Chemistry

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Chemistry

• 1.D Defining Chemistry

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What is Chemistry?

• Chemistry is the study of the composition,
  structure, and properties of matter, the
  processes that matter undergoes, and the energy
  changes that accompany these processes.

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Matter and Its Properties

• Everything around you is made up of matter, but
  what exactly is matter?
• Matter is defined as anything that has mass and
  takes up space.
• Mass the measure of the amount of matter
• Volume the amount of three dimensional space an
  object occupies.

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Basic Building Blocks of Matter

• Matter comes in many forms.
• But the fundamental building blocks of all matter
  are atoms.

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• An atom is the smallest unit of an element that
  maintains the identity of that element.
• An element is a pure substance that cannot be
  broken down into simpler, stable substances and
  is made of only one type of atom.
• Is water an element?

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• A compound is a substance that can be broken down
  into simple stable substances. Each compound is
  made from atoms of two or more elements that are
  chemically bonded.
• Water H2O
• Molecule is the smallest unit of an element or
  compound that retains all of the properties of
  that element or compound.
• H2O is a water molecule while H24O12 is still
  water.

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Properties and Changes of Matter

• Every substance, whether it is an element or a
  compound, has characteristic properties. Most
  chemical investigations are related to or depend
  on the properties of substances.
• Many elements are classified as metals. A well
  known property of metals is that they are
  conductors.
• Comparisons of several of these properties can
  help identify what an unknown substance is.

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Intensive and Extensive Properties

• Extensive properties depend on the amount of
  matter that is present. (volume, mass, amount of
  energy in a substance)
• Intensive properties do not depend on the amount
  of matter present. (boiling point, melting point,
  density)
• Intensive properties are the same for a given
  substance regardless of how much of the substance
  is present.

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Physical Properties and Physical Changes

• A physical property is a characteristic that can
  be observed or measured without changing the
  identity of the substance.
• Physical properties describe the substance
  itself. (melting point, boiling point)
• Physical change is a change in a substance that
  does not involve a change in the identity of the
  substance. (cutting, melting, boiling, distilling)

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Change of State

• Melting and boiling are part of an important
  class of physical changes called changes of
  state.
• A change of state is a physical change of a
  substance from one state to another.
• The three common state of matter are solid,
  liquid, and gas.

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Solid

• A solid has a definite volume and a definite
  shape.
• The particles in a solid are packed together in
  relatively fixed positions. The particles are
  held together by the strong attractive forces
  between them, and only vibrate about fixed
  points.

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Liquid

• A liquid has a definite volume but an indefinite
  shape.
• The particles in a liquid move more rapidly than
  those in a solid. This causes them to overcome
  temporarily the strong attractive forces between
  them, allowing the liquid to flow.

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Gas

• A gas has neither definite volume nor definite
  shape.
• A given quantity of gas will expand to fill any
  size container. All gases are composed of
  particles that move very rapidly and at great
  distances from one another compared with the
  particles of liquid and solids.

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Plasma

• Plasma is a high-temperature physical state of
  matter in which atoms lose most of their
  electrons. Plasma can be found in fluorescent
  bulbs.

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Change of State

• Melting is when a solid turns into a liquid.
• Boiling is the change from a liquid to a gas.
• Freezing is the change from a liquid to a solid.
• A change of state does not affect the identity of
  the substance.

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Chemical Properties and Chemical Change

• A chemical property relates to a substances
  ability to undergo changes that transform it into
  different substances. Chemical properties are
  easiest to see when substances react to form new
  substances.
• The ability of charcoal (carbon) to burn in air
  is a chemical property.
• Burning charcoal charcoal (carbon) combines with
  oxygen in the air to become carbon dioxide gas CO2

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• Iron will rust when combined with air.

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Chemical Change or Chemical Reaction

• A change in which one or more substances are
  converted into different substances is called a
  chemical change or a chemical reaction.
  (fermentation)
• The substances that react in a chemical change
  are called the reactants.
• The substances that are formed by the chemical
  change are called the products.

