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
Ionic Bonding:Ionic Bonding:The Formation of Sodium The Formation of Sodium
ChlorideChloride
Cl- 1s22s22p63s23p6
Na+ 1s22s22p6
This transfer forms ions, each with an octet:
Ionic Bonding:Ionic Bonding:The Formation of Sodium The Formation of Sodium
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
Writing Ionic Compound Writing Ionic Compound FormulasFormulas
Example: Ammonium sulfate
1. Write the formulas for the cation and anion, including CHARGES!
NHNH44++ SOSO44
2-2-2. 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
Writing Ionic Compound Writing Ionic Compound FormulasFormulas
Example: Iron(III) chloride
1. Write the formulas for the cation and anion, including CHARGES!
FeFe3+3+ClCl--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!
33
Writing Ionic Compound Writing Ionic Compound FormulasFormulas
Example: Aluminum sulfide
1. Write the formulas for the cation and anion, including CHARGES!
AlAl3+3+ SS2-2-2. 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 33
Writing Ionic Compound Writing Ionic Compound FormulasFormulas
Example: Magnesium carbonate
1. Write the formulas for the cation and anion, including CHARGES!
MgMg2+2+ COCO332-2-2. Check to see if
charges are balanced.
They are balanced!
Writing Ionic Compound Writing Ionic Compound FormulasFormulas
Example: Zinc hydroxide
1. Write the formulas for the cation and anion, including CHARGES!
ZnZn2+2+ OHOH--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
Writing Ionic Compound Writing Ionic Compound FormulasFormulas
Example: Aluminum phosphate
1. Write the formulas for the cation and anion, including CHARGES!
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 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