CHEM 11a Lecture Notes - Lecture 35: Ionic Bonding, Lewis Structure, Lewis Acids And Bases
12 Dec 2016
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Bond types
Interactions between protons and electrons
Ionic:
- Metal + non-metal
- Electrons transferred from metal to non-metal
- Metals - low ionization energies
- Non-metals - large neg. EA
Covalent:
- Non-metal + non-metal
- High ionization energies
- Shared electrons stabilized by interaction with nuclei of both atoms
Metallic:
Chemical Bonds (electrical forces)
- Oppositely charged particles have attractive forces, lower potential energy by getting
closer
- Same charges lower potential energy by getting farther away
Optimal internuclear distance
Lewis Theory
The lewis model focuses on the valence electrons in chemical bonding
- Chemical symbols represent the nucleus and core electrons
- Dots around the symbol are the valence electrons
Group # → # valence electrons
Lewis dot diagrams!
- 2 electron dots on each side of the chemical symbol, add one to each side first and then
pair them
Filling valence shells:
The transfer of one or two electrons or the sharing can fill the dots so there are 8 on each
chemical symbol → octet rule (8 valence electrons, noble-gas configuration)
Ionic bonding: electron transfer
- The dot can be moved from one element to the other to create 2 ions
- Ions must be in brackets for lewis diagrams and the charge is on the outside
- Must show the full octet around the ion that gains the electron(s)
The lewis diagrams can predict the ion ratio
- Some have a really high energy to transfer electrons so can only contribute one electron
- Ex: Li can only contribute one electron because of the difficulty to separate the next
electron
find more resources at oneclass.com
find more resources at oneclass.com
Covalent Bonding
- Electrons sharing 2 or more valence electrons
- Ex: Hydrogen → H:H → lewis diagram for diatomic hydrogen
A lewis structure shows us what bonds to what and how each atom gets the electrons needed
to be “satisfied”
Structures are stable with 8 valence electrons electrons:
- For H3O the element is unstable with 9 so it becomes H3O+
Multiple bonds:
If two atoms share one electron pair, the result is a single bond.
Sharing two or three electron pairs to gain an octet results in the formation of a multiple bond.
Two shared electron pairs constitutes a DOUBLE BOND.
- Triple bonds
Unequal sharing of electrons
- Sometimes one of the elements has a stronger pull on the electron
- This gives the elements a slight charge on either side
- One atom is slightly positive and one slightly negative but still bonded as a compound
If evenly shared between atoms, it is a pure covalent bond! → electrons shared equally
Polar covalent bonds - electrons slightly pulled to one side
Ionic bonds → electrons transferred completely from one atom to another
To represent polar bonds put a slight charge under the element
- A vector with a + at one end and the head of the arrow directed toward the negative end
of the molecule indicates that this bond is polar.
with partial positive (δ+) or negative (δ-) charge.
Electronegativity:
the ability of an atom to compete for electrons with the atoms it is bonded to
- The ability for the atom to draw in an electron in a covalent chemical bond
- Electronegativity scale (came from bond energies)
The most electronegative elements:
F,O,N,Cl,Br,I,C,S
The least electronegative elements are in the bottom left corner of the periodic table
Increases across a period
Decreases down a group
Electronegativity varies inversely with size (larger atom, less electronegative)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Shared electrons stabilized by interaction with nuclei of both atoms. Oppositely charged particles have attractive forces, lower potential energy by getting closer. Same charges lower potential energy by getting farther away. The lewis model focuses on the valence electrons in chemical bonding. Chemical symbols represent the nucleus and core electrons. Dots around the symbol are the valence electrons. 2 electron dots on each side of the chemical symbol, add one to each side first and then pair them. The transfer of one or two electrons or the sharing can fill the dots so there are 8 on each chemical symbol octet rule (8 valence electrons, noble-gas configuration) The dot can be moved from one element to the other to create 2 ions. Must show the full octet around the ion that gains the electron(s) Ions must be in brackets for lewis diagrams and the charge is on the outside. The lewis diagrams can predict the ion ratio.
