CHM Chp. 4 Studyguide

Expanded Octets

1. Atoms of the second-period elements cannot have more than eight valence electrons around them, but atoms of elements in and beyond the third period of the periodic table can 2. In addition to the 3s and 3p orbitals, elements in the third period also have 3d orbitals that can be used in bonding 3. These orbitals enable an atom to form an expanded octet.

Organic Compounds Definition

1. Contains carbon and hydrogen 2. Sometimes in combination with other elements such as oxygen, nitrogen, sulfur, and halogens

3 Types of Chemical Bonds

1. Covalent Bonds 2. Ionic Bonds 3. Metallic Bonds

Lattice Energy

1. Energy change associated with the formation of ionic bonds 2. Formationd of ionic bond is exothermic(more than compensates for energy input required to transfer electrons from metals to nonmetals)

Relationship between Formal Charge and Lewis Structure

1. For molecules, a Lewis structure in which all formal charges are zero is preferred to one in which there are nonzero formal charges 2. Lewis strucutres with small formal charges are preferred to those with large formal charges 3. The best skeletal arrangement of atoms will give rise to Lewis structures in which the formal charges are consistent with electronegativities

Formal Charge Rule

1. For molecules, the formal charges must sum to zero 2. For ions, the formal charges must sum to the overall charge on the ion 3. The best skeletal arrangements of atoms will give rise to Lewis structures in which the formal charges are consistent with elctronegativities.

Formal Charge Equation

1. Formal Charge= valence electrons - associated electrons 2. All the atom's nonbonding electrons(lone pairs) are associated with the atom. 3. Half of the atom's bonding electrons(shared) are associated with the atom

Choosing the Best Resognance Structure(Most Stable Resonance Structure)

1. Formal charges equal or close to zero 2. Negative formal charges on the more electronegative element 3. Minimize formal charge and make sure it matches electronegativity

Naming Molecular(Covalent) Compounds Rules

1. Name the first element that appears in the formula 2. Name the second element, changing the ending of its name with ide 3. Only use mono(one) with the second element Example: HCl= hydrogen chloride

Bond Enthalpy

1. One measure of stability 2. The enthalpy change associated with breaking a bond in 1 mole of gaseous molecules

Polar Bond

1. Partial negative and positive charges(positive symbol, negative symbol) 2. Direction of polarity indicated by arrow pointing to more negative end of bond, with + sign at positive end 3. Degree of polarity depends on differences in electronegativity

Exceptions to the Octete Rule: Odd Numbers of Electrons

1. Some molecules contain an odd number of electrons. The octet rule cannot be obeyed for all the atoms in these molecules 2. Molelcules with an odd number of electrons are sometimes referred to as free radicals 3. Many radicals are highly reactive, because there is a tendency for the unpaired electron to form a covalent bond with an unpaired electron on another molecule

Emperical Formula

1. Tells what elements are present jn a molecule and in what whole-number ratio they are combined 2. The formula is reduced to its smallest number

Electronegativity

1. The abilty of an atom in a compound to draw electrons to itself 2. High electronegativity atoms have a greater tendency to attract electrons 3. Upper right direction

Bond Length

1. The distance between the nuclei of two covalently bonded atoms in a molecule. 2. Multiple bonds are shorter(stronger) than single bonds.

Drawing Lewis Structures

1. The least electronegative(upper right) atom will be central atom 2. Draw a single covalent bond(dash) between central atom and surrounding atoms 3. Count number of valence electron present. For polytomic ions, consider the charges. 4. For each bond(dash) subtract two electrons from total valence electron to determine remaining electrons 5. Use remaining electrons to complete octets of the terminal atoms(those bonded to the central atom) by placing pairs of electrons on each atom. (If there is more than one type of terminal atom, then complete the octets of the most electronegative atoms first) 6. If any electrons remain after step 4, place them in pairs on the central atom. 7. If central atom has fewer than eight electrons after completing steps 1 to 5, move one or more pairs from the terminal atoms to form multiple bonds between the central atom and terminal atoms(unless central atom is Group 3A element)

