1. The Basics Bonding and Molecular Structure
Chapter 1

2. 1.2 Atomic Structure Compounds
made up of elements combined in different proportions
Elements
made up of atoms
Atoms
positively charged nucleus containing protons and neutrons
with a surrounding cloud of negatively charged electrons

3. 1.2 Atomic Structure
Each element is distinguished by its atomic number, Z
Atomic number = number of protons in nucleus
Isotopes: Atoms of the same element (same # of protons) may have different masses because they have different numbers of neutrons
12C 13C 14C
(6 protons
6 neutrons)
(6 protons
7 neutrons)
(6 protons
8 neutrons)

4. 1.2 Atomic Structure
Electrons that surround the nucleus exist in shells of increasing energy and at increasing distances from the nucleus. Valence Electrons Electrons in the outermost shell an atom uses in making chemical bonds with other atoms to form compounds The number of electrons in the valence shell is equal to the group number of the atom

5. 1.3 Chemical Bonds
Ionic (or electrovalent) bonds are formed by the transfer of one or more electrons from one atom to another to create ions
Covalent bonds result when atoms share electrons
In forming compounds, they gain, lose, or share electrons to give a stable electron configuration characterized by a full shell of valence electrons
For the second row elements this is 8 electrons – octet rule

6. Electronegativity (EN)
The measure of the ability of an atom to attract electrons
Electronegativity is based on an arbitrary scale, with F the most electronegative (4.0) and Cs the least (0.7)

7. 1.3A Ionic Bonds Li 1s22s1 F 1s22s2p5 Li 1s2 F 1s22s2p6
Atoms may gain or lose electrons and form charged particles called ions
An ionic bond is an attractive force between oppositely charged ions
Ionic bonds form between atoms with a large EN difference
Li 1s22s1
F 1s22s2p5
Li 1s2
F 1s22s2p6

8. 1.3B Covalent Bonds
Molecules may also contain ions and covalent bonds:

9. 1.4 Lewis Structures
Lewis structures show the connections between atoms in a molecule or ion using only the valence electrons of the atoms involved
For main group elements, the number of valence electrons a neutral atom brings to a Lewis structure is the same as its group number
If the structure is an anion (negative ion) we add one electron for each negative charge and if the structure is a cation (positive ion), we subtract one electron for each positive charge
In drawing Lewis structures we try to give each atom the electron configuration of a noble gas

10. 1.4 Lewis Structures Steps for Drawing Lewis Structures
Find the total # of valence electrons for all atoms
Adjust the # if any negative or positive charges are indicated
Arrange atoms logically – large elements in middle, hydrogens/halogens on the periphery
Connect the molecule with single bonds (2 e- each)
Assign remaining electrons to the most electronegative elements first as lone pairs
Complete octets (if possible) with multiple bonds
Assign formal charges, if necessary

11. Know Your Elements H fills its shell with two electrons or zero (H+)Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Know Your Elements
H fills its shell with two electrons or zero (H+)
Neutral C, N, O, F always follow octet rule (and usually Cl, Br, I)

12. Know Your Elements Group IA Metals only form +1 cationsH He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Know Your Elements
Group IA Metals only form +1 cations
Group IIA Metals only form +2 cations

13. H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Know Your Elements
Group IIIA may follow the octet rule or prefer a sextet of e-
The higher halogens usually follow the octet rule, but may expand their octet if they are the central element in the molecule (F always follows the octet rule)

14. H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Know Your Elements
The main group non-metals may follow the octet rule but very often expand their octet
The transition metals can form ions, follow the octet rule or expand their octets

15. 1.5 Formal Charge
Formal charge is the charge assigned to individual atoms in a Lewis structure.
Formal charge is calculated as follows:
The number of electrons “owned” by an atom is determined by its number of bonds and lone pairs.
An atom “owns” all of its unshared electrons and half of its shared electrons.

16. Know Your Lewis Structures
Once you practice enough Lewis structures you begin to see that the elements we cover in this course follow a similar pattern

17. Know Your Lewis Structures
Once you practice enough Lewis structures you begin to see that the elements we cover in this course follow a similar pattern

18. Know Your Lewis Structures
Once you practice enough Lewis structures you begin to see that the elements we cover in this course follow a similar pattern

19. 5A. A Summary of Formal Charges
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