Chemical Bonding: Online
cross over rule
If the charges on the cation and anion are NOT equal in magnitude, use the charge of the cation (numerical part only!) as the subscript for the anion. Use the charge on the anion (numerical part only!) as the subscript for the cation. Be sure subscripts are reduced to lowest whole-number ratio.
Ionic compounds exist in crystal lattice structure;
therefore, their chemical formulas are the lowest whole-number ratio of the ions in the compound. (ex: NaCl= 1:1 ratio)
ionic compound are brittle:when a strong forces act upon a ionic solid, it causes the ions to shift. this results in a lining up of like charges
(cations w/ cations and anions w/ anions) and the like charges repel. therefore the ions push away, thus cleaving the solid
Cations of Variable Charge, Stock System. examples
*THE 2,3,6 HAS TO BE IN ROMAN NUMERAL* Fe3+= Iron(III) ion Fe6+= Iron(VI) ion Fe2+= Iron(II) ion
Most of the rocks and minerals that make up Earth's crust consist of
+ and - ions held together by ionic bonding
the combined attractive and repulsive forces within a crystal lattice determine
- the distance between ions -the pattern of the ions' arrangement in the crystal
General Rules for Writing Formulas of Ionic Compounds: Combine the cation and anion to produce an electrically neutral compound by adding subscripts. examples
-If the charges of the cation and anion are equal in magnitude (i.e. 1+/1-, 2+/2-, 3+/3-) -combine ions in a 1:1 ratio. Be sure subscripts are reduced to lowest whole-number rat
octet rule: noble gas atoms are nonreactive because their electron configurations are especially stable.
. this stability results from the fact that the noble-gas atoms' outer s and p orbitals are completely filled by a total of 8 electrons
Why do atoms bond:
.eventually, a distance is reached in which the repulsive forces equal the attractive forces. Potential energy is at the minimum, and a stable molecule forms
Lewis structures: steps to predict the structure if a molecule
1. Determine the arrangement of the atoms (symbols) in the molecule. -you will need a detailed chemical analysis or formula of the compound -reasonable prediction by:
Lewis structures: steps to predict the structure of a molecule #2
2. determine the total # of valence e- available. (this is the number of dots that will appear in the structure and the total electron available for bonding)
formation of ionic compounds: Na atoms of one valence e- and the Cl atoms have
7 valence e-
Octet Rule
Atoms tend to gain, lose, or share electrons to attain the configuration of noble gases -an octet value in the valence (highest occupied) energy level - 8 valence electrons (for a full shell)
Nonpolar Covalent
Bond in which electrons are shared equally by the bonded atoms; a balanced distribution of electrical charge
nonpolar covalent bond
Bond in which electrons are shared equally by the bonded atoms; a balanced distribution of electrical charge
Polar Covalent Bond
Bond in which electrons are shared unequally by the bonded atoms; bonded atoms have an unequal attraction for the shared electrons; an unbalanced distribution of electrical charge
covalent bond
Results from the sharing of electron pairs between two atoms
Cations of Variable Charge, Stock System.
Since more than one possibility exists, one most indicate the charge formed by the atom in the name of the ion formed.
Cations of Variable Charge, Stock System
Some cations are capable of forming more than one charge -- multiple cation possibilities. This occurs in many transition metals & metals beneath the "staircase".
GENERAL RULES FOR NAMING MOLECULAR COMPOUNDS tips
The prefix "mono-" is never placed on the first atom in the name. A lack of prefix on the first element is understood to be a subscript of "1." The prefix "mono-" is used on the second atom in the name, and will indicate a subscript of "1." When using prefixes ending in "a" or "o" attached to an oxygen atom, the "a" or "o" is dropped. Example: "tetra-" w/ oxygen = tetroxide= O4
GENERAL RULES FOR WRITING FORMULAS OF MOLECULAR COMPOUNDS tips
The prefix "mono-" is never used on the first atom in the name. A lack of prefix on the first element is understood to be a subscript of "1." The prefix "mono-" is used on the second atom in the name, and will indicate a subscript of "1." When using prefixes ending in "a" or "o" attached to an oxygen atom, the "a" or "o" is dropped. Example: "tetra-" w/ oxygen = tetroxide= 04
Cations of Variable Charge, Stock System
These charges are indicated in the ion name by including a roman numeral equal to the positive charge of the cation.
