Definitions
Chemical Bonds Force that holds atoms together It’s all about the electrons (e-)
Electrons are attracted to positively charged nucleus of other atom
Types of Chemical Bonds
Ionic BondIonic Bond Bond between metal and nonmetal due to
“electrostatic interactions” Attraction between positively and negatively
charged ions (cations and anions) Electrons are transferred from metal to
nonmetal
Types of Chemical Bonds
Metallic BondsAtoms are bonded to one another (not to
other elements)Positive ions in a “sea” of negative
charge (e-)
Definitions
Octet rule (Rule of 8) 8 e- in the outer shell very stable
H2 and He want a “duet”
Electron configuration for duet = ns2
Electron configuration for octet = ns2 np6
Examples of Bonding Types
Ionic Bonding: NaCl, K2S
Covalent Bonding H2 , Cl2
Metallic Bonding Cu, Ag
Lewis Dot Diagrams
A Lewis dot diagram depicts an atom as its symbol and its valence electrons. Ex: Carbon
Carbon has four electrons in its valence shell (carbon is in group 14), so we place four dots representing those four valence electrons around the symbol for carbon.
Drawing Lewis Dot Diagrams
Electrons are placed one at a time in a clockwise manner around the symbol in the north, east, south and west positions, only doubling up if there are five or more valence electrons. Same group # = Same Lewis Dot structure
Ex. F, Cl, Br, I, At
Example: Chlorine (7 valence electrons b/c it is in group 17)
Paired and Unpaired Electrons
As we can see from the chlorine example, there are six electrons that are paired up and one that is unpaired.
When it comes to bonding, atoms tend to pair up unpaired electrons.
A bond that forms when one atom gives an unpaired electron to another atom is called an ionic bond.
A bond that forms when atoms share unpaired electrons between each other is called a covalent bond.
Writing Lewis Dots Structures for Ions
Uses either 0 or 8 dots, brackets and a superscript charge designate to ionic charge
Ex.) Li+, Be+2, B+3, C+4, N-3, O-2, F-1
Writing Lewis Dots Structures(Ionic Compounds)
Lewis Dot Diagrams of Ionic Compounds
Ex. 1) NaCl
Ex. 2) MgF2
A substance made up of atoms which are held together by covalent bonds is a covalent compound.They are also called molecules.
Lewis Dot Diagrams for Covalent Compounds
Covalent Compounds and Lewis Dot Diagrams Diagrams show bonds in a covalent compound
and tells us how the atoms will combine Shared e- = bonding e-
Non-shared e- = lone pair e- (a.k.a. non-bonding e-)
Ex. F2
Drawing Electron Dot Diagrams for Molecules
Chemists usually denote a shared pair of electrons as a straight line.
F F Sometimes the nonbonding pair of electrons
are left off of the electron dot diagram for a molecule
Types of Covalent Bonds
Single Bond 2 e- are shared in a bond (1 from each atom)
Double Bond 2 pairs of e- are shared (4 e- total, 2 from
each atom)Triple Bond
3 pairs of e- are shared (6 e- total, 3 from each atom)
Rules for Drawing Lewis Dot Diagrams
1. Add up the total number of valence e- for each atom in the molecule.
Each (-) sign counts as 1 e-, each (+) sign subtracts one e-
2. Write the symbol for the central atom then use one pair of e- to form bonds between the central atom and the remaining atoms.
3. Count the number of e- remaining and distribute according to octet rule (or the “duet” rule for hydrogen)
4. If there are not enough pairs, make sure the most electronegative elements are satisfied. Then, start shifting pairs into double and triple bonds to satisfy the octet rule.
5. If there are extra e-, stick them on the central atom.
Checking Your Work!
But Remember.... The Structure MUST Have: the right number of
atoms for each element, the right number of electrons, the right overall charge, and 8 electrons around each atom (ideally).
VSEPR: Shapes of Molecules
VSEPR Theory (definition) “Valence Shell Electron Pair Repulsion” Based on idea that e- pairs want to be as far
apart as possibleGives molecule its shape
VSEPR: Shapes of Molecules
Electron Pair Any two valence e- around an atom that repel
other e- pairsLone pair e- (unshared/non-bonding pair only on
one atom)Shared e- pair (bonding pair shared between two
atoms) – can be single, double, or triple bonds
VSEPR: Shapes of Molecules
Basic Shapes and Bond Angles
Total # e- Pairs
# of Bonded e- Pairs
# of Unshared Pairs
Molecular Shape
Bond Angles
Ex.
