Bonding

The Properties of a Compound are Different from the Properties of the Elements that make up that

Compound

Calcium Chlorine

Calcium Chloride

Copper Chloride

CopperChlorine

NaHCO3 MgCl2

Al(OH)3 Ca(NO3)2

Chemical Formula: Used to represent the kinds and numbers of atoms in a chemical compound.

HC2H3O2Subscript

Be(ClO2)2 Subscript multiplies to all subscripts in parentheses!

What must happen for elements to react with each other?

• Atoms of the elements must collide.

• The valence electrons are what actually collide in when elements form compounds.– This is because the valence

electrons are the outermost layer.

Valence Electrons

• The electrons in the outermost energy level of an atom

• Responsible for an atom’s chemical properties

LEWIS DOT DIAGRAMS

• A diagram where dots are placed around the chemical symbol of an element to illustrate the valence electrons

Octet Rule

• Octet = 8• States that atoms tend to gain, lose or share

electrons in order to acquire a full set of valence electrons. – For most elements this is 8 valence electrons– Hydrogen & Helium only require 2 valence

electrons• The elements are all trying to be like the Group 18

elements, the noble gases b/c they have 8 valence electrons– Atoms form compounds to become stable!

How do atoms obtain a noble gas configuration?

• By sharing or transferring electrons with other atoms– Example: Show how Na & Cl can become stable.

The bond between Na & Cl is due to:

ANIONS: Have gained electrons and have a negative charge (nonmetals)

CA+IONS: Have lost electrons and have a positive charge (metals)

ION: AN ATOM THAT HAS AQUIRED A CHARGE BY GAINING OR LOSING

ELECTRONS

If atoms transfer electrons to form a bond they become IONS

Ionic Compound: Compound formed from ionic bonds

• Ionic Bond: The strong attractive force between ions of opposite charge. Occurs when one atom transfers electrons to another atom to become stable

EMPIRICAL FORMULA Chemical formula for an ionic compound Lowest whole number ratio of ions in an ionic

compound

Types of elements in an ionic compound An ionic bond is formed between a

______________ and a __________ because: Ionic bonds are formed between ions of

opposite charge Therefore, ionic bonds form between

____________ and _____________ because metals form cations and nonmetals form anions.

metal nonmetal

metal nonmetal

How do Ionic Compounds Form? Electrons are _______________________ in an

ionic bond because: one atom is trying to lose electrons to become stable and the other atom is trying to gain electrons to become stable

transferred

EMPIRICAL FORMULA

Al2O3Subscript: # written to the lower right of a chemical symbol that shows the number of atoms of that element present in the compound

3 WAYS TO DETERMINE AN EMPIRICAL FORMULA

1. Use Lewis Dot Diagrams

2. Use charges

3. Use the Crisscross Method

Draw the Lewis Dot Diagram for each element Use arrows to show the transfer of electrons between atoms Determine the number of each element necessary to make

each atom

1DETERMINING THE EMPIRICAL FORMULA BY USING

LEWIS DOT DIAGRAMS TO ILLUSTRATE THE IONIC BOND

PROPERTIES OF IONIC COMPOUNDS

•Made of ions

•Typically a metal and nonmetal(s)

•Crystalline Solids

•Hard yet Brittle

•Strong Interparticle Forces

•High Melting and Boiling Points

•Will conduct electricity when molten or dissolved in water

INTERPARTICLE FORCES: Forces of attractions between neighboring particles (atoms, ions or molecules)

Ionic compounds have __________________ interparticle forces due to the strong electrostatic attraction between the cation(s) and anion(s)

Because of these ________________ interparticle forces, ionic compounds have _____________ melting points.

Strong

Strong

high

CRYSTAL: A regular, repeating arrangement of ions in an ionic compound

The arrangement of ions in an ionic compound determines the crystal structure (shape) of the crystal itself.

CRYSTAL

CaCl2

ELECTROLYTE: A compound that conducts an electric current when it is in an aqueous solution or in a molten state http://www.youtube.com/watch?v=EBfGcTAJ

F4o

IONIC COMPOUNDS Ions of opposite charge strongly

___________ each other. Ions of like charge strongly ______________ each other.

As a result of this, how are ions arranged in an ionic compound?

attract

repel

Positive ions tend to be near negative ions and farther from other positive ions.

