CHY 40 Chemical Bonding

Flashcards on Chemical Bonding

What is a chemical bond?

The force that holds atoms together to form ionic or molecular compounds.

Who is G.N. Lewis?

A scientist who proposed that atoms interact to gain stability by changing their outermost electron configuration to resemble that of a noble gas.

What are the two ways chemical bonding may result?

Transfer of one or more electrons (ionic bond), or sharing of electrons between atoms (covalent bond).

What is the octet rule?

Atoms transfer or share electrons until each atom acquires an octet of outer shell (valence) electrons.

What are the three general types of chemical bonds?

Ionic bond, covalent bond, and metallic bond.

Describe an ionic bond.

Electrostatic forces between ions of opposite charges; formed between a strong metal and a nonmetal.

Describe a covalent bond.

Results from the sharing of electrons between atoms; formed usually between nonmetals.

Describe a metallic bond.

The force that holds several metallic atoms together; between identical metallic atoms or different metals/alloys.

What do Lewis/Electron Dot Symbols show?

Valence electrons of the atom represented as dots around the element symbol.

How do you determine the number of valence electrons for main group elements?

Group number equals the number of valence electrons.

What are valence electrons?

Electrons that reside in the incomplete outer shell of an atom and are involved in chemical bonding.

What is an ionic/electrovalent bond?

Involves complete transfer of electrons, usually between metallic and nonmetallic elements, forming cations and anions.

What are some properties of ionic compounds?

Strong ionic bonds leading to hard crystals, high melting points, geometric patterns, simplest ratio formulas (NaCl, KCl, CaCl2), and good electrical conductivity in solution.

What is lattice energy?

The energy required to completely separate a mole of a solid ionic compound into gaseous ions; a measure of ionic compound stability.

How does ionic charge affect lattice energy and ionic radii?

Lattice energy increases with ionic charge, and ionic radii decrease with increasing ionic charge.

Describe a covalent bond.

Formed between nonmetals or metalloids resulting from the sharing of electrons to form molecules. It involves attraction between shared electrons and positive nuclei.

What is covalency?

The number of covalent bonds formed by an atom.

What are the types of covalent bonds?

Single bond (sharing one pair of electrons), double bond (sharing two pairs of electrons), and triple bond (sharing three pairs of electrons).

What are bonding electrons and nonbonding electrons?

Bonding electrons are involved in covalent bond formation, while nonbonding electrons (lone pairs) belong solely to an individual atom.

What is electronegativity?

The ability of an atom in a molecule to attract electrons towards its nucleus. It decreases down a group and increases from left to right in a period.

Describe a polar covalent bond.

Results from the unequal sharing of electrons due to electronegativity differences between atoms.

Describe a nonpolar covalent bond.

Results from the equal sharing of electrons, typically between two atoms of the same electronegativity or with zero electronegativity difference.

What is bond energy?

The energy required to break a particular bond in the gas phase, a quantitative measure of bond strength.

What is bond length?

The distance between the centers of two bonded atoms.

Describe the relationships between number of bonds, bond energy, and bond length.

Bond energy increases with number of bonds while bond length decreases with number of bonds.

What is formal charge?

The charge of an atom assuming equal electronegativity, calculated as: Group no. – Unshared electrons – Covalent bonds.

What are some exceptions to the octet rule?

Molecules with an odd number of electrons (e.g., NO, NO2). Molecules with less than an octet (e.g., BF3). Molecules with more than an octet for atoms in periods 3 to 7 (e.g., PCl5, SF6).

What is resonance?

The blending of structures (contributing/canonical structures) that represent the real ion or molecule, particularly in compounds with multiple or delocalized bonds.

Describe Valence Bond Theory.

The merging of valence atomic orbitals to form an overlap region, which can accommodate a maximum of two electrons of opposite spins to form a covalent bond.

What is hybridization?

The process of mixing atomic orbitals of the same atom to form degenerate orbitals (orbitals of the same energy) called hybrid orbitals.

How do you determine what hybrid orbitals are involved?

By counting the number of bonds and lone pairs around each atom in the Lewis structure.

Describe Valence Shell Electron Pair Repulsion (VSEPR) Theory.

The best arrangement of electron pairs is the one that minimizes repulsion among them. Valence electron pairs (electron domains) surrounding an atom repel one another so the orbitals containing those electrons are oriented as far apart as possible.

Describe the different types of electron repulsions.

lone pair - lone pair (lp-lp) > lone pair - bonding pair (lp-bp) > bonding pair - bonding pair (bp-bp)

What is a electron domain?

A region in which the electrons will most likely be found.

What is electron pair geometry?

Arrangement of electrons pairs whether lone pair or bonding pairs around the central atom.

What is molecular geometry?

Arrangement of the atoms in space which may be predicted from the electron pair geometry. It is the actual shape of the molecule.

State the rules on electronic repulsion.

Bonding pair–bonding pair < lone pair–bonding pair < lone pair–lone pair.

How do you state the geometry of molecules with more than one central atom?

Describe the shape around each central atom in molecule.

What is Metallic Bonding?

A type of chemical bonding in which electrons are relatively free to move throughout the three-dimensional structure.

What is Electron Sea Model for Metallic Bonding?

The metal is pictured as an array of metal cations in a sea of electrons. Electrons are confined to the metal by electrostatic attractions to the cations and they are uniformly distributed throughout the structure.

What is Molecular Orbital Model for Metals - Band Theory?

The number of atomic orbitals that interact or overlap is very large. Thus, the number of molecular orbitals is also very large. It is pictured to have an energy band - having numerous and continuous tiny energy separation of between metal orbitals.

What are some physical properties of metals?

Luster, High electrical conductivity, High thermal/heat conductivity, Malleability and ductility