Chemical Interactions
Biology 1 Notes
In order to be stable, an atom wants to have a filled outer energy level (also called the
valence level).
FILL
Krypton (noble gas)
Because electrons fill energy levels from the inside out, the energy level that would
not be filled would be the outer energy level. Except for the elements in the column
with Helium and Neon, called the Noble Gases, none of the other elements have a filled
outer energy (valence) level.
The only way they can have a filled valence level is to BOND with other elements to
form a compound.
 A compound is a substance made of two or more elements that are bonded
together.
 A bond is an interaction between two or more elements where outer energy
electrons are SHARED or EXCHANGED to make the two elements stable.
Chemical reactions occur when chemicals break and form new chemical bonds.
Review vocabulary from this page –
 Valence shell:
 Bond:
 Compound:
ELECTRON CONFIGURATION & BONDS
The electron configuration of an atoms involved in the chemical reaction will determine
how they will bond.
Looking at the valence level of a typical atom, there are 4 “orbitals” (think – “seats on a
carousel”)
Remember that electrons will first fill any open orbitals, then second pair within the
orbitals (pair = “share a seat”). The following guidelines will let you know what type of
bond they will form:
 If the 2 or more atoms involved in forming the compound each have at least 1
electron in each orbital (see below), they will SHARE unpaired electrons to form
Covalent bonds.
Define Covalent Bond in your own words:
Draw an example of a MOLECULE, show how bonds occur
Molecular Formula:
Bohr Model
Structural Model
 If the 2 or more atoms involved in forming the compound have an extreme
difference in the number of electrons in their valence level, they will
EXCHANGE (swap) electrons. This will cause these atoms with a charge, ION.
 There are 2 types of ions, positive (+) and negative (-)
o The element with more than half of their electron orbitals filled will be an
“electron taker” – (it is ‘electronegative’). In order to be stable, it will
gain electrons. Since electrons have a negative charge, for every electron
it gains, it adds a negative charge of 1. Therefore it becomes a
NEGATIVE ion. Oxygen, below, will take 2 electrons and become an ion
with a -2 charge  O-2 (we call it an Oxide ion)
Draw Lewis Dot Models of the following elements.
Are they going to be “givers” or “takers”?
Fluorine =
F
giver or taker?
Sodium =
Na
giver or taker?
B
giver or taker?
Boron =
o The element with less than half of the electron orbitals filled will be an
“electron giver”. Rather than trying to gain a lot of electrons, it releases
its relatively small number of outer energy level electrons. As a result, the
energy level below (that is filled) is its new valence level. Because it is
losing negatively charged electrons, it becomes a POSITIVE ion (+1 for
every electron lost).
Describe Ionic Bonding in your own words:
Draw an Example of an IONIC COMPOUND, show how ionic bonds occur:
Summary
Complete below
1. Most elements are unstable because they don’t have a ___________ outer energy level.
2. Elements that have a filled outer energy level are __________ and are called Noble Gases (He,
Ne, Ar, etc)
3. In order to become stable, elements __________ with other elements to fill the outer energy
level.
4. ______________ – made of 2 or more elements bonded together
a. Molecule – contains covalent bonds
b. Ionic compound – contains ionic bonds
5. Covalent Bonds
a. Unpaired outer electrons are _______________
b. Can share 1, 2, or 3 ___________ (single, double, or triple bond)
c. The number of bonds an element will form is equal to the number of ______________
electrons in its orbitals.
d. Sketch example of covalent bond:
6. Ionic Bonds
a. Most atoms have 4 orbitals in their outer energy level. Each orbital holds ___ electrons.
Each orbital first fills with ___ electron, then any additional electrons added will pair.
b. If an atom has unfilled orbitals, in order to be stable it will lose its electrons so that its
next innermost ring will be its new outer ring. As a result, it will become a
___________ (Positive or Negative) ION.
c. If an atom has filled orbital, but is missing just a few pairs, it takes electrons from
another atom that would become a positive ion. As a result, it will become a
___________ (Positive or Negative) ION.
d. Sketch example of ionic bonding: