Chapter 4 Notes Arrangement of Electrons in Atoms

Accelerated Chemistry

Chapter 4 Notes – Arrangement of Electrons in Atoms

Chapter 4 4.1 Refinements of the atomic model

Models of the atom so far:

Dalton – atoms are like little “bb’s” - then the ______gets discovered

Thomson – atom is like a ______“bb”

Rutherford - Gold foil experiment – ______“bb”

Bohr model of the atom (1913) – Neils Bohr – Danish Physicist

The Bohr model of the atom comes from the idea that light is ______

View vision learning example of hydrogen and helium atoms.

http://web.visionlearning.com/custom/chemistry/animations/CHE1.2-an-atoms.shtml

The Bohr Atom (1913)

In 1913, Neils Bohr, a Danish physicist proposed:
· All the positive charge was in the ______
· Electrons orbited the nucleus much like planets orbit the sun (at fixed distances)
· The ______the electrons to the nucleus, the ______energy it has.
· The ______the electron is from the nucleus, the ______energy it has. /

The Electromagnetic Spectrum - Defined

· Visible light, x-rays, ultraviolet radiation, infrared radiation, microwaves and radio waves are all part of the electromagnetic spectrum

· The spectrum consists of electromagnetic radiation – ______

· Waves can be described by the wave equation which includes velocity (c = speed of light), wavelength (λ) and frequency (ν).

· Wavelength (definition) = ______

· Light through prism leads to high energy (violet) low energy (red)

· ROYGBIV - colors of the visible spectrum

· Bright Line Spectrum (BLS) – caused by e- emitting energy as they ______to ______energy level.

· heat sodium - yellow light 2 colors

· heat lithium - red light 4 colors

· elements can appear to give off the same color light, but each will have its own bls

· BLS - used to determine ______

· BLS - validates Bohr’s idea that electrons jump to different energy levels and give off different wavelengths of light

Light from the sun (white light) appears as a continuous spectrum of light.

· Continuous Spectrum of Light (definition) = There are no discrete, individual wavelengths of light but rather all wavelengths appear, one after the other in a continuous fashion

Spectroscopy (definition) = ______

Show overhead #6

We will use spectroscopes (______) and flame tests to study elements because each element emits a different spectrum of light when exited .

Bohr proposed that the energy possessed by an e- in a H- atom and the radius of the orbit are quantized (bls)

· Quantized (definition): a specific value (of energy)

Bohr’s Energy Absorption Process:

· These energy levels are “ quantized “ (the e- cannot be in between levels), the e- disappears from one shell and reappears in another

· Ground State Analogy = a spring and two balls

· When energy is added, the electron is found in the “______.”

· The Excited State (definition) = ______

· An illustration of Bohr’s Hydrogen atom (from ground to excited state):

· The atomic line spectral lines - when an e- in an excited state decays back to the ground state

The Bohr Model - Summary

1. When an atom absorbs energy, its electrons are promoted to a higher energy level. When the electron drops back down, energy is given off in the form of ______.
2. Each distance fallen back is a specific energy, and therefore, a specific ______.
3. Since electrons can fall from level 5 to 4, 5 to 3, etc., ______
Click for animated H-atom:
Bohr's Atom: Quantum Behavior in Hydrogen - http://www.visionlearning.com/library/module_viewer.php?mid=51&l=15 /

Bohr also predicted that since electrons would occupy specific energy levels and each level holds a specific number of electrons

· The maximum capacity of the first (or innermost) electron shell is ______.

· Any element with more than two e-, the extra e- reside in additional ______.

Group IA / VIA / VIIA / VIIIA
/ / /
Lithium / Oxygen / Fluorine / Neon

Sodium
Electron Configurations for Selected Elements

· The number of e- per shell = 2n2 (where n is then shell number)

Draw Bohr Models for the elements with atomic numbers 1-10 below then abbreviate with nucleus and numbers on rings

Short Hand Bohr Model

o Write the symbol of the element

o Use a ) to represent each shell

o Write the # of e- in each shell

Element / Short-Hand e- Configuration
Hydrogen / H )1e-
Lithium / Li )2e- )1e-
Fluorine / F )2e- )7e-
Sodium / Na )2e- )8e- )1e-

At atomic # 19 (z = 19), there is a a break in the pattern. One would expect that energy level #3 would continue to ______. However, the next two electrons go into the ______energy level. Look at K and Ca.

