Chapter 4: Chemical Bonding Theories

compound

made of two or more different kinds of elements

molecule

made of two or more different kinds of atoms

chemical formula

gives the composition of a substance

molecular formulas

give the exact number of atoms of each element

empirical formulas

gives the lowest whole-number ratio of atoms of each element in a compound

structural formulas

sketch or diagram of how atoms in the molecule are bonded to each other where lines are covalent bonds

ball and stick models

represent atoms as balls and bonds as sticks

space-filling molecular models

atoms fill the space between atoms to more closely represent how a molecule might appear if scaled to visible size

ionic bonds

metal to nonmetal, electrons transferred from metal to nonmetal

covalent

nonmetal to nonmetal, electrons shared between molecules

metallic

metal to metal, electrons pooled into a sea

what are ionic compounds composed of?

a 3-D array of cations and anions called a crystal lattice, it has low energy

lattice energy

energy required to completely separate a mole of a solid ionic compound into its gaseous ions

coulomb’s law

states the degree of attraction between charged particles is inversely proportional to the distance between them and directly proportional to the product of the charges

covalent bonding

electrons are shared between two nonmetals

do covalent bonds have low energy configurations?

yes because attractive and repulsive forces are balanced

properties of ionic compounds

solids at room temp with high melting and boiling points

why are ionic compounds brittle?

attractions between ions are strong and hard to break, but they can separate by being displaced

properties of covalent compounds

low melting and boiling points, found in all three states of matter at room temperature, attractions are broken but not bonds between atoms

chemical nomenclature

the system used in naming substances, it is systemic and determined based on chemical structure

monovalent metals

charges can be determined from the periodic table (typically main group metals, but three transition metals are monovalent)

multivalent metals

transition metals, main group elements (Pb and Sn)

binary ionic compounds

contain only two different elements and their names (name of cation and base name of anion (-ide)

binary ionic compounds w/ multivalent cations

the name of the cation is followed by a roman numeral (in parentheses) that indicates the charge of the metal

polyatomic ions

multiple covalently bonded atoms

oxyanions

contain oxygen and another element in polyatomic ions

ammonium

NH4+

C2H3O2-

acetate

CN-

cyanide

SCN-

thiocyanate

HCO3-

bicarbonate

CO32-

carbonate

C2O42-

oxalate

ClO-

hypochlorite

ClO2-

chlorite

ClO3-

chlorate

ClO4-

perchlorate

CrO42-

chromate

CrO72-

dichromate

MnO4-

permanganate

NO2-

nitrite

NO3-

nitrate

OH-

hydroxide

O2-2

peroxide

H2PO4-

dihydrogen phosphate

HPO42-

hydrogen phosphate

bisulfite

HSO3-

SO32-

sulfite

HSO4-

bisulfate

SO42-

sulfate

S2O32-

thisulfate

what elements are in the series of oxyanions?

chlorine, bromine, and iodine

oxyanion tricks - second row

suffix “ate” / three oxygens

oxyanion tricks - third row

suffix “ate” / four oxygens

hydrates

ionic compounds containing a specific # of water molecules associated with each formula unit

naming hydrates

number prefix - hydrate

how are hydrates removed?

heat

anhydrous

water has been removed from a chemical formula

acids

compounds that begin with the letter “H”

binary acids

contain only two different elements

nomenclature for binary acids

hydro “base name of nonmetal ‘-ic’” acid

naming oxyacids - polyatomics with “ate”

ate is changed to “ic” and acid

naming oxyacids - polyatomics with “-ite”

ite is changed to “ouse” and acid

organic compounds

hydrocarbons that are composed primarily of hydrogen and carbon

nomenclature for simple organic compounds

the prefix denotes the number of carbons and the suffix denotes the bonding of carbons

name the prefixes of simple organic compounds

meth, eth, prop, but, the rest are the typical prefixes

what do bonding theories explain

bonding theories explain how and why atoms bond as well as why some molecules are stable, and others are not

who discovered the octet rule

american chemist G.N Lewis

what is the octet rule

main group elements gain, lose, or share electrons to achieve 8 valence electrons

what elements want less than the octet rule?

boron and beryllium want less than an octet

what elements want more than the octet rule?

sulfur, phosphorous, and chlorine

valence electrons

outer-shell electrons involved in a chemical bonding; typically s and p electrons only

core electrons

inner electrons that are typically represent by the noble gas in condensed electron configurations

what do lewis symbols represent?

dots around the chemical symbol represent valence electrons

how can lewis structures represent ionic bonding?

by representing which electron is being transferred from the metal to the nonmetal, the numbers of atoms are adjusted so the electron transfer comes out even

bonding pairs vs lone pairs

bonding pairs are shared by atoms and electrons on a single atom are lone pairs

use of dashed lines in lewis structures

dashes represent bonding pairs (one dash - single bonds, two dashes - double bonds, three dashes - triple bonds)

polar covalent bonds

when electrons are not shared equally between molecules, one molecule pulls harder on an electron than the other molecule

what is a dipole

a material with positively and negatively charged ends (the area with larger electron density has the negative charged, vice versa)

dipole moment

quantitative measure of this bond dipole; measure of the bond polarity; has a magnitude a direction

electronegativity

ability of atoms in a molecule to attract electrons to themselves

who discovered electronegativity

linus pauling

what is the trend of electronegativity on the periodic table

across a period increases, and up a group increases

value of a nonpolar covalent bond

0 to 0.4 (0 is purely covalent)

value of a polar covalent bond

0.5 to 1.9

value of ionic bond

2.0 or greater

how to determine the number of valence electrons for lewis structures

add all the valence electrons in each element, consider negative and positive charges

in lewis structures, which element goes in the center?

the least electronegative (not including hydrogen) considering that flourine is the most electronegative

how to fill the octets in lewis structures

start with the outer more electronegative elements, and then move towards the center element

how to make sure each element gets a full octect in lewis structures

add single, double, and triple bonds until each element is satisfied

formal charge

the charge an atom would have if all the bonding electrons were shared equally between the bonded atoms

formal charge of neutral atoms

sum of all the formal charges of an element has to be 0

formal charge of polyatomics

sum of all the formal charges of an element has to be equal to the charge of the ion

how to calculate formula charge

#of valence electrons - dots in lone pairs - # of bonds it sees (halved)

how to determine the best lewis structure

the best lewis structure is the one with the fewest charges and the one that puts a negative charge on the most electronegative atom

resonance structures

structures that differ in position of electrons (not the number of electrons or the placement of atoms)

list exceptions to the octet rule

ions/molecules with odd number of electrons, less than an octet, more than eight valence electrons

radicals

ions and molecules with an odd number of electrons called radicals (we will not be asked to draw these)