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Chapter 4 Formation of Compounds

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Chapter 4 Formation of Compounds Section 4.2 How Elements Form Compounds Objectives: Model two types of compound formation- ionic and covalent, Demonstrate how and ... – PowerPoint PPT presentation

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Title: Chapter 4 Formation of Compounds


1
Chapter 4 Formation of Compounds
  • Section 4.2
  • How Elements Form Compounds

2
  • Objectives Model two types of compound
    formation- ionic and covalent, Demonstrate how
    and why atoms achieve chemical stability by
    bonding, Compare the effect of covalent and ionic
    bonding on the physical properties of compounds
  • 29 min video
  • http//www.pbslearningmedia.org/resource/7eb9615f-
    f534-4772-b65d-6c5117768a66/chemistry-501-introduc
    tion-to-bonding/

3
Compound formation
  • When elements react, atoms of the elements must
    collide
  •  
  • Reactions between atoms only involve their
    electron clouds- v.e. of colliding atoms interact

4
Noble Gases
  • Group 18 elements
  • Unreactive elements, extreme stability
  • Noble gases are used in light displays, neon
    lights 
  • Lack of reactivity of noble gases indicates that
    atoms of these elements must be stable
  • Each noble gas has 8 valence electrons, except
    helium has 2

5
NOBLE GAS CONFIGURATION
  • Achieving the same configuration of v.e.s (a
    stable octet) as one of the noble gases

6
OCTET RULE
  • Atoms can become stable by having eight electrons
    in their outer energy level (or 2 for H and He)
  • If atoms collide with enough energy, their outer
    electrons may rearrange to achieve a stable octet
    of v.e.s ? the atoms will form a compound

7
Ions
  • ION Atom or group of combined atoms that has a
    charge because of the loss or gain of electrons.
  •  
  • Ions always form when v.e.s rearrange by
    electron transfer between atoms

8
Ions
  • If an element loses an electron it becomes a
    positively charged ion called a cation
  • If an element gains an electron it becomes a
    negatively charged ion called an anion
  • Where are these located on the periodic table?

9
Isoelectronic atoms/ions
  • Isoelectronic is a term used to describe atoms
    and ions that have the same number of electrons.
  • Practice by writing the following isoelectronic
    configuration for
  • Na1
  • Ne
  • F1-
  • O2-
  • N3-

10
Lewis Dot Ions vs atoms
  • See notes

11
Valence electron rearrangement
  • 2 possibilities
  • Transfer (ionic) - metal and nonmetal
  • Sharing (covalent) - 2 nonmetals
  • Video 4-3

12
Electron Transfer (Ionic Compound)
  • Can use Lewis dot structures to represent atoms
    and the rearrangement of v.e.s.
  •  
  • Colliding atoms transfer electrons only when one
    atom has stronger attraction for valence
    electrons than the other atom
  •  
  • Electrons will move from one atom (metal) to the
    other (nonmetal)

13
Electron Transfer (Ionic Compound)
  • Example Transfer gives both Chlorine and Sodium
    stable octet
  • . .
    . .
  • Na Cl ? Na Cl -


  •  
  • Try these Ca and Cl, Li and S, K and P
  •  
  • Atoms are no longer neutral- become ions

14
Electron Transfer (Ionic Compound)
  • IONIC COMPOUND A compound that is composed of
    ions
  • Once the ions have formed they are strongly
    attracted to each other.
  •  
  • IONIC BOND Strong attractive force between ions
    of opposite charge

15
Electron Transfer (Ionic Compound)
  • Ions in salt do not arrange themselves into
    isolated sodium ion/chloride ion pairs. They
    arrange themselves into a well-organized definite
    cube structure
  • CRYSTAL Regular repeating arrangement of atoms,
    ions or molecules

16
Electron Transfer (Ionic Compound)
  • INTERPARTICLE FORCES Forces between particles
    that make up a substance (strong for ionic
    bonds). They are key for determining state of
    matter of a substance at room temperature (RT)
    and other physical properties.
  • Ionic attractions are strong attractive forces so
    it is hard to break ionic compounds giving them
    high melting point temperatures.

