 Unit 2 – Electrons and Periodic Behavior

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Unit 2 – Electrons and Periodic Behavior
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Wave-Particle Duality
JJ Thomson won the Nobel prize for describing the electron as a particle. His son, George Thomson won the Nobel prize for describing the wave-like nature of the electron. The electron is a particle! The electron is an energy wave!

The Wave-like Electron
The electron propagates through space as an energy wave. To understand the atom, one must understand the behavior of electromagnetic waves. Louis deBroglie

Spectroscopic analysis of the visible spectrum…
…produces all of the colors in a continuous spectrum

Electron transitions involve jumps of definite amounts of energy.
This produces bands of light with definite wavelengths.

Quantum Numbers Each electron in an atom has a unique set of 4 quantum numbers which describe it. Principal quantum number Angular momentum quantum number Magnetic quantum number Spin quantum number

Pauli Exclusion Principle
No two electrons in an atom can have the same four quantum numbers. Wolfgang Pauli

Principal Quantum Number
Generally symbolized by n, it denotes the shell (energy level) in which the electron is located. Number of electrons that can fit in a shell: 2n2

Angular Momentum Quantum Number
The angular momentum quantum number, generally symbolized by l, denotes the orbital (subshell) in which the electron is located.

Magnetic Quantum Number
The magnetic quantum number, generally symbolized by m, denotes the orientation of the electron’s orbital with respect to the three axes in space.

Assigning the Numbers The three quantum numbers (n, l, and m) are integers. The principal quantum number (n) cannot be zero. n must be 1, 2, 3, etc. The angular momentum quantum number (l) can be any integer between 0 and n - 1. For n = 3, l can be either 0, 1, or 2. The magnetic quantum number (m) can be any integer between -l and +l. For l = 2, m can be either -2, -1, 0, +1, or +2.

Principle, angular momentum, and magnetic quantum numbers: n, l, and ml

Spin Quantum Number Spin quantum number denotes the behavior (direction of spin) of an electron within a magnetic field. Possibilities for electron spin:

An orbital is a region within an atom where there is a probability of finding an electron. This is a probability diagram for the s orbital in the first energy level… Orbital shapes are defined as the surface that contains 90% of the total electron probability.

Sizes of s orbitals Orbitals of the same shape (s, for instance) grow
larger as n increases… Nodes are regions of low probability within an orbital.

The s orbital has a spherical shape centered around
the origin of the three axes in space. s orbital shape

P orbital shape There are three dumbbell-shaped p orbitals in
each energy level above n = 1, each assigned to its own axis (x, y and z) in space.

Things get a bit more complicated with the five d orbitals that are found in the d sublevels beginning with n = 3. To remember the shapes, think of “double dumbells” d orbital shapes …and a “dumbell with a donut”!

Shape of f orbitals

Orbital filling table

Electron configuration of the elements of the first three series

Irregular confirmations of Cr and Cu
Chromium steals a 4s electron to half fill its 3d sublevel Copper steals a 4s electron to FILL its 3d sublevel

Mendeleev’s Periodic Table
Dmitri Mendeleev

Modern Russian Table

Stowe Periodic Table

A Spiral Periodic Table

“Mayan” Periodic Table

Period The Periodic Table Group or Family Group or family Period

The Properties of a Group: the Alkali Metals
Easily lose valence electron (Reducing agents) React violently with water Large hydration energy React with halogens to form salts

Properties of Metals Metals are good conductors of heat and electricity Metals are malleable Metals are ductile Metals have high tensile strength Metals have luster

Examples of Metals Potassium, K reacts with water and must be stored in kerosene Copper, Cu, is a relatively soft metal, and a very good electrical conductor. Zinc, Zn, is more stable than potassium Mercury, Hg, is the only metal that exists as a liquid at room temperature

Properties of Nonmetals
Carbon, the graphite in “pencil lead” is a great example of a nonmetallic element. Nonmetals are poor conductors of heat and electricity Nonmetals tend to be brittle Many nonmetals are gases at room temperature

Examples of Nonmetals Microspheres of phosphorus, P, a reactive nonmetal Sulfur, S, was once known as “brimstone” Graphite is not the only pure form of carbon, C. Diamond is also carbon; the color comes from impurities caught within the crystal structure

Properties of Metalloids
Metalloids straddle the border between metals and nonmetals on the periodic table. They have properties of both metals and nonmetals. Metalloids are more brittle than metals, less brittle than most nonmetallic solids Metalloids are semiconductors of electricity Some metalloids possess metallic luster

Silicon, Si – A Metalloid
Silicon has metallic luster Silicon is brittle like a nonmetal Silicon is a semiconductor of electricity Other metalloids include: Boron, B Germanium, Ge Arsenic, As Antimony, Sb Tellurium, Te

Determination of Atomic Radius:
Half of the distance between nucli in covalently bonded diatomic molecule "covalent atomic radii" Periodic Trends in Atomic Radius Radius decreases across a period Increased effective nuclear charge due to decreased shielding Radius increases down a group Addition of principal quantum levels

Table of Atomic Radii

Increases for successive electrons taken from the same atom
Ionization Energy - the energy required to remove an electron from an atom Increases for successive electrons taken from the same atom Tends to increase across a period Electrons in the same quantum level do not shield as effectively as electrons in inner levels     Irregularities at half filled and filled sublevels due to extra repulsion of electrons paired in orbitals, making them easier to remove Tends to decrease down a group Outer electrons are farther from the nucleus

Table of 1st Ionization Energies

Ionization of Magnesium
Mg kJ  Mg+ + e- Mg kJ  Mg e- Mg kJ  Mg e-

Another Way to Look at Ionization Energy

Electronegativity A measure of the ability of an atom in a chemical
compound to attract electrons Electronegativities tend to increase across a period Electronegativities tend to decrease down a group or remain the same

Periodic Table of Electronegativities

Summation of Periodic Trends

Ionic Radii Cations Anions Positively charged ions formed when
an atom of a metal loses one or more electrons Cations Smaller than the corresponding atom Negatively charged ions formed when nonmetallic atoms gain one or more electrons Anions Larger than the corresponding atom

Table of Ion Sizes

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