Chapter 1: Structure of Matter Flashcards
what is the basic unit of any material?
atom
Nucleus is the core of the atom and composed of:
✓ Positively charged protons.
✓ Uncharged neutrons.
The most outer electrons are cld:
valance electrons
& they affect the physical & chemical properties
Atomic number =
Number of electrons = number of protons
Atomic weight =
weight of protons + neutrons
To reach za configuration of 8 e in an
outer shell by:
- Releasing e ➔ become +ve charged
- Receiving extra e ➔ become –ve charged
- Sharing e w/ another atom
list the atomic bonds
- primary bond
- secondary bond
list the primary bonds
- covalent bond
- ionic bond
- metallic bond
examples of covalent bonds
Basic bond of diamond & polymer
Characteristics of covalent bond:
- Highly directional bond.
- High strength + hardness.
- High heat resistance.
- Thermal + electrical insulators.
- Dissolve in organic solvents.
general info on ionic bond
Occurs by e transfer from one atom (become +ve ion) to another (Become –ve ion), then electrostatic attraction b2ian them.
examples of ionic bonds
Basic bond for Ceramics, Glasses.
general info on covalent bond
- Arises by sharing e b2ian atoms, the atoms approach one another + orbital overlap happened.
- It May be same element (e.g. H2) or b2ian different elements (e.g. CH4)
- It may be single bond, double bond or triple bond
Characteristics of Ionic bond:
- Spherical in nature.
- High strength + hardness.
- High heat resistance.
- Insulators as solids.
- Electric conductors in solutions.
- Dissolve in ionizing solvents (not in organic solvents).
general info on metallic bond
➢ The metals have loosely held valence e, so they move freely b2ian atoms forming cloud of e.
➢ So, the metallic bond is the attraction between the +ve cores and –ve free electrons.
Characteristics of Metallic bond:
- High. strength + hardness.
- High thermal resistance.
3.High thermal conductivity - High electric conductivity
- Opaque
6.Lustrous - Leads to crystalline arrangement in metals
- Leads to easy of deformability of metals.
GR high thermal conductivity is a characteristic of Metallic bond:
as free electrons conduct heat
GR high electric conductivity is a characteristic of Metallic bond:
as free electrons carry the electric current
GR Opaque is a characteristic of Metallic bond:
as free electrons absorb light
GR Lustrous is a characteristic of Metallic bond:
as free electrons reflect the light
types of Secondary bonds (Van der Waals Forces):
a. FluctuatingDipole
b. Hydrogen Bond
info on fluctuating dipole:
➢develops b2ian atoms due to asymmetry of e distribution.
➢ This asymmetry gives the atom dipole character.
➢ It is a temporary bond.
info on hydrogen bond:
➢ develops b2iann molecules when each molecule has a dipole.
➢Attraction occurs b2ian the +ve part of molecule and -ve part of another molecule.
Characteristics of secondary bond:
- Low strength and hardness.
- Low heat resistance.
- High thermal expansion.
interatomic distance results from…
2 equal but opposite forces:
i. Repulsive forces➔ due to electrostatic field of each atom.
ii. Attractive forces➔ different types of atomic bonds.
list factors affecting interatomic Distance:
- Temperature
- Number of adjacent atoms
- Type of the bond
- Any external forces may displace atoms and change I.A.D.
affect of temp. on interatomic distance?
Heat ↑ I.A.D (as it ↑ energy of atoms)
affect of no. of adjacent atoms on interatomic distance?
More adjacent atoms will ↑ I.A.D (as less specific attraction to any
neighboring atom).
affect of type of the bond on interatomic distance?
↑ number of shared e in covalent bond will ↓ I.A.D (as it means stronger bond).
how r solids classified into?
I. According to Intermolecular Bond
II. According to Arrangement of Atoms
Bond between atoms =
inter-atomic bond = intra-molecular bond
**Must be primary bond
Bond between molecules=
inter-molecular bond
**May be primary or secondary
What’s Glass Transition temperature:
The temperature at which the amorphous solids start to soften or harden
The smallest repeated unit in a crystal lattice is cld?
unit cell
Crystalline Solids can be divided into:
- Cubic System
- Hexagonal Crystal
info on Cubic System:
➢ Axes: a = b = c
➢ Angles between axes: 90 degrees
cubic system is subdivided into:
a. Simple Cubic System (SC)
b. Body Centered Cubic (BCC)
c. Face Centered Cubic (FCC)
info on Hexagonal Crystal
➢ Axes: a = b ≠ c
➢ Angles between axes: α = β = 90 degrees
gamma = 120 degrees
Hexagonal Crystal is divided into:
- Simple Hexagonal System
- Hexagonal Closed Packed (HCP)
each unit cell contains how many atoms in simple hexagonal system?
3 atoms
each unit cell contains how many atoms in hexagonal closed packed (HCP)?
