# Chapter 2. ATOMS, MOLECULES AND IONS by XVgRWo

VIEWS: 108 PAGES: 50

• pg 1
```									        Chapter 2.
ATOMS, MOLECULES AND IONS
   Objectives:
   Describe atoms, ions and molecules
   Name compounds based on their
formula
   Write the formulas of compounds
based on their names
   Calculate oxidation numbers
   Determine the structure of
molecules using formulas and
oxidation numbers
2.1. Atoms

  Atom = the smallest particle used to form a
substance.
Inside an atom:
 Nucleus

 Electrons moving around the nucleus

http://web.jjay.cuny.edu/~acarpi/NSC/3-atoms.htm
Inside the nucleus:
 Protons

 neutrons
Basic properties of
subatomic particles
Particle       mass           charge
(relative)
   electron   1              -1
   proton     1831           +1
   neutron    1834            0

Atoms: electrically neutral
Consequence: # of electrons = # of
protons
Characteristics of an atom
 Symbol: abbreviation used to
represent an atom (building block of an
element)
Components of a symbol: one or two
letters. first letter = capital
 Atomic Number = # of protons

 Mass Number = number of protons &
neutrons
* Isotopes
   Definition: elements with same # of protons &
different # of neutrons
   Notation: mass #atomic#Symbol
isotope #protons #neutrons Natural
Abundance

12 C               6          6    98.9 %
6
   13 C               6          7    <1.1
6

14 C               6          8    trace
6
   http://isotopes.lbl.gov/education/isotopes.ht
m
Atomic Mass
Definition: mass of protons, electrons and neutrons in
an atom
Average atomic mass: weighted average of atomic
masses of all isotopes of an element according to
their proportions.
 units: atomic mass unit (amu)

O                  C                  H
15.9994            12.011             1.008
 Absolute units: too cumbersome

 1 atomic mass unit = 1.66053886 × 10-24 grams

http://isotopes.lbl.gov/education/isotopes.htm
RQ2-10C
    The atomic mass of Cl is 35.5. What does
that say about the isotopic composition of the
Cl element?
a.    The atomic number is calculated using
nearly equal amounts of 3517Cl and 3617 Cl
b.    The atomic mass is calculated using nearly
equal amounts of 3517Cl and 3617 Cl
c.    The mass number is calculated using nearly
equal amounts of 3517Cl and 3617 Cl
RQ2-10D
    How can you use the atomic mass to figure
out the # of neutrons of the most abundant
isotope of an element?
a.     Round the atomic mass to a whole # &
subtract the atomic mass from the atomic #
b.     Round the atomic mass to a whole # &
subtract the atomic # from the atomic mass
c.     Round the atomic mass to a whole # & add
the atomic # and the atomic mass
2.2. The Periodic Table
   Definition: Table in which elements
with similar properties are placed in
same columns
   Read 2.7, pg 58.
2.3. Molecules.
Molecule = Assembly of atoms that are bound
to one another using chemical bonds
 Used to build compounds

Examples
 Water: H-O-H

WYG,GWYG:2006-
30,GWYG:en&q=water+molecule&um=1&ie=
UTF-8
 Salt: Na-Cl
Characteristics of
a molecule

 Formula: abbreviation used to represent a molecule
(building block of a compound)
Shows the composition of the compound
 Subscript: to show repeats of an atom or group of
atoms (to the immediate left of the subscript) in a
molecule
 Parenthesis: to show a group of atoms.

ex: Al2(SO4)3
 Note: Coefficients: numbers before formulas. Show
the number of times an atom / molecule is used.
 Ex: 2Al2(SO4)3 = 2 molecules of Al2(SO4)3
Types of Formulas
 Molecular Formula: to show actual
numbers of atoms in a molecule
ex: Benzene: C6H6
 Empirical formula: to show simplest

ratio of atoms in molecule
 ex: Benzene: CH. C and H are in a 6/6

= 1/1 ratio. Same for acetylene
RQ2-1E, Previous Material
Review
   An atom is identified by its: a, symbol; b,
formula which is one or two letters, the first of
which must be: a, lower; b, upper case and the
second one: a, lower; b, upper case.
   Other characteristics of an atom are the atomic
number which shows the number of: a, protons; b,
neutrons of the atom, and the mass number
which shows the number of: a, protons; b,
neutrons; c, protons and neutrons of the atom.
   Atoms that have the same number of protons and
different numbers of neutrons are called: a,
homonyms; b, equivalents; c, isotopes.
RQ2-1E, Previous Material
Review 2
   Molecules are: a, mixtures; b, assemblies of
atoms bound together by: a, glue; b, chemical
bonds; c, wires.
   A molecule is characterized by a: a, symbol; b,
formula that shows the types and numbers of atoms
it is made of. The numbers of atoms in a formula is
shown using: a, subscripts; b, superscripts; c,
coefficients. Each subscript applies to the atom or
group of atoms to its immediate: a, right; b, left.
