CHEM 1405

1
CHEM 1405

• Class Meeting 4

2
Assignments and Reminders

• Reading Assignment
• Chapter 3 by Tuesday, Jan 31st
• Homework Problems due next Thursday, Feb 2nd
• Chapter 2 problems 2, 10, 12, 14, 16, 18, 20, 24,
  27, 28, 29, 36, 38, 44, 46, 48
• Chapter 3 problems 2, 4, 8, 10, 12, 14, 16, 18,
  20, 30, 32, 42, 44
• Class website
• http//iws.ccccd.edu/jstankus/

3
Chemical Bonds

• 1. What electronic configuration appears to be
  the most stable? How is an understanding of this
  important in determining the most common ion(s)
  formed from a given atom?
• 2. What are Lewis structures?
• 3. What is an ionic bond? How does it differ
  from a covalent bond?
• 4. How are the chemical formulas of ionic
  compounds determined? How are ionic compounds
  named?
• 5. What determines if a covalent bond is polar
  or nonpolar? How does electronegativity influence
  whether a bond is polar or nonpolar?
• 6. How are the chemical formulas of simple
  molecules determined? How are these molecules
  named?
• 7. What is a polyatomic ion?
• 8. What steps are followed in determining the
  Lewis structure for a given molecule or ion?
• 9. What is the octet rule? What are some
  exceptions to the octet rule?
• 10. How is VSEPR theory used to predict the
  shapes of molecules and ions?
• 11. How is the shape of a molecule important in
  determining whether the molecule is polar or
  nonpolar?

4
Chemical Bonds

• Forces responsible for holding together atoms in
  molecules and ions in crystals
• Determine shape of molecules
• Predict chemical and physical properties of
  materials
• Related to arrangement of electrons in compounds

5
Types of Chemical Bonds

• Ionic bonds are attractive forces between
  positive and negative ions, holding them together
  in a solid crystal.
• A covalent bond is a bond formed by a shared pair
  of electrons between atoms

6
Stable Electron Configurations

• Valence electrons outermost level with
  electrons
• Core electrons all other electrons in an atom

7
Full shells are particularly stable electronic
configurations
Noble gas electronic configuration is most stable
8
Valence Electrons and Core Electrons
The valence shell is the outermost shell of
electrons of an atom.
Mg example
The electrons in the valence shell determine the
chemical properties
1s22s22p6
3s2
Ne
3s2
The electrons in the inner shells are the core
electrons and dont affect the chemical
properties strongly
9
Lewis Dot Structures
The valence shell is the outermost shell of
electrons of an atom.
Mg example
1s22s22p6
3s2
Ne
3s2
2 electrons in the valence Shell
Use dots to represent Valence Electrons
Mg
10
Atomic Electronic
Valence Lewis Element Number
Configuration Electrons
Dot Structure
Hydrogen 1 1s1 Helium 2 1s2 Lithium 3 1s22
s1 Beryllium 4 1s22s2 Boron 5 1s22s22p1 C
arbon 6 1s22s22p2 Nitrogen 7 1s22s22p3 Oxygen
8 1s22s22p4 Fluorine 9 1s22s22p5 Neon 10 1s2
2s22p6 Sodium 11 1s22s22p63s1 Magnesium 12 1s2
2s22p63s2 Aluminum 13 1s22s22p63s23p1 Silicon
14 1s22s22p63s23p2 Phophorus 15 1s22s22p63s23p3
H He Li Be B C N O F Ne Na Mg Al Si P
1 2 1 2 3 4 5 6 7 8 1 2 3 4 5
11
Ions

• When an atom gains or loses electrons, it becomes
  charged and is called an ion.
• Tend to go to a noble gas configuration
• Ionization energy is the energy required to
  remove the least tightly bound electron from a
  ground-state atom (or ion) in the gaseous state.
• Creates a Positive Ion
• Electron affinity is the energy change that
  occurs when an electron is added to an atom in
  the gaseous state.
• Creates a Negative Ion

12
Electron-Dot Structures

• Valence electrons represented by dots
• Electron-dot symbols
• Examples Na, Mg,

13
ElectronDot Structures for Ions

• Add electrons for anions

Chlorine atomic number 17 1s22s22p63s23p5
7 Valence electrons
Add electron to form ion
-
Chloride ion atomic number 17 1s22s22p63s23p6
8 Valence electrons
Now has full shell with similar electronic
configuration to Argon --Stable noble gas
configuration
14
ElectronDot Structures for Ions

• Remove electrons for cations

Na
Sodium Atomic number 11 1s22s22p63s1
1 Valence electron
Remove electron to form ion

Na
Sodium Ion Atomic number 11 1s22s22p63s0
Now has full shell with similar electronic
configuration to Neon --Stable noble gas
configuration
15
Sodium Reacts with Chlorine

• Sodium dropped in flask filled with chlorine gas
• Produces sodium chloride (i.e., table salt)
• Chlorine extracts electron from sodium

-

Na
16
Ionic Bonds

• Na and Cl
• Opposite charges attract
• Ions organize themselves in orderly manner
• Crystal of NaCl

17
Octet Rule

• Atoms tend to gain or lose electrons to have
  eight valence electrons
• Same as noble gases
• He and H are exceptions, get only two valence
  electrons

18
More Ionic Compounds

• Compound of Magnesium and Chlorine

Remove 2 electrons
Add 1 electron
Add 1 electron
-
-
Mg2
Charge is not balanced
Need two Chloride ions to balance charge on
Magnesium ion
MgCl2
Magnesium Chloride
19
More Ionic Compounds
20
Naming Ions

• For cations, simple positive ions
• Add the word ion
• Examples Na sodium ion
• Al3 aluminum ion
• For anions, simple negative ions
• Change the usual ending to -ide
• Examples Cl chloride
• S2 sulfide

21
(No Transcript)
22
Naming Binary Ionic Compounds

• Two components in compound

23
Binary Compounds

• Zinc and Oxygen

Zn
O
O2-
Zn2
Zn2
O2-
2
2
Zn2O2
ZnO
24
Binary Compounds

• Iron (III) and Sulfur

Fe
S
S2-
Fe3
Fe3
S2-
2
3
Fe2S3
25
Covalent Bonds

• Bond formed by a shared pair of electrons
• Gives atom an octet of electrons
• Shared pair of electrons bonding pair
• Other electrons not involved in bonding
  nonbonding pairs

26
Covalent Bonds example
Chlorine does not occur in nature as an isolated
atom
Covalent Bond
Chlorine atoms share electrons to get full shell