Transcript L2 Ionic Bonding - Don`t Trust Atoms

Ionic Bonding
Learning Objectives:
1. Describe how ions are formed.
2. Draw dot and cross diagrams to represent ions
and ionic compounds.
3. Describe the lattice structure of ionic
compounds.
4. Explain how electrostatic forces hold ionic
compounds together.
Review: What are the types of bonding?
Different types of bonds are formed depending on the types
of atoms involved:
give/take e ionic bonding
– occurs between metal and non-metal atoms.
 covalent bonding
– occurs between non-metals atoms only. share e metallic bonding
– occurs between metal atoms only.
share e-
All bonds involve electrons and all bonding involve changes
to the number of electrons in the outer shells of atoms.
1. How do atoms form ions?
An ion is an atom or group of atoms that has an
electrical charge, either positive or negative.
Atoms have an equal number of protons and electrons and
so do not have an overall charge.
Atoms with incomplete outer electron
shells are unstable. By either gaining or
losing electrons, atoms can obtain full
outer electron shells and become stable.
Ions have an unequal number of protons and electrons and
so have an overall charge.
How does an atom become a positive or negative ion?
2. Positive and negative ions?
An atom that loses electrons has more protons
than electrons and so has a positive overall charge.
This is called a positive ion = cation.
An atom that gains electrons has more electrons
than protons and so has a negative overall charge.
This is called a negative ion = anion.
The electron configuration of an atom shows how many
electrons it must lose or gain to have a filled outer shell.
 Atoms with a nearly empty outer shell, will lose electrons
to obtain a full outer shell.
 Atoms with a nearly full outer shell, will gain electrons
to obtain a full outer shell.
3. How do atoms form positive ions?
An atom that loses one or more electrons
forms a cation.
Metal atoms, such as sodium, magnesium
and iron, form positive ions.
Positive ions have a small ‘+’ symbol and a number by this
to indicate how many electrons have been lost.
This number is usually the same as the number of electrons
in the atom’s outer shell. For example:
lithium atom 2.1
lithium ion [ 2 ]
= Li+
magnesium atom 2.8.2
magnesium ion [ 2.8 ] = Mg2+
aluminium atom 2.8.3
aluminium ion [ 2.8 ] = Al3+
4. How is a sodium ion formed?
Sodium atom:
11 protons
= +11
11 electrons = -11
Sodium ion:
11 protons
= +11
10 electrons = -10
Total charge =
Total charge =
0
+1
+
Na
loses
1 electron
2.8.1
(barely full outer shell)
Na
[2.8]+
(full outer shell)
5. How is a magnesium ion formed?
Magnesium atom:
12 protons
= +12
12 electrons = -12
Magnesium ion:
12 protons
= +12
10 electrons = -10
Total charge =
Total charge =
0
+2
2+
Mg
loses
2 electrons
2.8.2
(partially full outer shell)
Mg
[2.8]2+
(full outer shell)
6. How do atoms form negative ions?
An atom that gains one or more electrons
forms an anion.
Non-metal atoms, such as chlorine,
oxygen and nitrogen, form negative ions.
Negative ions have a small ‘-’ symbol and a number by this
to indicate how many electrons have been gained to fill their
outer shell. For example:
chlorine atom 2.8.7
chloride ion [ 2.8.8 ] = Cl-
oxygen atom 2.6
oxide ion [ 2.8 ]
= O2-
nitrogen atom 2.5
nitride ion [ 2.8 ]
= N3-
The name of the ion is slightly different to the atom’s name.
7. How is a fluoride ion formed?
Fluorine atom:
9 protons
= +9
9 electrons
= -9
Fluoride ion:
9 protons
= +9
10 electrons = -10
Total charge =
Total charge = -1
0
-
F
gains 1
electron
2.7
(partially full outer shell)
F
[2.8](full outer shell)
8. How is a sulphide ion formed?
Sulfur atom:
16 protons
= +16
16 electrons = -16
Sulfide ion:
16 protons
= +16
18 electrons = -18
Total charge =
Total charge = -2
0
2-
S
gains 2
electrons
2.8.6
(partially full outer shell)
S
[2.8.8]2(full outer shell)
Building an ion
9. Calculating ion charges
What is the charge on the ion of each element?
Element calcium hydrogen phosphorus fluorine beryllium
Electron
config. 2.8.8.2
1
2.8.5
2.7
2.2
Charge
on ion
+1
-3
-1
+2
+2
10. Electron configuration of ions
When different elements gain or lose electrons to complete
their outer electron shell, they can create ions that have the
same electron configuration.
For example, oxygen and fluorine both gain electrons to
become negative ions. The resulting ions have the same
electron configuration:
-
2O
F
But they have different numbers of protons and neutrons.
This means that each ion has different properties.
Comparing electron configurations
Comparing positive and negative ions
11. Ionic Compounds
Compounds that contain ions are called ionic
compounds. These compounds are usually
formed by a reaction between a metal and a
non-metal.
