Chemistry Midterm Review
Units 1 & 2
Science Review and Scientific Measurement
A Systematic Approach
• An observation is the act of gathering information.
• Qualitative data is obtained through observations that describe color, smell, shape, or some
other physical characteristic that is related to the 5 senses.
• Quantitative data is obtained from numerical observations that describe how much, how little,
how big, or how fast.
• A hypothesis is a tentative explanation for what has been observed.
• An experiment is a set of controlled observations that test the hypothesis.
A Systematic Approach
• A variable is a quantity or condition that can have more than one value.
• An independent variable is the variable you plan to change.
• The dependent variable is the variable that changes in value in response to a change in the
independent variable
• EXAMPLE: If you were trying to determine if temperature affects bacterial
growth, you would expose different petri dishes of the same bacteria to
different temperatures
• Temperature is your independent variable
• Bacteria growth is your dependent variable
Variables Song (Creepy guy)
Density
• “The degree of compactness of a substance
• Density = Mass / Volume
Accuracy vs Precision
• Accuracy refers to how close
a measured value is to an
accepted value.
• Precision refers to how close
a series of measurements are
to one another.
Sig Fig Rules
Significant Figures
Rules for significant figures:
• Rule 1: Nonzero numbers are always significant.
• Rule 2: Zeros between nonzero numbers are always
significant.
• Rule 3: All final zeros to the right of the decimal are significant.
• Rule 4: Placeholder zeros are not significant. To remove
placeholder zeros, rewrite the number in scientific notation.
• Rule 5: Counting numbers and defined constants have an
infinite number of significant figures.
Rounding
Rounding Numbers
Addition and subtraction
• Round the answer to the same number of decimal places as the
original measurement with the fewest decimal places.
Multiplication and division
• Round the answer to the same number of significant figures as
the original measurement with the fewest significant figures.
Units 3
Matter and Change
States of Matter
The physical forms of matter, either solid, liquid, or gas, are called the states of
matter.
Solids are a form of matter that have their own definite
shape and volume.
Liquids are a form of matter that have a definite
volume but take the shape of the container.
Properties of Matter
States of Matter
Gases have no definite shape or volume. They expand
to fill their container.
Vapor refers to the gaseous state of a substance that is
a solid or liquid at room temperature.
Properties of Matter
Physical Properties
• Let’s play 20 Questions!
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Physical Properties of Matter
A physical property is a characteristic that can be observed or measured
without changing the sample’s composition.
-ex: viscosity, hardness, density, malleability, melting point, boiling point,
etc.
Properties of Matter
Physical Properties of Matter
Extensive properties, such as mass, length, and volume, are dependent on the
amount of substance present.
Intensive properties, such as density, are dependent on the what the substance
is not how much there is.
Properties of Matter
Chemical Properties of Matter
The ability of a substance to combine with or change into one or more other
substances is called a chemical property. Examples include:
• Iron forming rust
• Copper turning green in the air
• Flammability
• Reactivity
Properties of Matter
Physical Changes
A change that alters a substance without changing its composition is known as a
physical change. A phase change is a transition of matter from one state to
another. Boiling, freezing, melting, and condensing all describe phase changes in
chemistry.
Changes in Matter
Phase Changes
• Phase change- reversible
physical change that occurs
when a substance changes
from one state of matter to
another.
• Melting, freezing,
vaporization, condensation,
sublimation, and deposition
are the six common phase
changes.
Chemical Changes
A change that involves one or more substances turning into new substances is
called a chemical change. Decomposing, rusting, exploding, burning, or
oxidizing are all terms that describe chemical changes.
Changes in Matter
Law of Conservation of Mass
The law of conservation of mass states that mass is neither created nor
destroyed in a chemical reaction, it is conserved. The mass of the reactants
equals the mass of the products.
massreactants = massproducts
Changes in Matter
Mixtures
A mixture is a combination of two or more pure substances in which each
pure substance retains its individual chemical properties.
A homogenous mixture is a mixture where the composition is constant
throughout. Homogeneous mixtures are also called solutions.
A heterogeneous mixture is a mixture where the individual substances
remain distinct.
Mixtures of Matter
Separating Mixtures
Filtration is a technique that uses a porous barrier to separate a solid from
a liquid in a heterogeneous mixture.
Distillation is a separation technique for homogeneous mixtures that is
based on the differences in boiling points of substances.
Crystallization is a separation technique for homogenous mixtures that
results in the formation of pure solid particles from a solution containing the
dissolved substance.
Mixtures of Matter
Separating Mixtures
Sublimation is the process of a solid changing directly to a gas, which can
be used to separate mixtures of solids when one sublimates and the other
does not.
Chromatography is a technique that separates the components of a
mixture on the basis of tendency of each to travel across the surface of
another material.
Mixtures of Matter
Elements
An element is a pure substance that cannot be separated into simpler
substances by physical or chemical means.
• 92 elements occur naturally on Earth.
• Each element has a unique name and a one, two, or three-letter symbol.
• The periodic table organizes the elements into a grid of horizontal rows
called periods and vertical columns called groups.
• Elements in the same group have similar chemical and physical
properties.
• The table is called periodic because the pattern of similar properties
repeats from period to period.
Elements and Compounds
Compounds
A compound is a made up of two or more elements combined chemically.
• Most of the matter in the universe exists as compounds.
