chm 1025 chapter 9 webfaculty.scf.edu/gambinc/chm 1025/chm 1025/chm 1025c lecture/pdf...

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Chapter 9

“Electrons in Atoms and the PeriodicTable”

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Blimps, Balloons, and Models for theAtom

• Hindenburg

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Blimps, Balloons, and Models for the Atom

• Properties ofElements– Hydrogen Atoms

– Helium Atoms

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Blimps, Balloons, and Models for the Atom

• Periodic Law– When elements are arranged in

order of increasingatomic number, certain sets ofproperties recur periodically.

• Hydrogen

• Helium

• Why similarity?

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What we know about the atom?

• Rutherford concluded that the nucleuscontained protons. He could account for thecharge of the nucleus, but the mass of wastoo large for the number of protons.

• Protons and neutrons make up most of themass of the atom and are in the nucleus.

• Electrons are very light and are flyingaround outside the nucleus.

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How are the electrons arranged inthe atom?

• In order to understand how electrons arearranged, we must know something aboutelectromagnetic radiation.

• Examples of electromagnetic radiation are:___________________________________________________

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Light and ElectromagneticRadiation

• Observation: When certain elements areheated or electronically excited, they emitlight of different colors. When the light isseparated into various colors by aspectroscope, a spectrum is observed.

• Light is one type of electromagneticradiation.

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• When certain elements areheated or electronicallyexcited, they emit light ofdifferent colors.

• The light can be separatedinto various colors by aspectroscope, a linespectrum is observed.

What does Light have to do with Atoms?

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Models for the Atom

• Model for Atomic Structure– Based on Scientific Method

• Bohr Model– Developed in early 1900s– Niels Bohr

• Quantum Mechanical Model– Developed in early 1900s– Caused a revolution in the

Physical Sciences

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Light: Electromagnetic Radiation

• Electromagnetic Radiation

• Photon

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• Wave–________________• Wavelength– Wave Nature of Light– Distance between

Adjacent Wave Crests

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Wavelength of Light

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• Color– Determined by

Wavelength– Visible Light

• What you can see

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• Energy– Wavelength determines Energy– ______________________________

• Frequency– Another Characterization– Cycles per Second– Wave Crest that pass per Second

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• Summary - Electromagnetic Radiation– Form of Energy– Speed of light = 3.0 X 108 m/s– Wavelength determines the Energy– Shorter Wavelength – Higher the Energy– Frequency has inverse relationship to

Wavelength

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The Bohr Model: Atoms with Orbits

• Atoms and Energy– Absorbed Energy Re-emitted as

Light– Atoms Emit Unique Spectra – Color

• Emission Spectrum– Light Emitted by Glowing Elemental

Gas– Elements have Unique Emission

Spectra– Spectra Characteristic of Element

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• White Light Spectrum– Continuous

• Emission Spectrum– Bright Spots at Specific Wavelengths

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• Emission Spectrum and theAtomic Model– Explanation of Bright Line

Spectra– Unique Spectra for Each

Element• Bohr Model

– Electrons Travel in CircularOrbits

– Planetary Model

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• Bohr Model– Specific Fixed Orbits– Energy of each Orbit

Specified• Quantum Numbers

– Specify Orbits– Quantized Orbits– Like Steps in a Ladder

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• Quantum Numbers– Steps on Ladder– Cannot Stand between

Steps– Principal Quantum Number

• “n”• Distance from the Nucleus• Energy

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• Excitation of Electrons– Absorbs Energy– Promoted to “higher”

Energy Orbit• Quantum of Energy

– Relaxes– Emits a Photon

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• Quantum of Energy– Relaxes– Emits a Photon

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• Summary– Electrons exist in Quantized Orbits

• Specific Fixed Energies• Specific Fixed Distances

– Energy Excites Electron• Electrons are Promoted to Higher Energy Orbits

– Atoms Emit Light• Electrons fall from Higher Energy Orbits

– Energy and Wavelength• Corresponds to the Difference in Energy between the Orbits• Energies are Fixed and Discrete

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The Quantum Mechanical Model:Atoms with Orbitals

• Orbitals– Replace Circular Orbits– Not Specific Path– Statistical Distribution of Electron