6 atoms
Atomic Packing Factor def:
It’s the fraction of space occupied by the atoms
Atomic Packing Factor=
Volume of atoms inside unit cell / Volume of unit cell
Clinical importance of APF:
↑ APF ➔ have ↑ densities + strength properties
GR Theoretical calculation of strength is much higher than actual strength
due to presence of defects in crystalline system.
list types of crystalline imperfections:
a. Point defect
b. Line defect
c. Plane defect
info on Point defect:
- Vacancy ➔ missing atom within the crystal
- Self-interstitial atom➔extra atom from same metal is lodged within crystal.
- Interstitial impurity➔ extra atom from another metal is lodged within crystal.
- Substitutional impurity➔atom from another metal replaced the space of the
original atom.
info on line defect:
➢ The most common type.
➢ Dislocation: it is the displacement of a row of atoms from their normal positions
in the lattice.
Clinical importance of line defect
plastic deformation in metals occurs by motion of
dislocations
info on Polymorphism
- Materials that have the same chemical composition but found naturally in different physical forms.
- The polymorphic forms have different physical properties as density, freezing point, optical properties, conductivities …etc
If the material is inorganic, the polymorphism is cld
allotropy
If the material is organic, the polymorphism is cld
isomerism
Silica showed two types of transformation:
- Displasive transformation: the same form just expanded at low temperature.
- Reconstructive form: involves transformation from one form to another.
Correlation Between Atomic Structure and Materials Properties:
in Density
controlled by ➔ atomic weight, atomic radius, atomic packing factor.
Correlation Between Atomic Structure and Materials Properties:
Bond strength leads to:
➢ High strength and hardness.
➢ High melting and boiling temperature.
➢ Low coefficient of thermal expansion.
Correlation Between Atomic Structure and Materials Properties:
Electrical and Thermal conductivity
➔ depends on nature of atomic bond
- Metallic solids conduct heat + electricity.
- Ionic solution conduct electricity, while ionic solids are electrical insulators.
- Covalent solids are insulators.
Correlation Between Atomic Structure and Materials Properties:
Crystalline solids
have low internal energy bc they send their internal energy in arranging their atoms.
GR FCC is more ductile than BCC
due to higher atomic packing factor
GR FCC is more ductile than HCP
due to symmetry of the cubic system
GR: Every element tries to complete its outer electronic shell
To reach the stable configuration
GR: Covalent bond is a highly directional bond
Bc the shared electrons occupy a specific direction.
GR: Ceramics and glasses have high strength and hardness
Bc they formed of primary bond (ionic bond).
GR: Ionic compounds conduct electricity in solutions
Bc they ionized in solution and ions can carry electricity.
GR: Metallic elements conduct heat and electricity.
bc free electrons carry heat and electricity
GR: Metallic elements are opaque
Bc free electrons absorb light so prevent its passage through the material
GR: Metallic elements are lustrous
bc free electrons reflect the light
GR: Metals are malleable and ductile
BC they contain dislocations (slip plane)
GR: Water molecules are bonded by hydrogen bond
BC each molecule has a permanent dipole.
GR: Increasing the number of adjacent atoms decrease the interatomic distance
Due to less specific attraction to any neighboring atom.
GR: Interatomic distance between CH-CH is more than CH=CH
BC the higher number of shared electrons
GR: Diamond (atomic solids) is stronger than polymer (molecular solids)
BC the inter-molecular bonds of diamond are primary bond while they are secondary bond in polymers.
GR: Crystalline solids have low internal energy
BC they spend their internal energy in arranging their atoms.
GR: Metals have definite melting temperature.
BC they are crystalline solids
GR: Wax have glass transition temperature
BC they are amorphous solids
GR: Amorphous solids have high internal energy
BC their atoms are randomly distributed
GR: Simple cubic system contains one atom per unit cell
BC it has 1/8 atom at each corner (1/8 X 8 = 1 atom).
GR: Body centered cubic system contains two atoms per unit cell
BC it has 1/8 atom at each corner + one atom at the center of the unit cell (1/8 X 8 + 1 = 2 atoms).
GR: Face centered cubic system contains four atoms per unit cell
BC it has 1/8 atom at each corner + 1⁄2 atom at each face (1/8 X 8 + 1⁄2 X 6 = four atoms)
GR: Face centered cubic materials have high density than body centered cubic materials
Due to higher atomic packing factor of FCC materials
GR: Theoretical calculation of the metal strength is much higher than actual strength.
Due to presence of crystalline imperfections.
GR: Different forms of silica have different physical properties and same chemical properties
BC they r allotropic forms (have same chemical structure)
GR: Reconstructive transformation requires more time and heat.
BC it requires breakdown of the atomic bonds and reconstruction of new bonds w/ different space lattice
GR: Face centered cubic system are more ductile than body centered cubic.
Due to higher atomic packing factor of FFC
GR: Face centered cubic system are more ductile than hexagonal closed pack
Due to the symmetry of the unit cell axes of FCC
