1. Notes 3- Chemical Bonds, Isotopes, Ions

2. Bonding properties Effect of electrons
chemical behavior of an atom depends on its electron arrangement
depends on the number of electrons in its outermost shell, the valence shell
Octet rule- atoms “want” to have 8 electrons in the valence shell
How does this atom behave?

3. Bonding properties
How does this atom behave?

4. Chemical reactivity Atoms tend to:
Complete a partially filled outer (valence) electron shell or
Empty a partially filled outer (valence) electron shell
8 is the magic number of valence electrons!!
This tendency drives chemical reactions

5. Chemical Bonds Strongest Bonds:
1. Covalent Bonds: two atoms need one electron, so they share a pair of electrons
Polar Covalent Bond: electrons are shared unevenly
ex) H2O- oxygen has the stronger “attraction” for electrons than hydrogen.
Nonpolar Covalent Bond: electrons are shared equally between the atoms. ex) O2

6. Chemical Bonds Double covalent bonds
Two atoms can share more than one pair of electrons
double bonds (2 pairs of electrons)
triple bonds (3 pairs of electrons)
Very strong bonds

7. Chemical Bonds
2. Ionic Bonds: electron is transferred from one atom to another
Forms one (+) and one (-) ion
(+) = cation
(-) = anion
Weaker than covalent bond
Generally occur between a metal and a nonmetal

8. Isotopes
# of neutrons varies, but same # of protons (same element, different mass)
Radioactive isotopes used as biological tracers (follow molecules, medical diagnoses)
Some are unstable- can also be a biological hazard

9. Ions Atom with a charge Remember... Cation= positive charge
Anion= negative charge

10. Na Ions 11 +1 23 How many protons does sodium have?
How many neutrons does sodium have?
How many electrons does sodium have? 11 Na +1 23

11. Ag Ions 47 -2 108 How many protons does silver have?
How many neutrons does silver have?
How many electrons does silver have? 47 Ag -2
108