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Bonding

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Chemical Bonding

Bonding: Force that holds atoms together

Bonding is determined by electronic configuraton:

How many valence electrons?

Mg 12e- 1s2 2s2 2p6 3s2

Cl 17e- 1s2 2s2 2p6 3s2 3p5

Octet Rule

Atoms Gain, Lose (transfer) Or Share electrons

To get a full shell of 8 valence electrons

(except H and He are full at 2)

Forms neutral compounds: both ionic & covalent

Don’t confuse valence electron # with the charge on the ion

Ex: OxygenValence electrons: _6_How many more to fill octet __2_So charge: _-2_

Ionic Bonds: transfer electrons

Bond forms between Metal and Nonmetal

+ ion - ion

Transfer electrons: creates ions Metals lose electrons: form + ion (cation)

Nonmetals gain electrons: form – ion (anion)

Opposite charges attract to create bond

Like magnets

Properties of Ionic Bonding

Ionic bonds are one of the strongest types of bonding.

Ionic bonds are very strong, so ionic compounds are usually hard, brittle, with very high melting points and boiling points.

Solids at room temp


Ions are packed into repeating patterns resulting in a crystal lattice structure.


No single particle of an ionic compound → represented by the simplest ratio of ions, called a formula unit.


Ionic compounds dissolve well in water and split up into their ions called dissociation.


Electrolytes: ions conduct an electric current when dissolved in water.


Good conductors of electricity as a liquid or when dissolved in water

Forming Ionic Compounds Metals (+) are always written first

Compounds are neutral, so…

Ions must come together in the ratio to balance (+) with (-)

Lewis Dot Diagrams for Ionic compounds

Superscript = charge H1+ O2-

Subscript = # of atoms (do not write subscripts of 1)

H2O = 2 hydrogen atoms and 1 oxygen atom

H2O2 = 2 hydrogen atoms & 2 oxygen atoms

If lithium and fluorine bond, Li+ and F- would make LiF, because the positive 1 charge balances a negative 1 charge.

Li F Li1+ F1-

If lithium (Li+) and oxygen (O-2) bond, more positive lithiums are needed to balance out the larger negative of oxygen. It would take 2 lithiums for every 1 oxygen. To show two lithiums are needed, a subscript of “2” is written after the lithium, Li2O

Li O Li1+ O2- Li1+

Li

If an ionic compound is made from Aluminum (Al+3) and Sulfur (S-2), the amounts of each element needed would be:

Al+3 S-2

Al+3 S-2

S-2

Totals: +6 and -6

So the resulting compound would be Al2S3

Al S

Al S

S

S-2 Al+3 S-2 Al+3 S-2

Writing Ionic formulas

Write Symbol Charge as

superscript “Criss-cross” – to

make subscripts Reduce if you can

Writing Ionic formulas

Write Symbol Charge as superscript “Criss-cross” – to make

subscripts Reduce if you can

Mg+2 O-2

Mg2 O2

Mg2O2

Mg O

Try

Calcium oxide, Ca2O2 CaO

Potassium nitride, K3N

Magnesium phosphide, Mg3P2

Polyatomic Ions

Ions with 2 or more atoms Acts as a single unit Use parenthesis if subscript is more

than 1

Sulfate: SO4-2

Aluminum sulfate:

Al+3 SO4-2 = Al2(SO4)3

Transition Metals

Can form more that 1 ion d block electrons sometime act as

valence

Roman numeral identifies the charge

Manganese (IV) = +4 charge

Iron (III) = +3 charge

Covalent Bonds

Forms between Nonmetal and Nonmetal

Share valence electrons to get full octets

Properties of Covalent Compounds

Smallest unit called molecules (remember, ionic compounds form formula units)

The bonds between the atoms in a molecule are strong, but the attraction between the molecules is relatively weak. These attractive forces are known as intermolecular forces, or van der Waals forces.

Weak bonds mean: Low melting points and boiling points b/c they’re easy to split apart from each other.

compounds are soft.

Examples : H20 melts at 0.0˚C CF4 melts at –150˚ and boils at –129˚C

Tend to be be gases and liquids at room temperature

Covalent compounds do not conduct electricity

Many are polar

The only purely covalent bond is between atoms of the same element

Polar bonds

Polar bonds - a covalent bond in which the electrons are not shared equally. One atom has a greater attraction for the electrons (a greater electronegativity), so the electrons spend more time around that atom, creating a slightly negative charge. The other atom then has a slightly positive charge.