1 1 0 Linear 180o F2
2 2 0 Linear 180o BeH2
1 1 Linear 180o
V. VSEPR: Shapes of Molecules
Total # e- Pairs
# of Bonded e- Pairs
# of Unshared Pairs
Molecular Shape
Bond Angles
Ex.
3 3 0 Trigonal Planar 120o BF3
2 1 Bent < 120o SO2
1 2 Linear 180o
V. VSEPR: Shapes of Molecules
Total # e- Pairs
# of Bonded e- Pairs
# of Unshared Pairs
Molecular Shape
Bond Angles
Ex.
4 4 0 Tetrahedral 109.5o CH4
3 1 Pyramidal < 109.5o NH3
2 2 Bent < 109.5o H2O
1 3 Linear 180o
To determine the electron pair geometry:
1. Draw the Lewis structure.2. Count the number of bonded (X) atoms and non-bonded or lone pairs (E) around the central atom. 3. Based on the total of X + E, assign the electron pair geometry. 4. Multiple bounds count as one bonded atom!
Electron-pair geometry around a central atom
Sum of X + E Shapes
2 linear
3 trigonal planar
4 tetrahedral
5 trigonal bipyramidal
6 octahedral
Bond and Molecule Polarity Polar Bond
Covalent bond in which the electrons are unequally shared Ex. H2O
Non-polar Bond Covalent bond in which the electrons are equally
shared Ex. F2 or CH4
Predicting Bond Polarity Use Electronegativity!! (see next slide)
Predicting Bond Polarity Calculate the difference between the Pauling
electronegativity values for the 2 elements
Type of BondIONIC
(COVALENT)
POLAR NON-POLAR
Types of Atoms1 metal & 1 nonmetal
(ex. NaCl)
(generally)
2 nonmetals
Ex. NH3, H2O
(generally)
2 nonmetals
Ex. CCl4, O2
Electronegativity Difference
≥ 1.7 ≥ 0.4 but < 1.7 ≤ 0.4
0 – 0.4 Non-polar covalent0.4 – 1.7 Polar covalent (more e/n element has greater pull)
1.7 and up Ionic (e- are transferred between atoms)
Polar Molecules
Polar Molecules (dipole) Molecule with separate centers of (+) and (-)
charge In other words, molecules are polar if the pull in
any one direction is not balanced out by an equal & opposite pull in the opposite direction
Polar Bonds and Polar Molecules
Drawing Polar Molecules Positive and Negative regions shown by
“delta”(δ) Ex. CH3Cl
Determining the Polarity of a Molecule
Shape is crucial (determine the VSEPR shape 1st)
All non-polar bonds = nonpolar molecule Polar bonds see if they cancel each other
out If they all cancel = nonpolar molecule If they are unbalanced = polar molecule
Examples: Polar or non-polar?
Determine if the following molecules are polar or nonpolar.
H2S
F2
H2O
Special Types of Bonding
Hydrogen Bonding Force in which a hydrogen atom covalently
bonded to a highly electronegative element (F, O, or N) is simultaneously attracted to a neighboring nonmetal atom
Hydrogen Bonding Elements that undergo H-bonding
Hydrogen bonding is FON! (Fluorine, Oxygen, and Nitrogen)
Effects on Physical Properties H2O is most notable example of H-bonds
Ice forms rigid, open structures Increases volume upon freezing (floats)
Molecules w/ higher molar mass have lower BP than H2O
Special Types of Bonding
Van der Waals (London Dispersion) Forces Intermolecular force between the molecules of a
substance Force of attraction between an instantaneous and
induced dipole Molecules “make these up” (more or less)
Solids Classes of Solids
Molecular Formed by molecules containing covalently bonded atoms
Ionic Formed by cations and anions
Network Covalent Formed by atoms, usually from Group IV A (Group 14)
Metallic Formed by positive ions in a “sea” of electrons
SolidsComparison of Solids
Type of Solid
Hardness Malleability ConductivityMelting Point
Ease of Phase
Change
Molecular(2 nonmetals)
Soft Shatters Insulator LowEasy to convert
to gas
Ionic(1 metal, 1 non)
Hard ShattersConducts if melted or in
waterHigh
Difficult to convert to gas,
solid
Network Covalent
Very Hard ShattersPoor
ConductorHigh
Difficult to convert to gas,
solid
MetallicVaries from soft to hard
Very MalleableGood
conductor as liquid or solid
Usually High
Difficult to convert to gas, Easy to covert
to solid
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