Atomic Building Blocks Flashcards
Classification of materials used in dentistry
Based on the chemical composition;
There are four classes of materials used in dentistry:
Metals
Polymers
Ceramics
Composites
Based on the use of materials
Permanent (final): eg. AmalgamComposites
Temporary: eg. Cements
Intermediary: egDental waxes
Other materials
Types of atomic bonding
Primary bonds:
Ionic bonds
Covalent bonds
Metallic bond
Secondary Bonds:
Hydrogen bond
Vander waal bond
Primary bonds ??
Atoms try to achieve a highly stable structure by having 8 electrons in the outer most shell either by receiving, releasing or sharing electrons.
✔Primary bonds are strong chemical irreversible bonds
Due to involvement of the valence electrons.
Ionic bond ??
Results from electrostatic attraction between positive and negative ions.
Requires electron transfer
Ex NaCl
Properties of ionic bond
1.Strong chemical bond.
- Non directional
3.Thermal insulator.
- Insoluble in organic solvent.
- Insulators as solid but in solution or in molten state can conduct electric current easily.
- Dissolve in ionizing solvents as water, acids and alkalis to produce the constituent ions; so, their solutions can conduct current.
- Basic bond for glasses and ceramics.
Give reason?
1. Ionic bond is non directional
2. Ionic materials could conduct electric current in solution
- as the electrostatic field surrounds the ion from all directions and this field will interact with any ions in the vicinity
- Dissolve in ionizing solvents as water, acids and alkalis to produce constituent ions; so, their solutions can conduct current
Covalent bond
Results from sharing of valence electrons between adjacent atoms
Ex H2 H2O CH4 O2
Properties of covalent bond
Strong chemical bond.
- Directional toward the region of orbits overlapping.
- Water insoluble.
- Thermal and electrical insulator.
- Basic bond for polymers (ex: acrylic resin).
Metallic bond
✓ The metal atoms have valence electrons that are loosely held and these electrons are free to move about all the atoms.
✓ Release of the valence electrons results in creation of
Positive ion cores
Cloud of free electrons
Related to metals.
The metallic bond results from the forces of attraction between the electron clouds and the positive ion cores
Properties of metallic bond
Strong chemical bond (weaker than ionic and covalent bond).
- High electrical and thermal conductivity
Opacity (free electrons absorb the incident light).
Lustrous surface
Can be plastically deformed
Give reasons
Metallic materials
1 High electrical and thermal conductivity
2 Opacity
3 Lustrous surface
4 Can be plastically deformed
- (free electrons carry temp and electric current from region to region easily).
- (free electrons absorb the incident light
- Free electrons emit some of the incident light
- Due to crystalline structure and its imprefictions
Secondary bonds
Secondary bonds are weak, physical, reversible bonds.
- ✔ Depend on dipolar attraction between molecules (physical attraction between opposite poles)
Hydrogen bond
PERMANENT DIPOLE
Inside water molecule
covalent bond -
✔ Between water molecules
physical attraction between -ve side of one water molecule & +ve side of another water molecule hydrogen bond (H-O bridge).
Ex. Absorption of water in synthetic resin
Classification of basis of solids’ atom arrangement
Crystalline
Non crystalline Amorphous
Semi crystalline
Crystalline solids
Atoms are regularly arranged with repetition in three dimensions in space
Having definite melting point
Exhibit long range order
Ex metals & alloys
