What is a ionic bond?
electron transfer between metals and nonmetals
What is a covalent bond?
electron sharing between nonmetals
What is a metallic bond?
electron pooling between metals
What do Lewis Symbols help predict?
What does the symbol represent?
What does the dots represent?
bonding
nucleus and core electrons
valence electrons
What is the number of valence electrons on the periodic table?
the A group number
What do lewis symbols number of dots tell us?
for main group metals, they equal the number of electrons the atom loses to form a cation
for nonmetals, they equal the number of electrons the atom gains to form a anion
Who created the octet rule?
Gilbert Lewis (1916)
What is the octet rule?
bonded atoms either gain, lose, or share electrons to attain a filled outer layer of 8 e-
atoms like to achieve noble gas configurations
What does the octet rule apply to?
almost all compounds made of the period 2 elements and some others
Why do ionic bonds cause attraction between 2 atoms?
transfer of electrons = opposing charges
What is ionization energy?
The energy absorbed by 1 mole of an atom when it loses 1 mole of electrons
What is electron affinity?
The energy released by 1 mole of an atom when it gains 1 mole of electrons
What is a lattice?
The structure of a crystalline solid formed from the attraction of multiple ions
What is lattice energy?
The energy to separate 1 mole of a solid to form 1 mole of gaseous ions
What kind of energy to atoms want?
Energy kept to a minimum
What happens to the overall energy when ionic bonds form?
Energy is released
Overall energy lowers
What are the physical behavior of an ionic solid?
Ionic solid is hard, rigid, and brittle
What are the electrical conductivity of an ionic solid?
Ionic solid does not conduct electricity, but it does once melted or dissolved
What are the thermal conductivity of an ionic solid?
In the normal state, there is no such thing as an individual ionic molecules, just interconnected solids or arrays
What must we understand to understand why and how covalent bonds are formed?
Electro negativity
What is electronegativity not the same as ?
Electron affinity
Who discovered electronegativity?
Linus Pauling (1932)
What is electronegativity?
The relative ability of a bonded atom to attract shared electrons
What are electronegativity values relative to?
The greatest value of 4.0 which is fluorine
How is electronegativity related to size?
EN is inversely related to size
Smaller the atom … the closer the shared pair can get to the nucleus
Do electrons share equally when a covalent bond is formed?
No
What is a unequal sharing of electrons?
Polar covalent bond
What is an equal sharing of electrons?
No polar covalent bond
What is used to determine bond polarity ?
Electronegativity
What sharing does two atoms of the same element form when bonded?
Equal sharing of electron
Non polar covalent bond
What sharing does two atoms of different elements form when bonded?
Unequal sharing of electrons
Polar covalent bond
What charge does the most electronegative element get? The least electronegative?
Most EN = partial negative charge
Least EN = partial positive charge
What helps is determine bond polarity?
The difference in electronegativity between two bonded species
Names the name— EN difference — bond type — example …
What’s the biggest difference in EN
Zero — (0-0.4) — polar covalent — Cl2
Intermediate — (0.4-2.0) — polar covalent — HF
Large — (2.0+) — ionic — NaCl
3.3
What is the difference between bond polarity and molecular polarity?
Bond polarity: if bond is polar or not
Molecular polarity: if molecule is polar or not
What do Lewis structures and Lewis symbols describe?
Lewis symbols : single atom
Lewis structures : molecules
What is a Lewis structure an outline for?
Bonding and arrangement of atoms in a molecule
What is a resonance structure?
The different Lewis model structures that can be made
What are equivalent resonance structures and what are no equivalent resonance structures?
Equivalent resonance structures: mirrored
No equivalent resonance structures: not the same/mirrored
What structure is the real molecule when choosing a where the double bond goes?
Hybrid
How is the bonding order calculated?
Bond Order = Bonding pairs / Atom pairs
How do we represent ions in a Lewis structure?
Braquets and charge outside top right corner
When do we want to limit formal charges on Lewis structures?
When we have non equivalent resonance forms
How do you calculate the formal charge?
FC= # valence e - # unshared e - (1/2)(# shared e)
What do the FC added together equal?
The charge of the ion molecule
What is the best resonance form ?
Limits formal charge
Places negative charge on the most EN atom
(Places positive charge on lease EN atom)
What happens to the d(distance form nucleuses) and lattice energy as the size of ions increase?
d increases
LE decreases
What two things can coulombs law predict?
strength of ionic bond
lattice energy
What kinds of ions and charges do we want?
small ions
large charges
= high LE
What is the equation for coulombs law?
E ∝ (q1q2)/d ∝ LE
Do lewis structures tell us anything about the shape of the molecule?
no
What are the five rules of lewis structures?
hydrogen can only form one bond and can never be a central atom no matter what EN
halogens generally form 1 bond and are generally surrounding atoms
carbon forms 4 bonds
nitrogen forms 3 bonds
oxygen forms 2 bonds
What are the three ways an octet rule can disobey the octet rule ?
electron deficient atom
odd electron atom
atoms with expanded valence shells
What are electron deficient atoms and what are examples?
these atoms often have fewer than 8 electrons around them when they are the central atom
Be and B
when not central is willing to follow octet rule after bond
What are odd electron atoms and what is an example?
electrons don’t always come in pairs
leaves one electron by itself
NO2
What is it called when one electron is left by itself on a lewis dot structure?
free radicals
What are expanded valence atoms and what is an example?
atoms that expand their valance shells to beyond 8 electrons
period 3 or higher
sulfur
Why can atoms in period 3 or higher bond more than 8 valance electrons?
it has 3d orbitals available to it
has 3s and 3p to place electrons
Do lewis structures tell us anything about the arrangement of molecules in space?
no
What do lewis structures tell us?
used to determine geometry
What does molecular shape determine?
functionality
What is electron group arrangement?`
the distribution of electrons (shared and unshared) around a central atom
What is molecular geometry?
the distribution of the atoms in 3D space
What do the following represent for drawing in three dimensions?
single lines
bold lines
dashed lines
bonds in the plane
bonds that are angled forward
bonds that are angled backward
What does VSEPR stand for?
valence-shell electron-pair repulsion
What is VSEPR?
the primary theory behind determining molecular geometry, based on 2 principles
What are the two principles of the theory of VSEPR?
e pairs repel each other … occupy space farthest away from each other as possible
a bond is sharing electrons … unpaired electrons are more localized on a single atom
How do we use VSEPR?
- determine the # of e- groups around central atom
- determine e- group arrangement
( identify optimal bond angles ) - consider lone pair repulsion impact on a bond angle
- determine molecular geometry
True or False: double and triple bonds are considered a single e- group?
true
In electron group arrangements, the total # of electron groups around a central atom can range from what?
Each e- group arrangement will provide us with various possible _______?
2-6
molecular geometries
What electron group arrangement is when there are only two electron groups around a central atom?
What are the other possible geometries?
linear electrons group arrangement
linear is the only one possible
