Chapter 8 lesson 1 Electrons and energy levels by pptfiles


									           Chapter 8 lesson 1
       Electrons and energy levels

By Miss Catie Brumit
   & Mrs. Shaw
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Re            The periodic table
• The periodic table has 115 blocks- one for each known

• Each block has the basic properties of the element like
  its state of matter at room temperature and its atomic

• The atomic number is the number of protons in an atom
  of each element.

• Each block also has an elements atomic mass or the
  average mass of all the isotopes of that element.
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Re          Periods and Groups
• You can learn about the elements on the periodic
  table based on its location.
• The elements are organized into periods (rows) and
  groups (columns)
• The periodic table lists the elements in order of
  atomic number increasing left to right across a
• Elements in the each group have similar chemical
  properties and react with other elements in similar
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     Metals, Non-metals, & Metalloids
• The three main elements on the periodic table are metals non
  metals and metalloids
• Except hydrogen, all the elements on the left side of the table
  are metals.
• Non metals are on the right side and Metalloids are the stair
  step or zigzag region between metals and nonmetals.

        Metals                 Metalloids              Nonmetals
                 Atoms bond
• A chemical bond is a force that holds
  two or more atoms together. These
  chemical bonds hold compounds
• In nature, pure elements are rare. Instead, atoms of
  different elements combine to form compounds.
• Compounds make up most matter, even in living and
  non living things.
 Electron number & arrangement
• The exact location of an electron cannot be
  determined because the electrons are always
  in motion around the nucleus. However the
  electrons in each of the elements is usually in
  a certain area of space around the nucleus.
• Some of the electrons are closer to the
  nucleus while some are farther away
            Electrons and energy
• Different electrons in an atom have different amounts of
  energy. The distance that the electron moves around the
  nucleus corresponds with its level of energy.

• Electrons that are closest to the nucleus have the least
  amount of energy. Electrons farthest from the nucleus have
  the most amount of energy.

• Only two electrons can be in the lowest energy level. But the
  second energy level can hold up to 8.
                          Lewis Dot Diagram of
                          Carbon showing only
Bohr Model of electrons   the valence electrons
          Electrons and bonding
• Think about having two magnets. The closer they are to each
  other the stronger the attraction is. There is a similar
  attraction between the negatively charged electrons and the
  positively charged nucleus.
• The outermost electrons (valence electrons) can be
  attracted to the nucleus of other atoms. This attraction is
  what causes a chemical bond.
            Let’s practice . . .
1. Where are the electrons with the most
   energy found in an atom?

2. How many electrons can the first shell hold?
   the second shell?

3. What causes one atom to be attracted to
       Let’s practice . . . Answers 
1. Where are the electrons with the most energy
   found in an atom? The electrons with the most
   energy are found farthest from the nucleus
2. How many electrons can the first shell hold?
   the second shell? The first shell holds 2 and the
   second shell holds 8
3. What causes one atom to be attracted to
   another? The negative charge of the valence
   electrons in one atom are attracted to the
   positive charge of a nucleus in another atom.
           Valence electrons 1
• The outer most electrons are the only electrons
  involved in chemical bonding.
• A valance electron is an outermost electron of an
  atom that participates in chemical bonding. Valence
  electrons have the most energy out of all the
  electrons in an atom.
• The number of valence electrons in each atom of an
  element can help determine the type and the
  number of bonds It can form.
Periods      •Each row is called a “period”
             •The elements in each period (row)
             have the same number of shells

                            1st Period = 1 Shell

                            2nd Period = 2 Shells
                              3rd Period = 3 Shells

                            4th Period = 4 Shells

Groups                          Group 8 = 8 electrons

Group 1 = 1 electron
                                         Except for He, it has 2
    Group 2 = 2 electrons                electrons

                                  •Each column is
                3, 4, 5, 6, 7     called a “group”

                                  •Each element in a
                                  group has the same
                                  number of electrons
                                  in their outer orbital,
                                  also known as

                                  •The electrons in the outer
                                  shell are called “valence
Transition Metals

                       •Transition Metals
                       have slightly
                       different rules for
                       shells and
                       valence electrons.

                       •This is
                       something you
                       will learn about in
                       High School
            Electron dot diagrams
• The electron dot diagram is a model that represents valence
  electrons in an atom as dots around the element’s chemical
  symbol. They help predict how an atom will bond with
  other atoms.

• Dots representing valence electrons, are placed one-by-one
  on each side of an element’s chemical symbol until all the
  dots are used. Some dots will be paired up; others will not.
  The number of unpaired dots is often the number of bonds
  an atom can form.
Practice with Electron Dot Diagrams
1. How many valence electrons does each element have?
2. How many bonds can each element form?

  1.Hydrogen     Valence:             Bonds:

  2. Neon         Valence:            Bonds:

  3. Calcium      Valence:            Bonds:

  4. Sulfur       Valence:            Bonds:

  5. Aluminum     Valence:            Bonds:
Practice with Electron Dot Diagrams
1. How many valence electrons does each element have?
2. How many bonds can each element form?

  1.Hydrogen     Valence: 1         Bonds: 1 (1 shell)

  2. Neon         Valence: 8        Bonds: 0 - stable

  3. Calcium      Valence: 2        Bonds: 6

  4. Sulfur       Valence: 6        Bonds: 2

  5. Aluminum     Valence: 3        Bonds: 5
               Nobel gases
• The elements in group 18 are Nobel gases.
• Except for helium, nobel gases have eight
  valence electrons and are chemically stable.
• Chemically stable atoms usually don’t react or
  form bonds easily with other atoms.
       Stable and Unstable atoms
• Atoms with unpaired dots in their electron dot diagrams are
  reactive, or chemically unstable.
• Many atoms become more stable by forming chemical bonds
  with other atoms.
• When an atom forms a bond, it gains, loses or shares valence
  electrons with the other atom(s). The most stable atoms have
  8 valence electrons.
            Chemical bonding
• Chemical bonding is the joining of atoms to
  form new substances. A chemical bond is an
  interaction that holds two atoms together.

• Most atoms form bonds by gaining, losing, or
  sharing valence electrons until they fill their
  outer shell to become “happy”.
       Types of Chemical Bonds
• There are two types of chemical bonds we will
  discuss: ionic bonds and covalent bonds.
               Covalent Bonds
• Covalent bonds happen when atoms share

• For example: Chlorine needs one electron to
  have a full outer shell so it can share 2 electrons
  with another Chlorine atom and become stable.
               Covalent Bonds
• Another very important covalent bond is

•     H    +     H      + O         =   H2O
                 Ionic Bonds
• Ionic bonds happen when electrons are
  transferred from one atom to another,
  causing the atom to become either positively
  charged or negatively charged.
•      Na +      Cl          =      Na Cl
    Table Salt
Ionic Bond
          Review of concepts



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