Chemical Bonding Anchem30.wdfiles.com/local--files/blog:33/Day 4_VSEPR_Worked.pdf · for Valence...
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Day 4_VSPER_Worked.notebook 1 May 01, 2017 Chemical Bonding There are two main types of chemical bonding that we are concerned with in this course. The first is ionic bonding. An ionic bond is formed when an electron is transferred from one substance to another. This is most often seen in the formation of metal ions and nonmetal ions. These compounds are known as ionic compounds.
Transcript of Chemical Bonding Anchem30.wdfiles.com/local--files/blog:33/Day 4_VSEPR_Worked.pdf · for Valence...
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Chemical Bonding
There are two main types of chemical bonding that we are concerned with in this course. The first is ionic bonding.
An ionic bond is formed when an electron is transferred from one substance to another. This is most often seen in the formation of metal ions and nonmetal ions. These compounds are known as ionic compounds.
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Ex. 2 Na(s) + Cl2(g) => 2 NaCl
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Different metal/nonmetal pairings result in different geometric arrangements. This leads to multiple different forms of crystal we see in geologic structures.
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We actually define bond type by the different in the two elements electronegativity (on your periodic table).
ΔEN = | element 1 element 2 |
If ΔEN < 0.5 => nonpolar covalent
If ΔEN is between 0.5 and 1.6 => polar covalent
If ΔEN > 1.6 => ionic (if a metal is involved; else polar covalent)
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Ex. HF
LiCl
FeO
MnS
OsAs
FrI
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Covalent bonds mostly occur between nonmetals. They result in a sharing of electrons between two different valence orbitals. This sharing results in the formation of a covalent compound.
nonpolar polar
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Covalent compounds do not form crystals. They form molecules. Individual chemical units that may or may not interact with others of their kind. They forms can be quite complex due to the fact that nonmetals can forms multiple bonds:
Carbon, Silicon 4 bonds
Nitrogen, Phosphorous, Arsenic 3 bonds
Oxygen, Sulfur, Selenium 2 bonds
Halogens 1 bond
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In the 1950's VSEPR theory was used to explain the relative shape and orientation of covalent chemical bonds. VSEPR stands for Valence Shell Electron Pair repulsion model. It is based on the concept that electrons will want to repel from each other to maintain the most stable form of compound. This means you want to create as large of angles between bonds and nonbonding pairs as possible. But first we need to draw their Lewis structures.
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Drawing Lewis Structures of Covalent Compounds1. Add up the valence electrons of all the atoms involved.2. You will need to pick a central atom, this is usually easy to
determine as it is often outnumbered (it is never H). We surround the central atom with the other elements.
3. We connect the outer atoms to the central atom with bonds (each bond represents 2 electons).
4. Starting with the outer atoms we fill their octets before moving inward (remember Hydrogen's octet is only 2).
5. If you are short electrons to fill all the octets, you may need to move outer pairs to form double or triple bonds.
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Ex. CCl4 Ex. CO2
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Now that we have drawn their Lewis Structures we can start to assess their geometry based on VSEPR.
We will use the AXE method for determining shape.
The A represents the central atom and always has an implied subscript one. The X represents each of ligands (atoms bonded to A). The E represents the number of lone electron pairs surrounding the central atom.
The sum of X and E is known as the steric number.
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SN 2 AX2 Linear
SN 3 AX3 Trigonal Planar
AX2E1 Bent
SN 4 AX4 Tetrahedral
AX3E1 Trigonal Pyramidal
AX2E2 Bent
AX1E3 Linear
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SN 5 AX5 Trigonal Bipyramidal
AX4E1 Seesaw
AX3E2 TShaped
AX2E3 Linear
AX1E4 Linear
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SN6 AX6 Octahedral
AX5E1 Square Pyramidal
AX4E2 Square Planar
AX3E3 TShaped
AX2E4 Bent
AX1E5 Linear
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Let's go back to our Lewis Structures and identify their shapes now.
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Lab #1 Model Building with
Covalent Molecules.