To name cations
Use the name of the metallic ion forming the cation. (Example: Na+ = sodium ion)
to name anions
Use the name of the nonmetallic ion forming the anion. Drop the ending, and change to -"ide" (Example: Cl- = chlorine = chloride ion; P3- = phosphorus = phosphide ion)
bond length and stability:
a bond forms when atoms are a certain distance from each other. At this distance, the atoms are in a low energy state.
molecular compound
a chemical compound whose simplest units are molecules; atoms are covalently bonded;; composed of neutral atoms that share valence electrons to form bond. There are no ions, or charged particles.
polyatomic ions
a group of covalently bonded atoms that lose or gain electrons as a unit --- > loss / gain of e- = ion formation
Electronegativity
a measure of the ability of an atom in a chemical compound to attract electrons from another atom in the compound
molecule
a neutral group of atoms that are held together by covalent bonds sharing electrons) -- no ions
a crystal of any ionic compound
a three-dimensional network of + and - ions mutually attracted to each other
General Rules for Writing Formulas of Ionic Compounds, polyatomic ions
all the ruled stay the same, but these rules are added: ❑ If the anion or cation is polyatomic and more than one is needed, place parentheses around the polyatomic ion, and place the subscript outside the parentheses, in the lower right, to indicate the number needed. ❑ Most polyatomic ions, but not all, end in the suffixes "-ate" or "-ite." The ending "-ide" generally denotes a monatomic anion
cation
an atom or group of atoms that lose an electron. They become positively charged. (# p+ > #e-)
ion
an atom or group of atoms that lose or gain electrons (# protons does NOT equal #of electrons)
anion
an atom or groups of atoms that gain and electron. They become negatively charged. (#p+ < #e-)
ionic structures dissolved or molten: when dissolved in water, the cations and anions
break free from 1 another and freely flow throughout the water. This allows the particles to carry a charge
the chemical formula of an ionic compound represents not molecules,
but the simplest ratio of the compounds ions
conductivity of ionic solids: ionic solids:
cannot conduct as a solid due to the network of attraction holding the ions in a fixed positions, in order to conduct the electricity, there must be free- flowing charged particles
Lewis structures: steps to predict the structure of a molecule #6
change the shared pairs to dashes. double check that wach atom satisfies the Octet rule. (watch out for exceptions)
Ionic Bond
chemical bond that results from the electrical attraction between cations & anions
ionic compound
composed of + and - ions that are combined so that the #s of + and - charges are equal
Binary Molecular Compounds
compounds formed by two (neutral) nonmetallic ions
in an ionic crystal, ions minimize their potential energy by combing in an orderly arrangement known as
crystal lattice
most ionic compounds exists as
crystalline solids
the approach nuclei and electrons are attracted to each other. This correspond to a
decrease in potential energy
Lewis structures: steps to predict the structure of a molecule #3
determine the total number of pairs (available for bonding) by dividing the # of valence e- available by 2
conductivity of ionic solids: ionic solids don't conduct electricity in the solid state, but
do not conduct electricity when dissolved in water to molten (melted to liquid form)
the bonding of 2 hydrogen atoms allows each atom to have the stable
electron configuration of helium, 1s2
electron-dot notation
electron-configuration notation in which only the valence electrons are shown, indicated by dots placed around the element's symbol. The inner-shell e- are not shown
Valence Electrons:
electrons occupying the outermost (occupied) energy level of the atom; electrons available for bonding
valence electrons
electrons occupying the outermost (occupied) energy level of the atom; electrons available for bonding
atoms of Cl and other halogens easily gain 1 e- to
form anions
exceptions to octet rule: main- group elements in period 3 and up
form bonds with expanded valence, involving more than 8 e-
formation of ionic compounds: atoms of Na and other alkali metals easily lose 1 e- to
form cations
exceptions to octet rule: hydrogen
forms bonds in which it is surrounded by only 2 e-
exceptions to octet rule: boron
has just 3 valence e-, so it tends to form bonds in which it is surrounded by 6 e-
high bond energy = short bond length =
high stability
polyatomic ions examples
hydroxide ion = OH- carbonate ion = CO3 2-
Bond length and stability
if they are closer together or farther apart, they will be in an unstable situation
ionic compounds combine
in a ratio that will result in a compound (and therefore formula) which is electrically neutral!
exceptions to octet rule.
include those for atoms that cannot fit 8 e-, for tor those that can fir more than 8 e-, into their outermost orbital.
at the same time, the 2 nuclei repel one another and the valence electrons of each atom repel one another. This results in __
increase in potential energy
As the electronegativity difference increase, the percent ionic character
increases
chemical forumla
indicated the relative #s of atoms each kind in a chemical compound by using atomic symbols and numerical subscripts.
binary ionic compound
ionic compounds formed by two nonatomic ions
in contrast to a molecular compound, an ionic compound
isn't composed of independent, neutral units that can be isolated
ionic bond strength: since lattice energy is a measure of the energy released during the bond formation..
it can used as a measure of bond strength
attractive forces exist between
like-charged ions within the lattice
repulsive forces exist between
like-charged ions within the lattice
low bond energy- long bond length =
low stability
formation of a covalent bond
most atoms have lower potential energy when they are bonded to other atoms than they have as independent particles
chemical bond
mutual attraction between the nuclei and valence electrons of different atoms that bind the atoms together
Chemical Bond
mutual attraction between the nuclei and valence electrons of different atoms that binds the atoms together
ionic structures dissolved or molten: when molten, the ions have partially overcome the attractive forces holding them together, and are no
no longer rigidly held in fixed positions. they now flow past one another which allows for the conduction of electricity
Lewis structures: steps to predict the structure of a molecule #4
place the # of bonding pairs between the atoms to show the bonds. Do all atoms obey the octet rule? are multiple bonds needed?
