Chemistry Exam 3

Chemical Bonds

Chemical Bonds

The force that holds atoms together in compounds

Compounds

Substances consisting of two or more elements

Ionic Bond

e- transferred from one atom to another. Formed between a metal and nonmetal, with the metal giving to the nonmetal. ex. NaCl

Covalent Bond

e- are shared between nuclei. Formed between nonmetals.

1 Line

A single bond of two e-

2 Lines

A double bond of 4 e-

3 Lines

A triple bond of 6 e-

Binary compound

Contains exactly two elements. Name the cation (+) and then the anion (-).

Naming a covalent compound

prefix + name of first element, then prefix + base name of 2nd element + ide ending

Binary Covalent bonds prefix for 1

None for the first element, mono for the second element.

Binary Covalent bonds prefix for 2

di

Binary Covalent bonds prefix for 3

tri

Binary Covalent bonds prefix for 4

tetra

Binary Covalent bonds prefix for 5

penta

Binary Covalent bonds prefix for 6

hexa

Binary Ionic compounds type 1

Metals. They form 1 type of ion. They are the usual names with -ide at the end of the anion (the second element). ex. potassium chloride

Binary Ionic compounds type 2

Transition metals. They form more than 1 type of ion. They follow the rules of ionic compound naming for regular metals, but also include a roman numeral after the first element to indicate the charge. ex. iron (II) oxide

Acid

Occurs with Hydrogen. Has two types in nomenclature.

Binary Acid naming

Prefix "hydro" + (name) + ic acid ex. Hydrochloric acid (HCl)

Polyatomic Ion Acid naming

No hydro prefix. Instead, (name) + orous (for 1 or 2)/oric(for 3 or 4) acid ex. Perchloric acid (HClO4)

Polyatomic Ions

Electrically charged molecules (a group of bonded atoms with an overall charge) that act as discrete units.

NH4+

Ammonium

NO2-

Nitrite

NO3-

Nitrate

SO3^2-

Sulfite

HSO3-

Hydrogen Sulfite

SO4^2-

Sulfate

HSO4-

Hydrogen Sulfate

OH-

Hydroxide

CN-

Cyanide

PO4^3-

Phosphate

HPO4^2-

Hydrogen phosphate

H2PO4-

Dihydrogen phosphate

CO3^2-

Carbonate

HCO3-

Hydrogen Carbonate

C2H3O2-

Acetate

C2O4^2-

Oxalate

MnO4-

Permanganate

Cr2O7^2-

Dichromate

CrO4^2-

Chromate

O2^2-

Peroxide

ClO-

Hypochlorite

ClO2-

Chlorite

ClO3-

Chlorate

ClO4-

Perchlorate

Molecular Formula

List of atoms in the molecule without information on arrangement

3C 8H

Structural Formula

Written in a way to indicate relative positions of atoms

CH3CH2CH3

Line Structure

A special type of structural formula where C and H are not shown.

/\

Lewis Structure

Expansion of the structural formula showing all bonds.

H-C-H etc.

The most stable state of a bond

The lowest possible energy, when the two atoms are a certain distance apart from one another.

What makes the arrangement less stable?

The repulsive interactions between the two positive nuclei and electrons.

What stabilizes an arrangement?

The attraction between the electrons and nuclei.

Bond Distance

The distance where the attraction is the most dominant over the repulsive forces, thus lowering the energy of the atoms to their minimum and making them the most stable.

Where is the central atom found on the periodic table?

The atom furthest to the left and lower.

The most stable configuration

Formal charges add up to 0

Formal Charge =

(number of valence electrons in a neutral atom) - (number of lone pair electrons) - .5 x (number of shared electrons)

Short version:

(# ve-) x (lone pair e-) - .5 x (shared e-)

Expanded octets

Possible for any elements in period 3 and below. The d orbital makes this possible. Iodine is a good example, it will bond 5 times.

Flourine

Never a good central atom.

Boron

Stable with an incomplete octet. It's fine bonding only 3 times.

Resonance Structure

More than one valid Lewis Structure for a given molecule.

What is the longest bond?

A single bond

What is the strongest bond?

