Chapter 8
Download
1 / 59

Chapter 8 - PowerPoint PPT Presentation


  • 55 Views
  • Uploaded on

Chapter 8 . Covalent Bonding VSEPR Theory Molecular Shape Polar or NonPolar Properties of Molecular Substances. Why Do Atoms Bond?. The stability of an atom, ion or compound is related to its energy lower energy states are more stable.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Chapter 8' - tatyana-clemons


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 8

Chapter 8

Covalent Bonding

VSEPR Theory

Molecular Shape

Polar or NonPolar

Properties of Molecular Substances


Why do atoms bond
Why Do Atoms Bond?

  • The stability of an atom, ion or compound is related to its energy

    • lower energy states are more stable.

  • Metals and nonmetals gain stability by transferring electrons (gaining or losing) to form ions that have stable noble-gas electron configurations.

    • Ionic Bonding

  • Another way atoms can gain stability is by sharing valence electrons with other atoms, which also results in noble-gas electron configurations.

    • Covalent Bonding


Chapter 8


The covalent bond
The Covalent Bond maximum net attraction, where the atoms bond covalently and form a molecule.

  • Atoms will share electrons in order to form a stable octet.

  • Covalent bond : the chemical bond that results from the sharing of valence electrons

  • also called a molecular bond


The molecule
The Molecule maximum net attraction, where the atoms bond covalently and form a molecule.

  • formed when two or more atoms bond covalently

  • The smallest piece in a covalent compound

  • Formed when the proton of one atom is attracted to the electron cloud of another atom.


Chapter 8

Models maximum net attraction, where the atoms bond covalently and form a molecule.

Molecules


Single covalent bonds
Single Covalent Bonds maximum net attraction, where the atoms bond covalently and form a molecule.

  • In a single covalent bond a single pair of electrons is shared

  • This can be represented with a Lewis structure

  • A single line represents a single covalent bond

  • A single pair of electrons


Chapter 8

  • Bonding pair maximum net attraction, where the atoms bond covalently and form a molecule.: a pair of electrons shared by two atoms

  • Lone pair: an unshared pair of electrons on an atom


Formation of water
Formation of Water maximum net attraction, where the atoms bond covalently and form a molecule.


Group 17 elements will form one covalent bond
Group 17 elements will form one covalent bond. maximum net attraction, where the atoms bond covalently and form a molecule.


Group 16 elements will form two covalent bonds
Group 16 elements will form two covalent bonds. maximum net attraction, where the atoms bond covalently and form a molecule.


Group 15 elements will form three covalent bonds
Group 15 elements will form three covalent bonds. maximum net attraction, where the atoms bond covalently and form a molecule.


Group 14 elements will form four covalent bonds
Group 14 elements will form four covalent bonds. maximum net attraction, where the atoms bond covalently and form a molecule.


Sigma bonds
Sigma Bonds maximum net attraction, where the atoms bond covalently and form a molecule.

  • Single covalent bonds are also called sigma bonds:

  • the electron pair is centered between two atoms.


Multiple covalent bonds
 Multiple Covalent Bonds     maximum net attraction, where the atoms bond covalently and form a molecule.

When more than one pair of electrons is shared, a multiple covalent bond is formed

Multiple bonds are made up of sigma bonds and pi bonds: formed when parallel orbitals share electrons.


Double covalent bond
Double Covalent Bond maximum net attraction, where the atoms bond covalently and form a molecule.

Two pairs of electrons are shared

Contains one sigma and one pi bond.


Triple covalent bond
Triple Covalent Bond maximum net attraction, where the atoms bond covalently and form a molecule.

Three pairs of electrons are shared

Has one sigma and two pi bonds.


Strength of covalent bonds
Strength of Covalent Bonds maximum net attraction, where the atoms bond covalently and form a molecule.

  • The strength of covalent bonds is determined by the bond length:

    • distance between the bond nuclei

  • Bond length is determined by:

    • The size of the atoms involved—larger atoms have longer bond lengths

    • How many pairs of electrons are shared—the more pairs of electrons shared, the shorter the bond length is.