Lewis structures: steps to predict the structure of a molecule #5
place the remaining (unshared) valence e- pairs around the atoms so that each atom satisfies the octet rule
When atoms get close enough, their outer electrons ____ each other. At the same time, however, each atom's outer electrons are strongly ___ to the nuclei of the surrounding atoms.
repel and attracted
Octet Rule: other atoms can fill their outermost s and p orbitals by
sharing electrons through covalent bonding
ionic bond strength: lattice energy
the energy released (exothermic) when 1 mol of an ionic crystal lattice is formed from cations and anions
ionic bond strength: all atoms bond to lower potential energy. Therefore, the more energy released (higher negative lattice energy)
the greater the strength of the bond formed
The degree to which these outer electrons are attracted to other atoms determines _______________ that occurs between the atoms.
the kind of chemical bonding
formula unit
the simplest collection of atoms from which an ionic compound's formula can be established
reasonable prediction by:
the single atom if central hydrogen is always a terminal, or end atom the atom with the lowest electronegativity is often the central atom (usually the leftmost atom on the periodic table) if not obvious, draw the most symmetric arrangement
As atoms approach each other
their charged particles (electrons and nucleus) interact
when two atoms for a covalent bond,
their shared electrons form overlapping orbitals. achieving a noble-has configuration
electron-dot notation
to keep track of valence e-, it is helpful to use electron-dot-notation
TIPS for Formula Writing
total positive charge = total negative charge (from cation) (from anion) (Another view of this: Total (+) charge + Total (-) charge = 0)
How to name a ionic compounds: Check whether the cation has a fixed or variable charge. If the cation has a fixed charge, no addition/adjustment is necessary. If the cation has a variable charge, a Roman numeral must be included as part of the cation name in order to indicate the charge of the cation...
▪ In order to determine the Roman numeral, determine the chare of the cation by using the charge of the anion, and the ratio necessary between the cation and anion to achieve a neutral compound. (See example from class.) ▪ The numeral of the charge = the Roman numeral [i.e., charge of 2+ = (II) Roman numeral]
General Rules for Writing Formulas of Ionic Compounds
❑ Identify the cation: The cation is always written first in both the name and formula of an ionic compound. Write the correct formula and charge for the cation. ❑ identify the anion: The anion is written last in both the name and formula of an ionic compound. Write the correct formula and charge for the anion ❑ Combine the cation and anion to produce an electrically neutral compound by adding subscripts. ❑ Do Not Show the Charges of the Ions when you write the final formula. ❑ Make sure the subscripts for the cation and anion are the smallest, whole-number ratio of the io
GENERAL RULES FOR NAMING MOLECULAR COMPOUNDS
❑ Identify the first element: The element name of the least electronegative element is written first. ❑ Identify the second element: The element name of the most electronegative element is written second, and the ending (suffix) is dropped & changed to "-ide" Example: If oxygen is the second element: oxygen -🡪 becomes oxide
GENERAL RULES FOR WRITING FORMULAS OF MOLECULAR COMPOUNDS
❑ Identify the first element: The symbol of the least electronegative element is written first (on the left) ❑ Identify the second element: the symbol of the most electronegative element is written second (on the right) ❑ Use look at the prefix attached to each element name. It will tell you the number of atoms of (the subscript for) that element in the compound. . Example: dinitrogen = N2 ❑ Tips: The prefix "mono-" is never used on the first atom in the name. A lack of prefix on the first element is understood to be a subscript of "1." The prefix "mono-" is used on the second atom in the name, and will indicate a subscript of "1." When using prefixes ending in "a" or "o" attached to an oxygen atom, the "a" or "o" is dropped. Example: "tetra-" w/ oxygen = tetroxide
Molecular Nomenclature Notes: backround info
❑ Molecular compounds are composed of neutral atoms that share valence electrons to form bond. There are no ions, or charged particles. ❑ Since there are no charged particles, the name must communicate the number of atoms (subscript)of each specific atom bonded. ❑ Molecular nomenclature utilizes a system of prefixes to communicate the subscripts in a molecular compound. ❑ Molecular compounds tend to be composed of nonmetals with other nonmetals (or metalloids).
general rules for naming ionic compounds with polyatomic ions
❑ No change in Rules! ❑ The cation is always written first in both the name and formula of an ionic compound. Write the correct element name of the cation. ❑ Check whether the cation has a fixed or variable charge. ❑ If a Polyatomic Ion is present, just use that polyatomic ion's name without changing its ending.
How to name a ionic compound
❑ The cation is always written first in both the name and formula of an ionic compound. Write the correct element name of the cation. ❑ Check whether the cation has a fixed (only one possibility for a charge) or variable charge (multiple possibilities for a charge). If the cation has a fixed charge, no addition/adjustment is necessary. If the cation has a variable charge, a Roman numeral must be included as part of the cation name in order to indicate the charge of the cation. ❑ The anion is written last in both the name and formula of an ionic compound. ❑ Write the correct element name for the anion. Adjust the suffix of the anion name. If the anion is monatomic, change the suffix to "-ide
