Chapter 11 chemical bonds the formation of compounds from atoms
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Chapter 11 Chemical Bonds: The Formation of Compounds from Atoms. Objectives: Describe the trends in the periodic table Know how to draw Lewis Structures of atoms Understand and predict the formation of ionic bonds Understand and predict covalent bonds Describe electronegativity

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Chapter 11 Chemical Bonds: The Formation of Compounds from Atoms

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Chapter 11 chemical bonds the formation of compounds from atoms

Chapter 11Chemical Bonds:The Formation of Compounds from Atoms

Objectives:

Describe the trends in the periodic table

Know how to draw Lewis Structures of atoms

Understand and predict the formation of ionic bonds

Understand and predict covalent bonds

Describe electronegativity

Know how to draw complex lewis structures of compounds

Understand the formation of compounds containing polyatomic ions

Describe molecular shape, including the VSEPR model


Periodic trends in atomic properties

Periodic Trends in Atomic Properties

  • Periodic table designed to show trends

    • Use trends to predict properties and reactions between elements

  • Trends include:

    • Metals, nonmetals, metalloids

    • Atomic radius

    • Ionization energy

    • Electronegativity


Metals nonmetals and metalloids

Metals, Nonmetals and Metalloids

  • Metals:

    • Left-hand side of table

    • Most elements are metals

    • Tend to


Metals nonmetals and metalloids1

Metals, Nonmetals and Metalloids

  • Nonmetals:

    • Right side of table

    • (Hydrogen displays nonmetallic properties under normal conditions but is UNIQUE element)


Metals nonmetals and metalloids2

Metals, Nonmetals and Metalloids

  • Metalloids

    • Found along border between metals and nonmetals

  • Metal + Nonmetal

    • Usually electrons are transferred


Atomic radius

Atomic Radius

  • Increases

    • Each step down =

    • More energy levels =

  • Decreases from

    • Electrons added to the same energy level

    • Increase in positive charge =


Atomic radius1

Atomic Radius


Ionization energy

Ionization Energy

  • The energy required to

    • More energy required to remove 2nd, 3rd, 4th, 5th, etc. electron

    • Noble gas structure is stable so takes


Ionization energy1

Ionization Energy

  • Ionization energy in Group A elements

  • Ionization energy

  • Metals –

  • Nonmetals –


Ionization energy2

Ionization Energy


Lewis structures

Lewis Structures

  • Diagram that shows

    • American chemist Gilbert N. Lewis

    • Dots =

    • Paired dots =

  • Simple way of showing electrons

  • Most reactions involve only outermost electrons


Lewis structures1

Lewis Structures

  • When drawing:

    • Use

    • Move in clockwise direction…

  • Examples: draw Lewis Structures of B, N, F, Ne


The ionic bond

The Ionic Bond

  • Ionic bond:

    • Transfer of electrons

    • Attraction between electrostatic charges is a strong force which holds atomstogether


The ionic bond1

The Ionic Bond

  • NOT A MOLECULE

    • Bond not just between (for example) one sodium and one chloride


The ionic bond2

The Ionic Bond

  • Typically

  • Metals usually

  • Nonmetals usually


Predicting formulas of ionic compounds

Predicting Formulas of Ionic Compounds

  • In almost all stable chemical compounds of representative elements, each atom attains a noble gas electron configuration. This concept forms the basis for our understanding of chemical bonding.


Predicting formulas of ionic compounds1

Predicting Formulas of Ionic Compounds

  • How many electrons must be gained or lost to achieve noble gas configuration?

