CHM1045 Exam 2 Flashcards (P2)

Chemical bonding and molecular geometry.

In ordinary chemical reactions, why is it that the identity of the element remains unchanged?

Only electrons participate in chemical reactions, by being gained, lost, or shared, while the nucleus of each atom remains unchanged.

How are the positive charges of cations predicted on the periodic table?

Far left to far right, charge = group number.

How are the negative charges of anions generally predicted on the periodic table?

Far right to far left, charge = number of groups moved left from a noble gas.

What are monatomic ions?

Ions formed from only 1 atom.

What are polyatomic ions?

Bonded atoms with an overall charge.

What are ionic bonds?

Chemical bonds formed by electrostatic forces of attraction between oppositely charged ions, resulting in the transfer of electrons from one atom to another

What are ionic compounds?

Compounds that contain ions and are held together by ionic bonds.

What are covalent bonds?

Chemical bonds formed by the sharing of electrons between two atoms, typically non-metals.

What are covalent compounds?

Compounds that exist as discrete, neutral molecules, are usually formed by a combination of nonmetals, and are formed when atoms share electrons.

What is chemical nomenclature?

The rules for naming compounds in chemistry.

How can the periodic table be used to identify covalent and ionic compounds?

Ionic compounds will be composed of metals and nonmetals, while covalent compounds will be composed of nonmetals.

What are Lewis Symbols?

Visual representations of the valence electron configurations of atoms and monatomic ions.

What are Lewis Structures?

Visual representations that describe electron arrangement of individual atoms in a molecule, and the formation of covalent bonds within molecules and polyatomic ions.

What is the Octet Rule?

The tendency of main group/representative group atoms to form enough bonds to obtain 8 valence electrons.

What are the steps to draw Lewis Structures?

1. Find the total number of valence (outer shell) electrons.

2. Draw a skeleton structure of the molecule or ion, arranging the atoms around a central (least electronegative) atom.

3. Distribute the remaining electrons as lone pairs on the terminal atoms (except hydrogen), completing an octet around each atom.

4. Place all remaining electrons on the central atom.

5. Rearrange the electrons of the terminal atoms to make multiple bonds with the central atom to obtain octets wherever possible.

What are Octet Rule exceptions?

Odd-electron molecules (free radicals), electron-deficient molecules, and hypervalent molecules.

What is different about an odd-electron molecule?

It has an odd number of valence electrons, and therefore an unpaired electron.

What is different about an electron-deficient molecule?

It has a central atom with fewer electrons than needed for a noble gas configuration.

What is different about a hypervalent molecule?

It has a central atom with more electrons than needed for a noble gas configuration.

In a Lewis Structure, where must leftover electrons be assigned?

The central atom.

What is VSEPER Theory?

Valence Shell Electron Pair Repulsion Theory; Model used to predict the geometry of molecules from the number of electron pairs surrounding their central atoms.

What are the 2 types of electron domains?

Bonding and nonbonding.

What electron pair geometry shapes do the VSEPER Theory electron domains correspond to?

2 Electron Domains = Linear.

3 Electron Domains = Trigonal Planar.

4 Electron Domains = Tetrahedral.

5 Electron Domains = Trigonal bipyramidal.

6 Electron Domains = Octahedral.

What is electron domain geometry?

The arrangement of the electron domains, determined by the number of electron pairs.

What is molecular geometry?

The arrangement of bonded atoms, which includes geometrical parameters like bond lengths, angles, and torsional angles that determine atoms position and the molecule's general shape.

What are the steps to draw 3D molecular geometry structures?

1. Draw the Lewis structure of molecule.

2. Count electron pair domains (bond pairs & lone pairs around central atom).

3. Arrange electron pair domains to minimize repulsions, determine electron domain geometry.

4. Name molecule geometry by the position of atoms considering bonding electrons only.

What is a pure covalent bond?

A covalent bond where electrons are shared equally between atoms.

What is a polar covalent bond?

A covalent bond where electrons are not shared equally between atoms, and the atom with greater electronegativity attracts more electrons.

What is bond polarity determined by?

Electronegativity.

What is electronegativity?

A measure of the tendency of an atom to attract electrons towards itself. The more strongly an atom attracts electrons, the larger its electronegativity.

How do Pauling's electronegativity values change on the periodic table?

Electronegativity values increase from left to right and decrease from top to bottom.

How are atoms in a polar covalent bond distinguished?

The atom with the greatest electronegativity is denoted with a partial negative charge, and the atom with the lesser electronegativity is denoted with a partial positive charge.

How can the polarity of a covalent bond be judged?

By determining the difference of the electronegativities of the two atoms involved in the covalent bond.

Considering molecular geometry, what does the overall polarity of a molecule with three or more atoms depend on?

The polarity of its individual bonds in the form of dipole moments/bond dipoles.

What is a bond dipole?

A vector quantity with the arrowhead pointing in the direction of a negative end, and the cross staying at the positive end.

What are the steps to finding molecular polarity using molecular geometry?

1. Draw a structure using proper molecular geometry.

2. Draw bond dipoles and take the vector sum. Dipoles cancel in nonpolar molecules, and have uneven distribution in polar molecules.