12554_atomic bonding lecture 2

7/29/2019 12554_atomic Bonding Lecture 2

1/49

ChemicalBONDING


2/49

Chemical Bond

A bond results from the attraction of nuclei forelectrons

All atoms trying to achieve a stable octet

IN OTHER WORDS

the p+ in one nucleus are attracted to the e- of

another atom Electronegativity


3/49

Bond Formation

exothermic process

Energyreleased

E

N

E

RG

Y

Reactants

Products


4/49

Breaking Bonds

Endothermic reaction

energy must be put into the bond in order to

break it

E

N

ER

G

Y Reactants

Products

Energy

Absorbed


5/49

Bond Strength

Strong, STABLE bonds require lots of energy

to be formed or broken

weak bonds require little E


6/49

Two Major Types of Bonding

Ionic Bonding forms ionic compounds

transfer of e-

Covalent Bonding

forms molecules sharing e-


7/49

One minor type of bonding

Metallic bonding

Occurs between like atoms of a metal in thefree state

Valence e- are mobile (move freely among allmetal atoms)

Positive ions in a sea of electrons

Metallic characteristics High mp temps, ductile, malleable, shiny

Hard substances

Good conductors of heat and electricity as (s) and (l)


8/49

Its the mobile electronsthat enable me-tals to

conduct electricity!!!!!!


9/49

IONic Bonding

electrons are transferred between valence

shells of atoms

ionic compounds are

made of ions

ionic compounds are calledSaltsorCrystals

NOT MOLECULES


10/49

IONIC BONDbond formed between

two ions by thetransferof electrons


11/49

IONic bonding

Always formed between metals and non-

metals

[METALS ]+ [NON-METALS ]-

Lost e-Gained e-


12/49

Ionic Bond

Between atoms of metals and nonmetals with

very different electronegativity

Bond formed by transfer of electrons

Produce charged ions all states. Conductors

and have high melting point.

Examples; NaCl, CaCl

2, K

2O


13/49

Formation of Ions from Metals

Ionic compounds result when metals react withnonmetals

Metals loseelectrons to match the number of valence

electrons of their nearest noble gas

Positive ionsform when the number of electrons are

less than the number of protons

Group 1 metals ion 1+Group 2 metals ion 2+

Group 13 metals ion 3+


14/49

IONic Bonding

Electronegativity difference > 2.0

Look up e-neg of the atoms in the bond and

subtract

NaCl

CaCl2

Compoundswithpolyatomic ionsNaNO3


15/49


16/49


17/49

1). Ionic bond electron from Na is transferred to Cl, thiscauses a charge imbalance in each atom. The Na becomes(Na+) and the Cl becomes(Cl-), charged particles or ions.


18/49

Properties ofIonic Compounds

hard solid @ 22oC

high mp temperatures nonconductors of electricity in solid phase

good conductors in liquid phase or

dissolved in water (aq)

SALTS

Crystals


19/49

COVALENT BOND

bond formed by thesharing of electrons


20/49

Covalent Bonding

Pairs of e- are shared

between non-metal atoms

electronegativity difference < 2.0

forms polyatomic ions

molecules


21/49

Covalent Bond

Between nonmetallic elements of similar

electronegativity.

Formed by sharing electron pairs

Stable non-ionizing particles, they are not

conductors at any state

Examples; O2, CO

2, C

2H

6, H

2O, SiC


22/49

d i ll h


23/49

Bonds in all the

polyatomic ionsand diatomics are

all covalentbonds

NONPOLAR


24/49

when electrons areshared equally

NONPOLAR

COVALENT BONDS

H2 or Cl2

2 Covalent bonds- Two atoms share one or more pairs of outer shell


25/49

2. Covalent bonds- Two atoms share one or more pairs of outer-shellelectrons.

Oxygen Atom Oxygen Atom

Oxygen Molecule (O2)

POLAR COVALENT
http://www.usfca.edu/fac-staff/Courses/BIOL104_USF/104_Fall03_ppt/Text%20Chapter%2002/OxgnMol.swfhttp://www.usfca.edu/fac-staff/Courses/BIOL104_USF/104_Fall03_ppt/Text%20Chapter%2002/OxgnMol.swfhttp://www.usfca.edu/fac-staff/Courses/BIOL104_USF/104_Fall03_ppt/Text%20Chapter%2002/OxgnMol.swfhttp://www.usfca.edu/fac-staff/Courses/BIOL104_USF/104_Fall03_ppt/Text%20Chapter%2002/OxgnMol.swfhttp://www.usfca.edu/fac-staff/Courses/BIOL104_USF/104_Fall03_ppt/Text%20Chapter%2002/OxgnMol.swfhttp://www.usfca.edu/fac-staff/Courses/BIOL104_USF/104_Fall03_ppt/Text%20Chapter%2002/OxgnMol.swfhttp://d/Chapter-2/ppp/Text%20Chapter%2002/OxgnMol.swfhttp://d/Sodium.swf/


26/49

when electrons areshared but shared

unequally

POLAR COVALENT

BONDS

H2O

P l C l t B d U l


27/49

Polar Covalent Bonds: Unevenly

matched, but willing to share.