• Table salt, NaCl, and water, H2O, are compounds.
• Unlike elements, compounds can be broken into smaller components by
chemical means.
Elements and Compounds
Units 4
Atomic Theory
Greek Philosophers
Table 1
Ancient Greek Ideas About Matter
Philosopher
Democritus
(460–370 B.C.)
Aristotle
(384–322 B.C.)
Ideas
•
Matter is composed of atoms, which move through empty space.
•
Atoms are solid, homogeneous, indestructible, and indivisible.
•
Different kinds of atoms have different sizes and shapes.
•
Size, shape, and movement of atoms determine the properties
of matter.
•
Empty space cannot exist.
•
Matter is made of earth, fire, air, and water.
Early Ideas About Matter
Dalton’s Atomic Theory
• John Dalton revived the idea of the atom in the early 1800s based on
numerous chemical reactions.
• Dalton’s atomic theory easily explained conservation of mass in a reaction as
the result of the combination, separation, or rearrangement of atoms.
Table 2
Dalton’s Atomic Theory
Scientist
Dalton
(1766–1844)
Ideas
•
Matter is composed of extremely small particles called atoms.
•
Atoms are indivisible and indestructible.
•
Atoms of a given element are identical in size, mass, and chemical
properties.
•
Atoms of a specific element are different from those of another element.
•
Different atoms combine in simple whole-number ratios to form
compounds.
•
In a chemical reaction, atoms are separated, combined or rearranged.
Early Ideas About Matter
The Electron
• J.J. Thomson measured the effects of both magnetic and electric fields on the
cathode ray to determine the charge-to-mass ratio of a charged particle, then
compared it to known values.
• The mass of the charged particle was much less than a hydrogen atom, then
the lightest known atom.
• Thomson received the Nobel Prize in 1906 for identifying the first subatomic
particle—the electron.
Defining the Atom
The Electron
• Matter is neutral. You know that matter is neutral from everyday experiences.
You do not receive an electric shock (except under certain conditions) when
you touch an object.
• If electrons are negative, then how is matter, which is made up of electrons,
neutral?
• J.J. Thomson proposed a model of the atom to answer this question.
Defining the Atom
The Electron
• J.J. Thomson's plum pudding model of the atom states that the atom is a
uniform, positively charged sphere containing electrons.
Defining the Atom
The Nucleus
• In 1911, Ernest Rutherford studied how positively charged alpha particles
interacted with solid matter.
• By aiming the particles at a thin sheet of gold foil, Rutherford expected the
paths of the alpha particles to be only slightly altered by a collision with an
electron.
Defining the Atom
The Nucleus
• Although most of the alpha
particles went through the
gold foil, a few of them
bounced back, some at
large angles.
Defining the Atom
The Nucleus
• Rutherford concluded that atoms are
mostly empty space.
• Almost all of the atom's positive
charge and almost all of its mass is
contained in a dense region in the
center of the atom called the nucleus.
• Electrons are held within the atom by
their attraction to the positively
charged nucleus.
• The repulsive force between the
positively charged nucleus and
positive alpha particles caused the
deflections.
Defining the Atom
Atomic Number
• Each element contains a unique positive charge in their nucleus.
• The number of protons in the nucleus of an atom identifies the element
and is known as the element’s atomic number.
How Atoms Differ
Subatomic particle
Location
Charge
Key feature
Proton
Nucleus
Positive
Atomic identity
Neutron
Nucleus
Neutral
Isotopes
Electron
Electron cloud
Negative
Charge
• Calculating the mass of an element
• The atomic mass is not really a whole number
• The atomic mass is the mass of an atom expressed in
atomic mass units
• Hydrogen has an atomic mass of 1.000797
• Where does this number come from?
• Calculating the mass of an element
• There are two different isotopes of copper
• Copper-63 (69% of earth’s copper is this type)
• Copper-65 (31% of earth’s copper is this type
• Steps
1. Convert percentages into decimals
2. Multiple decimal value by atomic mass
3. Add these amounts together to find the mass
Types of Radiation
Alpha Radiation
• Alpha radiation is made up of positively charged particles called alpha
particles.
• Each alpha particle contains two protons and two neutrons and has a 2+
charge.
• The figure shown below is a nuclear equation showing the radioactive
decay of radium-226 to radon-222.
• An alpha
particle is equivalent to a helium-4 nucleus and is represented
4
2
by He
or α.
• Thus, showing mass is conserved in a nuclear equation.
Unstable Nuclei and Radioactive Decay
Types of Radiation
Beta Radiation
• Beta radiation is radiation that has a negative charge and emits beta
particles.
• Each beta particle is an electron with a 1– charge.
• During Beta decay, a neutron is converted to a proton and an electron.
The electron is emitted and the proton stays in the nucleus.
Unstable Nuclei and Radioactive Decay
Types of Radiation
Gamma Radiation
• Gamma rays are high-energy radiation with no mass and are neutral.
• They usually accompany alpha and beta radiation.
• Gamma rays account for most of the energy lost during radioactive
decay.
Unstable Nuclei and Radioactive Decay
Electron Configuration
• Electron Configuration - a representation of the arrangement of electrons in an atom
Electron Configuration
• Examples of electron Configuration
• 1. Li 1s22s1
• 2. C 1s22s22p6
principle
azimuthal
# of e- in that
shell
Orbital Notation
H
1s
F
1s
2s
2p