Transcript Chapter 2
Chemical Nomenclature
Octet Rule
Atoms tend to achieve electron
configuration of Noble Gases
Octet = Eight
Noble Gases have eight electrons in their
highest energy level
General Equation for Noble Gases is S2P6
Atoms of Metallic Elements tend to lose
valence electron/s, leaving an octet in the
next lowest energy level
Atoms of a Non-Metallic Element tend to
gain a valence electron/s to achieve an Octet
There are EXCEPTIONS to the Octet Rule
Diatomic Molecules
These eight elements occur naturally as molecules
containing two atoms.
Astatine is considered a diatomic
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Ions
Atoms or groups of atoms with a charge
Cations- positive ions - get by losing
electrons(s)
Anions- negative ions - get by gaining
electron(s)
Ionic bonding- held together by the opposite
charges
Ionic solids are called salts
Even though atoms and cations have the
same name, there are many chemical
differences between metals and their
cations.
Example:
Na Metal; reacts explosively in water
Na Cation; quite unreactive
Cations
Positive ions.
Formed by losing electrons.
More protons than electrons.
Metals form cations.
+1
Has lost one electron
K
+2
Has lost two electrons
Ca
Anion
A negative ion.
Has gained electrons.
Non metals can gain electrons.
Charge is written as a super script on the right.
-1
F
-2
O
Has gained one electron
Has gained two electrons
Charges on ions
For most of the Group A elements, the
Periodic Table can tell what kind of ion
they will form from their location.
Elements in the same group have similar
properties.
Including the charge when they are ions.
Monatomic Ions- consist of a single atom
with a positive or negative charge resulting
from the loss or gain of one or more valence
electrons
Groups 1a, 2a, and 3a lose electrons and
form cations
Aluminum is the only common group 3a
element to lose electrons and form a cation
Non-metals tend to gain electrons and form
an anion.
Groups 5a, 6a, and 7a form anions
In group 5a, there are three non-metals
which form anions
N3-, P3-, & As3
Majority of elements in 4a & 0 do not form
ions
Group 0 rarely forms compounds
Ordinarily, two non-metals from group 4a,
C & Si are found in molecular compounds
+1+2
-3 -2 -1
Laws
Conservation of Mass
Law of Definite Proportion- compounds
have a constant composition by mass.
They react in specific ratios by mass.
Multiple Proportions- When two elements
form more than one compound, the ratios of
the masses of the second element that
combine with one gram of the first can be
reduced to small whole numbers.
Law of Constant Composition
Joseph Proust (1754–1826)
This is also known as the law of definite
proportions.
It states that the elemental composition of a
pure substance never varies.
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Law of Conservation of Mass
The total mass of substances present at the
end of a chemical process is the same as the
mass of substances present before the
process took place.
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Compounds
Follow the Law of Definite Proportion.
Have a constant composition.
Have to add the same number of atoms
every time.
Two types.
Molecular Compounds
Molecular compounds
Made of molecules.
Made by joining nonmetal atoms together
into molecules.
Ionic Compound
Ionic Compounds
Made of cations and anions.
Metals and nonmetals.
The electrons lost by the cation are gained
by the anion.
The cation and anions surround each other.
Smallest piece is a FORMULA UNIT.
Formula Unit
Formula Unit- lowest whole-number ratio
of the ions in the compound
Example
Na+Cl Ratio is 1:1
The formula unit is NaCl
Formula Unit
The
smallest whole number ratio of
atoms in an ionic compound.
Ions surround each other so you can’t
say which is hooked to which.
Two Types of Compounds
Smallest
piece
Types of
elements
State
Melting
Point
Ionic
Molecular
Formula Unit
Molecule
Metal and
Nonmetal
Nonmetals
solid
High >300ºC
liquid or gas
Low <300ºC
Types of Formulas
Empirical formulas give the lowest wholenumber ratio of atoms of each element in a
compound.
