1. Atoms can be joined to other atoms by chemical bonds

2. c) 2 (or more) atoms of different elements stuck together
Atoms = smallest piece of an element
Molecules = smallest piece of anything
can be….
a) individual atoms of and element
b) 2 atoms of same element stuck together
c) 2 (or more) atoms of different elements stuck together

4. To show that atoms are bonded ..
Write the element symbols right next to each other with no spaces in between
NaCl
Use subscripts to indicate how many atoms of each element are attached
MgCl or K2O
For 1 Mg atom with 2 Cl or 2 K with 1 O
Na(SO4)2 subscripts outside () apply to all elements inside ()

5. Atoms with 8 valence e- are stable and don’t form bonds
Why Atoms form bonds
Atoms form bonds to become stable
Stable atoms have full set of valence e-
(valence e- are outer-most electrons)
The max number of valence e- is 8
Atoms with 8 valence e- are stable and don’t form bonds
Atoms want a full outer energy level

6. Atoms form bonds to become stable
Atoms can from 3 kinds of bonds.
1) metal + non-metal forms ionic bonds
2) non-metal + non-metal forms covalent bonds
3) metal + metal forms metallic bond

8. Only He is stable with only 2 e-

9. How do you tell how many valence e- an atom has?
The one’s place of the group number tells you the number of valence electrons
EXCEPT for transition metals & He

10. Atoms can gain or lose electrons to get 8 valence e-
In ionic bonds atoms do what-ever is easier (gain or lose)
Metals lose e- to become positive cations
Non-metals gain e- to become negative anions

11. Atoms with less than 4 valence electrons lose e-
When the one e- in the outermost energy level is lost…
The outer energy disappears
Na becomes
Na+

12. Atoms with more than 4 electrons gain e-
Outer energy level full

13. After forming ionic bonds..
Lewis dot diagrams have either
NO dots or 8 dots

14. Writing Ionic Formulas
Write the element symbols (metal first)
Add subscripts to represent how many atoms of each element are used
Add oxidation numbers to show the charges on each atom
Overall charge of compound = 0

15. In covalent Bonds
Both atoms want to gain e-
Atoms share e- to get full outer energy level
Shared electrons count in the outer energy level of both atoms

16. Covalent bonds form:
Between 2 or more NON-Metals Or
Between NON-Metals and Hydrogen

17. Non-polar Bond
If electrons are shared equally then the molecule
that is formed is neutral

18. Polar Bonds have poles
When one atom pulls harder on the e-
the e- spends more time near that atom
That end of the molecule is slightly negative

19. partial charges shown by δ

20. Covalent bonds can share
1 pair of electrons =
single bond shown as 1 line C-C
2 pair of electrons =
double bond shown as 2 lines C=C
3 pair of electrons =
triple bond shown as 3 lines