chapter 10 the amazing colors in these fireworks explosions are the result of electrons transferring...

Chapter 10The amazing colors in these fireworks explosions are the result of electrons transferring between energy levels in atoms.

Chapter Outline

Copyright 2012 John Wiley & Sons, Inc 10-2

10.1 A Brief History

10.2 Electromagnetic Radiation

10.3 The Bohr Atom

10.4 Energy Levels of Electrons

10.5 Atomic Structures of the First 18 Elements

10.6 Electron Structures and the Periodic Table

Objectives for Today

Historical models of the atom Electromagnetic radiation & the atom Electron configurations

10-3

Democritus

• Greek natural philosopher• Concept of “Atomos”

4

Dalton’s Atomic Theory

In Dalton’s atomic theory, atoms• are tiny particles of matter. • of an element are similar and different

from other elements.• of two or more different elements

combine to form compounds.• are rearranged to form new

combinations in a chemical reaction.

5

Rutherford’s Gold Foil Experiment

6

Copyright © 2009 by Pearson Education, Inc.

Rutherford’s Gold Foil Experiment

In Rutherford’s gold foil experiment, positively charged particles were aimed at atoms of gold.

Most went straight through the atoms. A few were deflected.

Conclusion: There must be a small, dense, positively charged nucleus in the atom that deflects positive particles that come close.

7

Atoms

• Tiny…about 10-10 m– If the atoms in your body were 1 in. in diameter,

you’d bump your head on the moon.

• Huge number of atoms in even a small sample of an element– 1/2 carat diamond has 5 1021 atoms…if lined up,

would stretch to the sun.

Electromagnetic Radiation

Frequency tells how many waves pass a particular point per second.

Speed tells how fast a wave moves through space.

Figure 10.1 The wavelength of this wave is shown by λ. It can be measured from peak to peak or trough to trough.


The Electromagnetic Spectrum

Visible light is only a small part of the electromagnetic spectrum.


Your Turn!

• The number of waves that pass a particular point per second is known as

a. Frequencyb.Wavelengthc. Amplituded.Speed


Your Turn!

• The color of visible light is determined by itsa. Speedb.Wavelengthc. Amplitude


Bohr Model (1912-1913)

• Danish physicist Niels Bohr proposed that electrons in an atom are organized into discrete energy levels.

• He pictured the negative electrons in orbits around the positive nucleus.

• His evidence: the line spectra of the elements.


Line Spectrum

• Atoms absorb energy to give off light..• Prisms or diffraction gratings separate the

light into a line spectrum for the element.


Line Spectrum


Why so many lines?


Absorbed energy

Pote

ntial

ene

rgy

of h

ydro

gen

elec

tron

1

3

2

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Released energy

Each line in the spectrum corresponds to electrons moving from a higher energy level to a lower energy level.

Your Turn!

• The lowest possible energy level for an electron is known as

a. Low stateb.Ground statec. Basement stated.Excited state


Bohr Model

• Was based on electrons having fixed energy levels and therefore quantized amounts of energy.

• Accounted for spectral lines.• Worked very well for hydrogen but did not

work well for heavier atoms.• Another model is needed that describes the

behavior of electrons as waves.


Ways to deal with Complexity and Uncertainty

• Analogies In order to communicate something of the nature of the electron, scientists often use analogies. For example, in some ways, electrons are like vibrating guitar strings.

• Probabilities In order to accommodate the uncertainty of the electron’s position and motion, we refer to where the electron probably is within the atom instead of where it definitely is.

Guitar String Waveform

Allowed Vibrations for a Guitar String

Wave Character of the Electron

• Just as the intensity of the movement of a guitar string can vary, so can the intensity of the negative charge of the electron vary at different positions outside the nucleus.

• The variation in the intensity of the electron charge can be described in terms of a three-dimensional standing wave like the standing wave of the guitar string.

Wave Character of the Electron

• Although both the electron and the guitar string can have an infinite number of possible waveforms, only certain waveforms are possible.

• We can focus our attention on the waveform of varying charge intensity without having to think about the actual physical nature of the electron.

Waveform for 1s Electron

The Wave-Mechanical Model• This mathematical model

of the atom describes the energy of the electron with some certainty, but the actual location of the electron is uncertain.

• An orbital is the region in space where there is a high probability of finding an electron with a given energy.