• Probability Maps– Show where Electron is “likely” to be Found– Electrons Do Not Act like Particles– Non-Intuitive

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Quantum Mechanical ModelAtoms with Orbitals

• Baseballs and Electrons– Baseballs

• Trace the Baseball Path• Predict where the Baseball

crosses Home Plate– Electrons

• Impossible for Electron• Wave–Particle Duality• No Predictable Path

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The Quantum Mechanical Model:Atoms with Orbitals

• Orbits to Orbitals– Bohr Model

• Orbit• Circular Path around the Nucleus

– Quantum Mechanical Model• Orbital• Probability Map• Different Orbital Shapes

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Quantum Mechanical Orbitals

• Principal Quantum Number – n– Identifies the Principal Shell of the orbital– Higher Principal Quantum Number

denotes higher energy• Subshell– Indicated by Letter s, p, d, or f– Specifies Shape of Orbital

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• “s” Subshell– Spherical Shape– 3-D Probability Map– Dot Density is

proportional toprobability of findingElectron in that area

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• “n” = 2– Two Subshells– “s”

• Similar to 1s• Larger

– Has a “p”subshell

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Charge CloudRepresentationsof “s” Orbitals

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• “p”• Three

Orbitals• Different

Orientations

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Shapesof “p”

Orbitals

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• Orbital Diagrams– Similar Information– Electrons as Arrows

• Pauli Exclusion Principle• Electron Spin

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C

6 electrons

1s22s22p2

[He]2s22p2

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• Orbitals Fill to Minimize Energy

• 1s, 2s, 2p, 3s, 3p, 4s

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Ni

28 electrons

1s22s22p6 3s23p64s23d8

[Ar] 4s23d8

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• Summary of Electrons and Orbitals– Electrons Occupy Orbitals to Minimize

Energy• Lower Energy Orbitals Fill First• Aufbau Diagram gives Order

– Orbitals Hold 2 Electrons• Pauli Exclusion Principle• Opposing Spins

– Electrons Occupy Orbitals Singly First• Hund’s Rule• Parallel Spins

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• Electron Configuration– “s” Subshell

• 1 Orbital• 2 Electrons

– “p” Subshell• 3 Orbitals• 6 Electrons

– “d” Subshell• 5 Orbitals• 10 Electrons

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Electron Configurations and the Periodic Table

• Valence Electrons– Electrons in the Outermost

Principal Shell– Electrons Involved in

Chemical Bonding• Core Electrons

– Electrons Not in theOutermost Principal Shell

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Valence Electrons

• The outer electrons in an atom are valenceelectrons.

• Valence electrons can be represented withdots in the Lewis electron dot symbol.

• Each outer electron is represented by a dotaround the atomic symbol:

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• Patterns in the Periodic Table

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• Electron Configurations in the Periodic Table– Inner Electron Configuration is the Electron

Configuration of the Noble Gas that immediatelyprecedes that element in the Periodic Table.

– Outer Electrons can be deduced from the element’sposition within a particular block (s, p, d, and f).

– Highest Principal Quantum Number is equal to theRow.

– For “d” electrons, the Principal Quantum Number ofthe outermost “d” electrons is n – 1.

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Insert figure 5.32

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Insert figure5.33

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Quantum Mechanical Model

• Noble Gases– Group 8– Not Reactive– p6

– Completely Full Valence Shell

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• Alkali Metals– Group 1– Reactive– s1

– Ions lose 1 electron

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• Alkaline Earth Metals– Group 2– Reactive– s2

– Ions lose 2 electrons

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• Halogens– Group 7– Reactive– p5

– Ions gain 1 electron

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Periodic Trends: Ionization Energy

• Ionization Energy (IE)– Energy required to remove an electron

from an atom in the gaseous state

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Periodic Trends: Ionization Energy

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Periodic Trends: Atomic Size

• Atomic Size (AS)– Distance of outermost electrons from

the Nucleus

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Periodic Trends: Atomic Size

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Periodic Trends: Metallic Character

• Metallic Character (MC)– Metals lose electrons

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Periodic Trends: Metallic Character

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chm 1025 chapter 9 webfaculty.scf.edu/gambinc/chm 1025/chm 1025/chm 1025c lecture/pdf...

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