LESSON 2 Atomic Structure and Inter-atomic Bonding

Bohr Theory Model and Wave-Mechanical Model

Two Types of Models under Atomic Structure

+- 1.602176634 × 10^-19

Charge of subatomic particles (electron and proton)

Mass Number or Nucleon Number

number of protons and neutrons in an atom

Atomic Symbol

abbreviation used to represent atom in chemical formulas

Atomic Number

number of protons in an atom

Isotopes

atoms of some elements have two or more different atomic masses

Atomic Mass Unit (AMU)

unit of mass relative to a single constituent of a Carbon atom

Quantum Numbers

four parameters characterizing every electron in an atom in wave mechanics

1. Principle Quantum Number (n)

2. Azimuthal Quantum Number (l)

3. Magnetic Quantum Number (m)

4. Spin Quantum Number (s)

Four parameters of an atom

Principle Quantum Number (n)

determines the size of the shell in which a particular electron orbits around the nucleus and its energy

Principle Quantum Number (n)

expressed in letter notation to characterize electronic shells:
n = 1= K Shell

n = 2 = L Shell

n = 3 = M Shell, etc.

Second/Azimuthal/Orbital Quantum Number (l)

designates the subshell

Second/Azimuthal/Orbital Quantum Number (l)

specifies the angular momentum of orbiting electron and determines the shape of the orbit

Magnetic Quantum Number (m)

controls the number of allowed spatial orientations (degeneracy of each orbit) characterized by l in a given shell

Spin Quantum Number (s)

determines the direction of electron spin around its own axis of orbiting electron

Pauli Exclusion Principle

states that no two electrons may have the same quantum number within any atom; it follows that no more than two electrons with opposing electron spin may be present in each orbital

Electropositive Elements

indicate that they are capable of giving up their few valence electrons to become positively charged ions

Electronegative Elements

they readily accept electrons to form negatively charged ions

increases

Electronegativity ___________ in moving from left to right and from bottom to top in the periodic table

Net Force F_N

sum of both attractive and repulsive components of two atoms

Ionic Bonding

properties: high melting point, brittle, hard
examples: NaCl, MgO

Metallic Bonding

properties: variable hardness and melting point, conducting
examples: Fe, Mg

Covalent Bonding

properties: high melting point, hard, nonconducting
examples: C (diamond), SiO₂(quartz)

Ionic Bond

formed by the transfer of electron/s between two sharply different electronegative elements (metallic and nonmetallic elements)

Ionic Bonding

termed nondirectional—the magnitude of the bond is equal in all directions around an ion

Materials with Ionic Bonding

characteristically hard and brittle, and more electrically and thermally insulative

Covalent Bond

formed by sharing of electron/s between two similar electronegative elements that lie near one another in the periodic table

Covalent Bonds

may be very hard and have a very high melting temperature, and most of the materials with these bonds are electrical insulators or semiconductors; their mechanical behaviors failed in a brittle manner

Metallic Bond

formed between the metallic elements in which electropositive atoms donate their valence electrons to form a “sea” of electrons surrounding the atoms

Metals

good conductors of electricity and heat due to their free electrons

Metals and Alloys

fail in a ductile manner; fracture occurs after the materials have experienced significant degrees of permanent deformation

1. Hydrogen Bonding

2. Dipole-Dipole Interactions

3. London Dispersion Forces or Van der Waal’s Forces (vdW)

Molecular Bonding

Molecular Bonding

properties: low melting point, nonconducting
examples: H₂, CO₂

Dipole

a polarized molecule having partially positive and negative poles

Crystalline

the material’s atoms are arranged in a periodic fashion

Amorphous

the arrangement of the material’s atoms does not have a long-range order

Single Crystals

crystalline materials in the form of one crystal

Polycrystalline

crystalline materials with many crystals (crystalline) or grains

Grain Boundaries

regions between individual crystals in a polycrystalline material