons equally.
– nonpolar covalent bonds: bonds in which electrons are shared equally
– When two atoms of different elements share electrons, the electrons are not shared equally.
– polar covalent bond: a bond in which there is an unequal sharing of electrons.
• Electrons tend to be more attracted to atoms of elements that are located farther to the right and closer to the top of the periodic table.
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The Structure of Matter Section 2
Visual Concept: Comparing Polar and
Nonpolar Covalent Bonds
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The Structure of Matter Section 2
Metallic Bonds
〉What gives metals their distinctive properties?
〉Metals are flexible and conduct electric current well
because their atoms and electrons can move freely
throughout a metal’s packed structure.
〉 metallic bond: a bond formed by the attraction between
positively charged metal ions and the electrons around them
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The Structure of Matter Section 2
Polyatomic Ions 〉How are polyatomic ions similar to other ions?
〉A polyatomic ion acts as a single unit in a
compound, just as ions that consist of a single atom do.
• polyatomic ion: an ion made of two or more atoms
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The Structure of Matter Section 2
Polyatomic Ions, continued • There are many common
polyatomic ions.
• A polyatomic ion acts as a single
unit in a compound.
• Parentheses group the atoms of a polyatomic ion. • Example: the formula for
ammonium sulfate is written as (NH4)2SO4, not N2H8SO4.
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The Structure of Matter Section 2
Polyatomic Ions, continued • Some names of polyatomic anions relate to their
oxygen content.
– An -ate ending is used to name an ion with more oxygen atoms.
• Examples: sulfate (SO42–), nitrate (NO3
–), chlorate (ClO3
–)
– An -ite ending is used to name an ion with fewer oxygen atoms.
• Examples: sulfite (SO32–), nitrite (NO2
–), chlorite (ClO2
–)
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The Structure of Matter Section 2
Polyatomic Ions, continued
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The Structure of Matter Section 3
Naming Ionic Compounds
〉How are ionic compounds named?
〉The names of ionic compounds consist of the
names of the ions that make up the compounds.
• Names of cations include the elements of which they
are composed.
• Example: a sodium atom loses an electron to form a
sodium ion, Na+.
• Names of anions are altered names of elements.
• Example: a fluorine atom gains an electron to form a fluoride
ion, F–.
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The Structure of Matter Section 3
Naming Ionic Compounds, continued
• An ionic compound must have a total charge of zero. – If an ionic compound is made up of ions that have different
charges, the ratio of ions will not be 1:1.
• CaF2
• Some cation names must show their charge.
– Transition metals may form several cations—each with a different charge.
• Fe2O3 is made of Fe3+ ions, so it is named iron(III)oxide. • FeO is made of Fe2+ ions, so it is named iron(II) oxide.
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The Structure of Matter Section 3
Naming Ionic Compounds, continued
• To determine the charge of a transition metal cation, look at the total charge of the compound.
– Fe2O3
• The total charge of the compound is zero.
• The iron ion has a charge of 3+.
• An oxide ion, O2–, has a a charge of 2–.
• Fe2O3 : (2 × 3+) + (3 × 2–) = 0
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The Structure of Matter Section 3
Math Skills
Writing Ionic Formulas What is the chemical formula for aluminum fluoride? 1. List the symbols for each ion. Symbol for an aluminum ion: Al3+
Symbol for a fluoride ion: F–
2. Write the symbols for the ions, with the cation first. Al3+ F–
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The Structure of Matter Section 3
3. Find the least common multiple of the ions’ charges. The least common multiple of 3 and 1 is 3. To make a neutral compound, you need a total of
three positive charges and three negative charges. you need only one Al3+ ion: 1 × 3+ = 3+ you need three F– ions: 3 × 1– = 3–
4. Write the chemical formula. Show with subscripts
how many of each ion are needed to make a neutral compound.
Math Skills, continued
AlF3
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The Structure of Matter Section 3
Naming Covalent Compounds
〉What do the numerical prefixes used in
naming covalent compounds tell you?
〉For covalent compounds of two elements,
numerical prefixes tell how many atoms of
each element are in the molecule.
• Numerical prefixes are used to name covalent
compounds of two elements.
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The Structure of Matter Section 3
Naming Covalent Compounds, continued
• Examples:
– Boron trifluoride, Bf3,
contains one boron atom
and three fluorine atoms
BF3.
– Dinitrogen tetroxide, N2O4,
is made of two nitrogen
atoms and four oxygen
atoms.
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The Structure of Matter Section 3
Empirical Formulas
〉What does a compound’s empirical formula indicate?
〉An empirical formula tells us the smallest whole-number ratio of atoms that are in a compound.
• empirical formula: the composition of a compound in terms of the relative numbers and kinds of atoms in the simplest ratio
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The Structure of Matter Section 3
Empirical Formulas, continued • Different compounds can have the same
empirical formula.