28/49

- water is a polarmolecule because oxygen is more

electronegative than hydrogen, and therefore electrons are

pulled closer to oxygen.


29/49

Properties of Molecular Substances

Low m.p. temp and b.p. temps relatively soft solidsas compared

to ionic compounds

nonconductors of electricity in any

phase

Covalentbonding


30/49

METALLIC BOND

bond found inmetals; holds metal

atoms together

very strongly


31/49

METALLIC BONDING

Metallic bonding is the type ofbonding found in metalelements. This is the

electrostatic force of attractionbetween positively charged ionsand delocalized outer electrons.

The metallic bond is weaker

than the ionic and the covalentbonds.


32/49

METALLIC BONDING Metallic structures are typically rather empty (having large internuclear

spacings) and prefer lattice arrangements in which each atom hasmany nearest neighbors.

The weakness of the individual bonding actions in a metal is due to theenlargement of the internuclear spacing.


33/49

Valance electrons are relatively bound to the nucleus and

therefore they move freely through the metal and they are

spread out among the atoms in the form of a low-density

electron cloud.

A metallic bond result from the

sharing of a variable number of

electrons by a variable number of

atoms. A metal may be described

as a cloud of free electrons.

Therefore, metals have high

electrical and thermal conductivity.

+

+

+

+

+

+

+

+

+


34/49

All valence electrons in a metal combine to form a sea of

electrons that move freely between the atom cores. The

more electrons, the stronger the attraction. This means themelting and boiling points are higher, and the metal is

stronger and harder.

The positively charged cores are held together by these

negatively charged electrons.

The free electrons act as the bond (or as a glue) between

the positively charged ions.

This type of bonding is nondirectional and is rather

insensitive to structure.

As a result we have a high ductility of metals - the bondsdo not break when atoms are rearranged metals can

experience a significant degree of plastic deformation.

M t lli B d M ll d ith


35/49

Metallic Bonds: Mellow dogs with

plenty of bones to go around.


36/49

Metals Form Alloys

Metals do not combine with metals. They form

Alloys which is a solution of a metal in a metal.

Examples are steel, brass, bronze and pewter.


37/49

VAN DER WAALS BONDING It is a weak bond, with a typical strength of 0.2 eV/atom.

It occurs between neutral atoms and molecules.

The explanation of these weak forces of attraction is thatthere are natural fluctuation in the electron density of all

molecules and these cause small temporary dipoleswithin the molecules. It is these temporary dipoles thatattract one molecule to another. They are called van derWaals' forces.

The bigger a molecule is, the easier it is to polarise (to

form a dipole), and so the van der Waal's forces getstronger, so bigger molecules exist as liquids or solidsrather than gases.


38/49

The dipoles can be formed as a result of unbalanced distributionof electrons in asymettrical molecules. This is caused by the

instantaneous location of a few more electrons on one side of the

nucleus than on the other.

Therefore atoms or molecules containing dipoles are attractedto each other by electrostatic forces.

Display a marked

attractive forcesNo attraction is produced


39/49

These forces are due to the electrostatic attraction

between the nucleus of one atom and the electrons of

the other.

Van der waals interaction occurs generally between atoms

which have noble gas configuration.

van der waals

bonding


40/49

Types of Van der Waals Bonding

Dipole Dipole (Keesom interaction)

between two polar molecules.Strongest intermolecular force. e.g H-bonding

Dipole Induced Dipole (Debye Interaction)

b/w a polar & a non-polar molecule.(weakand short-lived) e.g CO2 (aq)

Dispersion (London Forces)between two non-polar molecules(weakest and very short-lived) e.g between Cl2


41/49

HYDROGEN BONDING A hydrogen atom, having one electron, can be covalently

bonded to only one atom. However, the hydrogen atom caninvolve itself in an additional electrostatic bond with a secondatom of highly electronegative character such as fluorine oroxygen. This second bond permits a hydrogen bo nd betweentwo atoms or strucures.

The strength of hydrogen bonding varies from 0.1 to 0.5ev/atom.

Hydrogen bonds connect water

molecules in ordinary ice.

Hydrogen bonding is also very

important in proteins and

nucleic acids and therefore in

life processes.


42/49

Hydrogen Bonding

Strong polarattraction

Like magnets

Occurs ONLYbetween H of one

molecule and N, O,F of another

H bond


43/49

The Unusual Properties of Water

Unusuallyhighboiling

point

Compared toothercompoundsin Group 16


44/49

Density????


45/49

H2O(s) is less dense than H2O(l)

The hydrogen bonding in water(l) molecules is

random. The molecules are closely packed.

The hydrogen bonding in water(s) molecules

has a specific open lattice pattern. The

molecules are farther apart.


46/49

van der Waals

Non-polar molecules can exist in liquid andsolid phases

because van der Waals forces keep the molecules

attracted to each other

Exist between CO2, CH4, CCl4, CF4, diatomicsand monoatomics


47/49

van der Waals periodicity

increase with molecular mass.

Greater van der Waals force?

F2 Cl2 Br2 I2

increase with closer distance betweenmolecules

Decreases when particles are farther away


48/49


49/49

The End

12554_atomic bonding lecture 2

Documents