Chem Exam 4

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Last updated 5:55 PM on 4/11/26
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88 Terms

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4 classifications of quantum numbers
n- principal quantum number, l- orbital angular momentum quantum number, ml- magnetic quantum number, ms- electron spin quantum number
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Format of quantum numbers
(n, l, ml, ms)
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Principal quantum number (n)

Relates to the size and energy of the orbital

Represented as a positive whole number, cannot be 0

As this value increases, the size and energy of the orbital increase

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Angular momentum quantum number (l)

Relates to the shape of the orbital

Must be a positive whole number, can be zero but cannot be greater than n-1

L number and corresponding letters: 0 → s, 1 → p, 2 → f, 4 → g

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Magnetic quantum number (ml)

Provides the orientation of the orbital

Ranges from -l to +l, it can be positive, negative, or zero

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Magnetic spin quantum number (ms)

Provides the orientation of the electron spin

Can be -½ (spin down) or +½ (spin up)

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Orbitals with the same value of n are…
In the same principal level/shell
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Orbitals with the same value of n and l are…
In the same subshell
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The number of orbitals can be obtained by using…
2l + 1
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Each orbital can hold…
2 electrons and they have opposite spins
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Shape of s orbitals
Spherical shape that gets larger as n increases
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Shape of p orbitals

Have 2 lobes, like dumbbells

Have 3 different orientations (vertical, horizontal, diagonal)

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Shape of d orbitals

They have 4 lobes

5 different orientations, 1 looks like a ring around a stick

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Node

Zero probability of finding electron density

Total number of nodes in different orbitals can be defined using n-1

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Pauli exclusion principle
No 2 electrons can have the same 4 quantum numbers (n, l, ml, ms)
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Single electron atom
Orbitals with the same principal quantum number (n) are degenerate (have the same energy)
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Multi-electron atoms
Shielding (screening) and penetration involved
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Penetration
The ability of inner electrons to get closer to the nucleus versus outer electrons
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Shielding (screening)
As a result of penetration, inner electrons shield/screen outer electrons from the nucleus
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In any quantum problem assume that…
You are dealing with a multi-electron atom
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Nuclear charge
The attraction electrons would experience in the absence of intervening electrons
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Effective nuclear charge
Zeff, the actual attraction that electrons feel from the nucleus
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Electrons with smaller effective nuclear charge…
Have greater energies
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In multi-electron systems…
Orbitals with the same principal quantum number (n) are not degenerate
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Ground state electron configuration
Represent the lowest total energy for the atom
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Aufbau principle
Electrons fill subshells of the lowest available energy first and then subshells with greater energy
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Hund's rule
The lowest energy configuration of an atom is the one having the maximum number of unpaired electrons in a set of degenerate orbitals
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Exceptions to electron configuration

Cr, Mo, Cu, Ag, Au

One of the s electrons moves up to the d subunit

Not excited state configurations, they are ground state with increased stability

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Excited state

An electron transitions from a lower energy to higher energy orbital or a neighbor degenerate orbital

Ex: N ground state: 1s2, 2p2, 2p3 N excited state: 1s2, 2p2, 2p2, 3d1

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Valence electrons
Most important in chemical bonding, electrons in outermost principal energy levels (not d or f)
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Configuration of cations

Take away from highest n value

If multiple orbitals have same n value, start by taking away electrons from highest n and l value

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Configuration of anions
Add electrons to the partially filled orbital having the lowest value of n
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Paramagnetic
An atom/ion that contains unpaired electrons and is attracted to an external magnetic field
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Diamagnetic
An atom or ion in which all electrons are paired and that is not attracted to an external magnetic field
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Atomic radii

Increases down a group because the n value of the electrons in the outermost orbital increases

Decreases across a period because of an increase in effective nuclear charge

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Nuclear effective charge (Zeff)
Increases across periods and groups because the number of protons increases and valence electrons increase but do not shield other electrons
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Order of size of element

Anion > neutral atom > cation

Increasing electrons increase electrons repulsion leading to less attraction to nucleus and expansion of the size of the ion

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Ionic radii of ions
Increases down a group if oxidation states are the same
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Isoelectronic series

Atoms and ions with identical number of electrons

Look at number of protons, higher protons = smaller ionic radii because Zeff creates more positive charge and constricts size

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Polarizability

The ease of distorting the electron density of an atom/ion

The larger the atom/ion size, the greater the polarizability

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Exothermic lattice energy

The change in energy when gaseous ions are packed together to form an ionic solid

M+ (g) + X- (g) → MX (s)

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Endothermic lattice energy

The energy required to separate one mole of a crystalline ionic solid into its gaseous ions

MX (s) → M+(g) + X-(g)

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The larger the magnitude of lattice energy…
The more energy that is released upon formation or the more energy required to disassociate the compound
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A more negative lattice energy represents…
A larger magnitude, or the strongest energy
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Lattice energy (ion size)

As ionic radii increases, the release of energy decreases (less negative, less favored) because ions cannot get as close to each other

Decrease in magnitude/strength of lattice energy

Increase in ion charge results in an increase of release of energy (more favored, more negative)

Increase in magnitude/strength of lattice energy. Ion charge has a more significant role than ion size

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Ionization energy

The energy required to remove an electron from an atom or ion in the gaseous state

The energy to remove the first electron is the first ionization energy, the second electron is the second ionization energy