Bond dissociation energy
Bond Dissociation Energy maximum net attraction, where the atoms bond covalently and form a molecule.

  • the amount of energy required to break a bond

  • Indicates the strength of a covalent bond

  • When a bond forms, energy is released;

  • When a bond breaks, energy must be added

  • Each covalent bond has a specific value for its bond dissociation energy.


Bond energy and bond length
Bond Energy and Bond Length maximum net attraction, where the atoms bond covalently and form a molecule.

  • A direct relationship exists between bond energy and bond length

    • Shorter Bond

    • Stronger Bond

    • Higher Bond Dissociation Energy

    • Longer Bond

    • Weaker Bond

    • Lower Bond Dissociation Energy


Energy changes
Energy Changes maximum net attraction, where the atoms bond covalently and form a molecule.

An endothermic reaction is one where a greater amount of energy is required to break a bond in reactants than is released when the new bonds form in the products.

An exothermic reaction is one where more energy is released than is required to break the bonds in the initial reactants.


Naming molecules
Naming Molecules maximum net attraction, where the atoms bond covalently and form a molecule.

  • Molecular Formula

    • Shows what atoms and how many are in a molecule

    • Examples:

    • Nonmetal-Nonmetal Combinations


Naming binary compounds
Naming (Binary Compounds) maximum net attraction, where the atoms bond covalently and form a molecule.

The first element is always named first using the entire element name

The second element is named using its root and adding the suffix -ide

Prefixes are used to indicate the number of atoms of each element that are present in the compound


Common names
Common Names maximum net attraction, where the atoms bond covalently and form a molecule.

Many compounds were discovered and given common names long before the present naming system was developed (water, ammonia, hydrazine, nitric oxide).


Binary acids
Binary Acids maximum net attraction, where the atoms bond covalently and form a molecule.

An acid that contains hydrogen and one other element Ex. HCl

ion ends –ide.

Name the acid with hydro-root of the anion-ic

HCl (hydrogen and chloride ) becomes hydrochloric.

HCl in a water solution is called hydrochloric acid.


Naming acids
Naming Acids maximum net attraction, where the atoms bond covalently and form a molecule.

  • Acids contain hydrogen as the first element

    • Binary Acids: H bonded to one other element

      • An ion that ends –ide

      • Name the acid with hydro-root-ic

      • Example: HCl

        • Hydrogen ion and chloride ion

        • Hydrochloric acid


Oxyacids
Oxyacids maximum net attraction, where the atoms bond covalently and form a molecule.

  • An acid that contains both a hydrogen atom and an oxyanion.

  • Example: HNO3

  • Identify the oxyanion present.

  • name ends with the suffix –ate, replace it with the suffix –ic.

  • If the name ends with suffix –ite, replace it with suffix –ous,

  • NO3 is the nitrate ion so the acid is nitric acid.


Acid naming summary
Acid Naming Summary maximum net attraction, where the atoms bond covalently and form a molecule.


Structural formulas
Structural Formulas maximum net attraction, where the atoms bond covalently and form a molecule.

A structural formula uses letter symbols and bonds to show relative positions of atoms.


Lewis structures
Lewis Structures maximum net attraction, where the atoms bond covalently and form a molecule.

Used to predict the structural formula

Show arrangement of the atoms and un-bonded electrons


Five steps to draw lewis structures
Five steps to draw Lewis structures: maximum net attraction, where the atoms bond covalently and form a molecule.

  • Count the total number of valence electrons in all atoms involved.

  • Decide how the elements are arranged in the structure and draw it out.

    • Hydrogen is always an end atom.

    • Central atom is usually written first in compound

    • Central atom has least attraction for the electrons

    • Usually closer to left on periodic table

  • Subtract the # of electrons used in the bonds.


Chapter 8

Satisfy the octets of the terminal atoms. maximum net attraction, where the atoms bond covalently and form a molecule.

Place any remaining electrons around the central atom to satisfy its octet. If the central atom cannot be satisfied, make a multiple bond using a lone pair from the terminal atoms.

Check your work 


Examples
Examples maximum net attraction, where the atoms bond covalently and form a molecule.


