Electrons in Atoms

Bohr Model of the Atom e- are arranged in

orbits around the nucleus

e- have a fixed energy level and cannot exist between energy levels

n=2n=3n=4

energy level

Energy Levels a “quantum” of energy is required to move an e- to a higher level

Like the rungs of the strange ladder, the energy levels in an atom are not equally spaced

The Quantum Theory

1. A quantum of energy is the amount of energy required to move an electron from its present energy level to the next higher one.

2. The higher an electron is on the energy ladder, the further it is from the nucleus.

3. Energy levels in an atom are not spaced equally.

4. The further the energy levels are from the nucleus, the more closely spaced they become.

5. The higher the energy level occupied by an electron, the easier the electron escapes from the atom.

Atomic Orbitals Different atomic orbitals are identified by letters.

s orbitals are spherical p orbitals are dumbbell-shaped

Four of the five d orbitals have the same shape but different orientations in space.

• Orbits (or energy levels) contain a limited number of e-

–1st orbit = 2 e- (s orbital)–2nd orbit = 8 e- (s and p orbitals)–3rd orbit = 18 e- (s, p and d orbitals)–4th orbit = 32 e- (s, p, d and f orbitals)

e- Configurations Arrangement of e- around the nucleus of an atom…

1) e- enter orbitals of the lowest energy 1st (Aufbau principle)

2) An atomic orbital may contain only 2 e – with opposite spins (Pauli exclusion principle)

3)Split up e- in orbitals before they pair up (Hund’s rule)

Aufbau Table

Aufbau Diagram

Orbitals s p d f

Maximum # of 2 6 10 14

e- allowed

H ____ 1s

Energy levelnumber of electrons in orbital

orbital

He ____ 1s

first level filled stable configuration

(noble gas)

1s1

1s2

Writing electron configurations:

C ___ ___ ___ ___ ___ 1s 2s 2p

Ne ___ ___ ___ ___ ___

1s 2s 2p

O ___ ___ ___ ___ ___

1s 2s 2p

1s22s22p2

1s22s22p4

1s22s22p6

Writing electron configurations:

Na = 11 e- 1s2 2s2 2p6 3s1

P = 15 e-

K = 19 e-

Pb = 82 e-

1s2

1s2

1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p2

[Xe] 6s24f145d106p2

2s2 2p6 3p3

2s2 2p6 3s23p6 4s1

3s2

***ExceptionsCr Family and Cu Family:

“rob” one electron from an s orbital to fill or half-fill a d orbital

Cr [Ar]4s23d4

Ag [Kr]5s14d10

[Ar]4s13d10Cu [Ar]4s23d 9

Mo

[Ar]4s13d5

[Kr]5s14d5

Dual properties (wave and particle) Ground state - lowest energy level Energy is needed to raise the e- from the

ground state to an excited state When the e- drops back down to the

ground state, light energy is emitted

Electrons