Models of the Atom

Lets Review! Orbitals

Ground vs Excited state

Electromagnetic spectrum

Photons and waves

Flame test

Atomic Emission Spectrum

Spectroscope

2

2

l. Models of the Atom

A. There were many different models over time

1. Dalton-billiard ball model (1803)

2. Thompson – plum-pudding model (1897)

3. Rutherford – Nuclear model of the atom (1911)

4. Bohr – uses quantized energy of the atom (1913)

5. Quantum Mechanical Model of the Atom (1926)

ll. Problems with the Bohr ModelA. The model is fundamentally

incorrect and only works with hydrogen.

B. Failed to explain the spectrum of any other element

C. Did not account for the chemical behavior of atoms

D. Electrons do not move around the nucleus in circular orbits

E. Laid ground for later atomic models.

lll. Quantum Mechanical Model of the Atom

A. Quantum Mechanical Model is the current description of electrons in atoms.

1. It does not describe the electron’s path around the nucleus

B. Quantum Mechanical Model based on several ideas including:

1. Schrodinger wave equation (1926) is mathematical equation describing the behavior of an electron and treats electrons as waves.

2. Heisenberg uncertainty principle (1927) states that it is impossible to know both the velocity and position of a particle at the same time.

lV. Atomic Orbital

A. Using the quantum mechanical model you can predict the electron’s location in an atom

B. An atomic orbital is a region of space in which there is a high probability of finding an electron

1. Orbitals are not necessarily spherical

How are these different from the orbitals found in Bohr’s model?

Question Time

What is the Schrodinger Equation?

How does it treat electrons?What is the Heisenberg

Uncertainty Principle?What is an atomic orbital?

V. Quantum Numbers

A. The Quantum Mechanical Model assigns quantum numbers to indicate the relative sizes and energies of atomic orbitals.

B. There are three things for every electron1. Principal energy level (principal quantum

number, n)

2. Energy Sublevel (s, p, d, f)3. Atomic orbital

Vl. Principal Energy Levels

A. Principal energy levels n =1 to 7. (Row # on the periodic table)

B. The electron’s principal energy level is based on its location around the nucleus.

C. Electrons closer to the nucleus are at a lower energy level and have lower energy than those farther away from the nucleus

How is this similar to Bohr’s model? Different?

What tool do you think we use to find the energy levels of the electrons?

Question Time

What do quantum numbers indicate?

What is the principal energy level based on?

Describe the energy as you go further from the nucleus

Vll. Energy Sublevels and Orbitals

A. Energy sublevels 1. assigned letters s, p, d or f (smart people do fine)

i. Energy sublevels correspond to a shape where the electron is likely to be found.

B. Orbitals – describes the electron’s location1. 2 electrons per orbital 2. s sublevel has 1 orbital (2 electrons total)3. p sublevel has 3 orbital (6 electrons total)4. d sublevel has 5 orbital (10 electrons total )5. f sublevel has 7 orbital (14 electrons total)

Looking at the periodic table can you see any connections to the orbitals and sublevels ?

Energy Level (n)

Sublevels(Type of orbital)

Number of orbitals per

sublevel

Number of electrons per

sublevel

1 s 1 2

2 sp

13

26

3 spdf

1357

261014

4 spdf

1357

261014

s orbital (1) - spherical

p orbitals (3) – dumb-bell shaped

d orbitals (5)

f-orbitals (7)

Question Time

What letters are assigned to the energy sublevels?

How many orbital(s) does the s sublevel have? p sublevel? d sublevel? f sublevel?

How many electrons can one orbital hold?