   If a formula shows the actual number of atoms a
molecule is made of, it is a(n): a, empirical; b,
molecular formula
RQ2-1E, Previous Material
Review 3
   In the periodic table, metals are found at: a,
right; b, left; c, both sides of the bold
zigzag line.
   The characteristics of an isotope are: a,
symbol, atomic number and mass
number; b, density and color; c, formula,
atomic mass and atomic number
   The subscript in a formula indicates the
repeats of the: a, atom; b, atom or group
of atoms; c, all atoms to the immediate left
of the subscript
Molecular mass
= sum of atomic masses of all atoms in a
molecule.
 Units: amu

 Ex:     H2O     H2SO4 Al2(SO4)3
18      98          342
RQ2-11
    For a molecule, how does the ratio of molecular /
empirical weight compare to the ratio of
molecular / empirical formula?
a.   The ratios are the same. The weight of a formula
is inversely proportional to the number of
atoms weighed
b.   The ratios are the same. The weight of a formula
is directly proportional to the number of atoms
weighed
c.   The ratios are different. The weight of a formula
is inversely proportional to the number of
atoms weighed
2.4. Ions
  DEMO: http://www2.nl.edu/jste/bonds.htm
  Ion: atom or group of atoms carrying an electric charge
Reason for charge: loss or gain of electrons.
  Cation: positive ion formed by loss of one or several electrons
  ex; Na+ from Na; Ca2+ from Ca
  Anion: negative ion formed by gain of one or several electrons.
ex: Cl- from Cl; O2- from O
 General trends:
* Metals lose electrons
* Nonmetals gain electrons.
  Reason for gain or loss of electrons: gaining stability
Mono & Polyatomic Ions
 Monoatomic ion: contains one atom
ex: Na(+), O(2-)
 Polyatomic ion: contains several
atoms
ex: NO3(-) from KNO3
Names of some common polyatomic ions:
see tbl 3.4 pg 91,
2.5. Ionic and covalent
compounds
 Ionic compounds: Made of metals
bound to non-metals.
Read #3.5, pg 87
 Covalent (Molecular) compounds:

Made of non-metals bound to one
another
Read #3.6, pg 93
RQ2-13
 How many and which ions make the
molecule LiClO4?
a. Two ions: Li(+) and ClO4(-)
b. Six ions: Li(+), Cl(+7), and four
O(2-).
c. Two ions: Li(-) and ClO4(+)
RQ2-7A: Previous Material
Review
   The charge of cations is: a, positive; b,
negative because after: a, losing; b,
gaining electrons atoms get a(n): a,
excess; b, deficit of protons which
have a: a, positive; b, negative
charge.
2.6. Oxidation Number
(State)
 Definition: charge of   a monoatomic
ion in a molecule
ex:
Molecule Cations ON       Anions   ON
KCl        K        +1    Cl       -1
BaF2       Ba       +2    F        -1
Na2O       Na       +1    O        -2
ON Determination Rules
   *1.Sum of ON's of all atoms must be
*   0 for a neutral compound
*   the indicated charge for a polyatomic ion
   *2. ON for O: -2 in most cases
   *3. ON for H:
*   +1 in compounds with nonmetals
*   -1        ,,                metals
ON Determination Rules
(Continued)
   *4. ON = 0 for pure elements or
molecules made of the same atom
   *5. Molecules made of a metal and a
nonmetal. Set ON of non-metal = the
expected charge of the corresponding
anion.
   *6. Molecules made of nonmetals: Set
ON of atom located in (a) rightmost
column or (b) highest in same column in
the periodic table = the expected charge of
the corresponding ion. Exception: species
containing F (set ON for F)
RQ2-11B: Previous
material Review
   In order to determine the ON of an ionic
compound, first set the ON of the: a, metal; b,
nonmetal to the expected charge and figure out the
ON of the: a, metal; b, nonmetal.
   In order to determine the ON for a covalent
compound, first set the ON of the nonmetal located
in the: a, leftmost; b, rightmost column of the
periodic table, and figure out the ON of the other
nonmetal
   For nonmetals from the same column, first set
the ON of the nonmetal located: a, uppermost; b,
lowermost position in the column of the periodic
table, and figure out the ON of the other nonmetal
RQ2-11B: Previous
material Review 2
   When an atom gains an electron, it produces a: a,
anion; b, cation; c, molecule
   In order to determine the ON of all atoms in a
compound such as MoI3, set the ON of a, Mo; b,
I3; c, I to the expected ON and figure out the
remaining ON.
