bonding between atoms bonds forces that hold groups of atoms forces that hold groups of atoms...

Bonding between atoms

BondsBonds Forces that hold groups of Forces that hold groups of atoms atoms

together and make them together and make them function function

as a unit.as a unit. Ionic bonds – transfer of Ionic bonds – transfer of electrons electrons Covalent bonds – sharing Covalent bonds – sharing of electronsof electrons

Molecule: collection of atoms that are bound together

• What holds a molecule together? Covalent bond

• Force of attraction that results from valence electrons being attracted to two nuclei.

• Valence electrons being shared between two nuclei

• Core electrons are not involved in bonding

ElectronegativityElectronegativity

The ability of an The ability of an atom in a molecule atom in a molecule to attract shared to attract shared electrons to itself.electrons to itself.

Linus Pauling 1901 - 1994

Table of Electronegativities

Polar-Covalent bonds

Nonpolar-Covalent bonds

Covalent BondsCovalent Bonds

Electrons are unequally shared Electronegativity difference between .3 and 1.7

Electrons are equally shared Electronegativity difference of 0 to 0.3

Energy is released when forming a covalent bond and absorbed when

breaking it

Octet Rule and electron sharing

Lewis Dot diagrams

• Show an atom’s valence electrons

• The number of dots is equal to the group number

• Pairs of dots(electrons) are electron pairs

• Single electrons are unpaired electrons

Examples of Lewis Dot diagrams

• All elements in group IA will have one dot• All elements in group IIA will have two dots• All elements in group IIIA will have three

dots• Group IV will have four dots, V five, VI

six, VII seven, and VIII eight dots

Metal Metalloids Nonmetals

I II III IV V VI VII VIII

Transition metals

CHH ..

Completing a Lewis Structure -CH3Cl

Add up available valence electrons:

C = 4, H = (3)(1), Cl = 7 Total = 14

Join peripheral atoms to the central atom with electron pairs.

Complete octets on atoms other than hydrogen with remaining electrons

Make carbon the central atom

H

H

Cl

..

..

..

..

Lewis Structures

1) Count up total number of valence electrons

2) Connect all atoms with single bonds

- “multiple” atoms usually on outside

- “single” atoms usually in center;

C always in center,

H always on outside.

3) Complete octets on exterior atoms (not H, though)

4) Check

- valence electrons math with Step 1

- all atoms (except H) have an octet; if not, try multiple bonds

- any extra electrons? Put on central atom

Comments About the Octet RuleComments About the Octet Rule

2nd row elements C, N, O, F observe the octet rule.

2nd row elements B and Be often have fewer than 8 electrons around themselves - they are very reactive.

3rd row and heavier elements CAN exceed the octet rule using empty valence d orbitals.

When writing Lewis structures, satisfy octets first, then place electrons around elements having available d orbitals.

Exceptions to the Octet Rule

• Atoms with less than an octet: BF3

• Atoms with more than an octet: most notably phosphorus and sulfur (SF4) additional electrons fill the 3d orbitals

• Molecules with odd number of electrons:

NO (nitrogen monoxide)

Multiple bonds

• Determine the total number of valence electrons that will be in the final diagram

• Connect atoms with single bonds• Put in remaining dots two at a time as lone

pairs• Send lone pairs to atoms that do not have an

octet(lone pairs must come from adjacent atoms)

Multiple Covalent Bonds:Multiple Covalent Bonds:Double bondsDouble bonds

Two pairs of shared electrons

Multiple Covalent Bonds:Multiple Covalent Bonds:Triple bondsTriple bonds

Three pairs of shared electrons

Ionic Bonding

Forms between metals and nonmetals There is a strong attraction between

oppositely charged ions Form ionic lattices (network of positively

and negatively charged ions) Examples: sodium oxide, magnesium

chloride, calcium phosphate

Properties of Ionic Properties of Ionic CompoundsCompounds

Structure: Crystalline solids Melting point:

Generally high

Boiling Point:

Generally high

Electrical Conductivity:

Excellent conductors, molten and aqueous

Solubility in water:

Generally soluble

Ionic BondsIonic Bonds Electrons are transferred

Electronegativity differences are generally greater than 1.7 The formation of ionic bonds is always exothermic!

