covalent bondlewis structure moleculeelectronegativity intermolecular forcessigma bond pi...
TRANSCRIPT
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Covalent bond lewis structureMolecule
electronegativityIntermolecular forces sigma bondPi bond orbitalChemical bond exothermic reactionEndothermic reaction bond lengthBond dissociation energy octet ruleResonance VSEPR modelPolar covalent bond structural formula
Vocab quiz moved to tomorrow - you have 20 minutes to work on them today
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Warm up: Write the molecular formula for:
Trinitrogen pentoxideAluminum nitrideCopper (II) sulfate
Write the names for:NO2
PCl3CaI2
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Chapter 8
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Covalent compounds consist of what? Only nonmetals
When naming, we use … Prefixes: mono, di, tri, tetra… Prefix = number of atoms (subscript)
N2O7
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Why are there no charges (like in ionic compounds)?
In ionic compounds, electrons are _______________, so atoms gain or lose charge
In covalent compounds, electrons are _____________, so no charges are formed
What does the octet rule state? In order to be stable, an atom wants a full outer
shell (which generally means 8 valence electrons) Which nonmetal is the only exception to this rule?
Hydrogen – how many does he need to be full?
transferred
shared
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When neither atom wants to give up their electrons, they will just share
When 2 electrons are shared between atoms, they form a single bond
When 2 or more atoms bondcovalently, this is called
a molecule
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Consider ionization energy and electronegativity– when 2 elements are near each other on the periodic table, these values will be very near each other
Ionization energy Energy required to remove an electron
Electronegativity How well an element attracts electrons in
a bond
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If both atoms have very similar strengths (for holding on to their electrons) then….
Neither one will be strong enough to take electrons away from the other
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Lewis structures – using electron dot diagrams, shows the arrangement of the atoms in a molecule
How many valence electrons does carbon have? How many more electrons does it need to be “happy”? How many times do you think carbon will bond? How about hydrogen? Oxygen? Generally, the # of “missing” electrons is equal to
the number of times an element will bond HONC 1234
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Calculate the number of valence electrons Arrange the atoms in the molecule
○ Generally, the atom you have one of will go in the middle
○ Hydrogen only bonds once, bonds on the outside○ How many times will carbon bond? Oxygen? (look
at their valence electrons)
Put pairs of electrons between the central atom and all of the outer atoms
Put electrons to fill the central atom Put remaining electrons around outer
atoms Check to see that every atom is “happy”
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When you are finished with the quiz, bring it up front and take out your notes from yesterday
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CCl4
PH3
H2S
SiH4
When 2 electrons are shared between atoms, you draw a line to show the bond
All other electrons that are not shared are called lone pairs and are included in the structure
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Single covalent bonds are also called sigma bonds
Orbitals – the area where you will most likely find an electron
When these orbitals overlap, they form a sigma bond (σ)
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Let’s try carbon dioxide…
Sometimes, atoms may share more than 2 electrons
If 4 electrons are shared, how many bonds would there be?
This is called a double bond How many electrons would a triple bond share?
Double or triple bonds consist of sigma and pi bonds (π)
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Don’t start using double bonds in every molecule, it is a last resort
Bond everything first, use up the rest of your electrons, THEN see if you need to double or triple bond
Try SO2
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Draw the Lewis structures for SO2 and OF2
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Look at the word… Molecules that contain how many atoms?
H. BrONClIF
In nature, when these elements are not bonded to another element, they like to exist with 2 of themselves. They are more stable that way.
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Draw: F2 O2 N2
What do you notice about the bonds? Bond length : the distance between two
bonding nuclei Which of these 3 do you think would have
the shortest bond length?
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As the number of bonds increases, the bond length becomes shorter
Which bond would be the strongest? Shorter = stronger
Bond dissociation energy : energy required to break a bond in a molecule
What is the relationship between bond length and dissociation energy? Shorter = more energy
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PO43- what is this called?
When an ion has a charge, that means it has lost or gained ______________
What has phosphate done?
Start the lewis structure like we did for the others – add up all valence electrons
Now we have 3 extra electrons
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ClO4-
NH4+
CO32-
H3O+
Be careful ! a negative
charge means we are gaining electrons, while a positive charge means we have lost electrons!