Chapter 8

Drawing Lewis structures for polyatomic ions is very similar to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bonding

  • Count the total number of valence electrons in all atoms involved.

  • If the polyatomic ion is negatively charged, ADD the charge to the number of valence electrons.

  • If the ion is positively charged, SUBRACT the charge from the number of valence electrons.

  • Follow the rest of the steps to drawing Lewis structures.


Examples1
Examples to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bonding


Resonance structures
Resonance Structures to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bonding

When a molecule or polyatomic ion has both a double bond and a single bond, it is possible to have more than one correct Lewis structure:


Resonance
Resonance to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bonding

a condition that occurs when more than one valid Lewis structure can be written for a molecule or ion.

The structures are called resonance structures.

A molecule that undergoes resonance behaves as if it has only one structure.


Exceptions to the octet rule
Exceptions to the Octet Rule to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bonding

Three Ways Molecules Might Violate the Octet Rule


Odd number of valence electrons
Odd Number of Valence Electrons to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bonding

  • Some molecules have an odd number of valence electrons and cannot form an octet around each atom

  • Example: NO2


Sub octet
Sub Octet to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bonding

  • Some compounds form with fewer than 8 electrons present around an atom.

  • Boron

  • BF3


Coordinate covalent bond
Coordinate covalent bond to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bonding

  • when one atom donates an entire pair of electrons to be shared with atoms or ions that need two more electrons.

  • Boron compounds often do this


Expanded octet
Expanded Octet to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bonding

  • Some elements can have more than eight electrons in their valence shell

  • Because of d-level electrons

  • PCl5


Chapter 8

  • How? to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bonding

    • The d orbital starts to hold electrons.

    • This occurs in atoms in Period 3 or higher.

    • When you draw Lewis structures for these compounds, extra lone pairs are added to the central atom OR the central atom will form more than four bonds.


Things to remember
Things to Remember to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bonding

  • Any exceptions to the Octet Rule are on the central atom


Molecular shape
Molecular Shape to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bonding

How a molecule “looks”

Determines properties

The shape of a molecule determines whether or not two molecules can get close enough to react

We describe shape using the VSEPR model


Vsepr
VSEPR to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bonding

This model is based on the fact that electrons pairs will stay as far away from each other as possible

Valence

Shell

Electron

Pair

Repulsion


How to apply vsepr
How to apply VSEPR to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bonding

Draw the Lewis Structure for a Molecule

Count the pairs of bonded electrons

Count the pairs of unbonded electrons

Match the information with the VSEPR chart to classify the shape of the molecule


Chapter 8

  • Atoms will assume certain to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bondingbond angles: the angle formed by any two terminal atoms and the central atom

  • Lone pairs take up more space than bonded pairs do.


Molecular polarity
Molecular Polarity to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bonding

Molecules are either polar or nonpolar depending on the bonds in the molecule.

We must look at the shape (geometry) of a molecule to determine polarity.

Symmetric molecules are nonpolar.

Asymmetric Molecules are Nonpolar


Polar or nonpolar
Polar or NonPolar to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bonding

  • Determine if a molecule is polar or nonpolar by

    • Looking at a model of the molecule

    • Looking at a Lewis Structure of the molecule


Solubility of polar molecules
Solubility of Polar Molecules to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bonding

Bond type and shape of the molecule determine solubility

Polar substances and ionic substances will dissolve in polar solvents

Nonpolar substances will only dissolve in nonpolar substances


Intermolecular forces
Intermolecular Forces to drawing Lewis structures for covalent compounds EXCEPT in finding the number of electrons available for bonding

  • Nonpolar Molecules: Van der Waals intermolecular Forces

    • Very Weak forces between molecules

  • Polar Molecules: have dipole-dipole intermolecular bonding.

    • Stronger intermolecular Forces

  • Polar Molecules with Hydrogen Bonding: hydrogen bonded to nitrogen, oxygen or fluorine, it will have hydrogen bonding between molecules. A very strong dipole-dipole interaction

    • Very strong intermolecular Forces

    • High boiling points, high melting points