• Molecular formulas are determined from empirical
formulas.
– molecular formula: a chemical formula that
shows the number and kinds of atoms in a
molecule, but not the arrangement of atoms
• Masses can be used to determine empirical formulas.
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The Structure of Matter Section 3
Math Skills
Finding Empirical Formulas One mole of an unknown compound contains 62 g of phosphorus and 80 g of oxygen. What is the empirical formula of this compound? 1. List the given and unknown values. Given: 62 g phosphorus, 80 g oxygen Unknown: empirical formula 2. Write the atomic masses. phosphorus: 30.97 g/mol
oxygen: 16.00 g/mol
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The Structure of Matter Section 3
Math Skills, continued
3. The molar ratio of elements in the compound will be the compound’s empirical formula. Empirical Formula: P2O5
62 g P 1 mol P2.0 mol P
30.97 g P
80 g O 1 mol O5.0 mol O
16.00 g O
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Section 4 The Structure of Matter
Organic Compounds
〉What is an organic compound?
〉An organic compound is a covalently bonded compound that contains carbon.
• organic compound:a covalently bonded compound
that contains carbon, excluding carbonates and oxide.
• Many ingredients of familiar substances contain carbon.
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Section 4 The Structure of Matter
Visual Concept: Organic Compound
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Section 4 The Structure of Matter
Organic Compounds, continued
• Carbon atoms form four covalent bonds in organic
compounds.
• hydrocarbon: a compound made of only carbon and
hydrogen atoms
• Alkanes: hydrocarbons that have only single covalent
bond
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Section 4 The Structure of Matter
Visual Concept: Hydrocarbon
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Section 4 The Structure of Matter
Visual Concept: Alkane
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Section 4 The Structure of Matter
Organic Compounds, continued
• Arrangements of carbon atoms in alkanes may vary.
– The carbon atoms in any alkane with more than three carbon atoms can have more than one possible arrangement.
– Carbon atom chains may have many branches, and they can even form rings.
• Alkane chemical formulas usually follow a pattern.
– The number of hydrogen atoms is always two more than twice the number of carbon atoms, except for cyclic alkenes.
CnH2n + 2
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Section 4 The Structure of Matter
Six-Carbon Alkanes
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Section 4 The Structure of Matter
Organic Compounds, continued
• Alkenes are hydrocarbons that have double carbon-
carbon bonds.
• The simplest alkene is ethene,
• Alcohols have hydroxyl, or –OH, groups.
• Example: methanol, CH3OH
– Alcohols have the suffix -ol in their names.
• Alcohol and water molecules behave similarly.
– Neighboring alcohol molecules are attracted to one
another.
H2C CH2
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Section 4 The Structure of Matter
Visual Concept: Alkene
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Section 4 The Structure of Matter
Visual Concept: Alcohol
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Section 4 The Structure of Matter
Polymers
〉What is a polymer?
〉A polymer is a molecule that is a long chain made of smaller molecules.
• Polymers have repeating subunits.
– Polyethene, or polyethylene, is made from many molecules of ethene.
– monomer: the smaller molecule that makes up the polymer
• Ethene is the monomer in polyethene.
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Section 4 The Structure of Matter
Polymers, continued
• Some polymers are natural, and others are artificial.
– natural polymers: rubber, starch, protein, and DNA
– human-made polymers: plastics and synthetic fibers
• A polymer’s structure determines its elasticity.
– Polyethene is made of long chains.
• It is flexible, but not elastic.
• milk jugs
– Polymers with connected chains are elastic.
• They can stretch.
• rubber bands
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Section 4 The Structure of Matter
Biochemical Compounds
〉What organic compounds are essential to life?
〉Biochemicals, which are essential to life, include carbohydrates, proteins, and DNA.
• Many carbohydrates are made of glucose.
• carbohydrate: a class of molecules that includes
sugars, starches, and fiber; contains carbon, hydrogen, and oxygen.
•
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Section 4 The Structure of Matter
Biochemical Compounds, continued
• Proteins are complex polymers of amino acids.
• protein: an organic compound that is made of one or more chains of amino acids and that is a principal component of all cells
• amino acid: a compound of a class of simple organic compounds that contain a carboxyl group and an amino group and that combine to form proteins.
• Each protein is made of a specific combination of a certain number of amino acids.
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Section 4 The Structure of Matter
Biochemical Compounds, continued
• DNA is a polymer that stores genetic information.
• DNA is a very long molecule made of carbon, hydrogen, oxygen, nitrogen, and phosphorus.
• It is in the form of paired strands.
• It has the shape of a twisted ladder known as a double helix.
• Most cells in your body have a copy of your genetic material in the form of chromosomes made of DNA.
• DNA is the information that the cell uses to make proteins.