U2 - Module 2: Looking for Patterns Flashcards
What is the structure of a molecule determined by?
- Atomic composition
- Atom connectivity
Why is understanding the molecular structure important?
Molecules can have the same number of each atom (structure), but different formulas.
What part of an atom is positive charged and which is negative charged?
Positive: Nucleus; protons
Negative: Electron Cloud; electrons
Electrostatic Model
The formation of covalent bonds is induced by a net attraction force between electrons and protons in different atoms.
What happens when atoms come too close together?
Repulsion forces take over
Bond strength
Energy needed to move two atoms apart (break bond)
Bond length
Sweet spot of atom distance (attractive = repulsion)
What happens to the potential energy when atoms move closer and further apart?
Closer: Decreases
Farther: Increases
Quantum Model
Explains more detail about covalent bonding
Electron Density
The measure of probabilities for atoms to bond
What does a higher electron density correlate to?
A higher probability of atoms bonding since more electrons are present.
Electron Delocalization
Energy decreases when forming a covalent bond.
What happens as a net result of electron delocalization?
The total energy goes down
What is delocalization doing to the atoms?
Stabilizing
- decreases potential energy
What does it take more energy to break?
Multiple bonds compared to a single bond
What does the frequency of atoms depend on?
- Strength of the force between atoms
- Their masses
What spectrum does atomic vibration occur in?
Infrared
Wavenumber formula
1/wavelength
What is the wavenumber directly proportional to?
The frequency and energy level
What happens if the exact frequency/wavelength isn’t applied?
The electrons will not change vibrational state.
What is low transmittance directly proportional to?
high absorbance
How is weight proportional to wavenumber?
The higher the wavenumber, the lighter the mass.
Do atoms with low or high wavenumbers have stronger bonds?
Higher wavenumbers
Higher energy
X Ray Radiation
Measures the distance between atoms
How is the atomic radius found?
Measuring the distance between bonded atoms
What is the trend for atomic size?
Larger for metals
- Going down
- Going left
Ionization Energy
The energy needed to remove 1 electron
What is the trend for ionization energy?
Increases for gases
- Going up
- Going right
What is the relationship between atomic size and ionization energy?
Inversely proportional
Isoelectronic
Having two or more atoms/molecules have the same number of electrons and electronic structure.
What model explains the trend in atomic radius size?
Shell Model
Shell Model
The further away electrons are from the nucleus, the easier they are to remove from the molecule.
What are the amounts of electrons allowed in each shell in the first 4 energy levels.
n=1: 2
n=2: 8
n=3: 8
n=4: 18
What does the shell model coordinate with?
The electron orbitals of each energy level.
Is it easier to remove an electron from a larger or smaller molecule?
Larger
- Lower ionization energy
What causes a molecule to have a larger nucleus charge?
More protons in the nucleus
What does a larger nucleus charge result in?
Smaller atomic radius (pulling electrons closer to the nucleus)
What is the relationship between radius size and ionization energy?
Inversely proportional
- Stronger the bond, smaller the radius
Photoelectron Spectroscopy (PES)
A graph that displays the peaks of electron amounts with the correlated ionization energy
What are the axis in a PES diagram?
y axis: Number of electrons
x axis: Ionization energy (increases to the left)
What do PES diagrams help us interpret?
The orbital formula of electrons in a molecule
How many electrons fit in each orbital?
S: 2
P: 6
D: 10
F: 14
What are each of the orbitals shapes?
S: Basic sphere
P: Dumbells
D: 2 Dumbells or a donut ring
What molecule is larger and why?
Ar
S^2-
S^2-
- More electrons than protons, so the nucleus cannot hold the electrons as closer together as it would if it had the same amount of protons.
What is the maximum occupancy in each orbital?
2
How do you draw the two electrons in an orbital?
One arrow up, and one arrow down
(spin opposite directions)
Quantum Mechanical Model
The modern model of the atom reveals a complex distribution of electrons within atoms
(orbital arrow diagrams)
How many sub shells are in the n=3 energy level?
S: one orbital
P: three orbitals
(hold 2 electrons each
Core Electrons
Electrons in lower energy levels that are not involved in creating bonds between other atoms
Valence Electrons
Electrons in the high energy levels that are involved in creating bonds between other atoms
Which is more accessible; core or valence electrons?
Valence electrons
Bonding Capacity
The number of bonds a nonmetal atom can form is determined by
8 - # of valence electrons
Octet Rule
Atoms are happiest when they have a full valence shell (8 electrons)
What 2 things is bond formation favored by?
- Electron delocalization
- Increased electron density between atoms
What is the formation of covalent bonds the result of?
Electrostatic interactions between electrons and protons in the bonding atoms.
What characteristic motion do molecules experience?
Vibrational motions
What can the absorption of EM Radiation at specific frequencies be used to detect?
Specific bonds
- IR Spectra graph
What can models of atomic structure be used to make predictions about?
Electron configurations
What does electron configurations help make predictions about?
Bonding behavior
What happens when two atoms combine?
Their valence electrons are reorganized
What makes the most stable structures?
Bonds with a full valence shell
- follow octet rule
