Transcript 9 Attractive Forces in Compounds GOB Structures

6.9 Attractive Forces in Compounds
The protein shape is
stabilized by attractive forces
between functional groups of
side chains (R groups) on
the amino acids, causing it to
twist and bend into a specific
three-dimensional shape.
Learning Goal Describe the
attractive forces between
ions, polar covalent
molecules, and nonpolar
covalent molecules.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Dipole-Dipole, Hydrogen Bonds
In covalent compounds, polar molecules
• exert attractive forces called dipole-dipole attractions.
• form strong dipole attractions called hydrogen bonds
between hydrogen atoms bonded to F, O, or N, and a lone pair on
F, O, or N.
Hydrogen bonds are the strongest force between molecules and play
a major role in the shape of DNA.
Core Chemistry Skill Identifying Attractive Forces
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Dispersion Forces
Dispersion forces are
• weak attractions between nonpolar molecules.
• caused by temporary dipoles that develop when molecules
bump into each other.
• weak but make it possible for nonpolar molecules to form
liquids and solids.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Melting Points and Attractive Forces
Melting points of compounds
• are related to the strength of attractive forces
between molecules or compounds.
• are lower due to weak forces such as
dispersion forces.
• are higher due to stronger attractive forces such as
hydrogen bonding.
• are highest in ionic compounds due to the strong
attractive forces between ions in the compound.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Melting Points and Attractive Forces
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Comparison of Bonding and
Attractive Forces
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
Identify the main type of attractive forces that are
present in liquids of the following compounds:
ionic bonds, dipole-dipole, hydrogen bonds, or
dispersion forces.
A. NCl3
B. H2O
C. Br-Br
D. KCl
E. NH3
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
Identify the main type of attractive forces that are
present in liquids of the following compounds:
ionic bonds, dipole-dipole, hydrogen bonds, or
dispersion forces.
A. NCl3
dipole-dipole forces
B. H2O
hydrogen bonds
C. Br-Br
dispersion forces
D. KCl
ionic bonds
E. NH3
hydrogen bonds
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Chemistry Link to Health: Attractive Forces,
Proteins
Proteins are biological molecules with many
different functions. They are needed for
• structural components such as cartilage,
muscles, hair.
• the formation of enzymes that regulate
biological reactions.
• myoglobin and hemoglobin, which transport
oxygen in blood and muscle.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Chemistry Link to Health: Attractive Forces,
Proteins
Proteins are composed of building blocks called amino acids. Every
amino acid has a central carbon atom bonded to
• an –NH3+, from an amine.
• a –COO−, from a carboxylic acid.
• an H atom.
• an R group, which is unique for each amino acid.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Chemistry Link to Health: Attractive Forces,
Proteins
Several amino acids have R
groups or side chains that contain
• an amide group, –CONH2.
• a hydroxyl, – OH, group.
• a carboxyl, –COOH, group
ionized as carboxylate, –COO−.
• an amine, –NH2, group ionized
as ammonium, –NH3+.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Chemistry Link to Health: Attractive Forces,
Proteins
The primary structure of a protein is its sequence of amino
acids. It is the sequence of amino acids that determines the
protein’s function.
Amino acids in a protein are linked by a peptide bond
between the COO− of one amino acid and the –NH3+ of the
next amino acid.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Chemistry Link to Health: Attractive Forces,
Proteins
Proteins have a higher
level of structure that is
determined by the
attractive forces between
the amino acids.
When hydrogen bonds
form between a hydrogen
atom in an N—H group and
the oxygen of the C═O
group, the protein forms an
alpha helix.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
H-bonds can form between the –OH of
serine and the –NH2 of asparagine.
© 2016 Pearson Education, Inc.
Chemistry Link to Health: Attractive Forces,
Proteins
Hydrogen bonds can
also form between
the polar side chains
of the amino acids
on the outside of the
protein and the –OH
and –H of polar
water molecules in
the external aqueous
environment.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
Attractive forces hold the protein in a
specific shape.
© 2016 Pearson Education, Inc.
Concept Map
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.