Chapter 6 Chemical Bonding. Section 1: Introduction to chemical bonding.
Chemical Bonding
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Transcript of Chemical Bonding
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Chemical Bonding
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Chemical Bonding
Molecules Atoms joined together that act as one unit Molecules come in three sizes:
Small Made of two atoms only Medium Made of 3-100,000 atoms Large Made of over 100,000 atoms
Called macromolecules
Even large molecules cannot be seen with the naked eye!
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Chemical Bonding
Small Molecules Examples:
NaCl KI CO LiF
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Chemical Bonding
Medium molecules Sugar Water Octane Alcohol
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Chemical Bonding
Large molecules (macromolecules) Plastics Proteins Medicine Viruses DNA
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Chemical Bonding
Molecule formation Molecules form when atoms gain, share, or lose
electrons from their valence shell (ring farthest away from nucleus) so their structure resembles a Noble Gas which is very stable
Octet Rule- all atoms want to have 8 valence electrons
Atoms with 1-3 valence electrons will lose them Atoms with 4 valence electrons will share them Atoms with 5-7 valence electrons will gain more
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Chemical Bonding
When atoms lose or gain electrons, they form ions, or charged particles.
Cations- positive ions formed from metals
Have more protons than electrons
Anions- negative ions formed from nonmetals
Have more electrons than protons
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Trends in Ion Formation
When metals lose electrons, they become positively charged. Group 1 loses 1 e +1 Group 13 loses 3 e
+3 Group 2 loses 2 e +2
When nonmetals gain electrons, they become negatively charged. Group 17 gains 1 e -1 Group 15 gains 3 e -3 Group 16 gains 2 e -2
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Chemical Bonding
When atoms rearrange their electrons, they can form forces of attraction with other atoms. These forces of attraction are called chemical bonds.
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Chemical Bonding
Chemical Bonds Ionic Bonds
Formed from positive and negative ions joining together
Involves a metal with a nonmetal
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Ionic Bonds Ionic bonds are formed in 2 steps:
1. Metal transfers an electron to a nonmetal, forming ions
2. Oppositely-charged ions attract, forming a bond
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Chemical Bonding
Covalent bonds Sharing electrons to
form a bond Usually occurs between
nonmetals or metalloids Can also occur between
two atoms of the same element
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Bell ringer
A magnet has two poles. What does that mean?
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Chemical Bonding
Polarity How electrons are shared in a chemical bond
Covalent bonds can be separated by polarity into: Polar bonds- unequal sharing of electrons Nonpolar bonds- equal sharing
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Chemical Bonding
Nonpolar bonds share the electrons equal amounts of the time
In polar bonds, one element is stronger than the other and controls the electrons for more of the time. This creates
a dipole.
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Chemical Bonding
Polarity of a bond can be represented in three ways: Bubble method Partial charge method Polarity arrow method
Arrow always faces element with larger EN
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Polarity
Polarity is determined by the EN difference between the 2 elements in the bond. 0.0-0.3 nonpolar (share equally) 0.4-1.6 polar (shared but not equally) 1.7+ ionic (completely transferred)
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Lewis Structures
1. Count the # of valence electrons
2. Draw a simple structure to represent the molecule
3. Place 8 e around the central atom
4. Fill the outside atoms 5. Move lone pairs to make
multiple bonds
1. CCl4 C- 4
Cl- 7 x 4 2. Cl
Cl C Cl
Cl 3. Cl
Cl C Cl
Cl 4.
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Chemical Bonding
Molecular GeometryShape of a molecule in 3D space
Bonded pair Lone pair
C : Br Br :
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Chemical Bonding
Linear
Bent
Trigonal planar
Tetrahedral
Trigonal pyramidal
Trigonal bipyramidal
Octahedral
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Bell ringer
What makes up aluminum foil?
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Metallic Bonding
Between atoms of the same metal Atoms share the electrons around, known as
the “sea of electrons” Responsible for many properties of metals-
malleability, conductivity
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Comparing Bonds
Ionic Covalent Metallic
State of Matter
Bond Length
BP
MP
Conductivity
Crystalline solid
Longer due to space between ions
Shorter due to overlapSolid
Liquid, gas, soft solid
Low
High
High
High
High
Low
Conduct very well
Do not usually conduct
Conduct when dissolved in water
Long and flexible
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Bell ringer
Is HCl polar or nonpolar?