Molecular formulas give the exact number
of atoms of each element in a compound.
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Writing Formulas
Two sets of rules, ionic and covalent
To decide which to use, decide what the
first word is.
If is a metal or polyatomic use ionic.
If it is a non-metal use covalent
Writing Formulas
Because compounds are electrically neutral, one
can determine the formula of a compound this
way:
– The charge on the cation becomes the subscript on the
anion.
– The charge on the anion becomes the subscript on the
cation.
– If these subscripts are not in the lowest whole-number
ratio, divide them by the greatest common factor.
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Ionic Formulas
Charges must add up to zero
get charges from table, name of metal ion,
or memorized from the list
use parenthesis to indicate multiple
polyatomics
Ionic Formulas
Sodium nitride
sodium- Na is always +1
nitride - ide tells you it comes from the table
nitride is N-3
Ionic Formulas
Sodium nitride
sodium- Na is always +1
nitride - ide tells you it comes from the table
nitride is N-3
doesn’t add up to zero
+1
Na
-3
N
Ionic Formulas
Sodium nitride
sodium- Na is always +1
nitride - ide tells you it comes from the table
nitride is N-3
doesn’t add up to zero
Need 3 Na
+1
Na
-3
N
Na3N
Writing Formulas
Write the formula for calcium chloride.
Calcium is Ca+2
Chloride is Cl-1
Ca+2 Cl-1 would have a +1 charge.
Need another Cl-1
Ca+2 Cl2-1
Crisscross
Switch the numerical value of the charges
2
2+
Ba
33
N
Ba3 N2
• Reduce ratio if possible
Polyatomic Ions
Polyatomic Ion- Tightly bound groups of
atoms that behave as a unit and carry a
charge
Unlike monatomic ions; Sulfate anion is
composed of 1 Sulfur atom and 4 oxygen
atoms
These five atoms form a Sulfate Anion
It has a –2 charge an is written SO42
Polyatomic anions either end in ITE or ATE
Out of the two similar polyatomic ions, the
polyatomic with less Oxygens ends in ite
Example:
Sulfite and Sulfate
Sulfite; SO32 Sulfate; SO42
There are three exceptions to the
Polyatomic Rule
1) Ammonium NH4+ ---- The only positive
polyatomic ion
2) Cyanide CN- ---- Ends in IDE
3) Hydroxide OH- --- Ends in IDE
Write the formulas for these
Lithium sulfide
tin (II) oxide
tin (IV) oxide
Magnesium fluoride
Copper (II) sulfate
Iron (III) phosphide
gallium nitrate
Iron (III) sulfide
Ionic Compounds
Sodium sulfite
calcium iodide
Lead (II) oxide
Lead (IV) oxide
Mercury (I) sulfide
Barium chromate
Aluminum hydrogen sulfate
Cerium (IV) nitrite
Write the formulas for these
Ammonium chloride
ammonium sulfide
barium nitrate
Naming compounds
Two types
Ionic - metal and non metal or polyatomics
Covalent- we will just learn the rules for 2
non-metals
There are two methods for naming cations
with multiple charges
The Stock System and Classical System
The Stock system is the preferred method
Stock System
The stock system uses roman numerals in
( ). The ( ) indicate the numerical charge of the
cation.
Example:
Fe2+ Name: Iron(II)
There is no space between the name and the
parenthesis
Example:
Cu1+ Name:
Copper(1)
Classical System
The classical system uses the root word
with different suffixes as the end of the
word
OUS- is used to name the cation with the
lower of the two ionic charges
IC- is used to name the cation with the
higher of the two ionic charges
Example:
Fe2+ and Fe3+
Name: Ferrous
Name: Ferric
What is the problem with the classical
system?
The classical system does not tell you the
charge of the ion.
The name only tells you which cation is
either larger or smaller out of the pair
Few transition metals have only one ionic
charge
These three elements don’t have roman
numerals next to there name
Exceptions:
Ag+
Cd2+
Zn2+
Ionic compounds
If the cation is monoatomic- Name the
metal (cation) just write the name.