Bohr Model illustrations for elements 1-20 on the periodic table examples:

IA / VIIIA
H
+ )
/ IIA / IIIA / IVA / VA / VIA / VIIA / He
+ )
Li
+ ) )
/ Be
+ ) )
/ B
+ ) )
/ C
+ ) )
/ N
+ ) )
/ O
+ ) ) / F
+ ) ) / Ne
+ ) )
Na
+ ) ) ) / Mg
+ ) ) )
/ Al
+ ) ) )
/ Si
+ ) ) )
/ P
+ ) ) )
/ S
+ ) ) )
/ Cl
+ ) ) )
/ Ar
+ ) ) )
K
+ ) ) ) )
/ Ca
+ ) ) ) )

So, there is a relationship between the main column # and the number of outershell electrons.

· Column # = the number of ______electrons

And, there is a relationship between the row # and the number of energy levels.

· Row # = the number of ______

The Bohr model truly works well for the H atom only – for elements larger than H the model does not work.

In sum, Bohr made 2 huge contributions to the development of modern atom theory

· He explained the atomic line spectra in terms of ______

· He introduced the idea of quantized electron ______in the atom

The Bohr atom lasted for about 13 years and was quickly replaced by the quantum mechanical model of the atom. The Bohr model is a good starting point for understanding the quantum mechanical model of the atom

Do Ch4 worksheet #1 – question #1

4.2 Quantum numbers and atomic orbitals & 4.3 Electron Configuration

The Bohr model describes the atom as having definite orbitals occupied by ______.

As with all chemistry, we soon learn that the Bohr model is a lie.

Schrödinger (1926) introduced wave mechanics to describe electrons

· Based his idea that electrons behaved like ______

· Electrons show diffraction (interference) properties like ______.

· Treats electrons as waves that are found in ______.

· Orbitals (definition) = ______.

So, the Bohr model really is ______

There are really many types of orbitals – we can see them on the periodic table

Draw spdf blocks on blank periodic table

Subatomic Orbitals

Type / # of Sublevels / Total # electrons / Shape
S / Sphere
p / Peanut
d / Dumbbell
f / Flower

Quantum Numbers

Quantum numbers show the “addresses” of electrons – each electron has 4 different quantum numbers:

principle (n): ______

azimuthal (l): ______

3. magnetic – ______

spin - ______

Electron Configuration - a representation of the arrangement of electrons in an atom

o Examples of electron Configuration

n 1. Li 1s22s1

n 2. C 1s22s22p6

-Take note that after 4s is filled, 3d is than filled before 4p. This is because 4s has a lower energy than 3d.

-…… 6s than 4f than 5d than 6p

-When writing out the electron configuration, always write your numbers in numerical order

n Y 1s22s22p63s23p64s23d104p65s24d1 – NO!

n Y 1s22s22p63s23p63d104s24p64d15s2

- Note: 3d has a few exceptions exceptions

o Cr is 4s1 3d5 and Cu is 4s1 3d10 - students should be able to identify these elements simply based on how many electrons they have.

Examples:

Be O

Ca Mn

Pb Os

We can also do shorthand electron configuration. Use previous row’s noble gas in brackets, then present the electron configuration for the current row.

Be Na Si

Orbital notation is another way to represent electron arrangement in atoms.

Electrons enter orbitals in a set pattern. For the most part, they follow these rules:

The Aufbau Principle - electrons must fill lower energy levels before entering ______.

Draw energy level diagram here: Draw diagonal diagram here:

Orbitals are like "rooms" within which electrons "reside".

The s subshell has one s-orbital. The p subshell has three p-orbitals.

Each orbital can hold at most 2 electrons

See a good online illustration at http://www.avogadro.co.uk/light/aufbau/aufbau.htm

Hund’s Rule (better known as the ______)

Before any second electron can be placed in a sub level, all the orbitals of that sub level must contain at least one electron – spread out the e- before pairing them up.

Pauli Exclusion Principle - electrons occupying the same orbital ______.

Examples:

Li F

Na Sc

We can also do shorthand orbital notation (outer shell only)

Ca N Fe

Significance of electron configurations

Valence shell electrons - ______

no atom has more than ______

Noble gases - 8 valence electrons - ______reactive of all elements

Lewis Dot structures: NSEW (cheating) also show correct way, count to 8

/ Lewis Dot Structures /

Exception – He

Try Lewis Dot structures for additional elements here:

04 Notes - Atoms 10-11 Page 1 of 13