Bonding
In your notebook:
What does bonding mean?
What types of things do we use to
bond items/materials together?
Why choose one over the other?
Bonding
• What does it mean?
• How do we bond things
together in the “real world”
• https://www.youtube.com/watch?v=WcWe
UUzOuHk
Compound
Element
Atom
Molecule
A particle containing 2 or more
atoms (of the same or different
types
The simplest type of particle
A substance made of 2 or more
types of atom chemically
combined
A substance made of
only 1 type of atom
Atoms bond by
• Sharing electrons – covalent bonds
(between non-metals only)
• Gaining or losing electrons – ionic bonds
(between metal and non-metal)
• Unfixed sharing electrons – metallic bonds
(between metals only)
All three types involve changes in the electrons in the outermost
electron shells of the atoms
Electron shells and bonding
• Atoms are only “happy” when their outer
shell is full
• They will either lose or gain electrons in
order to become “happy”
• If they lose electrons they become positive
ions (the number of protons is bigger than
the number of electrons)
• If they gain electrons they become
negative ions (the number of protons is
smaller than the number of electrons)
General rule
• Non-metals usually form negative ions
• Metals usually form positive ions
What are the two types
of bonds?
•Who are they
between… No notes!
2. Ionic bonding
Made from reaction of
metals with non-metals.
Electron
donation
Li
F
F-
Li+
Attraction
Positive metal ions and negative non-metal ions attract each other strongly to
make potentially infinitely large continuous and uniform structures.
+
Ions in uniform
structure
Water
Ions moving freely
in solution
2. Ionic bonding
Ionic compounds’ characteristics:
• High melting points
• Hard but brittle
• Uniform, repeat structure (alternating + & – ions)
• Unreactive when solid (especially “ordinary”
ionic compounds, e.g. NaCl, MgO)
• Dissolve in water to create solutions
• Do not conduct electricity when solid, but do in
solution or when molten
Ionic bonding
E.g. Sodium + Chlorine → Sodium chloride
Na
Cl
Outer shells not full!
Ionic bonding
E.g. Sodium + Chlorine → Sodium chloride
NaCl (Na+Cl-)
Na
Cl
Both ions have full outer shells
Beryllium fluoride - BeF2
Beryllium fluoride - BeF2
• Each beryllium atom need to loose two
electrons, but each fluorine only needs 1
2+
F
Be
F
Questions
1. Describe the formation of positive and
negative ions
2. Draw dot and cross diagrams for ions of:
•
•
Potassium and bromine
Lithium and chlorine
3. Draw dot and cross for ions of:
•
•
Calcium and oxygen
Beryllium and oxygen
Warm Up!!
• Show the bonds of PbI2
• Show the bonds of AgCl
1. Simple covalent bonding
Normally small molecules made from non-metals bonded to non-metals
Methane, CH4
Ammonia, NH3
Sulfur dioxide,
SO2
But it also applies to relatively large molecules,
like proteins and polymers
Nylon
Small protein molecule
1. Simple covalent bonding
Covalently bonded compounds are small
and use covalent bonds (share electrons).
• Low melting points
• Solids, liquids or gases at room temperature
• Small, finite structures (although polymers are
finite but very long)
• Can be very reactive due to size and
combination of non-metals
• Normally soft and brittle when solid
• Volatile (e.g. iodine, I2, evaporates from solid
to gas easily at room temperature)
Covalent Bonding
• Describe the formation of covelant bonds.
• Draw dot and cross diagrams.
• Describe the electron arrangement in
covelant molecules with 3 or more
different types of atoms.
• Describe the formation of double and triple
bonds.
Covalent compounds
•
Covalent compounds are formed when NON-METAL
atoms react together.
•
Covalent bonding – bonding in which a pair of
electrons, one from each atom, is shared between two
atoms.
Covalent bonds
•
Covalent compounds are held together by this sharing
of electrons.
•
It is sometimes represented in full bonding diagrams
(see figure 1). Often these bonds are just shown as a
line (see figure 2).