17
Properties of Ionic Compounds
  • Generally, ionic compounds
  • 1) Crystalline solids at room temperature (Why?)
  • 2) Hard, rough and brittle (Why?)
  • 3) High temperatures in order to melt (Why? What
    does this look like?)
  • 4) They tend to conduct electricity when they
    dissolve in water or are melted (Why? What does
    this look like?)
  • http//education-portal.com/academy/lesson/ionic-c
    ompounds-formation-lattice-energy-and-properties.h
    tml
  •  
  • ELECTROLYTE Compound that conducts electricity
    when melted or dissolved in water.

18
  • Predict
  • 1. Would NaCl dissolved in water conduct
    electricity?
  • Would this be an electrolyte? Why or why not?
  • 2. Would NaCl dissolved in ethanol conduct
    electricity?
  • Would this be an electrolyte? Why or why not?
  • 3. Would distilled water conduct electricity?
  • Why or Why not?

19
Polyatomic Structures
  • http//education-portal.com/academy/lesson/lewis-d
    ot-structures-polyatomic-ions-and-resonance-struct
    ures.html

20
Chemical Formulas
  • Formulas of compounds tell
  • What elements make up the compound
  • How many atoms of each element are present in the
    compound
  •  
  • Ex Water H2O has 2 hydrogen atoms and 1
    oxygen atom
  • Sodium Chloride- NaCl has 1 sodium and 1 chlorine
    atom

21
Electron Sharing/ Covalent Compounds (molecules)
  • When atoms collide with enough energy to react,
    but neither attracts electrons strongly enough to
    take electrons from the other atom, the atoms
    combine by sharing v.e.s
  •  

22
Electron Sharing/ Covalent Compounds (molecules)
  • Ex Sharing gives both H and O stability
  •  
  • Hydrogen has 2 valence electrons and oxygen has
    an octet when they share electrons.
  • H O ? H O (O has 7 e-s)
  •  
  • H O H ? H O

23
Electron Sharing/ Covalent Compounds (molecules)
  • COVALENT BOND Attraction of two atoms for a
    shared pair of electrons
  •  
  • In a covalent bond, atoms (2 nonmetals) share
    electrons and neither atom has an ionic charge
  •  
  • COVALENT COMPOUND Compound whose atoms are held
    together by covalent bonds
  •  

24
Electron Sharing/ Covalent Compounds (molecules)
  • MOLECULE Uncharged group of two or more atoms
    held together by covalent bonds
  •  
  • Covalent bonds molecular compounds

25
Sharing More than 2 e-s
  • More than 2 electrons can be shared in some cases
    of electron sharing
  • Example Carbon Dioxide
  • . . .
    . .
  • O C O ?

  •  
  • O C O

26
Properties of Covalent bonds
  • INTERPARTICLE FORCES Forces between particles
    that make up a substance (weaker for covalent
    bonds). They are key for determining state of
    matter of a substance at room temperature (RT)
    and other physical properties
  • Attractive force between molecules are usually
    weak
  • All have very strong bonds between the atoms, but
    much weaker forces holding the molecules
    together.
  •  

27
Properties of Covalent bonds
  • Many covalent compounds
  • 1) Are liquids or gases at RT or are solids that
    melt at low temperatures
  • 2) Do not conduct electricity
  • 3) do not usually dissolve in water
  • 4)In general, are usually less soluble in water
    than ionic compounds.
  • http//ed.ted.com/lessons/how-atoms-bond-george-za
    idan-and-charles-mortonreview
  • http//education-portal.com/academy/lesson/covalen
    t-compounds-properties-naming-formation.html

28
Lewis Dot Structures (Structural Formulas)
  • http//education-portal.com/academy/lesson/lewis-s
    tructures-single-double-triple-bonds.html
  • Steps to determine the number of bonds
  • 1) Have -Total number of V.E.
  • 2) Need - Total number of V.E. (Happy)
  • 3) Subtract Need Have
  • 4) Divide by 2
  • 5) Draw with that number of bonds
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