A triple bond

VSEPR

The model used to predict the 3D shape of molecules. The structure around a given atom is determined by minimizing e- pair repulsions. Valence electron pairs therefore orient so their orbitals are as far away as possible.

Steric Number

The number of bonds (attatchments) a central atom has (double and triple bonds still count as 1)

Lone pairs

Electrons that must be near the atom and take up space. They compress angles between bonding pairs because they are more negative and push just a little harder.

Electron pair geometry

Electron groups are all equivalent around the central atom

Molecular geometry

Distinguishes between lone (unbonded) pairs vs bonded groups

A molecule has a steric number of 2 and no lone pairs.

It's name is Linear, and it's angle is 180.

A molecule has a steric number of 3 and no lone pairs.

It's name is Trigonal Planar, and it's angle is 120.

A molecule has a steric number of 3 and 1 lone pair.

It's name is Trigonal Planar (Bent or angular), and it's angle is less than 120.

A molecule has a steric number of 4 and no lone pairs.

It's name is Tetrahedral, and it's angle is 109.5.

A molecule has a steric number of 4 and 1 lone pair.

It's name is Tetrahedral (Trigonal Pyramid), and it's angle is less than 109.5.

A molecule has a steric number of 4 and 2 lone pairs.

It's name is Tetrahedral (Bent or angular), and it's angle is more less than 109.5.

A molecule has a steric number of 5 and no lone pairs.

It's name is Trigonal Bipyramid, and it's angle is 90 and 120.

A molecule has a steric number of 5 and 1 lone pair.

It's name is Trigonal Bipyramid (Sawhorse or seesaw), and it's angle is less than 90 and 120.

A molecule has a steric number of 5 and 2 lone pairs.

It's name is Trigonal Bipyramid (T-Shape), and it's angle is more less than 90 and 120.

A molecule has a steric number of 5 and 3 lone pairs.

It's name is Trigonal Bipyramid (Linear), and it's angle is 180.

A molecule has a steric number of 6 and no lone pairs.

It's name is Octahedral, and it's angle is 90.

A molecule has a steric number of 6 and 1 lone pair.

It's name is Octahedral (Square Pyramid), and it's angle is less than 90.

A molecule has a steric number of 6 and 2 lone pairs.

It's name is Octahedral (Square Planar), and it's angle is more less than 90.

A molecule has a steric number of 6 and 3 lone pairs.

It's name is Octahedral (T-Shape), and it's angle is much less than 90.

A molecule has a steric number of 6 and 4 lone pairs.

It's name is Octahedral (Linear), and it's angle is 180.

What can affect the bond angle?

Both lone pairs and double/triple bonds can affect the space around the atom, shrinking the angle.

Electronegativity's Trend

It decreases as you go down periods, and increases as you move left to right across a period.

Electronegativity

Vital to bonding. It is the ability of an atom in a molecule to attract shared electrons to itself. Decreases as you go down a group, and increases from left to right in periods. Noble gases are nonreactive and do not really apply here.

Electron Density

Goes to the more electronegative atom. The bigger the electronegativity difference, the more different the bond type.

When bonding electrons are shared unequally

It creates a polar covalent bond

The partial negative charge

Goes to the more electronegative atom, because the bonding electrons are closer to it.

Electronegativty difference is less than 0.4.

Nonpolar covalent

Electronegativity is between 0.4 and 1.8.

Polar covalent

Electronegativity is more than 1.8.

Ionic

If all non-central atoms are the same element

The individual bond dipole moments cancel out, meaning a nonpolar molecule is possible even if the individual bonds are polar.

If a molecule has a lone pair

This usually offsets the symmetry that leads to an imbalance, causing a polar molecule.

Hydrocarbons

Are usually nonpolar.

If one of the elements is either F or O

The bond will usually be polar.

Dipole moment

Uneven pulling of a molecule that causes polarity. Any molecule with polar bonds has the potential for a dipole moment.

Hybridization

A way to describe how atomic orbitals share electrons, and how VSEPR shape is achieved.

If the electron pair geometry is Linear

The Hybridization is sp

If the electron pair geometry is Trigonal Planar

The Hybridization is sp^2

If the electron pair geometry is Tetrahedral

The Hybridization is sp^3