Why do these substances react together and form bonds?
The metal and non-metal atoms have incomplete outer
electron shells and so are unstable.
Electrons are transferred from each metal atom to each
non-metal atom. The metal and the non-metal atoms form
ions with completely full outer shells and become stable.
Ionic bonding happens because the positive and negative ions
are strongly attracted to each other (electrostatic forces).
12. How are ionic bonds formed?
Sodium chloride is an ionic compound formed by the reaction
between the metal sodium and the non-metal chlorine.
2.8.1
Cl
Na
Chlorine
atom
Sodium
atom
-
+
Na
Sodium
ion
2.8.7
[2.8]+
Cl
[2.8.8]-
chloride
ion
13. How are ionic bonds formed?
The positive sodium ions and the negative chloride ions
are strongly attracted to each other.
+
Na
Cl
It is this electrostatic force of attraction that forms ionic
bonds in sodium chloride and other ionic compounds.
14. example
Lithium bonding to Fluorine
2.1
Li
-
+
Li
[2]+
2.7
F
F
[2.8]-
So what do we call ionic
compounds?
15. Naming Simple Ionic Compounds
Metal + Non-Metal
1. First word: Write out the full name of the first
element (metal) of the chemical formula.
2. Second word: Write out the root of the second
element (non-metal) and add –ide to the end.
Numbers do NOT matter!
Example: MgO = magnesium oxide
CaF2 = calcium fluoride
16. Name that Compound!
Chemical Formula
A. NaCl
B. CuO
C. KBr
D. CaCl2
E. ZnS
Name
A. Sodium Chloride
B. Copper Oxide
C. Potassium Bromide
D. Calcium Chloride
E. Zinc Sulphide
17. What is the ratio of ions (formula)?
Sodium chloride (NaCl) and magnesium oxide (MgO) are
simple ionic compounds.
In each compound, the metal needs to lose the same
number of electrons that the non-metal needs to gain.
1 electron
Cl
Na+
Cl-
Mg 2 electrons
O
Mg2+
O2-
Na
Both compounds have a 1:1 ratio of metal ions to non-metal
ions, which is shown by the formula of each compound.
18. What if isn’t the same?
What is the ratio of ions needed to make sodium oxide?
Sodium (2.8.1) needs to lose 1 electron to form a sodium ion
but oxygen (2.6) must gain 2 electrons to form an oxide ion .
Na+
Na
Na
1 electron
from each
Na atom
O2-
O
Na+
Two sodium atoms are required for each oxygen atom
and so the ratio of sodium ions to oxide ions is 2:1.
From this ratio, the formula of sodium oxide is Na2O.
19. What is the ratio of ions in magnesium chloride?
What is the ratio of ions needed for magnesium chloride?
Magnesium (2.8.2) needs to lose 2 electrons to form a
magnesium ion but chlorine (2.8.7) needs to gain 1 electron
to form an chloride ion.
Cl
Mg
1 electron
for each
Cl atom
Cl-
Mg2+
Cl
Cl-
Two chlorine atoms are required for each magnesium atom
and so the ratio of magnesium ions to chloride ions is 1:2.
From this ratio, the formula of magnesium chloride is MgCl2.
20. Chemical Formulae
1. Write the symbols for
the ions (metal first).
2. Write the charges.
3. Balance the charges
so the total = 0.
4. Complete the formula.
5. Write the final answer.
+2 + (-1x2) = 0
+2
-1 X 2
Mg Cl 2
Ex. Formula of aluminium bromide
What is the formula of aluminium bromide?
Symbol
Al
Br
Ion charge
+3
-1
Balance the
number of ions
3 bromide ions are needed
for each aluminium ion
Ratio of ions
1:3
Formula
AlBr3
Al
1 electron
for each
bromine
atom
Br-
Br
Br
Br
Al3+
BrBr-
Ex. Formula of aluminium oxide
What is the formula of aluminium oxide?
Symbol
Al
O
Ion charge
+3
-2
Balance the
number of ions
2 aluminium ions are
needed for 3 oxide ions
Ratio of ions
2:3
Formula
Al
2 electrons for
each oxygen atom
Al
Al2O3
O
Al3+
O2-
O2-
O
Al3+
O
O2-
21. Ionic Formulae
What are the formulae of all the possible ionic compounds
from combinations of these metals and non-metals.
metals
nonmetals
Li
F
O
N
Br
S
Cl
LiF
Li2O
Li3N
LiBr
Li2S
LiCl
Ca
CaF2
CaO
Ca3N2
CaBr2
CaS
CaCl2
Na
NaF
Na2O
Na3N
NaBr
Na2S
NaCl
Mg
MgF2
MgO
Mg3N2
MgBr2
MgS
MgCl2
Al
AlF3
Al2O3
AlN
AlBr3
Al2S3
AlCl3
K
KF
K2O
K3N
KBr
K2S
KCl