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Chemical Reaction

• In the case of burning charcoal, carbon and
  oxygen are the reactants and the carbon dioxide
  is the product.
• Carbon plus oxygen yields (or forms) carbon
  dioxide
• carbon oxygen carbon dioxide
• carbon C oxygen O2
• C O2 CO2

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• In a chemical reaction we saw that two elements
  or compounds came together to form a new product.
  However, one compound can break down into two
  elements in a process known as decomposition.
• Water H2O
• H2O H2 O
• Water breaks down to form hydrogen and oxygen

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• Chemical changes do not change the amount of
  total matter present. There is the same amount of
  matter at the beginning and end of a chemical
  reaction, therefore the mass remains the same.
  This is the law of conservation of matter.

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Law of Conservation of Mass

• 3C6H1206 3C6 18H20
• If 120 grams of sugar are broken down into 103
  grams of water, how many grams of carbon are
  produced?

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Energy and Changes in Matter

• When physical or chemical changes occur, energy
  is always involved.
• The energy can take several different forms, such
  as heat or light.
• Sometimes heat provides enough energy to cause a
  chemical change, such as boiling water to make
  hydrogen gas and oxygen gas.

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• Accounting for all the energy present before and
  after a change is not a simple process.
• However, scientists are confident that the total
  amount of energy remains the same.
• Although energy can be absorbed or released in a
  change, it is not destroyed or created. It simply
  assumes a different form. This is the law of
  conservation of energy.

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Endothermic Reaction

• An endothermic reaction is a reaction in which
  energy is absorbed during the reaction.
• A temperature drop is one way to distinguish an
  endothermic reaction.

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Exothermic Reaction

• An exothermic reaction is a reaction in which
  energy is released during the reaction.
• Many chemical reactions release energy in the
  form of light, sound, or heat.

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Specific Heat

• The quantity of energy transferred as heat during
  a temperature change depends on the nature of the
  material changing temperature, the mass of the
  material changing temperature, and the size of
  the temperature change.
• One gram of iron heated to 500C and cooled to
  50C transfers 22.5 J of energy. But one gram of
  silver transfers 11.8 J of energy under the same
  conditions.
• A quantity called specific heat can be used to
  compare heat absorption capacities for different
  materials.

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Specific Heat (cp)

• Specific heat is the amount of energy required to
  raise the temperature of one gram of a substance
  by one degree Celsius or one kelvin.
• Specific heat derived unit J/gK or J/gC or
  cal/gC
• To find specific heat cp q/(m?T)
• q is the energy lost of gained
• m is the mass of the sample
• ?T represents the difference between the initial
  and final temperatures. ?T T(final)
  T(initial) this can cause you to have a
  negative sign and this indicates that you are
  losing heat or energy

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When finding q in specific heat..

• If you have a ?T that is negative, when finding
  the q (energy) you could end up with a negative
  number. You do not need to write the negative
  sign if the question asks you how much energy is
  lost or gained. If it just asked for the change
  in energy, you must write the negative sign
  because it is not already understood in the
  problem.

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• For those changes which REQUIRE energy
• solid energy --gt liquid     Q is positive
• liquid energy --gt gas      Q is positive
• You have to ADD energy to melt solid ice
• You have to ADD energy to vaporize the liquid
  water.

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• for those changes which GIVE OFF energy
• gas --gt  liquid energy    Q is negative
• liquid --gt solid energy   Q is negative
• When gaseous steam condenses on your hand, OUCH! 
  Energy is being given off by the steam to your
  hand.
• When liquid water freezes, it MUST give off
  energy to the surroundings.

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Sample Problem for Specific Heat

• 1. A 4.0 g sample of glass was heated from 274K
  to 314K, a temperature increase of 40 K, and was
  found to have absorbed 32 J of energy as
  heat.
• a. What is the specific heat of this type of
  glass?
• B. How much energy will the same glass sample
  gain when it is heated from 314 to 344K?

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Sample Problems for Specific Heat

• 2. Determine the specific heat of a material if a
  35g sample absorbed 96J as it was heated from
  293K to 313K.
• 3. A piece of copper alloy with a mass of 85.0g
  is heated from 30C to 45C. In the process, it
  absorbs 523J of energy as heat.
• a. What is the specific heat of the copper
  alloy?
• b. How much energy will the same sample lose if
  it is cooled from 45C to 25C?