    • Ba must

      • Forms the ion

    • S must

      • Forms the ion

    • So…


Predicting formulas of ionic compounds2

Predicting Formulas of Ionic Compounds

  • Elements in a family usually form compounds with the same atomic ratios

    • Because they have the same number of valence electrons

      • Must gain or lose the same number of electrons

    • See table 11.4 pg 233


Predicting formulas of ionic compounds3

Predicting Formulas of Ionic Compounds

  • The formula for sodium oxide is

  • Predict the formula for

    • Sodium sulfide


Predicting formulas of ionic compounds4

Predicting Formulas of Ionic Compounds

  • Rubidium Oxide


The covalent bond

The Covalent Bond

  • A pair of electrons

  • Most common type of bond

  • Stronger

  • Electron orbital expands to include both nuclei

    • most often found between two nuclei

    • Negative charges allow positive nuclei to be drawn close to each other


The covalent bond1

The Covalent Bond

  • Atoms may share more than one pair of electrons

  • Covalent bonding between identical atoms means

  • Covalent bonding between different atoms leads to


Electronegativity

Electronegativity

  • The attractive force that an atom of an element has for shared electrons

  • Atoms have different electronegativities


Electronegativity1

Electronegativity

  • Electronegativity trends and periodic table

    • See table 11.5 page 237


Electronegativity2

Electronegativity


Electronegativity3

Electronegativity

  • Polarity is determined by difference in electronegativity

    • Nonpolar covalent

    • Polar covalent

    • Ionic compound


Electronegativity4

Electronegativity

  • If the electronegativity difference is greater than 1.7-1.9 then the bond will be more ionic than covalent

  • Above 1.6 = ionic bond

  • Below 0.3 = nonpolar covalent

  • See Continuum on page 239


Electronegativity5

Electronegativity

  • Polar bonds form between two atoms

  • Molecules can also be polar or nonpolar

    • Dipole

    • Polar

    • Nonpolar


Lewis structures of compounds

Lewis Structures of Compounds

  • Convenient way of showing ionic or covalent bonds

  • Usually the single atom in a formula is the central atom


Lewis structures of compounds1

Lewis Structures of Compounds

  • Obtain the total number of valence electrons

    • Add the valance electrons of all atoms

    • Ionic – add one electron for each negative charge and subtract one electron for each positive charge


Lewis structures of compounds2

Lewis Structures of Compounds

  • Write the skeletal arrangement of the atoms and connect with a single covalent bond

  • Subtract two electrons for each single bond

    • This gives you the net number of electrons available for completing the structure


Lewis structures of compounds3

Lewis Structures of Compounds

  • Distribute pairs of electrons around each atom to give each atom a noble gas structure

  • If there are not enough electrons then try to form double and triple bonds


Lewis structures of compounds4

Lewis Structures of Compounds

  • Write the Lewis Structure for methane CH4


Complex lewis structures

Complex Lewis Structures

  • Some molecules and polyatomic ions have strange behaviors…

    • No single Lewis structure is consistent

    • If multiple structures are possible the molecule shows


Complex lewis structures1

Complex Lewis Structures

  • Carbonate ion, CO32-

2-

2-

2-

Carbon only has 6 electrons – try double bonds – more than one location…..form resonant structures…

O

C

O O

O

C

O O

O

C

O O


Compounds containing polyatomic ions

Compounds ContainingPolyatomic Ions

  • Polyatomic ion: stable group of atoms that has a positive or negative charge

    • Behaves as a

  • Sodium carbonate (Na2CO3)


Compounds containing polyatomic ions1

Compounds ContainingPolyatomic Ions

  • Easier to dissociate ionic bond than break covalent bond

    • More in chapters 6 and 7


Molecular shape

Molecular Shape

  • Three-dimensional shape of molecule important

  • Helpful to know how to predict the geometric shape of molecules…


The vsepr model

The VSEPR Model

  • Valence Shell Electron Pair Repulsion Model

    • Make predictions about shape from Lewis structures


The vsepr model1

The VSEPR Model

  • Linear Structure


The vsepr model2

The VSEPR Model

  • Trigonal Planar


The vsepr model3

The VSEPR Model

  • Tetrahedral structure

    • When drawing:


The vsepr model4

The VSEPR Model

  • Pyramidal shape


The vsepr model5

The VSEPR Model

  • Electron pairs determine shape BUT name for shape is determined by position of atoms


The vsepr model6

The VSEPR Model

  • V-shaped or bent

    • But, moledule is “bent”


The vsepr model7

The VSEPR Model

  • Predict the shape for CF4, NF3, and BeI2.

    • Draw the Lewis Structure

    • Count the electron pairs and determine the arrangement that will minimize repulsions

    • Determine the positions of the atoms and name the structure


The vsepr model8

The VSEPR Model

  • CF4

  • NF3


The vsepr model9

The VSEPR Model

  • BeI2


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