Chemical Bonding
What holds things together?
Bonding
• Involves the valence electrons or outermost electrons
• Outermost electrons in the last energy shell
How many valence electrons does N have?
Group 5A – 5 valence electrons
Bonding…
• Lewis dot structures show the valence electrons around at atom and for most molecules and compounds a complete octet for the elements
N Al
Write out the electron configuration for the following atoms and ions:
He
Ne
Ar
Kr
Na Cl
NaCl
+ -
electron transfer
and the formation of ions
This is the formation of an ionic bondionic bond.
ClCl
Cl2 This is the formation of a covalent bondcovalent bond.
sharing of a pair of electrons
and the formation of molecules
Ionic Bond
• Between atoms of metals and nonmetals with very different electronegativity
• Bond formed by transfer of electrons• Produce charged ions all states.
Conductors and have high melting point.
• Examples; NaCl, CaCl2, K2O
Ionic Bonds: One Big Greedy Thief Dog!
1). Ionic bond – electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions.
COVALENT BONDbond formed by the sharing of
electrons
Covalent Bond
• Between nonmetallic elements of similar electronegativity.
• Formed by sharing electron pairs• Stable non-ionizing particles, they
are not conductors at any state
• Examples; O2, CO2, C2H6, H2O, SiC
Chlorine atom 2,8,7
2 Chlorine atoms
Outer shells only
Chlorine molecule Cl2
Molecules have no overall electric charge
Molecular or covalent compounds are usually gases or liquids – they have low melting points and low boiling points
Forces between molecules very weakForces (bonds) between atoms in the molecule very strong
Each outer shell has 8 electronsElectrons shared
Covalent Bonds:
Water H2O
Methane CH4
Ammonia NH3
Hydrogen H2
Hydrogen Chloride HCl
Oxygen O2
N.B. Oxygen has a double bond
Oxygen
O168
Oxygen atom 2,6
2 Oxygen atoms (outer shells only)
Double covalent bond
O O
More sharing examples
O2
N2
O O
N N
O O O O
N N N N N N
double bond (2 pairs)
triple bond (3 pairs)
Share until octet is complete.
octet complete
NH3
NH
H
H
normal covalent bond
(each atom supplies an electron)
Some more sharing examples
ionic covalent
valence electrons
Comparison of Bonding Types
sharing of electrons
transfer of electrons
ions moleculesconductive non-
conductive