How Will an Element Behave or Its All About Electrons'

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How Will an Element Behave?orIts All About
Electrons.

• J. Hoback, M. Scully, and J. Cano John Jay High
  School
• C. Johannesson Communications Arts High School

http//www.nisd.net/secww/science/science-taks/Ele
ment20Behavior_files/frame.htm
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First, a quick review

• Atoms are composed of protons, neutrons, and
  electrons.
• For more information on each particle, click on
  the ovals in the diagram below.

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Element Symbols

• Each element is represented on the periodic table
  by a symbol.
• For example, here is the symbol for the element
  carbon

Atomic Number (number of protons)
Atomic Mass (average mass of all isotopes)
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But as we have said
Its all about electrons!

• Click on the headings below to jump to a specific
  section. Click on the home button in the
  lower-right corner of the screen to return to
  this page.
• Part I Electron Configuration
• Electrons are arranged in a predictable pattern.
  
• Part II The Periodic Table
• The layout of the periodic table is determined by
  the electron configurations of the elements.
• Part III Chemical Bonds
• Electrons influence the chemical properties of an
  element and how it combines with other elements.

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Part I Electron Configuration
Energy Levels

• Electrons occur in discrete energy levels around
  the nucleus of an atom. These energy levels are
  often represented as circles.
• Within an energy level, electrons can be found in
  orbitals.
• The first, or innermost, energy level can hold
  two electrons. The second and third energy
  levels can each hold eight.

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Part I Electron Configuration
Valence Electrons

• Valence Electrons are defined as
• the electrons in the outermost energy level that
  are involved in chemical bonding.
• Example An atom of chlorine has 7 valence
  electrons.
• Octet Rule To become more stable, atoms will
  gain, lose, or share valence electrons in order
  obtain an octet (8 valence electrons).

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Part I Electron Configuration
Lewis Dot Diagrams

• Valence electrons are the most important in
  forming chemical bonds.
• Lewis dot diagrams show only the valence
  electrons as dots surrounding the element symbol.

7 valence electrons
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Part II The Periodic Table
Lewis Dot Diagrams

• The chart below shows the Lewis dot diagrams for
  several elements in their position on the
  periodic table.
• Notice that the elements within each group, or
  column, have the same dot diagram.

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Part II The Periodic Table
Periodic Law

• When the elements are arranged in order of
  increasing atomic number, there is a periodic
  repetition of their physical and chemical
  properties.

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Part II The Periodic Table
Metals vs. Non-Metals

• Metalloids have properties that are intermediate
  between the metals and nonmetals.

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Part II The Periodic Table
Periods

• A period is a row on the periodic table.
• As you go from left to right across a period,
  there is a regular, or periodic, change in
  properties. With the start of each new period, a
  similar pattern begins again.
• Everyday Analogy
• During a class period at school, you have roll
  call, collection of homework, lecture, practice
  problems, and assignments. When that period
  is over you go to another class period and the
  same general pattern starts over, even though
  its not exactly the same.

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Part II The Periodic Table
Groups

• A group is a column on the periodic table.
• Elements within a group have similar chemical
  properties. Because of these similarities, they
  are also called chemical families.
• Everyday Analogy
• A group on the periodic table is like a family.
  Members of a family share many characteristics,
  even though each member has a unique identity.
• The Noble Gases are in the last group on the
  table.
• Just as nobility (kings and queens) dont
  interact with regular people, these elements
  dont react easily with other elements.

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Part II The Periodic Table
Back to Electrons

• Groups Elements in the same group have the same
  number of valence electrons.
• Periods Each period represents an energy level.
  Notice how the first period contains 2
  electrons, the second contains 8 electrons, and
  so on.

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Part III Chemical Bonds
Intro to Chemical Bonds

• What is a chemical bond?
• A chemical bond is a strong attractive force
  between atoms or ions in a molecule or compound.
• Why do chemical bonds form?
• Atoms form bonds in order to become more stable.
• According to the Octet Rule, atoms will form
  bonds by gaining, losing, or sharing valence
  electrons in order to obtain an octet (8 valence
  electrons).
• What are the three main types of chemical bonds?
• Metallic
• Ionic
• Covalent

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Part III Chemical Bonds
Metallic Bond

• A metallic bond is formed when metal atoms give
  up their valence electrons to form an electron
  sea.

Magnesium
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Part III Chemical Bonds
Metallic Bond

• The attraction between the loose electrons and
  the positively charged metal cations creates the
  chemical bond.

Magnesium
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Part III Chemical Bonds
Ionic Bond

• An ionic bond is formed when an electron is
  transferred from a metal atom to a nonmetal atom.

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Part III Chemical Bonds
Ionic Bond

• The metal becomes a positively charged cation and
  the nonmetal becomes a negatively charged anion.
• The attraction between the opposite charges
  creates the chemical bond.
• Notice that both ions now have 8 valence
  electrons.

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Part III Chemical Bonds
Covalent Bond

• A covalent bond is formed when electrons are
  shared between two nonmetals.
• The overlapping orbitals create the chemical
  bond.
• Notice that both atoms now have 8 valence
  electrons.

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Conclusion

• You have discovered that the behavior of an
  element is dependent on its valence electrons.
  These electrons determine the position of
  elements on the periodic table. Valence electrons
  can also be used to predict bond types between
  elements.
• Once the chemical behavior of an element is
  known, the type of compounds and mixtures it
  forms can be predicted. Continue on to the next
  lesson to learn more about the classification of
  matter.