1. Chemical Bonds

2. Atom – the smallest unit of matter “indivisible”
Helium
atom

3. electron shells Atomic number = number of Electrons
Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells.
Electron shells determine how an atom behaves when it encounters other atoms

4. Electrons are placed in shells according to rules:
The 1st shell can hold up to two electrons, and each shell thereafter can hold up to 8 electrons.

5. Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons
C would like to
N would like to
O would like to
Gain 4 electrons
Gain 3 electrons
Gain 2 electrons

6. Why are electrons important?
Elements have different electron configurations
different electron configurations mean different levels of bonding

8. Electron Dot Structures
Symbols of atoms with dots to represent the valence-shell electrons
H He:
          
Li Be  B   C   N   O  : F  :Ne :
       
          
Na Mg  Al  Si  P S :Cl  :Ar :
       

9. Chemical bonds: an attempt to fill electron shells
Ionic bonds –
Covalent bonds –
Metallic bonds

10. Learning Check A. X would be the electron dot formula for
A. X would be the electron dot formula for
1) Na 2) K 3) Al
 
B  X  would be the electron dot formula
1) B 2) N 3) P

11. IONIC BOND bond formed between two ions by the transfer of electrons

12. Ionic Bonds
Between atoms of metals and nonmetals with different charges (electrostatic attraction
Good conductors and have high melting points
Crystal Lattice structure
Examples; NaCl, CaCl2, K2O

13. Crystal lattice structure shown on the left

14. COVALENT BOND bond formed by the sharing of electrons

15. Covalent Bond Nonmetal/Nonmetals involved
Formed by sharing electron pairs to satisfy octet
Not good conductors of electricity
Low strength/low melting points

16. Covalent Bonds (cont’d)
Include biological molecules C6H12O6, CO2
Examples; O2, CO2, C2H6, H2O, F2

17. when electrons are shared equally
NONPOLAR COVALENT BONDS
when electrons are shared equally
H2 or Cl2

18. 2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons.
Oxygen Atom
Oxygen Atom
Oxygen Molecule (O2)

19. when electrons are shared but shared unequally
POLAR COVALENT BONDS
when electrons are shared but shared unequally
Ex. H2O

20. Polar Covalent Bonds: Unevenly matched, but willing to share.
Oxygen electronegativity: 3.5
Hydrogen electronegativity : 2.1
Difference greater than 1=then the molecule is polar

21. Polarity and Solutions
“like dissolves like” important rule of solutions
Oil (nonpolar)/water (polar)….what happens?

22. METALLIC BOND bond found in metals; holds metal atoms together very strongly

23. Metallic Bond Metals/Metals
Electron cloud around atoms (sea of electrons)

24. Metals Form Alloys do not combine with metals
form alloys which is a solution of a metal in a metal
Ex. steel (Fe mostly), brass (Cu and Zn), bronze (Cu mostly some Sn) and pewter (Cu, Sb, Bi).

25. Metallic bond properties
Good conductors, have luster, very high melting points
Ductile and malleable
Examples; Na, Fe, Al, Au, Co,