chapter 6 chemical bonding. what is electronegativity? why does it matter?
TRANSCRIPT
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Chapter 6 CHEMICAL BONDING
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WHAT IS ELECTRONEGATIVITY? WHY DOES IT MATTER?
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Section 5.1
INTRODUCTION TO CHEMICAL BONDING
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Electronegativity- The ability for an atom to attract an electron to itself
There are 3 types of bonds Ionic BondCovalent BondPolar Covalent Bond
SECTION 6.1
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Ionic bond- Electrons are transferred forming ions. These ions are attracted to each other. The bond is a strong force between the two atoms.
Covalent bond- two or more atoms sharing pairs of electrons
TYPES OF BONDS
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Polar Covalent- two or more atoms sharing a pair of electrons unevenly
TYPES OF BONDS (CONT)
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The type of bond between two or more atoms depends on the diff erence in electronegativity of the atoms.
ELECTRONEGATIVITY AND BONDING
Type of Bond Difference in Electronegativity
Ionic 1.8 - 3.3
Polar- Covalent 0.4 - 1.7
Covalent 0.0 - 0.3
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What is the main distinction between ionic and covalent bonding?
How is electronegativity used in determining the ionic or covalent character of the bonding between two elements?
What type of bond would be expected between the following atoms? Li and F Cu and S I and Bf
SECTION 6.1: LEARNING CHECK
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Section 6.2
COVALENT BONDING AND MOLECULAR
COMPOUNDS
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Molecule- a neutral group of atoms that are held together by covalent bonds
Chemical formula- the relative numbers of atoms of each kind in a chemical compound by using atomic symbols and numerical subscripts
Octet- 8 electronsSingle bond- 1 electron pair sharedDouble bond-
TERMS TO KNOW
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EXAMINE THESE COVALENT MOLECULES. WHAT DO YOU
NOTICE?
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Overall goal: Obtain an octetCreate a stable atomLowest amount to energy
FORMATION OF A COVALENT BOND
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Bond length: distance between two bonded atoms
Bond energy: the energy required to break a chemical bond and form neutral isolated atoms.
CHARACTERISTICS OF THE COVALENT BOND
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Atoms will gain, lose, or share electrons to get 8 electrons in their highest occupied energy level
Exceptions: Helium and Hydrogen- only need 2 valence electronsBoron- has 3 electrons and is stable with 6 electrons
Example: BF3
Expanded Octet- Some atoms can hold more than 8 when they are bonded to extremely electronegative atoms. Example: PF5 and SF6
THE OCTET RULE
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An electron configuration notation in which only the valence electrons of an atom of a particular element are shown.
ELECTRON-DOT NOTATION
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Visual representation of molecules Element symbol- nuclei and inner-shell electrons Dot-pairs- non-bonding valence electrons Dashes- bond between two elements
LEWIS STRUCTURES
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1. Determine the type and number of atoms in the molecule2. Write the electron-dot notation for each type of atom in the
molecule3. Determine the total number of valence electrons available
to be combined4. Arrange the atoms
1. If carbon is present it is in the center2. If not, the least electronegative atom is in the center
5. Add unshared pairs of electrons to each nonmetal atom (except hydrogen) Each atom needs to be surrounded by 8 electrons.
6. Count the electrons in the structure to be sure that the number of valence electrons used equals the number available.
7. Place non-bonding valence electrons in pairs around atoms without an octet
HOW TO DRAW LEWIS STRUCTURES?
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NH3
H2S
SiH4
PF3
EXAMPLES:
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Indicates the kind, number, arrangement, and bonds but not the unshared electrons.
STRUCTURAL FORMULA
H-Cl
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Double or triple bonds Triple bonds are the shortest and strongest
covalent bondsThe need for a multiple bond becomes
obvious if there are not enough valence electrons to complete octets by adding unshared pairs.
MULTIPLE COVALENT BONDS
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Compare the molecules H2NNH2 and HNNH
REVIEW
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Bonding in molecules or ions that cannot be correctly represented by a single Lewis structure.
RESONANCE STRUCTURES