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Sample Problems for Specific Heat

• 4. Specific heat of gold is .129J/gC. How much
  energy is needed to raise the temperature of 5.0g
  of gold by 25C?
• 5. Energy in the amount of 420J is added to a 35g
  sample of water at a temperature of 10C. What
  will be the final temperature of the water?

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Classification of Matter

• Matter exists in an enormous variety of forms.
  Any sample of matter can be classified either as
  a pure substance or as a mixture.
• Pure substances have the same composition
  throughout and does not vary from sample to
  sample. A pure substance can be an element of a
  compound.
• Mixtures, in contrast, contain more than one
  substance. They can vary in composition and
  properties from sample to sample and sometimes
  from one part of a sample to another part of the
  same sample.

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Mixtures

• You deal with mixtures everyday. Nearly every
  object around you, including most things you eat
  and drink and even the air you breathe, is a
  mixture.
• A mixture is a blend of two or more kinds of
  matter, each of which retains its own identity
  and properties.
• The parts, or components, of a mixture are simply
  mixed together physically and can usually be
  separated.

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• As a result, the properties of a mixture are a
  combination of the properties of its components.
• Because mixtures can contain various amounts of
  different substances, a mixtures composition
  must be specified. This is often done by mass or
  by volume. For example, a mixture might be 5
  sodium chloride and 95 water by mass.

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• Some mixtures are uniform in composition.
• These mixtures are said to be homogeneous. They
  have the same proportions of components
  throughout.
• Homogeneous mixtures are also called solutions.
  A salt-water solution is an example of such a
  mixture.

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• Heterogeneous mixtures are not uniform
  throughout. In a mixture of clay and water,
  heavier clay particles concentrate near the
  bottom of the container.

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Methods of Separating Mixtures

• Filtration Using filter paper to separate the
  components of a mixture.

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• Centrifuge A centrifuge can be used to separate
  some solid-liquid mixtures, such as blood.

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• Paper chromatography Often used to separate
  mixtures of dyes or pigments because the
  different substances move at different rates on
  the paper.

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• Titration the controlled addition and
  measurement of the amount of a solution of known
  concentration required to react completely with a
  measured amount of a solution of unknown
  concentration.

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• Distillation components of a mixture are
  separated on the basis of boiling point, by
  condensation of vapor in a fractionating column.

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Pure Substances

• A pure substance has a fixed composition and
  differs from a mixture in the following ways
• 1. Every sample of a given substance has exactly
  the same characteristic properties.
• 2. Every sample of a given pure substance has
  exactly the same composition.

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• Pure substances are either compounds or elements.
  A compound can be decomposed, or broken down,
  into two or more simpler compounds or elements by
  chemical change.
• Sucrose (sugar) C6H12O6 Under intense heating,
  sucrose breaks down to produce carbon and water.

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Laboratory Chemicals and Purity

• The chemicals in the laboratory are generally
  treated as if they are pure. However all
  chemicals have some impurities.
• The purity ranking of the grades can vary where
  agencies differ in their standards.

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Introduction to the Periodic Table

• Each small square on the periodic table shows the
  symbol for the element and the atomic number.

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Groups or Families

• These are the vertical columns on the periodic
  table.
• Each group contains elements with similar
  properties

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Periods

• The horizontal rows of elements in the periodic
  table. Elements across a period change regularly
  in their physical and chemical properties.
  However, elements closer together in a period
  tend to be more similar than those spread farther
  apart.

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Metals, Nonmetals and Metalloids

• The periodic table in organized in these three
  particular groupings. Metals are found on the
  left side of the staircase. Nonmetals are found
  on the right side of the staircase.
• Metalloids make up the staircase and have
  properties intermediate between metals and
  nonmetals.

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Specific Group Names

• Alkali metals Group 1 (hydrogen is the
  exception)
• Alkaline earth metals Group 2
• Transition metals Groups 3 12
• Halogens Group 17
• Noble (rare) gases Group 18