Covalent Bonding Definition

1. When two atoms share a pair of electrons 2. Occurs only between two nonmetals

Rules for Using Prefixes

1.) do not use prefix mono when naming first element 2.) prefixes ending with "o" or "a" are modified when used with elements beginning with vowels

Ionic(Electronegativity)

A bond between atoms whose electroneavities differ by 2.0 or more

Covat or Nonpolar(Electronegativity)

A bond between atoms whose electronegativities differ by less than 0.5

Polar Covalent(Electronegaivity)

A bond between atoms whose electronegativities differ by the range of 0.5 to 2.0

Double Bond

A muliple bond in whoch the atoms share two pairs of electrons in a lewis structure. EX. C=C

Alkanes

Among hydrocarbons, the simplest examples of compounds

Anion Definition

An ion whose net charge is negative due to an increase in the number of electrons

Formal Charge

Can be used to dtermine the most plausible Lewis structures when more than one possibility exists for a compound

Metallic Bond Definition

Chemical bond consisting of the nuclei of metal atoms surrounded by a "sea" of shared electrons(makes for good conductivity)

Ionic Bond Definition

Chemical bond resulting from the electrostatic attraction of a cation for an anion

Covalent Bonds Definition

Chemical bond that results from a sharing of outermost electrons

Ionic Compound Defition

Compound consisiting of cations and anions

Hydrates Definition

Compounds that have a specific number of water molecules within their solid structure

Lewis Dot Symbol Ingredients

Consists of 1. Element's symbol 2. Surrounded by dots that represents their valence electrons(the groups shows you how many there are) 3. Lone pair is two dots in one group

Binary Molecular Compounds

Consists of just two different NONMETAL elements

Transitions Metals Rule

Designate different cations with Roman Numerals

Naming Acids

HCl is a gaseous compound, when it is dissolved in water we call it hydrochloric acid

Exceptions to the Octete Rule: Incomplete Octets

In some compounds the number of electrons surrounding the central atom in a stable molecule is fewer than eight.

Polyatomic Ions Definition

Ions that consist of a combination of two or more atoms

Pure Covalent Bond

Nuetral atoms held together by equally shared electronns

Resonance Structure

One of two or more Lewis structures for a single molecule that cannot be represented accurately by only one Lewis structure

Atomic or Monatomic Ion

One that consists of just one atom with a positive or negative charge

Ionic Bond

Opposit charged ions held together by electrostatic attraction

Polar Covalent Bond

Partially Charged atoms held together by unequally shared electrons

Oxoanions Definition

Polytomic anions that contain one or more oxygen atoms and one atom(the"central atom") of another element.

Ionic Bonding

Refers to the ELECTROSTATIC ATTRACTION that holds these OPPOSITELY CHARGED ION TOGETHER in an ionic compound

Hydrocarbons

Simplest Organic Compounds that contain only carbon and hydrogen

Formal Charge Equation(Nobile's Way)

Supposed to have-actually has

Lattice Energy Definition

The AMOUNT OF ENERGY required TO CONVERT A MOLE OF IONIC SOLID to its constituent IONS IN THE GAS phase

Lattice Energy Effect

The greater the lattice energy, the more stable the compound.

Cation Definition

The loss of one ormore electrons from an atom

Lewis Structures Tip

The octet rule works best for elements in the second period of the periodic table

Metallic bonding

The positive nucleus of each atom is attracted to the electrons of the atoms that surround it(overlapping valence electrons)

Evidence of bonds

The potential energy of a shared bond is lower than isolated atoms which proves that covalent bonds do form.

Covalent Bond Definition

The shared pair of electrons

Dipole Arrow

The shft of electron density in a polar bond is symbolized by a crossed arrow