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Intermolecular Forces
Forces that occur between molecules- require more than one molecule to occur
There are four types: 1. Dipole-dipole forces 2. Induced dipole forces 3. Dispersion forces 4. Hydrogen bonding
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To recap… Dipole-dipole: 2 polar molecules have opposite sides facing
each other. Opposites attract.
Induced dipole forces: 1 polar molecule causes a neighboring nonpolar molecule to become polar by shifting electrons. Opposite sides are facing each other. Opposites attract.
Dispersion forces: Temporary dipole formed by random movement of electrons. Induces dipoles. Opposites attract.
Hydrogen bonding: Positive hydrogen from 1 molecule is attracted to negative end of neighboring molecule. VERY STRONG!!
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Chemical Bonding
Chemical Formulas Represent a compound without having to write the
name Show the number of atoms in the compound There are two types:
Ionic- metals with nonmetals Covalent- nonmetals with nonmetals
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Chemical Bonding
Ionic Formulas Naming Ionic Compounds
1. Write the name of the first element
2. Write the name of the second element but add –ide to the end of the name.
Examples: MgS magnesium sulfide
ZnCl2 zinc chloride
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Chemical Bonding
Ionic Formulas Charge numbers
Each group is assigned a charge number based on how many electrons are gained or lost by the elements in that group.
Group 1 1 Group 14 4 Group 2 2 Group 15 3Group 133 Group 16 2
Group 17 1
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Chemical Bonding
Ionic Formulas Charge numbers
Tansition elements have individual charge numbers
Cr 2 Cu 1 Sn 2Mn 2 Zn 2 Au 3Fe 3 Zr 2 Hg 1Co 2 Ag 1 Pb 2Ni 2 Cd 2 Bi 3
U 6
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Chemical Bonding Writing Ionic Formulas
1. Write the symbols for the elements in the compound.
2. Look up the charges for each element and write them as superscripts behind the elements.
3. Cross the numbers in an “X” until they are behind the other element.
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Chemical Bonding
Examples: Aluminum fluorideAl FAl3 F1
AlF3
Calcium oxideCa OCa2 O2
CaO
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Chemical Bonding
Covalent Formulas Naming Covalent Compounds
1. Write the name of the first element.
2. Write the name of the second element but add –ide to the end of the name.
3. Find the prefix that matches the subscript in the formula.
4. Write the prefix in front of the element’s name.
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Chemical Bonding
Examples: NO3
Nitrogen oxide3 = triNitrogen trioxide
As2S3
Arsenic sulfide2 = di 3 = triDiarsenic trisulfide
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Chemical Bonding
Writing Covalent Formulas1. Write the symbols for the elements.
2. Find the number that matches the prefix in the name.
3. Write the number as a subscript behind the appropriate element.
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Chemical Bonding
Examples: Carbon monosulfide
C Smono = 1CS
Dinitrogen pentachloride
N Cl Di = 2 penta = 5
N2Cl5
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Chemical Bonding
Polyatomic Ions Groups of elements that act as one element in a
compound Polyatomic ions are given special names
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Chemical Bonding
Naming compounds with polyatomic ions1. Write the name of the first element.2. Find the polyatomic ion on your sheet. Write
its name as it appears on the sheet. Examples: Na3PO4
Sodium phosphate
KMnO4
Potassium permanganate
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Chemical Bonding
Writing Formulas with Polyatomic Ions1. Write the symbols for the element and the
polyatomic ion.
2. Find the charge number for the element and the polyatomic ion. Write them as superscripts.
3. Cross the charge numbers over.
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Chemical Bonding
Examples: Sodium hydroxideNa OHNa1 OH1
NaOH
Boron nitrate
B NO3
B3 NO31
B(NO3)3
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Molar Mass
Mass in 1 mole of a compound Add all of the atomic masses to find the total
with significant figures!!NaF Na- 22.98977 AlCl3 Al- 26.98154 + F – 18.998403 + 3 Cl- 3(35.453)
41.988173 133.34054
Rounded: 41. 98817 g/mol 133.341 g/mol
Now… you do Ba(ClO3)2
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Molar Conversions
The Mole
A quantity that represents the number of atoms in 12 g of C-12
1 mole = 6.02 x 10 ^23 atoms
Avogadro’s number
For a compound, it is 6.02 X 1023 molecules in one mole.
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Q: If a mole of moles is digging a mole of holes, what do you see?
Molar Conversions
0.25 mol WO3 = _____ g WO3
15.79 g MgS = _____ mol MgS
4.17 x 1025 molec. CH4 = _____ g CH4
3 mol HCl = _____ molec. HCl
A: A mole of molasses