Reported as a positive value since energy is required to remove as electron

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Ionization energy equations

General equation: X (g) → X+(g) + e-

First ionization energy: Li (g) → Li+(g) + e-

Second ionization energy: Li+(g) → Li2+(g) + e-

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Ionization energy trends

Decreases down a group because n increases

Increases across a period because Zeff increases

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Ionization energy exceptions

Switch groups 2 and 13 → Group 2 = higher because of full s subshell, group 13= lower since electron in p is easier to remove

Switch groups 15 and 16 → group 15= higher since half filled subshell is stable, group 16= lower since p electron is easier to remove because it reduces repulsions and results in half filled shell

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Noble gases have…
Very high ionization energies since they are very stable and it is hard to lose an electron, they also have a more positive electron attachment enthalpy since adding electrons to higher subshells is not favorable
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It takes a lot more energy to remove a…
Core electron compared to a valence electron
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Electron attachment enthalpy

The energy associated with adding an electron to a gaseous atom

Typically a negative number since energy is released as a result of attraction between incoming electron and nucleus (Zeff)

X(g) + e- → X-(g)

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Electron attachment enthalpy trends

Becomes more negative across a period because Zeff increases so more energy is being releases

Becomes more positive down a group because orbital size increased and the electron has less interaction with nucleus and less energy is released

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The more energy released in electron attachment enthalpy…
The more favored the enthalpy is
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Nonmetals have…
More favored electron attachment enthalpy because they typically form an anion
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Electron attachment enthalpy exceptions

Switch groups 1 and 2 → group 1 = more negative because of full s shell, group 2= more positive because adding electron goes to higher subshell

Switch groups 14 and 15 → group 14 = more negative because adding electrons gives half-full p shell, group 15= more positive because adding electrons causes repulsions and less interactions with the nucleus

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Electron affinity

The energy required to remove an electron from an anion with a -1 charge which is opposite of electron attachment enthalpy

Some resources call electron attachment enthalpy electron affinity

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Electronegativity
The ability of an atom to attract electrons
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Electronegativity trends

Increases across a period and decreases down a group

N, O, F, and Cl have specially high values

Noble gases excluded

Fluorine = most electronegative and francium = least electronegative

Hydrogen exists between B and C

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Lewis structures

Start filling in electrons first then pair them

Unpaired electrons are likely to form bonds

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Lewis symbols for ions

Draw lewis symbol

Take away or add electrons

Put chemical symbol in brackets and write charge on the outside

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Bond

2 electrons shared between 2 atoms

1 double bond = 2 bonding pairs

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Lone pair
2 electron that are only on one atom
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Lewis structures for ionic compounds
Write lewis structure for each ion including its charge
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Lewis structures for covalent compounds

Write general skeletal structure, central atom is the least electronegative, hydrogens are always terminal

Distribute electrons giving octets to as many as possible

Polyatomic ions follow same rule but must have brackets surrounding it

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Octet rule

An atom surrounded by 8 electrons

Hydrogen may only have 2 electrons in their valence shells

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Lewis structures for organic compounds

Same rules as covalent

C is usually central atom and forms 4 bonds

Take note of how molecules are written

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Odd electron species/ free radicals

Have an unpaired electron pair in their lewis structures making them very reactive

Count valence electrons to see if its an odd number, if compound has a dot next to it means there is an unpaired electron

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Incomplete octets

Molecules from with atoms that do not have a full octet of electrons

Typically seen in beryllium, boron, and aluminum

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Expanded octets

Only seen in elements of the 3rd period

Can hold more than 8 electrons

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Formal charge

Charge assigned to atoms in a lewis structure assuming bonding electrons are shared equally between atoms

Assumes an electron own all of its bonding electrons and one half of its bonding electrons

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Formal charge calculation
Number of valence electrons - number of bonds - number of lone pairs
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Formal charge rules

Sum of all formal charges in neutral molecules should be 0

Sum of all formal charges in ion should be equal the charge of ion

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Resonance

More than 1 valid lewis structure

Atom arrangement is always the same, only electron density changes

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The actual structure of a molecule is represented by…
The average of resonance structures which are not equal averages (resonance hybrids)
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Electrons in lone pairs are…
Localized while those in bonds are delocalized
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How to determine the best resonance structure

Formal charges closer to 0 on individual atoms are between than smaller/larger ones

Negative charges should reside on most electronegative charges and positive charges on the less electronegative atoms

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The more favorable a resonance structure…
The more contribution it makes to overall identity
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If an element is eligible for expanded octets…
That can be used to minimize formal charge and find the best structure
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Bond order

Bond order of single bond = 1

Bond order of double bond = 2

Bond order of triple bond = 3

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Bond order trends

As bond order increases, strength increases and length decreases

Single bonds are the longest and weakest while triple bonds are the shortest and longest

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Reasoning for bond order trends

More electrons shared results in more overlap between electron clouds and shorter bonds

More electrons shared required more energy to break so it is stronger

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The larger an atom… (bond order)
The longer its bond length
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Bond order in resonance structures
All are the same and are equal to the average of bond orders
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If a molecule does not have equivalent resonance structures…
You can say which bonds it is more likely to have according to the best lewis structure
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Bond energy diagrams

3 energies- nuclei-electron attractive forces, electron-electron repulsive forces and nuclei-nuclei repulsive forces

The bottom of the curve represents bond length and strength

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The bottom of the curve in a bond energy diagram is where…
Attractive forces outweigh repulsive forces
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Behind the curve of a bond energy diagram…
Repulsive forces outweigh attractive forces