1. CHAPTER 2: Atomic structure and interatomic bonding
ISSUES TO ADDRESS...
• What promotes bonding?
• What types of bonds are there?
• What properties are dependent on bonding?

2. } 1.67 x 10-27 kg Atomic Structure
atom – electrons – x kg  protons neutrons
atomic number = # of protons in nucleus of atom = # of electrons of neutral electrically
or complete atom
atomic mass = the sum of the masses of proton and neutrons within the nucleus 
Atomic wt = wt of x 1023 molecules or atoms  amu – atomic mass unit 1 amu/atom = 1g/mol
C H etc.
} 1.67 x kg

3. Atomic Structure
Valence electrons are those that occupy the outermost shell. These electrons are extremely important, they participate in the bonding between atoms to form atomic and molecular aggregates.
Valence electrons determine all of the following properties
Chemical
Electrical
Thermal
Optical

4. Electronic Structure
Electrons have wavelike and particulate properties.
This means that electrons are in orbitals defined by a probability.
Each orbital at discrete energy level determined by quantum numbers.   Quantum # Designation
n = principal (energy level-shell) K, L, M, N, O (1, 2, 3, etc.)
l = subsidiary (orbitals) s, p, d, f (0, 1, 2, 3,…, n -1)

5. Electron Energy States
Electrons...
• have discrete energy states (2,6,10,14)
• tend to occupy lowest available energy state. 1s 2s 2p
K-shell n = 1
L-shell n = 2 3s 3p
M-shell n = 3 3d 4s 4p 4d
Energy
N-shell n = 4

6. The order by which the electrons fill up orbitals is as follows:
The electron configuration of the elements is determined experimentally. It is noted that there are some irregularities inconsistent with the previously listed system. For ex, copper ( Z=29) has the outer electron configuration to be
One would expect
The reason for these irregularities is not precisely know

7. SURVEY OF ELEMENTS • Most elements: Electron configuration not stable.
... 1s 2 2s 2p 6 3s 3p 3d 10 4s 4p
Atomic # 18 36
Element 1
Hydrogen
Helium 3
Lithium 4
Beryllium 5
Boron
Carbon
Neon 11
Sodium 12
Magnesium 13
Aluminum
Argon
Krypton

8. Electron Configurations
Valence electrons – those in unfilled shells
Filled shells more stable
Valence electrons are most available for bonding and tend to control the chemical properties
example: C (atomic number = 6)
1s2 2s2 2p2
valence electrons

9. Electronic Configurations
ex: Fe - atomic # = 26
1s2 2s2 2p6 3s2 3p6
3d 6 4s2
valence
electrons 1s 2s 2p
K-shell n = 1
L-shell n = 2 3s 3p
M-shell n = 3 3d 4s 4p 4d
Energy
N-shell n = 4

10. The Periodic Table • Columns: Similar Valence Structure give up 1e
inert gases
accept 1e
accept 2e O Se Te Po At I Br He Ne Ar Kr Xe Rn F Cl S Li Be H Na Mg Ba Cs Ra Fr Ca K Sc Sr Rb Y
Atomic #
Electropositive elements:
Readily give up electrons
to become (+ ions).
Electronegative elements:
Readily accept electrons
to become (- ions).

11. The Periodic Table
all elements have been classified according to electron configuration in the periodic table
Here the elements are situated, with increasing atomic number, in seven horizontal rows called period
The arrangement in such that all elements arrayed in a given column or group have similar valence electron structures, as well as chemical and physical properties

12. Electronegativity • Ranges from 0.7 to 4.0,
• Large values: tendency to acquire electrons.
Smaller electronegativity
Larger electronegativity

13. Atomic bonding in solid
Primary ( or chemical) bonds :
metallic
ionic
covalent
secondary ( or physical) forces:
van der walls bonding
Are weak in comparison to the primary o chemical ones
Secondary bonding is evidenced for the inert gases, which have stable electron structures, and, in addition, between molecules in molecular structures that are covalently bonded
Hydrogen bonding, a special type of secondary bonding, is found to exist between some molecules that have hydrogen as one of the constituents

14. Metallic Bonding It is found in metals and their alloys
Is nondirectional in character
Bonding may be strong or weak; bonding energies range from 68 kJ/mol for mercury to 850 kJ/mol for tungsten. Their respective melting temperatures are -39 and 3410 C

15. Ion cores + + + + + + + + +
Sea of valence electrons

16. Some general behavior of the various material types (i. e
Some general behavior of the various material types (i.e., metals, ceramics, and polymers) may be explained by bonding type.
For example, metals are good conductors of both electricity and heat, as a consequence of their free electrons.
By the way of contrast, ironically and covalently bonded materials are typically electrical and thermal insulators, due to the absence of large numbers of free electrons.

17. Ionic bond – metal + nonmetal
donates accepts electrons electrons  
Dissimilar electronegativities  
ex: MgO Mg 1s2 2s2 2p6 3s O 1s2 2s2 2p4
[Ne] 3s2 
Mg2+ 1s2 2s2 2p O2- 1s2 2s2 2p6

18. Ionic Bonding
• Occurs between + and – ions.( metalic+nonmetalic) elem
• Requires electron transfer.( high electroneg+high electropoz)
• Large difference in electronegativity required.
• Example: NaCl ( Na=11, Cl=17)
Na (metal)
unstable
Cl (nonmetal)
electron + -
Coulombic
Attraction
Na (cation)
stable
Cl (anion)

19. Examples: Ionic Bonding
• Predominant bonding in Ceramics
NaCl
MgO
Give up electrons
Accept electrons
CaF 2
CsCl

20. Covalent Bonding similar electronegativity  share electrons
bonds determined by valence – s & p orbitals dominate bonding
Example: CH4
shared electrons
from carbon atom
from hydrogen
atoms H C CH 4
C: has 4 valence e-,
needs 4 more
H: has 1 valence e-,
needs 1 more
Electronegativities
are comparable.

21. Summary: Bonding Type Bond Energy Comments Ionic Large!
Nondirectional (ceramics)
Covalent
Variable
Directional
(semiconductors, ceramics
polymer chains)
large-Diamond
small-Bismuth
Metallic
Variable
large-Tungsten
Nondirectional (metals)
small-Mercury
Secondary
smallest
Directional
inter-chain (polymer)
inter-molecular

22. Summary: Primary Bonds
Ceramics
Large bond energy
large Tm
large E
small a
(Ionic & covalent bonding):
Metals
Variable bond energy
moderate Tm
moderate E
moderate a
(Metallic bonding):
Polymers
Directional Properties
Secondary bonding dominates
small Tm
small E
large a
(Covalent & Secondary):
secondary bonding