Unit 2 - Atomic Bonding and Structure Flashcards
4 properties of atoms
- Indivisible and indestructible
- All atoms of an element are identical
- Atoms of different elements have different weights and chemical properties
- A chemical reaction is a rearrangement of atoms
Primary Bonding
sharing or donating electron between atoms to form a more stable electron configuration
Secondary Bonding
Weak compared to primary bonds. They occur when there are dipoles in molecules
Sub-divisions of Primary Bonds
- Covalent - sharing electrons in saturated bonds
- Ionic - isolated ions only exist in gaseous form, the bonds exert forces in all directions
- Metallic - Electrons share orbitals with multiple atoms
Materials Characteristics for Covalent bonds (4)
For a solid; V. High elastic Modulus High inherent strength High melting point Low electrical conductivity
Material Characteristics for Ionic bonds (4, 3 examples)
High strength High elastic modulus High melting point Poor electrical conductivity Magnesia, Alumina and Cement
Material Characteristics for Metallic bonds
High melting points high boiling points Electrical conductivity Opaqueness Malleability
describe a ceramic and its bonding
inorganic non-metallic materials made from compounds of a metal and non-metal. the bonds are a mix of covalent and ionic
Material characteristics of ceramics
Electrical and thermal insulators
Brittle
What is an intramolecular force
the force which holds together the atoms making up the molecule or compound
what are the relationships between r, r0 and F between atoms
r > 10r0 there is a very little F (gas)
r < 10r0 Attractive forces increase
r < r0 Repulsive forces dominate
r=r0 F = dU/dr = 0
Seven properties that describe metals ceramics and polymers
- Hardness
- Resistance to corrosion
- Elastic Modulus
- Ductility
- Wear Resistance
- Conductivity
- Density
how many molecules per m^3 are there for solids. liquids and gases
10*28
1025
Elastic modulus of metals ceramics and polymers
Ceramics >200GPa
Metals 20-200GPa
Polymers <10GPa
Young Modulus
axial stiffness (shape volume) easy to measure in a tensile test