Polar bonds

Ex. H2O: big difference in electronegativity for oxygen and hydrogen. Oxygen pulls the electrons most of the time creating a slightly (-) charge, leaving the hydrogen with a slightly (+) charge

Example of a covalent bond

Hydrogen and Bromine. Hydrogen has 1 valence electron, Bromine has 7. Both need 1 more electron to form a stable noble gas configuration…so they form a single covalent bond

Use Lewis dot diagrams to show electrons, and a line to show covalent bond

H Br H – Br Or H Br

Oxygen and Hydrogen

H O

H

H – O Or H O

H H

Carbon and Chlorine:

C Cl Cl

Cl Cl – C – Cl

Cl Cl

Cl

Carbon and Chlorine:

C Cl Cl

Cl Or Cl C Cl

Cl Cl

Cl

http://www.youtube.com/watch?v=QXT4OVM4vXI



Rules: drawing Lewis dot diagrams1. Find central atom (fewest in number or

one to the left on periodic table)2. Add up total number of valence electrons

(all atoms plus any charge)3. Attach other atoms to central atom with

1 bonding pair4. Fill octet for each outside atom5. Must use up all electrons6. Check Octet Rule – if needed borrow a

pair of electrons to make double or triple bond

Try

NH3

N = 5 valence electron H = 1 H = 1 H = 1 8 valence electrons total

Which element in the middle H – N – H

H

Start filling, using all 8 electrons:Remember: H valence shell is full at 2

So where will last pair be?

H – N – H or

H

Multiple Covalent

Multiple Covalent bonds: sharing more than 1 pair of electrons between two atoms (double or triple bonds)

Oxygen gas, O2

O O O=O Or O O

Nitrogen gas, N2

N N

N N Or N N

Carbon dioxide, CO2

C O

O

O=C=O Or O C O

Try

SO2

Both S & O have 6 valence electrons S = 6 O = 6 O = 6

18 valence electrons total

Which element goes in the middle O – S – O

Start filling with 18 electrons

Oh, don’t have enough to satisfy Octet rule

so borrow 1 pair to make a double bond

VSEPR: Covalent compound shapes

Valence Shell Electron Pair RepulsionGeometric shape forms to keep

electrons as far apart as possible This shape will help determine

whether molecule is polar or nonpolar If molecule is symmetrical = nonpolar,

even if individual bonds are polar.

VSEPR: Covalent compound shapes

Ionic CovalentFormula Unit Smallest

UnitMolecule

Transfer Electrons

How Formed Share Electron

Strong Bonds Bond Strength

Weak Bonds

Repeating Patterns Crystal Structure

Shape Geometric Shape VSEPR Model

Ionic Covalent

Metal To Nonmetal

Forms Between

Between Nonmetals

Good Conductor When Dissolved

Conduct Electricity

Poor Conductors

Attraction Between (+) Ion and (-) Ion Cation metals Anion nonmetal

When Forming

Unequal Sharing = Polar BondEqual Sharing = Nonpolar Bond

High Melting and Boiling Points, Hard, Brittle Solids

Properties Low Melting and Boiling Points, Soft, Solids, Liquids, or Gases

Both Ionic and Covalent

Trying to fill outer shell (valance)

Compounds are neutral overall (no charge)

Can create many different compounds

Contains more than 1 electron/atom




Metallic bonding

In metals the electrons are delocalized, which means they do not belong to any one atom but move freely from atom to atom. These electrons form a sea of electrons around the metal atoms. Metallic bonding is the attraction between metal atoms and the surrounding sea of electrons.

These freely moving electrons can act as conduct both heat and electricity which is why solid and liquid metals are good conductors.

Physical properties

Metallic bonding accounts for many physical properties of metals

Metals have high melting & boiling

points because of the strength of the metallic bond

Malleability is the ability of a solid to bend or be hammered into other shapes without breaking since the electrons can slide past each other easily.

Ductility is sustaining large permanent changes in shape without breaking b/c the atoms can slide over each other easily.

Ex. A piece of metal is drawn into a wire.

Maleable & Ductile

Heat conduction (or Thermal conduction) is the transfer of energy between particles in a solid. The temperature of the material measures how fast the atoms are moving and the heat measures the total amount of energy due to the vibration of the atoms.

When one part of a metal is heated, the atoms in this part vibrate faster and are more likely to hit their neighbors. When collisions take place, the energy is passed on to the neighboring atoms allowing the energy to travel through the solid.

In general, the strength of the metallic bond depends on two factors

1. the number of electrons in the delocalized 'sea' of electrons. (More delocalized electrons results in a stronger bond and a higher melting point.)

2. packing arrangement of the metal atoms. (The more closely packed the atoms are the stronger the bond is and the higher the melting point.)

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ionic compoundssuperscript

ionic compoundsmetals

al2s3 als als s s

sulfur s

ionic covalent dont

oxygen atoms

aluminum al

oxygenvalence electrons