1s Orbital

Particle Interpretation of 1s Orbital

Energy Levels of Electrons

• Electrons in atoms are organized into discrete principal energy levels (n, where n is an integer).

• Lowest energy level is n = 1, then n = 2, etc.

• As n increases, the energy of the electron increases, and the electron is on average further from the nucleus.


SublevelsEnergy levels are subdivided

into sublevels.n = 1 has the sublevel 1s.n = 2 has the sublevels 2s

and 2p.Each sublevel is made up of

orbitals of the same type and energy.


Electron Spin

Each electron in an atom appears to be spinning on its axis.

Pauli exclusion principle states that an atomic orbital can hold a maximum of two electrons, which must have opposite spin.

What is the maximum number of electrons in any orbital?

22


Electron Spin

Pauli Exclusion Principle

• No two electrons in an atom can be the same in all ways.

• There are four ways that electrons can be the same:

Electrons can be in the same principal energy level.

They can be in the same sublevel.

They can be in the same orbital.

They can have the same spin.

Some Allowed Waveforms

s Sublevels

• Every principal energy level has an s sublevel that contains a single s orbital. (1s, 2s, 3s, etc.)

• There is a 90% probability of finding the electron within a spherical region surrounding the nucleus.

• Each s orbital holds 2 electrons with opposite spin.


p Sublevels• Every principal energy level starting at n = 2 has a p sublevel (2p, 3p, etc.) that contains 3 equal energy p orbitals. The orbitals only differ by their orientation in 3-D space.


Your Turn!

• What is the maximum number of electrons in a 2p orbital?

a. 2b.4c. 6d.8


A 2p sublevel holds 6 electrons, 2 electrons per orbital.

d Sublevels

• Every principal energy level starting at n = 3 has a d sublevel (3d, 4d, etc.) that contains 5 equal energy d orbitals. These orbitals have more complex shapes and are higher in energy than the s and p orbitals.


Your Turn!

• What is the maximum number of electrons in a 3d sublevel?

a. 2b.4c. 6d.10


A 3d sublevel has 5 orbitals, so it holds 10 electrons, 2 electrons per orbital.


Historical models of the atom Electromagnetic radiation & the atom Electron configurations

10-39


Atomic configurations The Periodic Table

40

Principal Energy Levels

Principal Energy levels • are assigned numbers n = 1,

2, 3, 4, and so on.• increase in energy as the

value of n increases.• are like the rungs of a ladder

with the lower energy levels nearer the nucleus.

41

Summary of Electronic Configurations

Principal Energy Levels (n) have a maximum number of electrons equal to 2n2.

Principal Energy level Maximum number of electrons n = 1 2(1)2 = 2(1) = 2 n = 2 2(2)2 = 2(4) = 8 n = 3 2(3)2 = 2(9) = 18

The number of subshells is the same as n

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Summary of Electronic Configurations

• Each subshell is composed of orbitals• The number of orbitals depends on the

subshell• Maximum of 2 electrons per orbital

Subshell s p d fNumber of Orbitals 1 3 5 7Electrons 2 6 10 14


Orbitals

An orbital • is a three-dimensional space around a nucleus, where

an electron is most likely to be found.

• has a shape that represents electron density (not a path the electron follows).

• can hold up to 2 electrons.

44

Orbitals

A p orbital

• has a two-lobed shape.

• is one of three p orbitals in each energy level from n = 2.

Three p orbitals make up a p subshell

45

An s orbital

•has a spherical shape around the nucleus.

•is found in each energy level.

Orbitals

46

Electron Level ArrangementIn the electron level arrangement for the first 18 elements • electrons are placed in energy levels (1, 2, 3, etc.),

beginning with the lowest energy level• there is a maximum number in each energy level.

Energy level Number of electrons1 2 (up to He)2 8 (up to Ne)3 8 (up to Ar)4 2 (up to Ca)

47

Rules for Distributing Electrons

1. No more than two electrons can occupy one orbital.

2. Electrons occupy the lowest energy orbitals available. s < p < d < f for a given value of n

3. Each orbital in a sublevel is occupied by a single electron before a second electron enters. (Hunds Rule)


Your Turn!

• In the fourth principal energy level (n = 4), which sublevel contains electrons with the greatest energy?

a. 4sb.4pc. 4dd.4f


Your Turn!

