Unit 2 – Electrons and Periodic Behavior

Unit 2 – Electrons Unit 2 – Electrons and Periodic and Periodic

BehaviorBehavior

Cartoon courtesy of NearingZero.net

Wave-Particle DualityWave-Particle DualityJJ 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 ElectronThe Wave-like Electron

Louis deBroglie

The electron propagates through space as an energy

wave. To understand the atom, one must

understand the behavior of

electromagnetic waves.

…produces all of the colors in a continuous spectrum

Spectroscopic analysis of the visible Spectroscopic analysis of the visible spectrum…spectrum…

This produces bandsof light with definitewavelengths.

Electron Electron transitionstransitionsinvolve jumps of involve jumps of definite amounts definite amounts ofofenergy.energy.

Quantum NumbersQuantum 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 PrinciplePauli Exclusion Principle

No two electrons in an atom can have the same four quantum numbers.

Wolfgang Pauli

Principal Quantum NumberPrincipal Quantum NumberGenerally 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 Angular Momentum Quantum NumberQuantum Number

The angular momentum quantum number,

generally symbolized by l, denotes the orbital (subshell) in which the electron is located.

Magnetic Quantum NumberMagnetic Quantum NumberThe 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 NumbersAssigning 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 Principle, angular momentum, and magnetic quantum numbers: numbers: nn, , ll, and , and mmll

Spin Quantum NumberSpin Quantum NumberSpin quantum number denotes the behavior (direction of spin) of an electron within a magnetic field.

Possibilities for electron spin:

1

2

1

2

Orbital shapes are defined as the surface that contains 90% of the total electron probability.

An orbital is a region within an atom where thereAn orbital is a region within an atom where thereis a probability of finding an electron. This is a is a probability of finding an electron. This is a probability diagram for the s orbital in the probability diagram for the s orbital in the first first energy level…energy level…

Orbitals of the same shape (s, for instance) grow larger as n increases…

Nodes are regions of low probability within an orbital.

Sizes of Sizes of ss orbitals orbitals

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

s 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.

PP orbital shape orbital shape

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”

…and a “dumbell with a donut”!

d orbital shapes

Shape of f orbitalsShape of f orbitals

Orbital filling tableOrbital filling table

Electron configuration of the Electron configuration of the elements of the first three elements of the first three

seriesseries

Irregular confirmations of Cr and CuIrregular confirmations of Cr and Cu

Chromium steals a 4s electron to halffill its 3d sublevel

Copper steals a 4s electron to FILL its 3d sublevel

Mendeleev’s Periodic TableMendeleev’s Periodic Table

Dmitri Mendeleev

Modern Russian TableModern Russian Table

Stowe Periodic TableStowe Periodic Table

A Spiral Periodic TableA Spiral Periodic Table

““Mayan” Mayan” Periodic Periodic

TableTable

The Periodic TableThe Periodic Table

Period

Group or family

PeriodGroup or Family

Easily lose valence electron (Reducing agents)

React violently with water Large hydration energy React with halogens to

form salts

The Properties of a Group: The Properties of a Group:

the Alkali Metalsthe Alkali Metals

Properties of MetalsProperties 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 MetalsExamples of Metals

Potassium, K reacts with water and must be stored in kerosene

Zinc, Zn, is more stable than potassium

Copper, Cu, is a relatively soft metal, and a very good electrical conductor.

Mercury, Hg, is the only metal that exists as a liquid at room temperature

PropertiesProperties of Nonmetalsof 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 NonmetalsExamples of Nonmetals

Sulfur, S, was once known as “brimstone”

Microspheres of phosphorus, P, a reactive nonmetal

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 MetalloidsProperties 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 MetalloidSilicon, 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

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 dueto decreased shielding

Radius increases down a group Addition of principal quantum levels

Determination of Atomic Radius:Determination of Atomic Radius:

Table of Table of Atomic Atomic

RadiiRadii

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 groupOuter electrons are farther from thenucleus

Ionization EnergyIonization Energy - the energy required to - the energy required to remove an electron from an atomremove an electron from an atom

Table of 1Table of 1stst Ionization Energies Ionization Energies

Ionization of MagnesiumIonization of Magnesium Mg + 738 kJ Mg+ + e-

Mg+ + 1451 kJ Mg2+ + e-

Mg2+ + 7733 kJ Mg3+ + e-

Another Way to Look at Ionization EnergyAnother Way to Look at Ionization Energy

ElectronegativityElectronegativity

A measure of the ability of an atom in a chemicalcompound to attract electrons

Electronegativities tend to increase across a period

Electronegativities tend to decrease down a group or remain the same

Periodic Table of ElectronegativitiesPeriodic Table of Electronegativities

Summation of Periodic TrendsSummation of Periodic Trends

Ionic RadiiIonic Radii

Cations

Positively charged ions formed when an atom of a metal loses one or more electrons Smaller than the corresponding atom

Anions

Negatively charged ions formed when nonmetallic atoms gain one or more electrons Larger than the corresponding atom

Table Table of Ion of Ion SizesSizes