Metallic Bonding:Metallic Bonding: The attraction of free The attraction of free floating valence electrons for the floating valence electrons for the

positively charged metal ions.positively charged metal ions.

Made of just Made of just metal metal atomsatoms

Pure metals are not simply 1 atom of Pure metals are not simply 1 atom of the metal. They are multiple atoms of the metal. They are multiple atoms of

that metal bonded by a sea of electrons.that metal bonded by a sea of electrons.

Metallic Properties Come From Metallic Properties Come From their “Sea of Electrons”their “Sea of Electrons”

Metallic bonds form from a “Sea of Metallic bonds form from a “Sea of Electrons”: The pool of electrons shared Electrons”: The pool of electrons shared by all the atoms in a metallic substanceby all the atoms in a metallic substance

Malleability:Malleability: The ability to The ability to be hammered be hammered into sheetsinto sheets

Metals are malleable because the metal Metals are malleable because the metal atoms can slide through the electron sea atoms can slide through the electron sea to new positionsto new positions

Ductile:Ductile: Able to be Able to be pulled into wirespulled into wires

Metals are ductile Metals are ductile because electrons because electrons in the sea of in the sea of electrons move to electrons move to allow atoms to align allow atoms to align like a wirelike a wire

ConductivityConductivity

Electricity is Electricity is caused by moving caused by moving electronselectronsMetals conduct Metals conduct because the sea of because the sea of electrons is free to electrons is free to move and, move and, therefore, free to therefore, free to conduct electricityconduct electricity

Interparticle ForcesInterparticle Forces

Metallic bonds have strong interparticle Metallic bonds have strong interparticle forces. For this reason metals:forces. For this reason metals: Are typically solidsAre typically solids Are crystallineAre crystalline

Metals are arranged in very compact and orderly Metals are arranged in very compact and orderly patternspatterns

Have average to high meltingHave average to high melting

ALLOY:ALLOY: A mixture composed of 2 or more A mixture composed of 2 or more elements, at least 1 is a metalelements, at least 1 is a metal

NAME OF ALLOYNAME OF ALLOY % MAKE UP% MAKE UP EXAMPLEEXAMPLE

Stainless SteelStainless Steel 73-79% Fe73-79% Fe14-18% Cr14-18% Cr7-9% Ni7-9% Ni

Sterling SilverSterling Silver 92.5% Ag92.5% Ag7.5% Cu7.5% Cu

18-karat white gold18-karat white gold 75% Au75% Au12.5% Ag12.5% Ag12.5% Cu12.5% Cu

14 karat gold14 karat gold 58% Au58% Au14-28% Ag14-28% Ag14-28% Cu14-28% Cu

Covalent Bonding: Bonding in which electrons are shared Electrons spend most of their time between

the atoms.

The attraction between the nucleus and the shared electrons holds the atoms together.

Molecular Compound

Compound formed by covalent bonds (from the sharing of electrons)

Covalent Bonds Form molecules instead of crystals.

Molecule: The combination of atoms formed by a covalent bond

Types of Elements in a Covalent Bond Therefore, covalent compounds are formed

between 2 or more ____________________ because _____________ are the type of element that want to gain, not lose, electrons.

In a covalent bond, the atoms share electrons because both atoms want to gain electrons.

nonmetals

nonmetals

Ionic Compound (Metal & Nonmetal) or Covalent Compound (All Nonmetals)

Which type of bond would form between the following elements?MgCl2 NI3 AlN

CO2 F2 SnO2

How do Covalent Bonds Form?

Two nonmetals share electrons to form a bond

Covalent Bonds Structural Formula: Shows the arrangement

of atoms in a molecule or polyatomic ion

O

HH

Space Filling Model Ball & Stick Model Structural Formula

LEWIS STRUCTURES

• Uses dashes and dots to show the bonding arrangement of atoms in a covalent compound– Drawn to model the bonding in a covalent compound.– Based on: Lewis Dot Diagrams– Dashes (): Each dash represents a bond (or 2

shared electrons)

LONE PAIR

Single Covalent Bond 1 shared pair of electrons between 2 atoms

Represented by: Example:

Double Covalent Bond 2 shared pairs of electrons between 2 atoms

Represented by: = Example:

