Chemical Bonds and Ions

Report
Ionic Bonds and Ions
Chemical Bonding
A Chemical Bond is the force of attraction that
holds two atoms together as a result of the
rearrangement of electrons between them.
When atoms bond, electrons may be transferred
from one atom to another, or they may be
shared between the atoms.
The change results in a Chemical Reaction
Ionic Bonding
Ionic Bonds = valence electrons are transferred from
one atom to another to make both atoms more
stable.
Atoms want to reach a stable 8 valence electrons
• Atoms with 5, 6, or 7 valence electrons usually
become more stable when this number increases to
8.
• Atoms with 1, 2, or 3 valence electrons become more
stable when they lose electrons
Valence Electron Review
• Where on the periodic table do you find
atoms with 5,6, 7 valence electrons and atoms
with 1, 2, 3?
Ions
• An ION is an atom that has gained or lost an
electron, giving it an electrical charge.
–
The addition of electrons to an atom
creates a negatively (-) charged atom
– The loss of electrons from an atom creates
positively (+) charged ions
Atoms will gain or lose electrons
to reach a stable 8 valence
electrons. (VIDEO)
Forming Ionic Compounds
• When ionic bonds form, the opposite charges of the
ions cause the ions to stick together. But the
compound formed is neutral because the charges
cancel each other.
• Li
(1+)
+
Cl (1-)  LiCl (neutral)
• When a metal and a nonmetal combine by ionic
bonding, the resulting compound has different
properties than the metal and nonmetal did.
• Ionic compounds are brittle and highly soluble, with
high melting and boiling points.
Examples
Sodium has 1 valence electron that it wants to
lose to become stable:
Chlorine has 7 valence electrons and it wants 1
more to become stable:
When Sodium’s valence electron is transferred
to Chlorine, both elements become ions.
Because Sodium loses an electron it becomes a
positive (+) ion.
Because Chlorine gains an electron it becomes a
negative (-) ion.
The two atoms bond to form:
+
-
Examine Figure 4 on page 233.
• Here we can see what is happening with the
valence electrons.
• Working with your partner, begin the ionic
bonds side of the worksheet
Ionic Bonding Review
• Ionic bonds are bonds that form when electrons
are transferred from one element to another
• Ionic bonds form between metals and nonmetals
• Elements in groups 1,2, 13 lose electrons and
become positive ions (+ charge)
• Elements in group 15, 16 , 17 gain electrons and
become negative ions (- charge)
• The ionic compound has no charge
Steps for forming Ionic Bonds
1. Identify the two elements that will bond
2. Figure out which will give and which will take
valence electrons
3. Figure out which element is the positive and
which is the negative ion
4. Calculate the number of each element you
need
5. Write the compound name: The positive ion
goes first, then the negative
Step 1: Identify Elements
Lithium and Bromine
Step 2: Atoms do what is easiest
• When deciding whether an element will gain
or lose valence electrons in an ionic bond, go
with the smaller number:
1. Lithium has 1 valence electron, it needs 7 –
what will it do?
2. Bromine has 7 valence electrons, it needs 1
So when these two elements bond Li will give
its 1 electron to Br
Atoms do what is easiest
• When deciding whether an element will gain
or lose valence electrons in an ionic bond, go
with the smaller number:
1. Sodium has 1 valence electron, it needs 7 –
what will it do?
2. Sulfur has 6 valence electrons, it needs 2,
what will it do?
3. Bromine has 7 valence electrons, it needs 1
4. Aluminum has 3 and needs 5
Step 3: Ions
Since Li is giving away its electron it has more
protons (+) than electrons (-).
Since Br is taking an electron it has more
electrons (-) than protons (+)
Li is the positive ion, Br is the negative ion
(if it gains weight (electrons) it is sad (negative),
if it loses it is happy (positive)
Charges of Ions
• Since atoms do what is easiest, it is easy to
figure out the charge on an ion:
1. B loses 3 electrons, so the charge is _______
2. S gains 2 electrons, so the charge is _______
3. Cl gains 1 electron, so the charge is _______
4. What about As, K, Ca?
Step 4: How many of each?
Since Li has one to give away and Br only needs
one the ratio of elements in this compound is
1:1
Step 5: Write out the compound
The positive ion goes first, the negative ion goes
second:
LiBr (Lithium Bromide)
Naming Ionic Compounds
1. Always put the positive ion (metal) name first
2. The name of the negative ion that is formed
in the compound usually changes to end with
–ide.
EXAMPLE: Sodium Chloride
• The ions that make up an ionic compound are
bonded in a repeating three-dimensional
pattern called a crystal lattice.
Ionic Compound Diagrams
You can draw the electron dot diagrams for ionic
compounds
• To draw ionic compound diagrams:
1. draw the compound formula
2. Draw the charges of the ions (number & sign)*
3. Draw the 8 valence electrons around them
*Draw the charge = the number given or taken and
the + or – sign (2+, 2-, 3+ etc)
Examples
Sodium has 1 valence electron that it wants to
lose to become stable:
Chlorine has 7 valence electrons and it wants 1
more to become stable:
When Sodium’s valence electron is transferred
to Chlorine, both elements become ions.
Because Sodium loses an electron it becomes a
positive (+) ion.
Because Chlorine gains an electron it becomes a
negative (-) ion.
The two atoms bond to form:
+
-
Elements do not always have to have the exact number
of electrons to give and take in order bond. But you must
use more of them in order to form the correct amount of
valence electrons:
• Because Sodium only has 1 electron, it wants to lose 1
and becomes a positive (+) ion.
• Because Oxygen has 6 valence electrons, it wants to
gain 2, to become a negative (-) ion.
• In order to form a bond, you need 2 Sodiums for every
1 Oxygen:
• When drawing ionic compounds –
REMEMBER:
- The positive ion goes on the left, the negative ion
goes on the right
- Always write the number and charges above the
chemical symbol
- Don’t forget the subscript if it has one!
- The number of electron dots is always 8
Draw the electron dot diagram and charges for the
compounds:
1. Magnesium Sulfide
2. Potassium Chloride
5. Aluminum Chloride
3. Magnesium Oxide
4. Calcium Oxide
Ending Questions
1.
2.
3.
4.
5.
6.
7.
8.
What is an ionic bond?
What category of elements form ionic bonds?
What is an ion?
How do ions form?
How many valence electrons does sodium have?
Will Sodium gain or lose electrons?
How about Magnesium, Oxygen?
When atoms gain electrons, what charge do they
have?
9. When atoms lose electrons, what charge do
they have?
Exit Tickets
• Complete the exit ticket and turn in to Ms.
Gorence in order to be dismissed today!

similar documents