Download Document

CPO Science
Foundations of Physics
Unit 9, Chapter 29
Unit 9: The Atom
Chapter 29 Chemical Reactions
 29.1 Chemistry
 29.2 Chemical Bonds
 29.3 Chemical Reactions
Chapter 29 Objectives
1. Classify matter as substances, homogeneous or
heterogeneous mixtures, or solutions.
2. Tell the difference between chemical change and
physical change.
3. Describe the types of chemical bonds and the role of
electrons in forming bonds between atoms.
4. Write and balance the chemical equation for a simple
reaction.
5. Explain how the terms acid, base, organic, and
solution relate to living systems.
6. Describe the role of photosynthesis in maintaining
life on Earth.
Chapter 29 Vocabulary Terms
















substance

mixture

physical change

compound

heterogeneous mixture 
solute

double bond

solubility

solvent

homogeneous mixture 
dissolve

Solution

polar molecule

chemical bond

alkali metal

noble gas

element
valence electrons
transition metal
balanced equation
pH
covalent bond
amino acid
acid
organic chemistry
ion
ionic bond
hydrocarbon
protein
activation energy
products
reactants














carbohydrate
reaction
exothermic reaction
refine
octane
halogen
photosynthesis
endothermic reaction
base
chemical change
cracking
petroleum
Lewis dot diagram
fat
29.1 Chemistry
Key Question:
What techniques are
used to separate
heterogeneous
mixtures?
*Students read Section 29.1
AFTER Investigation 29.1
29.1 Relationship between sciences
 Chemistry is the science
of how atoms and
elements create the world
we experience.
 Our world contains
millions of chemicals
made from the basic
elements and even more
interactions between
chemicals.
MATTER
MIXTURES
Homogeneous Heterogeneous
mixtures
mixtures
SUBSTANCES
Elements
Compounds
29.1 Physical Changes
 The concept of temperature and changes of phase
between solid, liquid, and gas are traditionally
considered part of chemistry, as are the gas laws.
 These kinds of changes in matter are called physical
changes, because matter changes physical form but
one substance does not change into a completely
different substance.
29.1 Chemical Changes
 Evidence of chemical change:
—
—
—
—
bubbling (formation of gas)
turning cloudy (formation of a new solid)
temperature change (heat or light released)
color change (formation of a new solid)
29.1 Solutions
 A solution is a mixture of two or more substances
that is homogeneous at the molecular level.
 The particles in a solution exist as individual
atoms, ions, or molecules.
 A solution is a mixture of solute
dissolved in a solvent.
 Solubility describes the
amount of solute that will
dissolve in a given amount of
solvent.
29.1 Solutions
 Several factors affect solubility:
—
—
—
—
chemical nature of the solvent
the volume of solute
temperature
solute particle size
 The solubility of solids in liquids usually rises with
temperature.
 Powders dissolve quickly because they have a
tremendous amount of surface area exposed to the
solvent.
29.2 Chemical Bonds
Key Question:
Why do atoms form
chemical bonds?
*Students read Section 29.2
AFTER Investigation 29.2
29.2 Chemical Bonds
 A chemical bond forms
when atoms exchange or
share electrons.
 Most of the properties of
substances come from
how they form chemical
bonds with other
substances.
29.2 Chemical Bonds
 Electrons that make bonds
are called valence electrons.
 Not all electrons in an atom
participate in making
chemical bonds.
 Only the electrons in the
highest unfilled energy level
make bonds.
29.2 Chemical Bonds
 Molecules of the chemical
benzene have six carbon
atoms and six hydrogen
atoms shaped in a ring.
 An atom can make one
chemical bond for each
valence electron.
 Bonds can also involve two
or more valence electrons.
29.2 Chemical Bonds
 Elements with the same number of valence
electrons are chemically similar.
 The same number of chemical bonds are made with
the same elements.
29.2 Chemical Bonds
 Atoms are most stable when they have either 2 or 8
valence electrons.
 The Lewis dot diagram shows the element symbol
surrounded by one to eight dots representing the
valence electrons.