Triple Covalent Bond 3 shared pairs of electrons between 2 atoms

Represented by: ≡ Example:

Lone Pairs (): Represents an unshared pair of electrons

Using Lewis Dot Diagrams to Determine the Lewis Structure Draw the Lewis Dot Diagrams for each atom

in the Molecular Formula Determine how the atoms will SHARE

electrons so that all atoms are

(N-A)/2 = # of Bonds in Molecule N = # of electrons needed to make an each element

in the compound stable N = 8 electrons for all elements except H and He which

need 2 electrons A = # of valence electrons each element in the

compound has There are 2 electrons per bond so we divide the # of

electrons they need to share by 2 to determine the number of bonds

Some General Guidelines• Carbon is typically in the center of the molecule• If possible, keep the molecule symmetrical• Hydrogen & the halogens can only accept one

electron and, therefore, tend to be on the perimeter of the molecule

• Sometimes, the formula will help you figure out the structure

• Check your work: Do all atoms have 8 electrons? Does H have only 2 electrons?

NH3 Cl2 CH4

(N-A)/2 = # of Bonds in Molecule

H2CO C2H2 NH4+

(N-A)/2 = # of Bonds in Molecule

Resonance Structures: Two or more equally valid structures of a molecule or polyatomic ion

Exceptions to the Octet Rule

1) Atoms with less than an octet Boron may not acquire a full octet, it may

only obtain 6 electrons--it has only 3 valence electrons to start

2) Atoms with more than an octet Especially phosphorus & sulfur

3) Molecules with Odd Numbers of Electrons Any molecule that has an odd number of

available electrons, especially compounds of Nitrogen

Coordinate Covalent Bond

A covalent bond in which one atom contributes both bonding electrons

C

C OO

Properties of Covalent Compounds Made of molecules All nonmetals Often liquids or gasses Brittle if solid Weak Interparticle Forces Low Melting and Boiling Points Do not conduct electricity when molten or

dissolved in water

More Properties… Covalent compounds have ______________

interparticle forces Because of these _______________ interparticle forces,

covalent compounds have low melting and boiling points

Bond Dissociation Energy: The energy needed to break the bond between two covalently bonded atoms A high bond dissociation energy corresponds to a strong

covalent bond

weak

weak

Ionic Ionic CovalentCovalent MetallicMetallic

Type of Type of ElementsElements

StateState

Electrons Electrons are…are…

Hard or Hard or brittle?brittle?

Melting Melting PointsPoints

Made of…Made of…

MOLECULAR GEOMETRY

• VSEPR THEORY– Valence Shell Electron Pair Repulsion Theory

• In small molecules, the pairs of valence electrons are arranged as far apart from each other as possible

NO!!!

YES!!!

Ball-and-Stick Models

• Drawings that represent molecular compounds. The balls are used to represent atoms and the sticks are used to represent bonds.

VSEPR Theory: Electrons repel (bonds & lone pairs move as far apart as possible)

Bond Angles

The geometric angle between 2

bonds

Geometry Bonds Lone Pairs Bond Angles

Example

Tetrahedral 4 0 109.5

Trigonal Planar

3 0 120

Trigonal

Pyramidal 3 1 107

Bent 2 2 105

Linear 2 or

Diatomic molecules

0 180

Other Shapes

T-Shaped

ICl3Square Planar

XeF4

Octahedral

SF6

Trigonal Bypyramid

al

PF5

EXAMPLES

CO2 PF3 CBr4

Bond Length • Different pairs of atoms form bonds

with different lengths– Not represented in a ball-and-stick

model

• As you move down a group on the periodic table, the atoms form longer bonds because the atoms become larger

• Multiple bonds are shorter than single bonds– The more electrons there are, the

more attraction there is for the opposite nuclei

– Bonds are “electrical glue”

Electronegativity: The ability of an atom to attract electrons when the atom is in a compound

• Shows how much an atom will attract valence electrons

• The higher the electronegativity the more an atom attracts the electrons towards it

EN

The difference between two atoms electronegativities determines the type of bond formed between those two atoms EN = EN1-EN2

is the Greek Letter delta and means change EN is always positive (always subtract the

smaller number from the larger number) Example: Calculate the EN between

Cesium and Fluorine

You can think of bonding as a tug-of-war for electrons

between atomsThe electronegativity of the atom tells you how hard

that atom is pulling for the electrons

Ionic Bond

When one atom wants the electrons so much more than the other atom that it pulls the electron off the other atom (a tug-of-war where one side wins) EN > 2.0 (greater than 2.0)

