Chemical Bonding Forces that Ties
Chemical BondingForces that Ties
Behind the Ties
The term “Valence” has various meaning.
• It came from a latin word “Valentia” meaning “power” or “capacity”
• It is also known as valency or valency number, which is the number of chemical bonds formed by atoms.
• Valence electrons refer to the electrons in the outer most energy level that are involved in the chemical bonding or reaction.
Behind the TiesLewis Dot Structure• The Lewis structure was named
after Gilbert Newton Lewis, who introduced it in 1916.
• Dots and dashes were used in representing valence electrons, lone pairs and bonds between electrons of elements.
• In the diagrams, only the valence electrons are shown.
• A dot represents an electron and a dash represents a bond of 2 electrons .
Behind the Ties
Lewis Dot Structure
Behind the Ties
Lewis Dot Structure (Group A Elements)
Behind the Ties
Oxidation States – hypothetical charge of an ion.
**a neutral (free) atom (or element) has an oxidation number of zero.
• Group IA = +1 (Alkali Metals)• Group IIA = +2 (Alkali Earth Metals)**These groups are metals and are
highly reactive. They have the highest metallic property (Group IA).
Behind the Ties
Group IIIA = +3 (Boron Group: Earth Metals) except Tl +1
Group IVA = +4 (Carbon Group)Group VA = -3 for 3 elements, +3 for
Sb and Bi (Nitrogen Group)
Group VIA = -2 (Chalcogen Group) except for Po
+4Group VII = -1 (Halogen Group)
The Objective: Quest for Stability
• Elements would try to have 8 electrons in their outermost energy level to become stable to have the same configuration with the noble gases.
• Octet Rule – is a rule of thumb that states the atoms (or ions) combine to have 8 electrons in their valence shell (outer most).
** this is mostly applicable to Group A elements. There are exemptions to the rule.
The Objective: Quest for Stability
• Duet rule – where they follow He as their noble gas structure. Applicable for H, Li, Be, B and sometimes C.
• 18 electron rule – applicable to transition elements (d block elements)
**in this quest, atoms (ions) may either give (Ionic Bonding) or share (Covalent Bonding) their electrons to be stable and become noble (as to noble gases)
Ionic or Covalent
Electronegativities can predict the nature of bond in a compound.
**subtract the electronegativity values of the involved elements.
Electronegativities and Bond Polarity
0 – less than 0.4 = non-polar covalent bond
0.4 – 1.78 = polar covalent bondGreater than 1.78 = ionic bond
Ionic or Covalent
Examples:F – Na: 4.0 – 0.9 = 3.1 Ionic BondBr – Fr: 2.8 – 0.7 = 2.1 Ionic BondN – C: 3.0 – 2.5 = 0.5 Polar
CovalentS – Se: 2.5 – 2.4 = 0.1 Non-polar
CovalentBr – O: 3.5 – 2.8 = 0.7 Polar
Covalent
Ionic or Covalent
Ionic Bonding: Giving of Electrons
Ionic bond – is the giving or donation of electrons.
** being observed by metals (Group IA – IIIA and non-metals (Some of Group VA – VIIA).
Ionic Bonding: Giving of Electrons
Atoms donate or accept their electrons giving them a net charge.
The one that donates an electron becomes a positively charged ion and the one that receives becomes a negatively charged ion.
This would cause an attraction that will form the IONIC COMPOUND.
Ionic Bonding: Giving of Electrons
Ionic Bonding: Giving of Electrons
Properties of Ionic Compounds:They form a Crystal Lattice Structure.
Because of the opposite charges, they arrange themselves alternately.
Ionic Bonding: Giving of Electrons
Properties of Ionic Compounds:• High melting and boiling pointsIt takes high amount of thermal energy to
separate the strong electrical forces.
• Electrical ConductivitySolid ionic compounds do not conduct
electricity because once attracted, they become neutral. There are no free charges to carry the electricity. Electrons are bonded tightly
Ionic Bonding: Giving of Electrons
Properties of Ionic Compounds:Once dissolved or molten, the structure
breaks thus opening the charges. Electrons now move freely and can carry electricity. They become electrolytes. There are also solid electrolytes.
• HardnessMost ionic compounds are hard because
ions are strongly bound to the lattice and are not easily displaced.
Ionic Bonding: Giving of Electrons
Properties of Ionic Compounds:
• Brittleness Most ionic compounds are brittle, they
shatter when distorted. Once distorted, the structures is ruined, they do not stick together anymore for the charges will not be placed as they were before. Broken ends will end up repelling each other.
Covalent Bonding:Sharing of Electrons
Covalent Bonding – the sharing of electrons. This happens commonly to non-metals (Groups IVA – VIIA ) where both attract electrons. The energy levels overlap to share the electron.
Covalent Bonding:Sharing of Electrons
2 Subtypes of Covalent Bonding:Nonpolar Bond – happens to atoms with
similar attraction (affinity). Commonly observed in diatomic molecules. (H2, N2, O2) The difference in their E.N. is less 0.4. The electrons are evenly shared.
Polar Bond – happens when one atom has a greater affinity. The electrons spend most of the time with the atom of greater affinity. This will cause an uneven sharing of electrons and will form partial charges.
Covalent Bonding:Sharing of Electrons
Non-Polar Covalent Bond
Polar Covalent Bond
Covalent Bonding:Sharing of Electrons
Covalent Bonding:Sharing of Electrons
Covalent Bonding:Sharing of Electrons
Properties of Covalent Compounds• Generally are weak compounds, they are
usually liquid or gases. But there are also hard and solid covalently bonded compounds like granite and diamonds.
• They are known as network solids or covalent network solids. They are bonded continuously in a network leaving no free molecule thus making a solid structure.
Covalent Bonding:Sharing of Electrons
Properties of Covalent Compounds• The more bonds the compound has, the stronger
their bonds.
• Limited amount of electricity is conducted, sometimes none. There are no open electrons for they are shared by atoms. Polar bonds has the tendency to conduct electricity because of the partial charges.
• They are soft because the attraction is quite weak (compared to ionic compounds) and could easily be displaced.
Covalent Bonding:Sharing of Electrons
Properties of Covalent Compounds• They have low melting and boiling
points. The weak attraction requires a little amount of thermal energy to separate these compounds.
A snowflake’s symmetry reflects the ordering of water molecules when frozen.