Chemistry Module 3

ionic bonds

electrostatic forces of attraction between oppositely charged cations and anions

properties of ionic solids

• crystalline structure

• rigid

• brittle

• high melting/boiling points (suggesting strong ionic bonds)

• poor conductors

• dissolve readily in water (excellent conductors once dissolved/melted)

binary ionic compounds

composed of two elements

nonmetal atoms have _______ electron affinities

relatively high

• readily gain electrons

the formula for an ionic compound does not represent:

the physical arrangement of its ions

isotropic

the same in all directions

the Ca²⁺ cation is _____ with the noble gas Ar

isoelectronic

for groups 13-17, the group numbers exceed the number of valence electrons by ___;

Thus, the charge of a cation formed by the loss of all valence electrons is equal to the group number minus ____

10; 10

inert pair effect

reflets the relatively low energy of the valence s-electron pair for atoms of the heavy elements of groups 13, 14, and 15

• Tl⁺, Sn²⁺, Pb²⁺, and Bi²⁺ ions

• these exception to expected behavior involve elements toward the bottom of the groups

although the d orbitals of the transition elements are the last to fill, _______are the first to be lost when these atoms ionize

the outermost s electrons

most monatomic anions form when:

a neutral nonmetal atom gains enough electrons to completely fill its outer s and p orbitals, reaching the electron configuration of the next noble gas

ionic bonding results from

the electrostatic attraction of oppositely charged ions that are typically produced by the transfer of electrons between metallic and nonmetallic atoms

covalent bonds

bonding resulting from mutual attraction of atoms for a “shared” pair of electrons

covalent bonds are formed between two atoms when:

both have similar tendencies to attract electrons to themselves

• both atoms have identical or fairly similar ionization energies and electron affinities

the attraction between molecules (electrically neutral) is _____ than the electrostatic attraction between molecules (elect electrically charged ions

weaker

covalent compounds generally have _________ melting and boiling points than ionic compounds

much lower

many covalent compounds are ______ at room temperature

liquids or gases

covalent compounds are typically _____ than ionic solids

much softer

most covalent compounds are ____ in water

insoluble

nonmetal atoms frequently form ____ with other nonmetal atoms

covalent bonds

bond length

• the internuclear distance at which the lowest potential energy is achieved

• determined by the distance at which the lowest potential energy is achieved

energy must be ______ to break chemical bonds

added (endothermic process)

forming chemical bonds ______ energy

releases (exothermic process)

if the atoms that form a covalent bond are identical (i.e. H₂ or Cl₂), then the electrons in the bond must be shared ______

equally

a covalent bond in when two identical atoms share electrons equally

pure covalent bond

electrons shared in pure covalent bonds have _______ of being near each ________

an equal probability;

nucleus

polar covalent bond

characterized by a partial positive charge on one atom and a partial negative charge on the other

• due to atoms linked by covalent bond being different and thus sharing electrons unequally

• bonding electrons are more attracted to one atom than the other, shifting electron density toward that atom

Greek letter “delta” (δ)

used to designate the positive and negative atoms in a polar covalent bond

• with a plus or minus sign to indicate whether the atom has a partial positive charge (δ+) or partial negative charge (δ-)

electronegativity

a measure of the tendency of an atom to attract electrons (or electron density) towards itself

• determines how the shard electrons are distributed between the two atoms in a bond

the more strongly an atom attracts the electrons in its bonds…

the larger its electronegativity

electrons in a polar covalent bond are shifted toward….

the more electronegative atom

the greater the difference in electronegativity, the more…..

polarized the electron distribution

the greater the difference in electronegativity, the larger…

the partial charges of the atoms

____ is the most electronegative of all elements

Fl (EN = 4.0)

group ___ have the lowest electronegativities

1 metals

Linus Pauling

• twentieth century chemist that proposed (derived) electronegativity values following periodic trends with higher electronegativities toward the upper right of the periodic table

• derived the first electronegativity values by comparing the amounts of energy required to break different types of bonds

• chose an arbitrary relative scale ranging from 0 to 4

difference between electronegativity vs. electron affinity

• electron affinity is a measurable physical quantity (the energy released/absorbed when an isolated gas-phase atom acquires an electron, measured in kJ/mol)

• electronegativity describes how tightly an atom attracts electrons in a bond

electronegativity is a _______ quantity that is ______

dimensionless

calculated, not measured

the absolute value of the difference in electronegativity (ΔEN) of two bonded atoms provides _______, and thus, _______

• a rough measure of the polarity to be expected in the bond

• the bond type

then the difference in electronegativity of two bonded atoms is large, the bond is

polar covalent or ionic

when the difference in electronegativity of two bonded atoms is very small or zero,

the bond is covalent and nonpolar

as the electronegativity difference increases between two atoms, the bond becomes

more ionic

electronegativity difference between bonding atoms: zero

bond type: pure covalent

electronegativity difference between bonding atoms: intermediate

bond type: polar covalent

electronegativity difference between bonding atoms: large

bond type: ionic

covalent character decreases =

ionic chracter increases

the best guide to covalent or ionic character of a bond is to consider:

the types of atoms involved and their relative positions in the periodic table

bonds between tow nonmetals are generally

covalent

bonds between a metal and a nonmetal are often

ionic

some compounds contain both ____ and _____ bonds

covalent and ionic

electronegativity difference of pure covalent bond

< 0.4

electronegativity difference of polar covalent bond

between 0.4 and 1.8

electronegativity difference of ionic bonds

> 1.8

nomenclature

a collection of rules for naming things

binary compounds

compounds containing only two elements

inorganic compounds

compounds that are composed principally of elements other than carbon

questions for naming inorganic compounds:

• ionic or molecular?

  • If ionic: fixed charge or variable charge?

  • If molecular: does compound contain hydrogen? If so, does it also contain oxygen?

name of a binary compound containing monatomic ions consists of:

• the name of the cation (name of the metal)

• followed by name of anion (nonmetallic element) with its ending replaced by the suffix -ide

compounds containing polyatomic ions named by:

• first name cation

• then anion

  • if anion is monatomic, then ending is changed to -ide

naming compounds containing a metal ion with a variable charge:

• name cation first

• then anion: charge of metal ion is specified by a Roman numeral in parentheses after name of metal

  • charge of the metal ion is determined from the formula of the compound and the charge of the anion

  • i.e. FeCl₂: iron(II) chloride or FeCl₃: iron(III) chloride

hydrates

ionic compounds that contain water molecules as integral components of their crystals

name for ionic hydrate

• derived by adding a term to the name for the anhydrous compound that indicates the number of water molecules associated with each formula unit of the compound

• added word begins with a Greek prefix denoting the number of water molecules and ends with “hydrate”

• written by appending a vertically centered dot (a coefficient representing the number of water molecules) and the formula for water

• i.e. “copper (II) sulfate pentahydrate” (CuSO₄ ∙ 5 H₂O) or “sodium carbonate decahydrate” (Na₂CO₃ ∙ 10 H₂O)

anhydrous

not hydrated

Greek prefix for 1

mono-

Greek prefix for 2

di-

Grek prefix for 3

tri-

Greek prefix for 4

tetra-

Greek prefix for 5

penta-

Greek prefix for 6

hexa-

Greek prefix for 7

hepta-

Greek prefix for 8

octa-

Greek prefix for 9

nona-

Greek prefix for 10

deca-