• How many orbitals are found in a 5p sublevel?a. 1b.3c. 5d.7


Your Turn!

• What is the maximum number of electrons that can occupy the third principal energy level (n = 3)?

a. 2b.6c. 8d.18


An atom consists• of a nucleus that

contains protons and neutrons.

• of electrons in a large, empty space around the nucleus.

52


Different Expressions of Atomic Structure

• One way to indicate atomic structure shows the structure of the nucleus and the number of electrons in each energy level.


Electron Configuration

• Another useful atomic structure shows the distribution of electrons in the atom.


Orbital Diagrams

• Electron configurations can also be shown with orbital diagrams. Each box represents an orbital.

• Up and down arrows represent electrons of opposite spin.


Atomic Structure•

3Li 1s22s1 4Be 1s22s2

•5B 1s22s22p1

•6C 1s22s22p2

• •

7N 1s22s22p2 • •

8O 1s22s22p2 •


2s 1s

2p 2s 1s

2s 1s

2p 2s 1s

2p 2s 1s

2p 2s 1s

Atomic Structure


Atomic Structure


Remember to sum the superscripts in the electron configuration. They should add up to the atomic number for the element.

Valence Electrons

• The valence electrons include all of the electrons in the highest principal quantum number (the outermost energy level).

• These electrons are the electrons that are involved in bonding.

• Phosphorus: 1s2 2s2 2p6 3s2 3p3

• Phosphorus has 5 valence electrons.


Your Turn!

• Atoms of which element have the following electron configuration?

• 1s2 2s2 2p6 3s23p6

a. Clb.Cac. Ard.S


Periodic Table

61

Groups and Periods

62


Groups and Periods

On the periodic table,

• elements are arranged according to similar properties.

• groups contain elements with similar properties in vertical columns.

• periods are horizontal rows of elements.

63

The Periodic Table

• Each horizontal row in the periodic table is called a period.

• The number of each period corresponds to the outermost energy level of the element.

• For example, Ar is in period 3 and its outermost energy level is 3.

• 1s2 2s2 2p6 3s23p6

• Argon has 8 electrons in energy level 3.Copyright 2012 John Wiley & Sons, Inc 10-64

The Periodic Table

• Groups or Families contain elements whose properties are similar.

• Representative Elements – A Groups• Alkali Metals –1A• Alkaline Earth Metals – 2A• Halogens – 7A• Noble Gases – 8A


Other Groups to Know

• Transition Metals – B Groups

• Inner Transition Metals– Lanthanides (Rare Earth) – Atomic Nos. 58 -71– Actinides – Atomic Nos. 90 – 103


Your Turn!

• Which element is a transition element?a. sodiumb.fluorinec. copperd.lead


Your Turn!

• Chlorine is a member of what family of elements?

a. Noble gasesb.Alkali metalsc. Halogensd.Chalcogens


Valence Electrons and Groups

10-69

In the following groups, the group number is the number of valence electrons.Elements within a group have the same valence electron configuration.

Your Turn!

• In which category of the periodic table does each element contain valence electrons in the second principal energy level?

a. The alkaline earth elementsb.The alkali metalsc. Group 2Ad.Period 2


Your Turn!

• On the periodic table, elements in the same group contain the same number of

a. Protonsb.Electronsc. Principal energy levels in their ground stated.Valence electrons in their ground state


Electron Configurations and the Periodic Table


Electron Configurations and the Periodic Table

1. The number of the period corresponds with the highest occupied energy level.

2. The group numbers for the representative elements are equal to the total number of valence electrons.

3. The elements within a group have the same number of valence electrons.

4. The elements within each of the s, p, d, f blocks are filling s, p, d, f orbitals.

5. There are discrepancies within the transition elements.


Order of Electron Energies

Abbreviated Electron Configurations

Use the symbol of the nearest preceding noble gas to represent the electron configuration of the core electrons.

Phosphorus: 1s2 2s2 2p6 3s2 3p3

[Ne] 3s2 3p3


Core Electrons

Valence Electrons

Your Turn!

• The electron configuration, [Ar] 4s1, is the ground state electron configuration of

a. Potassiumb.Phosphorousc. Fluorined.Sodium


Your Turn!

• The electron configuration, [Ne] 3s2 3p1, is the ground state electron configuration of

a. Sodiumb.Aluminumc. Argond.Sulfur



Atomic configurations The Periodic Table

79

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