Chapter 7
Sponsored Links
This presentation is the property of its rightful owner.
1 / 46

Chapter 7 PowerPoint PPT Presentation


  • 75 Views
  • Uploaded on
  • Presentation posted in: General

Chapter 7. The Structure of Atoms and Periodic Trends. Arrangement of Electrons in Atoms. Electrons in atoms are arranged as: Shells (n) Subshells ( l ) Subshell orientation (m l ). Pauli’s Exclusion Principle. discovered in 1925 by Wolfgang Pauli

Download Presentation

Chapter 7

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Chapter 7

The Structure of Atoms and Periodic Trends


Arrangement of Electrons in Atoms

Electrons in atoms are arranged as:

Shells (n)

Subshells (l)

Subshell orientation (ml)


Pauli’s Exclusion Principle

  • discovered in 1925 by Wolfgang Pauli

    • -No two electrons in an atom can have the same set of 4 quantum numbers

Practice:What are the 4 quantum numbers for

each electron in He?


Aufbau Principle

Describes the electron filling order in atoms

-electrons are placed in the lowest available energy orbital

-the periodic table is a

function of electron

configurations for the

elements


Electron Configuration

To remember the correct filling order for electrons in atoms:


Electron Configuration


Example: H atomic number = 1

1

no. of

s

1

electrons

value of l

value of n

Writing Electron Configurations

Two ways to express electron configuration:

1. spdf notation


Writing Electron Configurations

2. Orbital box notation

spdf notation


Electron Configurations

Using the Aufbau Principle to determine the electronic configurations of the elements

1st row elements:


Electron Configurations

Hund’s rule: electrons fill suborbitals by placing electrons in each suborbital unpaired first with the same spin direction, then the electrons pair


Electron Configurations


Electron Configurations and Quantum Numbers

We can write a complete set of quantum numbers for all of the electrons in every element:

  • Na

  • Ca

  • Fe


Electron Configurations and Quantum Numbers

l

l

The ml and ms are interchangeable


Electron Configurations and Quantum Numbers

Noble Gas Notation (or short hand notation):

The first 18 electrons in Ca are represented with the preceding noble gas ([Ar])

- we only concern ourselves with the outermost e-

Skip the first 18 electrons


Electron Configurations and Quantum Numbers

l

l


Electron Configurations and Quantum Numbers

There is only one set of 4 quantum numbers for each of the 26 electrons in Fe:

  • To save space, we use the symbol [Ar] to represent the first 18 electrons in Fe


Electron Configurations of Ions

Electrons are removed from subshell of highest energy level (n-level)

P0 [Ne] 3s2 3p3 -3e- ---> P3+ [Ne] 3s2 3p0


Electron Configurations of Ions

For transition metals, remove the highest s-orbital electrons first:

Fe [Ar] 4s2 3d6

-2 electrons Fe2+ [Ar] 3d6

-3 electrons

Fe3+ [Ar] 3d5

To form cations, always remove electrons of highest n value first!


More About the Periodic Table

Representative Elements

Groups IA, IIA, IIIA-VIIIA

  • These elements will have their “outermost” electron in an outer s or p orbital

  • Variations in their properties are similar from top-to-bottom


More About the Periodic Table

d-Transition Elements

All have d electrons

-With n s-orbitals

-With n-1 d–orbitals

Have small property variations from row-to-row


More About the Periodic Table

f - transition metals

-Sometimes called inner transition metals

-Electrons are being added to f orbitals

Extremely small variations in properties from one element to another


More About the Periodic Table

Noble Gases

-Have filled electron shells

-have similar chemical reactivities

-similar electronic structures

He1s2

Ne[He] 2s2 2p6

Ar[Ne] 3s2 3p6

Kr [Ar] 4s2 4p6

Xe[Kr] 5s2 5p6

Rn[Xe] 6s2 6p6


Periodic Properties

  • Atomic radii describes the relative sizes of atoms

  • Atomic radii increase within

    a column

  • Atomic radii decrease within

    a row


Periodic Properties

Example: Arrange these elements based on their atomic radii:

Se, S, O, Te

O < S < Se < Te


Periodic Properties

Example: Arrange these elements based on their atomic radii:

P, Cl, S, Si

Cl < S < P < Si


Periodic Properties

Electronegativity: measure of the tendency of an atom to attract electrons to itself

-Fluorine is the most electronegative element

-Cesium is the least electronegative element

Electronegativity increase from left-to-right and decrease from top-to-bottom

increase

decrease


Periodic Properties

Example: Arrange these elements based on their electronegativity:

Se, Ge, Br, As

Ge < As < Se < Br


Periodic Properties

Example: Arrange these elements based on their electronegativity:

Be, Mg, Ca, Ba

Ba < Ca < Mg < Be


Periodic Properties

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

First ionization energy (IE1)

  • Energy required to remove the first electron from an atom in the gas state to form a 1+ ion

    Atom(g) + energy  Atom+(g) + e-

Example:

Mg(g) + 738kJ/mol  Mg+ + e-


Periodic Properties

Second ionization energy (IE2)

  • The amount of energy required to remove the second electron from a gaseous 1+ ion

    Atom+ + energy  Atom2+ + e-

  • Mg+ + 1451 kJ/mol Mg2+ + e-

  • - Atoms can have 3rd (IE3), 4th (IE4), etc.

  • - Each IE is significantly higher than the previous IE


Periodic Properties

Ionization Energy:

  • IE2 > IE1

    always takes moreenergy to remove a second electron from an ion

  • IE1 increases to the right

    Important exceptions are Be & Mg, N & P, etc. due to filled and half-filled subshells

  • IE1 decrease down


First Ionization Energies

He

Ne

F

Ar

N

Cl

C

P

H

Be

O

Mg

S

Ca

B

Si

Li

Al

Na

K


Periodic Properties

Example: Arrange these elements based on their first ionization energies:

Sr, Be, Ca, Mg

Sr < Ca < Mg < Be


Periodic Properties

Example: Arrange these elements based on their first ionization energies:

Al, Cl, Na, P

Na < Al < P < Cl


Periodic Properties

Electron Affinity: Energy absorbed when an electron is added to an atom to form a negative ion

Sign conventions for electron affinity:

  • If electron affinity > 0 energy is absorbed

  • If electron affinity < 0 energy is released

    Electron affinity is the measure of an atom’s ability to form negative ions

atom(g) + e- + EA  atom-(g)


Periodic Properties

Examples of electron affinity values:

Mg(g) + e- + 231 kJ/mol Mg-(g)

EA = +231 kJ/mol

  • Br(g) + e- Br-(g) + 323 kJ/mol

    • EA = -323 kJ/mol

Increasing ability to

add electrons

decreasing ability

to add electrons


Electron Affinity

He

Be

B

N

Ne

Mg

Al

Ar

Ca

P

Na

K

H

Li

O

C

Si

S

F

Cl


Periodic Properties

Example: Arrange these elements based on their electron affinities:

Al, Mg, Si, Na

Si < Al < Na < Mg


Periodic Properties

Ionic Radius: diameter of an atom in its ionized form

-Cations are always smaller


Periodic Properties

Anions are always larger


Periodic Properties

Cation radii decrease from left to right across a period

  • Increasing nuclear charge attracts the electrons and decreases the radius.


Periodic Properties

Anion radii decrease from left to right across a period

  • Increasing electron numbers in highly charged ions cause the electrons to repel and increase the ionic radius


Ionic Radii

Active Figure 8.15


Periodic Properties

Example: Arrange these elements based on their ionic radii:

Ca2+, K+, Ga3+

K1+ > Ca2+ > Ga3+


Periodic Properties

Example: Arrange these elements based on their ionic radii:

Cl-1, Se-2, Br-1, S-2

Cl1- < S2- < Br1- < Se2-


  • Login