Electrons in Atoms
Historical figures in development of electron arrangement –
Bohr: planetary model of the atom
Orbits correspond to specific energy levels – still correct today!!
Planck: Energy is quantized!! A specific amount of energy is needed to move an e- from
one energy level to the next. Planck’s constant, h = 6.626 x 10-34 J/s
E = h
Electromagnetic Radiation: all forms of light or energy from radio waves to gamma rays
 Visible light has a wavelength range from 400-700 nm.
 Energy (light) travels as a wave in specific quantities (quantized energy)
 Wavelength () the distance between two peaks or two troughs in m or nm
 Amplitude – height of the wave
 All light travels at the speed of light, which is c=3.00 x 108 m/s
 Frequency – (), the number of waves that pass a given point per second. (/s,
Hz, s-1 = per sec) Hz is Hertz
x c
E = h x
For every source of electromagnetic radiation, we can calculate the following:
wavelength, frequency and the energy of the light.
Einstein: named these packets of energy (EMR), photons
 Photon – light emitted (EMR) when an e- goes from a higher energy level to a
lower energy level
 Duality of light – has properties of both matter and energy, has mass, but it
travels as a wave
De Broglie: study the gain and loss of energy as e- make transitions between energy
levels in an atom
Ground state – only one, and it’s the lowest energy possible
Excited States – many excited states, each have greater energy than the ground state
Schrodinger: quantum/wave mechanical model of an atom,
 Discovered wave theory – e- travels like light (EMR)
 Places electrons in orbitals, which are nothing like an orbit. Orbitals are
probability maps created by the movement of the e-. Greatest probability of
finding an electron is near the nucleus. Orbitals are 3D shapes, sphere,
 Still uses the idea of quantized or certain energy levels
Heisenberg: Uncertainty Principle – impossible to know the velocity and position of an esimultaneously
Can you compare and contrast the planetary model with the wave (quantum)
mechanical model of the atom?
Compare:
Both have a positive nucleus
Quantized energy levels
Contrast:
Bohr – e- move in orbits
Wave Mechanical – e- are in
orbitals
Distribution of Electrons
Principle energy levels - state where you live
– energy level designated by numbers called the principle
quantum numbers (n) n = 1-7
- the larger the value for n the greater energy there is
Sublevels – city where you live
- the energy within an energy level is slightly different
- each electron in a given sublevel has the same energy
- order of sublevels s, p, d, f
Increasing Energy
Orbital – street you live on, most exact location
- no more than two electrons can occupy an orbital
- an orbital can be empty, half-filled or filled
s = 1 orbital
p = 3 orbitals
d = 5 orbitals
f = 7 orbitals
How many electrons in the sublevel?
2
6
10
14
Principle
Energy Level
# of sublevels
1
2
3
4-7
1
2
3
4
# orbitals
present
s p d f
1
1 3
1 3 5
1 3 5 7
Total # of
Orbitals
Maximum # of
electrons
1
4
9
16
2
8
18
32
Shapes and Energies of Orbitals
s orbitals – SPHERE
- diameter increases as the principle energy level increases
p orbitals – INFINITY SYMBOL STRETCHED OUT
- same size and shape within a principle energy level
d orbitals – dumbbell shape with a doughnut around the middle
Electron Arrangement
Electron configuration – describes the arrangement of every e- in the atom
-
represents core and valence electrons (outermost e-, highest energy)
Three Rules that Govern Filling Orbitals with Electrons:
1) Aufbau Principle: e- enter the lowest energy level first, every e- configuration
starts with 1s
2) Pauli Exclusion Principle: only 2e- can occupy an orbital and they must have
opposite spin (move in opposite directions)
3) Hund’s Rule: each orbital in a sublevel gets 1e- before any gets a 2nd e-
Electron Configurations Reveal Four Pieces of Information:
1)
2)
3)
4)
Principle energy level (coefficient 1-7)
Sublevel (s,p,d,f)
# of e- in a sublevel (superscript # 1-14)
Orbital diagram – describes placement of electrons in orbitals
_____
full
______
half full
______
empty
Hints:
1) For neutral atoms , the atomic number will be the sum of the superscripts
which is the number of electrons
2) d sublevel goes back one principle energy level
3) f sublevel goes back two principle energy levels
Examples:
HHe –
BeC–
Cl –
Cu –
Pb –
Noble Gas Electron Configuration: short cut for writing electron
configurations
Examples:
Cu –
Pb –
Valence Electrons
-
electrons in the outermost or highest principle energy
level of an atom
- critical for bonding
- Valence e- can only be found in the s and p sublevels
- maximum of 8 valence e- represented with a Lewis Dot Diagram
1) write the electron configuration
2) determine the valence electrons (highest principle energy level)
3) put one dot on each side of the symbol, maximum of two on
each side
Examples: Go back to the ones we wrote the electron configurations for.
Ions
Atom – has zero net charge
Ion – ___________ entity produced by taking a _________ atom and
________or _______________ one or more _______________
- form when metals react with nonmetals
Cation – __________ ion, produced when one or more electrons are _______
from a neutral atom
- always a metal
Anion – _____________ ion, produced when one or more electrons are
___________ by a neutral atom
- nonmetals
Let’s label common charges/oxidation states on your periodic table.
Let’s try some electron configurations for ions.