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H2SO4
C2H4
N2H2
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Determine the chemical formula and draw the Lewis structures for the following compounds or ions:
Carbon disulfide
Phosphorus trihydride
Sulfate ion
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What does it mean when something resonates?
Resonance structures are different ways to draw Lewis structures for a molecule or ion
Only the arrangement of the electrons is changed – keep the skeleton structure
Let’s draw the structure for NO3-
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How many resonance structures do each of these have?
O3
NO2-
SO2
CO3-2
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Sometimes an atom may not obey the octet rule
1. Odd number of valence electrons (NO2)
2. Less than 8 electrons present around an atom (BH3)
3. Expanded octet: happens with elements in period 3 and below – d orbital electrons Generally, the central atom gets the extra
electrons PCl5
SF6
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If you have a 75 or lower on your progress report, you must get it signed by a parent and returned to me by Wednesday
Try the following, and refer to notes from yesterday:
ICl3
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ClF5
More than an octet on chlorine
ICl4 -1
More than an octet on iodine
BeH2
Less than an octet - Beryllium and boron generally follow the less than 8 exception
NO Odd number of valence - Nitrogen generally
takes the odd number of electrons
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Draw the Lewis structure for the following:
ICl3
BeCl2
NS2
Any progress reports?
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Valence Shell Electron Pair Repulsion – used to determine the shape of a molecule
What determines how a molecule will arrange itself? What part of the atom are we generally
concerned about?... ELECTRONS
Something to keep in mind: lone pair electrons occupy more space than bonded electrons
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Draw the Lewis structures for each of the compounds on the handout (1st one is already done)
Let’s see how many things the central atom is bonded to, and how many lone pairs on the central atom there are
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Linear
Bent
Trigonal planar
Tetrahedral
Trigonal pyramidal
Trigonal bypramidal
Octahedral
107.3o
104.5o
120o
109.5o
90o/ 120o
180o
90o
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NCl3 OCl2 HOF NHF2
CO2
H2Se CH2O NH4
+1
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Pick one of the VSEPR shapes and build a molecule
Include: label the type, an example of a specific molecule, the angle between the atoms, represent lone pairs (if there are any)
Use anything you would like to build this – no drawings, and the model must be an accurate representation of the shape
Due Friday, Feb. 12th
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If something is polar, it means it has opposing ends
Need to know electronegativity and shapes
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Influenced by the electronegativities of atoms in a molecule
What is electronegativity? How well an atom attracts electrons in a bond
What is the trend for electronegativity? (remember shielding and nuclear strength) Increases up and over
Who has the highest electronegativity value? Fluorine
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Ionic: Look at the electronegativities of Na and Cl – who has more attraction for the electrons?
Covalent: look at the values for the nonmetals Polar covalent – unequal sharing of the
electrons in a bond Nonpolar covalent – equal sharing of
electrons in a bond
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Electronegativity Difference Bond Type
Less than 0.4 Nonpolar covalent
0.5 to 1.9 Polar covalent
Greater than 2.0 Ionic
What kind of bond would carbon and oxygen form?
Phosphorus and fluorine? Chlorine and chlorine?
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C – OSi – OGe – OC – ClC - Br
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Draw the Lewis structure for water What is water’s shape? Who is stronger? Who will the electrons be closer to?
This makes partial charges.
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Draw carbon tetrachloride and label the partial charges
Compare carbon tetrachloride’s structure to water’s Polar molecules are asymmetric, while
nonpolar are symmetrical Which one of these would you consider
symmetrical?
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Determine if the following molecules/ion are polar:
H3O+
NCl3H2S
oxygenCF4
CS2
SF6
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Solubility (what is this?) is determined by polarity
What is the universal solvent?
Are most substances polar or nonpolar?
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Write the formulas for the following compounds:
Aluminum sulfate Iron (III) phosphide Hydronitric acid Sulfurous acid Dicarbon trisulfide
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Grab a chemistry book, and work on the following questions –
p. 274 83, 85, 89, 96, 98, 101, 108, 112 (don’t worry about hybrid orbitals), 114, 120, 127
Be sure to look through my powerpoints and study guide on my website
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Draw the Lewis structure for SO3 and draw its resonance structures
Draw the Lewis structure for ClF3
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Name the following compounds: ZnCl2
KNO3
H2S
NF3