Chemistry Midterm Review

Units 1 & 2Science 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 3Matter and Change

States of Matter

The physical forms of matter, either solid, liquid, or gas, are called the states of matter.

Properties 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.

States of Matter

Properties 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.

Physical Properties

• Let’s play 20 Questions!

QUESTIONS QUESTIONS

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19 20

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 4Atomic Theory

Greek Philosophers

Early Ideas About Matter

Table 1 Ancient Greek Ideas About MatterPhilosopher Ideas

Democritus(460–370 B.C.) 

  

•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.

Aristotle(384–322 B.C.)

 

 

• Empty space cannot exist.

• Matter is made of earth, fire, air, and water.

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.

Early Ideas About Matter

Table 2 Dalton’s Atomic TheoryScientist IdeasDalton(1766–1844) 

   

• 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.

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

• Steps1. Convert percentages into decimals2. Multiple decimal value by atomic mass3. Add these amounts together to find the mass

Types of RadiationAlpha 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 by He or α.

• Thus, showing mass is conserved in a nuclear equation.

2

4

Unstable Nuclei and Radioactive Decay

Types of RadiationBeta 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 RadiationGamma 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

principleazimuthal

# of e- in that shell

Orbital Notation

H1s

1s 2s 2p

F