Ionic Bonding:Ionic Bonding:The Formation of Sodium The Formation of Sodium

ChlorideChloride

Sodium has 1 valence electron

Cl 1s22s22p63s23p5

Na 1s22s22p63s1

Chlorine has 7 valence electrons

An electron transferred gives each an octet


ChlorideChloride

Cl- 1s22s22p63s23p6

Na+ 1s22s22p6

This transfer forms ions, each with an octet:


ChlorideChloride

Cl- Na+

The resulting ions come together due to electrostatic attraction (opposites attract):

The net charge on the compound must equal zero

Sodium Chloride Crystal LatticeSodium Chloride Crystal Lattice

Ionic compounds form Ionic compounds form solids at ordinary solids at ordinary temperatures.temperatures.

Ionic compounds Ionic compounds organize in a organize in a characteristic crystal characteristic crystal lattice of alternating lattice of alternating positive and negative positive and negative ions.ions.

Monatomic Cations

Name

H+ Hydrogen Li+ Lithium Na+ Sodium K+ Potassium Mg2+ Magnesium Ca2+ Calcium Ba2+ Barium Al3+ Aluminum

Writing Ionic Compound Writing Ionic Compound FormulasFormulas

Example: Barium nitrate

1. Write the formulas for the cation and anion, including CHARGES!

BaBa2+2+ NONO33--2. Check to see if charges are

balanced.

3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion.

Not balanced!

( )( ) 22


Example: Ammonium sulfate


NHNH44++ SOSO44

2-2-2. Check to see if charges are balanced.


Not balanced!

( )( )22


Example: Iron(III) chloride


FeFe3+3+ClCl--2. Check to see if charges are balanced.


Not balanced!

33


Example: Aluminum sulfide


AlAl3+3+ SS2-2-2. Check to see if charges are balanced.


Not balanced!

22 33


Example: Magnesium carbonate


MgMg2+2+ COCO332-2-2. Check to see if

charges are balanced.

They are balanced!


Example: Zinc hydroxide


ZnZn2+2+ OHOH--2. Check to see if charges are balanced.


Not balanced!

( )( )22


Example: Aluminum phosphate


AlAl3+3+ POPO443-3-2. Check to see if charges are

balanced.

They ARE balanced!

Naming Ionic CompoundsNaming Ionic CompoundsNaming Ionic CompoundsNaming Ionic Compounds•1. Cation first, then anion 1. Cation first, then anion

•2. Monatomic cation = name of the 2. Monatomic cation = name of the element element

•CaCa2+2+ = calcium = calcium ionion

•3. Monatomic anion = 3. Monatomic anion = rootroot + + -ide-ide •ClCl = chlor = chlorideide

•CaClCaCl22 = calcium chlor= calcium chlorideide

Naming binary covalent compounds

• Name less electronegative element first

• The more electronegative element takes a suffix-ide

• For each element, use a prefix to indicate number of atoms present

Naming Binary Covalent Naming Binary Covalent CompoundsCompounds

Naming Binary Covalent Naming Binary Covalent CompoundsCompounds

Compounds between two Compounds between two nonmetals nonmetals First element First element in the formula is in the formula is named firstnamed first. . Second element Second element is named as if it were an is named as if it were an

anionanion. . Use prefixes Use prefixes Only use Only use monomono on second element - on second element -

PP22OO55 ==COCO22 = =

CO =CO =

NN22O =O =

didiphosphorus phosphorus pentpentoxideoxide

carbon carbon didioxideoxide

carbon carbon monmonoxideoxide

didinitrogen nitrogen monmonoxideoxide

Covalent compounds

• Phosphorous trichloride

• Carbon dioxide

• Sulfur hexafluoride

Naming chemical compounds

• Compounds are named according to atoms or ions that compose them

• Binary molecular are named after component atoms, with prefixes

• An acid is named after its characteristic anion

Bond type by electronegativity

• Electronegativity difference less or equal to 0.4 bond type nonpolar covalent

• Between 0.4 and 2.0 polar covalent

• Greater than 2.0 ionic

bonding between atoms bonds forces that hold groups of atoms forces that hold groups of atoms...

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