Atomic Structure Atomic Structure and Periodicityand Periodicity

The Puzzle of the AtomThe Puzzle of the Atom Protons and electrons are attracted to each other because of opposite charges

Electrically charged particles moving in a curved path give off energy

Despite these facts, atoms don’t collapse

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!

Confused??? You’ve Got Confused??? You’ve Got Company!Company!

“No familiar conceptions can be woven around the

electron; something unknown is doing we

don’t know what.”

Physicist Sir Arthur Eddington

The Nature of the Physical World

1934

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.

c = C = speed of light, a constant (3.00 x 108 m/s)

= frequency, in units of hertz (hz, sec-1)

= wavelength, in meters

Electromagnetic radiation Electromagnetic radiation propagates through space as a wave propagates through space as a wave moving at the speed of light.moving at the speed of light.

Types of electromagnetic radiation:Types of electromagnetic radiation:

E = hEE = Energy, in units of Joules (kg·m= Energy, in units of Joules (kg·m22/s/s22))

hh = Planck’s constant (6.626 x 10-34 J·s)= Planck’s constant (6.626 x 10-34 J·s)

= frequency, in units of hertz (hz, sec= frequency, in units of hertz (hz, sec-1-1))

The energy (The energy (E E ) of electromagnetic ) of electromagnetic radiation is directly proportional to radiation is directly proportional to the frequency (the frequency () of the radiation.) of the radiation.

Long Wavelength

=Low Frequency

=Low ENERGY

Short Wavelength

=High Frequency

=High ENERGY

Wavelength TableWavelength Table

Relating Frequency, Relating Frequency, Wavelength and EnergyWavelength and Energy

c hE

hc

E

Common re-arrangements:

E

hc

…produces all of the colors in a continuous spectrum

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

…produces a “bright line” spectrum

Spectroscopic analysis of the Spectroscopic analysis of the hydrogen spectrum…hydrogen spectrum…

This produces bandsof light with definitewavelengths.

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

Electron Energy in HydrogenElectron Energy in Hydrogen

2

21810178.2

n

ZJxEelectron

***Equation works only for atoms or ions with 1 electron (H, He+, Li2+, etc).

Z = nuclear charge (atomic number)

n = energy level

Calculating Energy Change, Calculating Energy Change, E, E, for for

Electron TransitionsElectron Transitions

2

2

2

21810178.2

initialfinal n

Z

n

ZJxE

Energy must be absorbed from a photon (+EE) to move an electron ) to move an electron away from the nucleusaway from the nucleus

Energy (a photon) must be given off (-EE) when an electron moves toward ) when an electron moves toward the nucleusthe nucleus

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 Quantum Angular Momentum Quantum NumberNumber

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 (ml) can be any integer between -l and +l. For l = 2, m can be either -2, -1, 0, +1, +2.

Principle, angular momentum, and Principle, angular momentum, and magnetic quantum numbers: magnetic quantum 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…

Schrodinger Wave EquationSchrodinger Wave Equation

22

2 2

8dh EV

m dx

Equation for probabilityprobability of a single electron being found along a single axis (x-axis)Erwin Schrodinger

Heisenberg Uncertainty Heisenberg Uncertainty PrinciplePrinciple

You can find out where the electron is, but not where it is going.

OR…

You can find out where the electron is going, but not where it is!

“One cannot simultaneously determine both the position and momentum of an electron.”

WernerHeisenberg

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

Orbitals in outer energy levels DO penetrate intolower energy levels.

This is a probabilityDistribution for a 3s orbital.

What parts of thediagram correspondto “nodes” – regionsof zero probability?

Penetration #1

Which of the orbital types in the 3rd energy levelDoes not seem to have a “node”?

WHY NOT?

Penetration #2

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:

…and a “dumbell with a donut”!

d orbital shapes

“double dumbells”

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

Element Configuration notation

Orbital notation Noble gas notation

Lithium 1s22s1 ____ ____ ____ ____ ____ 1s 2s 2p

[He]2s1

Beryllium 1s22s2 ____ ____ ____ ____ ____ 1s 2s 2p

[He]2s2

Boron 1s22s2p1 ____ ____ ____ ____ ____ 1s 2s 2p

[He]2s2p1

Carbon 1s22s2p2 ____ ____ ____ ____ ____ 1s 2s 2p

[He]2s2p2

Nitrogen 1s22s2p3 ____ ____ ____ ____ ____

1s 2s 2p

[He]2s2p3

Oxygen 1s22s2p4 ____ ____ ____ ____ ____ 1s 2s 2p

[He]2s2p4

Fluorine 1s22s2p5 ____ ____ ____ ____ ____ 1s 2s 2p

[He]2s2p5

Neon 1s22s2p6 ____ ____ ____ ____ ____ 1s 2s 2p

[He]2s2p6

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

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

Table of Atomic Radii

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 thenucleus

Ionization Energy: the energy required to remove an electron from an atom

Mg + 738 kJ Mg+ + e-

Mg+ + 1451 kJ Mg2+ + e-

Mg2+ + 7733 kJ Mg3+ + e-

Ionization of Magnesium

Table of 1st Ionization Energies

Affinity tends to increase across a period

Affinity tends to decrease as you go down in a period

Electrons farther from the nucleusexperience less nuclear attraction

Some irregularities due to repulsive forces in the relatively small p orbitals

Electron Affinity - the energy change associated with the addition of an electron

Table of Electron Affinities

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

Electronegativity

Periodic Table of Electronegativities

Cations Positively charged ions

Smaller than the corresponding atomAnions

Negatively charged ions Larger than the corresponding atom

Ionic Radii

Table of Ion Sizes

Summary of Periodic Trends