Chapter 9 Electrons in Atoms and the Periodic Table

Chapter 9 Electrons in Atoms and the Periodic Table

by Dr. Luis Bello

Previous... Chapter 8 Quantities in Chemical Reactions 

Previously: Chapter 8

8.3 Making Molecules: Mole-to-Mole Conversions 

8.4 Making Molecules: Mass-to-Mass Conversions 

8.5 More Pancakes: Limiting Reactant, Theoretical Yield, and Percent Yield 

8.6 Limiting Reactant, Theoretical Yield, and Percent Yield from Initial Masses of Reactants 

8.7 Enthalpy: A Measure of the Heat Evolved or Absorbed in a Reaction 

Checking Comprehension

Multiple Choice

What is Avogadro's Number? 

• 6.02 x 10²³
• - 6.02 10²³
• 6.02 x 10²²
• 6,020,000,000,000

Multiple Choice

Which has more molecules?

• 1 mole H₂O

• 1 mole Al(OH)₃

• 1 mole NaCl

• There are all the same

Multiple Choice

The limiting reactant

• slows the reaction down

• is used up first

• is the reactant that is left over

• controls the speed of the reaction

Multiple Choice

How many molecules are in 2.5 mol of NaCl?

• 1.51x10²³

• 146

• 4.15

• 1.51x10²⁴

Multiple Choice

How many grams is 1.20 x10²⁴ atoms of Silver?

• 1.99 grams

• 215 grams

• 6.022 x10¹ grams

• 1.2 x10¹² grams

Multiple Choice

What is the molar mass of Ba(OH)₂?

• 153.49 g/mol

• 171.33 g/mol

• 56.24 g/mol

Multiple Choice

What is the limiting reactant if 10 moles of NH₃  react  with 30.0 moles of NO?
4NH₃+6NO --> 5N₂ + 6H₂O

• NH₃
• NO
• N₂
• water

Multiple Choice

CH₄  +  2O₂  →  CO₂  +  2H₂O
24 grams of CH₄ was added to the above reaction. Calculate the theoretical yield of CO₂.

• 66 grams
• 132 grams
• 33 grams
• 8.72

Chapter 9- Electrons in Atoms and the Periodic Table 

9.2 Light: Electromagnetic Radiation 

9.3 The Electromagnetic Spectrum 

9.4 The Bohr Model: Atoms with Orbits 

9.5 The Quantum-Mechanical Model: Atoms with Orbitals 

9.6 Quantum-Mechanical Orbitals and Electron Configurations 

9.7 Electron Configurations and the Periodic Table 

9.8 The Explanatory Power of the Quantum-Mechanical Model 

9.9 Periodic Trends: Atomic Size, Ionization Energy, and Metallic Character 

Light: Electromagnetic Radiation

Light is more properly called electromagnetic radiation

What we know as light is more properly called electromagnetic radiation. We know from experiments that light acts as a wave.

As such, it can be described as having a frequency and a wavelength.

The wavelength of light is the distance between corresponding points in two adjacent light cycles, and the frequency of light is the number of cycles of light that pass a given point in one second.

Wavelength and frequency

Wavelength is typically represented by λ, the lowercase Greek letter lambda, while frequency is represented by ν, the lowercase Greek letter nu (although it looks like a Roman “vee,” it is actually the Greek equivalent of the letter “en”).

Wavelength has units of length (meters, centimeters, etc.), while frequency has units per second, written as s−1 and sometimes called a hertz (Hz). 

Electromagnetic radiation 

Electromagnetic radiation can be described in terms of a stream of mass-less particles, called photons, each traveling in a wave-like pattern at the speed of light. Each photon contains a certain amount of energy.

​

The different types of radiation are defined by the amount of energy found in the photons.

Speed of light 

Problem

What is the frequency of light if its wavelength is 5.55 × 10⁻⁷ m?

Light also behaves like a package of energy

It turns out that for light, the energy of the “package” of energy is proportional to its frequency. (For most waves, energy is proportional to wave amplitude, or the height of the wave.)

