Chemistry 109- Chapter 8

Electron Configurations

Summarizes the distribution of electrons in an atom’s orbital

Electron spin

Ms

-the fourth quantum number

-electrons spin up or down and result in the generation of a tiny magnetic field

M= +1/2 or -1/2

-only quantum number that is observable

-half of all electrons can spin up and the other half spin down

Pauli Exclusion Principal

No two electrons in an atom can have the same set of four quantum numbers

-one orbital can have two electrons as long as they have opposite spins

degenerate

All of the orbitals within the same shell have the same amount of energy

-only in non multi electronic atoms 

ex: Hydrogen

Orbital energies in a H atom depend only on, but multi electron atoms depend on n and ____

they depend on n and l

In a shelf of orbitals in a multi electron atom, which orbitals have higher energies?

Orbitals with higher l values have higher energies due to Colomb’s Law, shielding, and penetration

Coulomb’s Law

The closer an electron is to an atom’s nucleus, the mores table it is

-lower energy=more stable=the greater magnitude of a negative number

E=ke + q + q-/ r

Shielding

Electron Electron repulsions in an atom reduce the nuclear charge experienced by outer electrons

-electrons in shells closer to the nucleus shield outer electrons from the full magnitude of the nuclear charge

Effective nuclear charge (Zeff)

Nuclear charge experienced by the outer electrons

Zeff= Z ( Nuclear Charge ) - S (Amount of shielding) 

-always smaller than the actual charge of the nucleus in multi electron atoms

Penetration

Describes a particular electron’s proximity to the nucleus

-Orbitals with lower l values penetrate closer to the nucleus and are lower in energy than orbitals with higher l values

Aufbau Principle

The principle of building up and filling orbitals from the lowest energy orbital to the highest energy orbital

-2s is filled before 2p because 2s penetrates closer to the nucleus and is therefore lower energy than 2p

-fill lower energy orbitals first for stability

Hund’s Rule

Electrons fill degenerate orbitals singly before pairing to maximize the total electron spin and minimize energy 

-all electrons in degenerate, singly occupied orbitals have the same spin. This isn ecrus electrons with the same spin avoid each other, so they are less likely to screen each other from the nucleus positive charge. This overall lowers the energy of the atom.

Periodic Law

Certain properties and behaviors of elements occur periodically when the  elements are arranged in order of increasing atomic number

What are the main group elements

Elements that appear in the s and p blocks of the periodic table

Valence electrons

The electrons associated with an atom’s chemical reactivity and bonding

-furthest away from the nucleus, and the most loosely held electrons

Valence shell

Orbitals that contain the valence electrons

-in main group elements, valence electrons are those in the outer most energy level 

Core electrons

Occupy lower energy orbitals and are found in completed principal energy levels. Do not participate in bonding or chemical reactivity 

What do elements in the main group lose or gain electrons to achieve?

A noble gas electron configuration

Elements in the same group have the same number of ___ electrons

valence electrons

Which way does Zeff increase across a period

left to right, and down the groups

-nuclear charge increases across a period while shielding remains relatively constant

Atomic Radius

The size of an atom or ion quantified

-atom’s radius is often determined by internuclear distance

Internuclear Distance

Distance between two adjacent nuclei

Metallic Ratio

One half the internuclear distance between two adjacent atoms in a crystalline sample of a metal

-hard sphere model can be used to identify ratios of noble gases when solifdified and metals

Non-bonding atomic radius

One-half the internuclear distance between two atoms that touch but do not bond with eachother

ex: Solidified noble gases

Covalent Radius

One-half the internuclear distance between two atoms joined by a covalent bond

-most non metals form covalent bonds between their atoms and require orbitals of bonding atoms to slightly overlap

Atomic Radius increases

Down a group and from the right to the left cross a period

-as electrons are added, but shielding does not increase, stronger attraction between electrons and nucleus result in small radius

-trend does not apply for transition metals

Transition metal atomic radius trend

Radii stays relatively constant across a period because 3d shielding increases

Ionization Energy (IE)

Energy required to move 1 mol of the most weakly bonded electrons from 1 mol of a gas phase atom or ion

-weakest held electrons are in the highest orbitals

Ionization Energy trend across a periodic table

From left to right because because the radius gets nuclear charge grows while shielding remains constant, so electrons are more attracted to the nucleus and therefore have a smaller radius, making it harder to remove an electron

Also increase from bottom to top because principal quantum number decreases meaning electrons are closer to the nucleus requiring more energy to remove them.

Electron Affinity (EA)

Describes the energy absorbed or released when an electron is added to a gas phase atom/ion 

-first EA is usually negative because adding electrons and making them more stable decreases energy, whereas the second is aways positive due to repulsive forces

When an atom loses electrons to form a cation, the ______ energy electrons are lost first

highest energy

If there are two sub shells with the same n, then which electron is removed first?

The electron with the highest n and l are removed first

0

s

1

p

2

d

3

f

When atoms gain electrons to form anions, electrons enter the ____ energy orbitals first

lowest energy orbitals

Isoelectric

Particles with the same electron configurations

Why do elements tend to lose or gain electrons

to achieve the same electron configuration of the nearest noble gas

-noble gases are stable because of their high ionization energy

Why do electrons generate a magnetic field

because of their intrinsic spin character

Paramagnetic

A substance has at least one unpaired electron, net magnetic field of its own and is attracted to an external magnetic field

Diamagnetic

When all electrons in a substance are paired, magnetic fields generated by each electron cancel

-not attracted to an external magnetic field, may even be repulsed by them

Ionic Radius

Distance between the center of an ion’s nucleus and the outer electrons of the ion

-ions treated as hard spheres, sum of ionic radii of two adjacent ions in a crystal lattice is equal to the internuclear distance between them

Why did cations have smaller radii than their parent atoms

Decrease in electrons leads to a decrease in shielding and increase of nuclear effective chargee

Isoelectronic Series

Series of particles that have different atomic numbers, but an equal number of electrons in the same electron configuration

-particles with lowest atomic number have bigger size and vice versa