Figure 1
Figure 2
H
- O- H
Covalent and electron structures bonding
•
The purpose of covalent bonding is to gain a full outer
electron shell.
•
This is achieved by sharing electrons where the shared
electrons count towards the outer shells of both atoms.
H
H
O
Cl
H
Cl
H
C
Water
C
O
H
Chlorine
Carbon dioxide
H
H
Methane
O
H
N
Ammonia
H
Critical Thinking Checkpoint
• How many atoms of each
element are in this
compound?
• Sr3(PO4)2
Covalent bonding in chlorine
Chlorine (2,8,7) needs 1 more electron to
attain a full electron shell.
Cl
(2,8,7)
Cl
Cl-Cl
(2,8,7)
Cl
(2,8,8)
Cl
(2,8,8)
•
Hydrogen (1) needs 1 more electron.
•
How many does carbon (2,4) need?
4
•
How many hydrogen's per 1 carbon?
4
H
H
H
C
H
H
H
C
H
H
Covalent bonding - multiple bonds
•
•
•
•
Mostly electrons are shared as pairs.
There are some compounds where they are shared in
fours or even sixes.
This gives rise to single, double and triple covalent
bonds.
Again, each pair of electrons is often represented by a
single line when doing simple diagrams of molecules.
Cl-Cl
O=O
N=N
Single bond
Double bond
Triple bond
Please Grab A Project Sheet,
• If 2 fathers and 2 sons
go on a fishing trip and
each one catches one
fish, why do they only
bring home 3 fish?
Riddle Me This
•What starts out on all
fours, lives most of its
life on two, and dies
on three?
Relationship between bond
order, strength and length
• We have learned that covalent bonds can
come as either single, double or triple
bonds. We also saw in the last section that
we identify these different types of bonds
by their bond order.
• In what way does a bond
change as the bond order
increases? It turns out
that both the length and
strength of a bond change
with bond order.
Bond
# of electrons
Bond Order
Single
2
1
Double
4
2
Triple
6
3
Bond Strength Bond Length
Weakest
Longest
Strongest
Shortest
• One analogy you can use is to think about
atoms as nerf balls and bonds as rubber
bands. The rubber bands act as the force
which holds the balls together, as we
increase the number of rubber bands the
balls are squished closer together and it
takes more force to pull them apart.
• In a molecule as you increase the number
of electrons shared between two atoms,
you increase the bond order, increase the
strength of the bond, and decrease the
distance between nuclei.
Covalent bonding in oxygen
Oxygen (2,8,6) needs 2 more electrons to attain a
full electron shell.
O
X
X
O
O=O
4 electrons
X
X
X
O
X
X
X
X
O
X
Three or more atoms present
CH3OH - Methanol
Draw a dot and cross diagram for:
Chloromethane CH3Cl
Bonding and physical properties
•
Covalent compounds are insoluble in water unlike ionic
•
Covalent compounds don’t conduct electricity in water
– There are no ions in covalent compounds, unlike ionic
compounds.
H
O
•
H
electrons
fixed in
covalent
bonds
Covalent compounds generally have much lower melting and
boiling points than ionic.
–
Interact with each other through ‘weak’ INTERMOLECULAR
FORCES
Questions
1. Describe the formation of covelant bonds
2. Draw dot and cross diagrams for
hydrogen, water, and hydrogen chloride
3. Describe the electron arrangement in
covelant molecules with 3 or more
different types of atoms
4. Describe the formation of double and
triple bonds
Quiz
• Which one of the following pairs atoms is
most likely to form an ionic bond?
• A. Na and F
• B. C and F
• C. N and F
• D. O and F
I know what is meant by a
covalent bond.
I can draw a diagram to show
a covalent bond.
I know the properties and
characteristics of covalent
structures.
Keywords: Covalent, Electrons, Molecular, Giant Covalent,
Define the following terms:
Ionic Structure
A substance that is made of ions (where ions are
transferred) which are held together by strong attraction.
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