1. Daily Science
Label the following as a molecule, atom, compound, or both (molecule and compound) H3
H2O Ca
NaCl
How many and what kind of atoms do you see here: KMnO4

2. Chemical Bonds
Biology 1

3. Chemical Bonds
Atoms in molecules and compounds are held together by chemical bonds.
Valence electrons are the electrons that form bonds.
There are two main types of bonds:
Ionic
Covalent
Hydrogen Atoms Bonding

4. Chemical Bonds
Ionic Bonds – form when one or more valence electrons are transferred from one atom to another. (Metal + Nonmetal)
Ion – an atom that has a charge because it has either lost or gained electrons.
If an atom loses electrons, what is its charge?
Positive
If an atom gains electrons, what is its charge?
Negative
Positively charged ions are called cations. Negatively charged ions are called anions.

5. Each resulting ion has a completed valence shell
Fig
Ionic Bonding Na Na Cl Na Cl Na Cl
Na+
Cl–
Sodium atom
Chlorine atom
Sodium ion
(a cation)
Chloride ion
(an anion)
Figure 2.14 Electron transfer and ionic bonding
Sodium chloride (NaCl)
Each resulting ion has a completed valence shell 5

6. Draw this Staircase!

7. Metals and Nonmetals
Metals are to the left of the staircase on the periodic table
Ex: Iron (Fe), Cobalt (Co), Lithium (Li)
Nonmetals are to the right of the staircase on the periodic table
Ex: Carbon (C), Neon (Ne), Hydrogen (H)

8. Chemical Bonds
Covalent Bonds – form when electrons are shared between two atoms.
Valence electrons travel in the valence shell of both atoms.
Electrons must be shared in pairs (one from each atom).
Two electrons  Single Covalent Bond
Four electrons  Double Covalent Bond
Six electrons  Triple Covalent Bond

9. Covalent Bonding in Four Molecules
Fig. 2-12
Name and
Molecular
Formula
Electron-
distribution
Diagram
Lewis Dot
Structure and
Structural
Formula
Space-
filling
Model
Covalent Bonding in Four Molecules
(a) Hydrogen (H2)
(b) Oxygen (O2)
(c) Water (H2O)
Figure 2.12 Covalent bonding in four molecules
(d) Methane (CH4) 9

10. Ionic and Covalent Bonds Video
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 10

11. Chemical Bonds Why do bonds form?
Atoms want to have full valence shells.
Having a full valence shell makes an atom inert (unreactive).
Atoms will lose/gain/share electrons until their valence shell is full.
The closer a valence shell is to being full, the more reactive an atom is.
Check out this video!