29.2 Periodic Table and Valence
The periodic table arranges elements from left to right
by the number of valence electrons.
29.2 Chemical Bonds
 Most chemical bonds fall into two categories,
depending on whether the valence electrons are
transferred or shared.
 Electrons in an ionic bond are effectively
transferred from one atom to another.
 In a covalent bond the electrons are shared
between atoms.
29.2 Ionic bonds
 The ionic bonds in a salt
crystal (NaCl) come from
electrical attraction
between:
— negative chloride ions (Cl-)
— positive sodium ions (Na+)
29.2 Covalent bonds
 A diamond crystal is
made of pure carbon
connected by a strong
network of covalent
bonds.
 The hardness of
diamonds is due to the
fact that four covalent
bonds must be broken to
move each carbon atom.
29.2 pH
 When substances are dissolved in water they
divide into two categories called acids and bases.
 An acid creates a sour taste and can dissolve
reactive metals like zinc. Vinegar and lemon juice
are examples of acids.
 A base creates a bitter taste and tends to feel
slippery. Ammonia is an example of a base.
 The pH is scale that measures how acidic or basic
a solution is.
29.2 Acids
 Acid molecules include ionic bonds.
 When an acid dissolves in water, the ionic bond
breaks to create two ions- one is a hydronium ion.
 The strong chemical reactivity of the hydronium ion
(H3O+)is what results in the properties of acids.
29.2 Bases
 Bases have a strong attraction for hydrogen ions
(H+).
 When a base such as ammonia (NH3) dissolves in
water, the molecules of ammonia take a hydrogen
ion (proton) from water molecules and become
ammonium ions (NH4+).
 The pH is a measure of the concentration of H3O+
(acid) ions in a solution.
 The higher the pH, the stronger the base.
29.2 Organic Chemistry
 Organic chemistry is the
chemistry of carbon and its
compounds.
 The mass of your body is
mostly oxygen, carbon, and
hydrogen.
 Proteins, amino acids, fats
and carbohydrates are types
of carbon molecules found in
the body.
29.3 Chemical Reactions
Key Question:
How can you predict the
yield of a chemical
reaction?
*Students read Section 29.3
AFTER Investigation 29.3
29.3 Chemical Reactions
 In chemical reactions you start with reactants that
are combined into products.
 The reactants and products may include atoms,
molecules, and energy.
29.3 Chemical Reactions
 The formation of rust
from oxygen and iron is
an example of a
common chemical
reaction.
29.3 Chemical Reactions
 Chemical reactions proceed in two stages.
 First, the chemical bonds must be broken
between the atoms in the reactants.
 In the second stage, new bonds form between
atoms to make the products of the reaction.
29.3 Activation energy
 The energy needed to break chemical bonds in the
reactants is called the activation energy of the
reaction.
 A spark supplies the activation energy to start the
reaction between hydrogen and oxygen.
29.3 Activation energy
 A chemical equation is balanced when the
number of each type of atom is the same in
reactants and products.
29.3 Mass in chemical reactions
 A balanced chemical equation is like a recipe.
 The mass of the products must equal the mass of
the reactants.
 Counting molecules is not
practical so we usually
need the mass of
reactants and products of
a chemical reaction.
29.3 Calculating mass
1. Calculate the mass of each molecule or atom.
29.3 Calculating mass
2. Use a balanced equation to calculate mass of
reactants or products.
29.3 Photosynthesis
 The energy that supports life on Earth starts with
a reaction that takes energy from sunlight and
stores it as chemical bonds in molecules of
glucose.
 This reaction is called photosynthesis.
29.3 Photosynthesis
 Nearly all energy in living things can be traced to
this important reaction.
 Energy and oxygen are two useful products of
photosynthesis.
29.3 Photosynthesis
 A third crucial function of photosynthesis is to
remove carbon dioxide from the atmosphere.
 If too much carbon
dioxide is present, the
Earth cannot cool itself
by radiating energy into
space.
Application: Energy from Gasoline