Nonpolar Covalent Bond

Like an even tug-of-war—both atoms want the electrons equally so the electrons stay between them EN < 0.4 (less than 0.4)

Polar Covalent

One atom wants the electrons more than the other but not enough to pull it all the way towards itself—like an uneven tug-of-war EN is between 0.4 & 2.0

EN = EN1 –EN2

0.0 0.4 2.0

Nonpolar Polar Ionic

Polar Covalent Bonds

Polar bonds have partially charged atoms due to the unequal sharing of electrons Dipole: A partial charge on an atom.

If the EN on a bond is between 0.4 and 2.0 then that bond has a dipole (partial charge)

This is because one atom wants the electrons more than the other but not enough to cause a complete transfer

DIPOLE

: Symbol for a dipole or a partial charge Used to label the partial charges on a

polar bond Two ways to label the dipoles

(partial charges) on a polar bond

FEN = 4.0-2.1=0.9 (polar)

H FHor

+ -

2.1 4.0 C-Cl

Images of Polar/Nonpolar

Nonpolar

Polar

Polar

To determine the polarity of a molecule:

1) Does the molecule have only nonpolar bonds? YES: It is nonpolar

2) Is the molecule completely symmetrical in all dimensions?

YES: It is nonpolar

If the molecule contains at least 1 polar bondand is not completely symmetrical in all

dimensions, then the whole molecule is POLAR

Polarity of Carbon Dioxide

CO2

Polarity of Ammonia

NH3

H2O

CH4

The Periodicity of Electronegativity

Electronegativity Differences & Bonding

The greater the difference between the electronegativities of the bonding atoms, the more unequally those atoms share electrons

The symbol for electronegativity difference: EN

Ionic Bonds

EN is > 2.0 This is because one atom wants the

electrons much more than the other Because of the high EN you can

assume that the electron on the less electronegative atom is transferred to the other atom

Nonpolar Covalent Bonds

EN is < 0.4 This is because both atoms have almost

an equal attraction for the electrons Because of the low EN the atoms are

shared equally These molecules are gases or low-boiling

point liquids at room temperature These bonds are also known as Nonpolar

Covalent Bonds

Example

Label the dipoles on a CCl bond.

Could also use vectors to label a polar bond.

Example: Use a vector to label the dipoles on a C-Cl bond.

To determine the polarity of a molecule:

• Draw the Lewis Structure of the Molecule with the correct geometry

• Use electronegativity values to determine if any of the individual bonds are polar. If so, label the dipoles.

• Using vector addition, check to make sure the dipoles do not cancel out.– If at least 1 vector/dipole does not cancel out, the

molecule is polar.– If all the vectors/dipoles do cancel out, the molecule is

nonpolar• Vectors will only ALL cancel out if the molecule is linear or

tetrahedral and completely symmetrical!

•Involves vector addition.

=

=

= 0

=

Polarity of Ammonia

NH3

H2O

Iodine—I2

Methanol: CH3OH

Dimethyl Ether (CH3)2O

EXAMPLES

CO2 CH4 CH2O

Properties of Polar Covalent Bonds

• Higher Boiling Points than Nonpolar Covalent Bonds

• Molecules can “stick” together and form puddles

• Hydrophilic: ionic & polar (mix easily with water)– Like dissolves like

Large Molecules

In a large molecule the polarity oftentimes

helps determine the molecule’s shape.

ATTRACTIONS BETWEEN MOLECULES

Responsible for determining whether a

molecular compound is a gas, liquid or

solid at a given temperature.

Van der Waals Forces

Consist of Dipole Interactions & Dispersion

Forces

Dipole Interactions: Occur when polar molecules are attracted to one another

Similar to but much weaker than ionic bonds

Dispersion Forces: Caused by the motion of electrons•Weakest of all molecular interactions

Hydrogen Bonds

The attraction to a hydrogen atom already

bonded to a strongly electronegative atom• Strongest of intermolecular forces. • Extremely important in determining the properties of

water and biological molecules