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Chemistry Review
Chapter 2
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Outline
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Structure of Atoms
Isotopes
– Radioactive Isotopes
Electrons and Chemical Behavior
Chemical Bonds
– Ionic versus Covalent
Water Chemistry
– Hydrogen Bonding
pH
Functional groups
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Atoms
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All matter is composed of atoms.
– Protons (+) and neutrons (neutral) are
found on the atom’s nucleus, while
electrons (-) circle the nucleus.
 Atomic number - number of protons
 Atoms with the same atomic number
belong to the same element, and thus
have the same inherent properties.
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Atoms
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Atoms
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Mass refers to the amount of a substance.
Weight refers to the force exerted on a
substance by gravity.
Atomic mass of an atom refers to the sum of
the masses of protons and neutrons.
– measured in Daltons
What is atomic weight? Can it be determined
for a single atom? How is it determined?
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Isotopes
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Isotopes - Atoms of an element that possess
a different number of neutrons.
– Radioactive isotopes - Spontaneously
decay into elements of lower atomic
number.
 emit energy and/or subatomic particles
 Half-life refers to the amount of time
necessary to decay half the atoms of
a given sample.
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Isotopes
Carbon-12
6 Protons
6 Neutrons
6 Electrons
Carbon-13
6 Protons
7 Neutrons
6 Electrons
Carbon-14
6 Protons
8 Neutrons
6 Electrons
Electrons
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Atoms with the same number of protons as
electrons are electrically neutral.
– Ions - Atoms in which the number of
protons and electrons differ.
 Cation - Contains more protons than
electrons, and carries a positive charge.
 Anion - Contains fewer protons than
electrons, and carries a negative charge.
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Electrons and Atomic Behavior
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Orbital refers to the area around a nucleus
where an electron is most likely found.
– Chemical behavior of an atom is
determined by the number and
arrangement of its orbitals.
 Electrons are attracted to the positively
charged nucleus, thus it takes energy to
hold electrons in place.
 potential energy of position
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Atomic Energy Levels
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Electrons and Atomic Behavior
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During some chemical reactions, electrons
are transferred between atoms, while still
retaining their energy of position.
– Oxidation - loss of an electron
– Reduction - gain of an electron
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Kinds of Atoms
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Ninety-two naturally occurring elements
– Periodic table arranged by grouping atoms
based on valence electrons (electrons in
the outer energy levels).
 Octet rule
 Inert atoms have outer level filled.
 Reactive atoms do not have outer
level filled.
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Periodic Table of the Elements
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Chemical Bonds
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A molecule refers to a group of atoms held
together by energy in a stable association.
– Compound is composed of two or more
different types of atoms.
 Atoms in a molecule are joined by
chemical bonds.
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Chemical Bonds
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Ionic bonds are formed because ions of
opposite charge attract one another.
– table salt
Covalent bonds are formed when two or more
atoms share pairs of valence electrons.
– Strength depends on number of shared
electrons.
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Chemical Reactions
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A chemical reaction occurs during the
formation or breaking of chemical bonds.
– Reactants refer to original molecules.
– Products refer to resultant molecules.
Chemical reactions can be influenced by:
– temperature
– concentration of reactants and products
– catalysts
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Water Chemistry
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Water consists of an oxygen atom bound to
two hydrogen atoms by two single covalent
bonds.
– stable atom with no electrical charge
 most outstanding property is its ability to
form weak chemical associations
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Hydrogen Bonding
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In a water molecule, both the oxygen and
hydrogen atoms attract the shared electrons
in the covalent bond (electronegativity).
– Oxygen atom is more electronegative than
the hydrogen atoms.
 distinct ends with partial charge (polar)
 hydrogen bonds
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Water Chemistry
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Water clings to polar molecules.
– Cohesion refers to attraction to other
water molecules.
 responsible for surface tension
– Adhesion refers to attraction to other
substances.
 Water is adhesive to any substance with
which it can form hydrogen bonds.
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Water Chemistry
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Water stores heat.
– High specific heat
 Amount of heat that must be absorbed
or expended to change the temperature
of 1g of a substance 1o C.
– High heat of vaporization
 Amount of energy required to change 1g
of liquid water into a gas (586 calories).
 large number of hydrogen bonds
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Water as a Solvent
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Water is an effective solvent as it can form
hydrogen bonds.
– Water clings to polar molecules causing
them to be soluble in water.
 Hydrophilic - attracted to water
– Water tends to exclude nonpolar
molecules.
 Hydrophobic - repelled by water
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pH
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pH scale expresses hydrogen ion (H+)
concentration in a solution.
– logarithmic scale ranging from 0-14
 neutral = 7
Acids dissociate in water to increase the
concentration of H+.
– pH values lower than 7
Bases combine with H+ ions when dissolved in
water, thus decreasing H+ concentration.
– pH values above 7
Buffers act as a reservoir for hydrogen ions,
donating or removing them from solution as
necessary.
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pH
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The pH scale
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The pH scale is the concentration of
hydrogen ions in a given substance.
 
pH   log H

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Definitions of Acids and Bases
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An acid is a substance that breaks
into H   ions in an aqueous
solution.
A Base (alkaline) is a substance
that breaks into OH   ions in an
aqueous solution.
Note: aqueous solution is any
solution where H 2 O is the
solvent.
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Characteristics Of Acids
Acids can be characterized by:
1.
A sour taste.
2.
It turns blue litmus paper red
3.
It tastes sour. Try drinking lemon juice (citric acid)
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Characteristics of Bases
A Base is characterized by:
1.
A bitter taste. (Milk of Magnesia)
2.
It feels slippery. (Soapy Water)
3.
It turns Red Litmus Blue.
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Test Your Knowledge
What is the range of an ACID on the pH
scale?
Ans: 0-7
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What is the range of a BASE and what is
another name for a BASE?
Ans: 7-14, Alkaline
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Functional
Group
Structural
Formula
Hydroxyl
OH
Carbonyl
C
O
O
Carboxyl
C
OH
H
Amino
N
H
Sulfhydryl
S H
O–
Phosphate
Methyl
Example
H H
H C C OH
H H
Ethanol
H O
H C C H
H
Acetaldehyde
H
O
H C C
OH
H
Acetic acid
O H
H
HO C C N
CH3 H
Alanine
H H
HO C C S H
H H
b-mercaptoethanol
OH OH H
O
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O P O– H C C C O P O–
H H H
O–
O
Glycerol phosphate
H
O O H
•
–
O C C C H
C H
•
H
H
Pyruvate
Functional Groups tend to act
as units during chemical
reactions and confer specific
chemical properties on the
molecules that posses them.
– Ex. amino groups make a
molecule more basic while
carboxyl groups make a
molecule more acidic.
Functional groups have
definite chemical properties
that they retain no matter
where they occur.
– The hydroxyl group is
polar because oxygen
draws electrons toward
itself
A bunch more on this later!!
Eventually you will have to
memorize this (and more!)
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