​

​

The mathematical equation that relates the energy (E) of light to its frequency is

Problem

What is the energy of light if its frequency is 1.55 × 10¹⁰ s⁻¹?

The Electromagnetic Spectrum 

The electromagnetic spectrum is the range of frequencies of electromagnetic radiation and their respective wavelengths and photon energies.

The Bohr Model: Atoms with Orbits 

The Quantum-Mechanical Model: Atoms with Orbitals 

Quantum-Mechanical Orbitals and Electron Configurations 

Quantum mechanics

Quantum mechanics is the study of the motion of objects that are atomic or subatomic in size and thus demonstrate wave-particle duality.

One of the fundamental principles of quantum mechanics is that the electron is both a particle and a wave.

In the everyday macroscopic world of things we can see, something cannot be both. But this duality can exist in the quantum world of the submicroscopic at the atomic scale.

Quantum-mechanical model

In the quantum-mechanical model of an atom, electrons in the same atom that have the same principal quantum number (n) or principal energy level are said to occupy an electron shell of the atom.

 Orbitals define regions in space where you are likely to find electrons.

Electron Configurations and the Periodic Table 

Principles of electron distribution

Aufbau Principle,

Pauli-exclusion Principle,

and Hund's Rule

Aufbau Principle

The word 'Aufbau' is German for 'building up'. The Aufbau Principle, also called the building-up principle, states that electrons occupy orbitals in order of increasing energy. The order of occupation is as follows:

​

1s<2s<2p<3s<3p<4s<3d<4p<5s<4d<5p<6s<4f<5d<6p<7s<5f<6d<7p

​

Another way to view this order of increasing energy is by using Madelung's Rule:

Hund's Rule

Hund's Rule states that when electrons occupy degenerate orbitals (i.e. same n and l quantum numbers), they must first occupy the empty orbitals before double occupying them. Furthermore, the most stable configuration results when the spins are parallel (i.e. all alpha electrons or all beta electrons).

Pauli-Exclusion Principle

Wolfgang Pauli postulated that each electron can be described with a unique set of four quantum numbers.

Therefore, if two electrons occupy the same orbital, such as the 3s orbital, their spins must be paired.

Although they have the same principal quantum number (n=3), the same orbital angular momentum quantum number (l=0), and the same magnetic quantum number (ml=0), they have different spin magnetic quantum numbers (ms=+1/2 and ms=-1/2).

Problem

Find the values of n, l, ml, and ms for the following:

a. H

b. He

c. Mg

Periodic Trends: Atomic Size, Ionization Energy, and Metallic Character 

Periodic Table – Royal Society of Chemistry

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Multiple Choice

How many electrons can the s sublevel hold?

• 14
• 10
• 2
• 6

Multiple Choice

Each row on the periodic table represents:

• an energy level

• a sublevel

• an electron

• an orbital

Multiple Choice

How many electrons can the s sublevel hold?

• 14
• 10
• 2
• 6

Multiple Choice

How many electrons can the d sublevel hold?

• 14
• 10
• 2
• 6

Multiple Choice

Which electron configuration belongs to Chlorine (Cl)?

• 1s² 2s² 2p⁶ 3s² 3p⁵
• 1s² 2s² 2p⁶ 3s² 3p⁶
• 1s² 2s² 2p⁶ 3s² 3p⁷

Multiple Choice

The electron configuration of an atom is 1s²2s²2p⁶.  The number of electrons in the atom is 

• 3
• 6
• 8
• 10

Multiple Choice

What atom matches this electron configuration?
1s²2s²2p⁶3s²3p⁶4s²3d¹⁰

• Zinc
• Copper
• Nickel
• Germanium

Multiple Choice

Which of the following has the shortest wavelength?

• Infrared

• The color Indigo

• Infrared

• TV

Multiple Choice

Which of the following has the longest wavelength?

• microwaves

• UV rays

• Infrared

• Gamma rays

Multiple Choice

Which of the following has the longest wavelength?

• microwaves

• UV rays

• Infrared

• Gamma rays