Essential Concepts in Atomic Structure and Chemical Bonding

Classification of Elements by Common Oxidation States

The following lists categorize elements based on their typical oxidation states or group characteristics:

• +1 State: H, Li, Na, K, Rb, Cs, Fr, Zn, Ag, F
• +2 State: Be, Mg, Ca, Sr, Ba, Ra, Cd, O
• Variable States:
  • Mn: (+2, +7)
  • Fe, Ni, Co: (+2, +3) (Co assumed from Ci)
  • Cu, Hg: (+1, +2)
  • Pd, Pt, C, Si, Ge, Sn, Pb: (+2, +4)
  • Au: (+1, +3)
• Group 13 (+3 State): B, Al, Ga, In, Tl
• Group 15 (+3, +5 States): N, P, As, Sb, Bi
• Group 16 (-2, +4, +6 States): S, Se, Te, Po
• Group 17 Halogens (+1, +3, +5, +7 States): Cl, Br, I

Fundamental Periodic Trends

Ionization Energy (IE)

The minimum energy required to remove an electron from a gaseous atom in its ground state, forming a positive ion (cation). Trend: Increases moving right and up across the Periodic Table.

Electron Affinity (EA)

The energy change when a ground-state gaseous atom incorporates an electron, forming a negative ion (anion). Trend: Generally increases (becomes more negative/exothermic) moving right and up.

Electronegativity (EN)

The tendency of an atom to attract the shared electron pair in a chemical bond towards itself. Trend: Increases moving right and up.

Atomic Size (Atomic Radius)

Defined as half the internuclear distance between two identical bonded atoms. Trend: Increases moving left and down.

Ionic Size Comparison

• Positive ions (cations) are smaller than their corresponding neutral atoms.
• Negative ions (anions) are larger than their corresponding neutral atoms.

Chemical Bonding and Material Properties

Metallic Characteristics

Metals typically exhibit low electronegativity, high melting and boiling points, very high electrical conductivity, and are ductile and malleable.

Ionic Bonds

Formed between a very electropositive metallic element and a very electronegative non-metal element (typically elements from the far left and far right of the Periodic Table). These bonds create a crystal lattice structure.

Properties of Ionic Compounds

• Exist as solids at room temperature.
• Good solubility in polar solvents (e.g., water).
• High melting and boiling points.
• Zero electrical conductivity in the solid state (conductive when molten or dissolved).

Covalent Bonds

Formed between nonmetallic elements or between nonmetals and hydrogen atoms, characterized by similar and generally high electronegativities (elements found on the right side of the table).

Properties of Covalent Compounds

• Generally have lower melting and boiling points due to weak intermolecular forces.
• Nonpolar Molecules: High solubility in nonpolar solvents; null electrical conductivity.
• Polar Molecules: Higher boiling and melting points than nonpolar counterparts; exhibit polar solubility and conductivity (if they ionize).

Lattice Energy

The energy released when gaseous ions combine to form an ionic solid. It is proportional to the product of the charges ($q_1 q_2$) divided by the distance ($d$) between the ions.

Atomic Structure and Molecular Geometry

Periodic Table Representation

H                                                               He
Li Be B  C  N  O  F  Ne
Na Mg Al Si P  S  Cl Ar
K  Ca Sc Ti V  Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y  Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I  Xe
Cs Ba Lu Hf Ta W  Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra Lr Rf Db Sg Bh Hs Mt Ds Rg

Electron Configuration Example

Example configuration (Nickel, Ni): 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁸ 4s²

Quantum Numbers and Orbitals

• s orbital: Azimuthal quantum number $l = 0$.
• p orbital: $l = 1$. Magnetic quantum numbers ($m_l$): +1, 0, -1.
• d orbital: $l = 2$. Magnetic quantum numbers ($m_l$): +2, +1, 0, -1, -2.
• f orbital: $l = 3$.

Hybridization and Geometry

The geometry is determined by the number of electron domains (sites) surrounding the central atom:

• 2 Sites: sp hybridization, Linear geometry (180º bond angle).
• 3 Sites: sp² hybridization, Trigonal Planar geometry (120º bond angle).
• 4 Sites: sp³ hybridization, Tetrahedral geometry (109.5º bond angle).

Intermolecular Forces

Dispersion Forces (London Forces): Weak attractive forces present in all molecules, but particularly significant in nonpolar molecules.