DM- Ch 2 Materials Science and Dentistry

Materials science

Area of the physical sciences that seeks to explain the properties and performance of materials by examining their internal structure

Bond

To connect or fasten; to bind

Adhesion

The tendency of dissimilar particles or surfaces to cling to one another

-Materials, substances, and objects they may up stay together because the molecules they are made of attract each other

Mechanical adhesion (physical interlocking)

• Attachment by mechanical forces, requires at least one rough surface

Chemical adhesion (Chemical bonding)

• Occurs when the surface atoms of two separate surfaces form ionic, covalent, or metallic bonds

• A force of attraction between atoms that allows chemical compounds to form

Atomic bonding phases

gases, liquids, and solids

Gases

• Atomic bonds between gas molecules are very weak, easily broken

• The weakest bonds, no organization

• If thermal energy is removed by cooling, gases condense into liquids

• Condensation of water vapor on the outside of a cold beverage on a hot day

Liquids

• Stronger atomic bond between molecules than gases but attraction is not strong enough to carry a load or to maintain a shape without support

• Attraction between molecules results in "short-range order"

Solids

• Strongest attraction between atoms and molecules

• Atomic bonds of solids maintain the shape of objects and resist external forces placed on them, can carry a load

Solids classification

crystalline or amorphous

Crystalline Solids

Distances and angles among atoms or molecules are uniform, like rooms in a hotel

- Table salt, diamonds, and hydroxyapatite of teeth are crystalline structures

Amorphous Solids

Distances and angles among atoms or molecules are

not uniform, they are irregular or disorganized

• Glass in a window is an example

Electromagnetic force

Atomic bonds are a result of electromagnetic force

• The electronic force causes positive charges to attract negative charges and vice-versa

• Opposites attract

Solids can be thought of as a collection of millions of springs

• When you put force on an object, the atomic bonds are compressed and oppose the force

• The solid changes size at a microscopic level when forces are applied and

released

Ex. Teeth compress when biting

Primary bonds

the strong bonds between atoms

• Involve the transfer or sharing of electrons between atoms

Valence electrons

The electrons in the outer shell of atoms are involved in chemical reactions & atomic bonding

3 types of primary bonds

ionic, covalent, metallic

- all bonds are an effort to reduce energy

Ionic Bonds

• Both metals and non-metals

• When one atom gives up an electron and it is accepted by another atom

Covalent Bonds

• Non-metals only

When 2 atoms share a pair of electrons, many materials are the result of long chains of covalently bonded atoms

Metallic Bonds

• Metals

Electrons are shared, but between many atoms

Materials are classified

based on their primary bond

Ceramics

have atoms bonded with ionic bonds

Polymers

are composed of long chains of covalent bonds

Composites

materials made of two or more different materials

• Mixture of a polymer and a ceramic