If the cation is polyatomic- name it
If the anion is monoatomic- name it but
change the ending to -ide
If the anion is poly atomic- just name it
practice
Naming Binary Ionic Compounds
Write the name of CuO
Need the charge of Cu
O is -2
copper must be +2
Copper (II) chloride
Name CoCl3
Cl is -1 and there are three of them = -3
Co must be +3 Cobalt (III) chloride
Naming Binary Ionic Compounds
Write the name of Cu2S.
Since S is -2, the Cu2 must be +2, so each
one is +1.
copper (I) sulfide
Fe2O3
Each O is -2
3 x -2 = -6
3 Fe must = +6, so each is +2.
iron (III) oxide
Ternary Ionic Compounds
Will have polyatomic ions
At least three elements (3 capital letters)
Still just name the ions
NaNO3
CaSO4
CuSO3
Ternary Ionic Compounds
LiCN
Fe(OH)3
(NH4)2CO3
NiPO4
Ionic Compounds
Have to know what ions they form
off table, polyatomic, or figure it out
CaS
K2S
AlPO4
K2SO4
FeS
CoI3
Ionic Compounds
Fe2(C2O4)
MgO
MnO
KMnO4
NH4NO3
Hg2Cl2
Cr2O3
Ionic Compounds
KClO4
NaClO3
YBrO2
Cr(ClO)6
Molecular Compounds
Writing names and Formulas
Molecules & Molecular Compounds
Elements are the building materials of the
substances that make up all living and
nonliving things
Only about 100 elements but there are
millions of different compounds made from
their atoms
Thus, naming compounds is an essential
skill in chemistry
In nature, only Noble Gases tend to exist as
isolated atoms.
They are monatomic; that is, they consist of single
atoms
Many elements found in nature are in the form of
molecules
Molecule- is the smallest electrically neutral unit
of a substance that still has the properties of the
substance
Molecules are made up of two or more atoms that
act as a unit
Atoms of different elements may combine
chemically to form compounds
In many compounds, the atoms combine to form
molecules.
Molecular Compounds- Compounds composed of
molecules
Molecular Compounds tend to have relativity low
melting and boiling points
Many of these compounds thus exist as gases or
liquids at room temperature.
Molecular compounds
made of just nonmetals
smallest piece is a molecule
can’t be held together because of opposite
charges.
can’t use charges to figure out how many of
each atom
Naming Covalent Compounds
Two words, with prefixes
Prefixes tell you how many.
mono, di, tri, tetra, penta, hexa, septa, nona,
deca
First element whole name with the
appropriate prefix, except mono
Second element, -ide ending with
appropriate prefix
Practice
Nomenclature of Binary
Compounds
The less electronegative
atom is usually listed first.
A prefix is used to denote
the number of atoms of each
element in the compound
(mono- is not used on the
first element listed,
however) .
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Nomenclature of Binary
Compounds
The ending on the more
electronegative element is
changed to -ide.
– CO2: carbon dioxide
– CCl4: carbon tetrachloride
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Nomenclature of Binary
Compounds
If the prefix ends with a or
o and the name of the
element begins with a
vowel, the two successive
vowels are often elided into
one.
N2O5: dinitrogen pentoxide
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Naming Covalent Compounds
CO2
CO
CCl4
N2O4
XeF6
N4O4
P2O10
Name These
N2O
NO2
Cl2O7
CBr4
CO2
BaCl2
Covalent compounds
The name tells you how to write the
formula
duh
Sulfur dioxide
diflourine monoxide
nitrogen trichloride
diphosphorus pentoxide
Write formulas for these
diphosphorus pentoxide
tetraiodide nonoxide
sulfur hexaflouride
nitrogen trioxide
Carbon tetrahydride
phosphorus trifluoride
aluminum chloride