   In order to determine the ON of all atoms in a
compound such as V2(SO3)3, use first the ON of: a,
V; b, SO3 group to figure out the ON of: a, O; b, S;
before figuring out the ON of the remaining: a, O, b,
S; c, V atom on the molecule
RQ2-11B: Previous
material Review 3
   When determining the ON’s of the atoms in
P2O5, first set the ON of: a, O; b, P to the
expected charge and figure out the ON of the
remaining atom
   When determining the ON’s of the atoms in
H2CrO4, first set the ON of: a, O; b, O and
H; c, Cr to the expected charge and figure
out the ON of: a,H; b, Cr; c, O
RQ2-12
    Find the ON of Cr in Al2(CrO4)3
a.   (+3) + Cr + (-2) = 3 + Cr -2 = 0, which
leads to ON of Cr = -1
b.   2*(-3) + 3Cr + 12*(+2) = -6 + 3Cr +24
= 0, which leads to ON of Cr = -18/3 =
-6
c. 2*(+3) + 3Cr + 12*(-2) = 6 + 3Cr -24 =
0, which leads to ON of Cr = 18/3 = 6
2.7. Nomenclature
   Definition= The way a substance is named
   Procedure to name a compound: Find the
category to which it belongs & follow the rules.
   *1. Compounds made of metals & non-metals:
   Main group (IA, IIA, IIIA, IVA, VA, VIA) metal: Use
Case a.
   Main group metals with polyatomic ions: Case b
   Transition metals: use Case ab.
a. Compounds of main
group metals & with
nonmetals
   Naming procedure: name of metal +
1st part of name of nonmetal + ide
   ex; NaCl           Sodium Chloride
      LiH       Lithium hydride
      Na2O            Sodium Oxide
b. Compounds of a main
group metal & a polyatomic
anion
 Naming procedure: name of metal +
name of polyatomic anion
Ex:
NaNO3         Sodium nitrate
CaSO4         Calcium sulfate
KMnO4         Potassium
permanganate
More polyatomic anions: pg 91
ab. Compounds of transition
metals & with nonmetal
 Transition metals have several possible
ON's:
 Specify the oxidation number using a

roman number in parentheses
Ex: FeSO4: iron (II) sulfate.
Fe2O3: iron (III) oxide
Practice: #37, 39, 41, 43, pg121
c. Inorganic Compounds
of Hydrogen & a nonmetal
 * General Case:
 Naming procedure: Hydrogen + 1st
part of name of nonmetal + ide
ex: HCl (g) hydrogen Chloride
HI (g) hydrogen iodide
H2S (g) hydrogen sulfide
* Case of Water Solutions
of Case c Compounds
   Naming procedure: hydro + 1st
part of name of nonmetal + ic +
acid
ex: HCl (aq) hydrochloric acid
HI (aq) hydriodic acid
H2S (aq) hydrosulfuric acid
Note: aq = aqueous (water) solution
d. Acids of H and
polyatomic ions
 *. Ions ending with "ate" (nitrate, sulfate,
phosphate, perchlorate):
 Naming procedure: 1st part of name of
anion + ic + acid
 ex:

HNO3             Nitric acid
HClO4            Perchloric acid
H3PO4            Phosphoric acid
H2SO4            Sulfuric acid
Practice: #51, 53, pg 121
*. Ions ending with "ite":
Case of nitrite, sulfite, phosphite, …
 Naming procedure: 1st part of
name of anion + ous + acid
 ex:     HNO2         Nitrous acid
H2SO3 Sulfurous acid
H3PO3 Phosphorous acid
e. Compounds of 2
nonmetals
 Naming Procedure: name of non-metal from
leftmost column or lowermost position in same
column of periodic table + 1st part of name of the
other nonmetal + ide
 Use Greek prefixes to show repeats of elements
or to resolve conflicting cases
 prefixes: mono (one), di (two), tri (three), tetra
(four), penta (five), ...
ex:    Si3P4         Trisilicon tetraphosphide
N2O5          Dinitrogen pent(a)oxide
Practice: #47, 49 , pg 121
*2. Compounds made of
nonmetals
   H with non-metals: use Case c
   H and polyatomic ions: use Case d
   Compounds of 2 nonmetals other
than H: use Case e
Compounds of 2
nonmetals (Continued)
  Exceptions to previous rule
a. No prefix if first atom in formula is
used once.
Example: CO2 = carbon dioxide
a.  All molecules containing O are
oxides
Example: Cl2O = dichlorine monoxide
Exception: F2O = oxygen fluoride
RQ2-13: Previous Material
Review
   When naming a compound made of a main
group metal and a non-metal, first name
the :a, metal; b, non-metal, followed by
the name of the: a, first; b, second part of
the name of the: a metal; b, nonmetal,
ending with the suffix: a, “ite”; b. “ate”;
c,“ide”,
   For example Ca3N2 is: a, tricarbon di
nitride; b, calcium nitride; c, tricalcium
dinitride.
RQ2-13: Previous Material
Review 2
   Naming ionic compounds made of transition
metals requires the specification of the: a,
atomic; b, oxidation; c, mass number as a
roman number in parentheses directly after
the name of the: a, metal; b, nonmetal.
   For example, as Pb3(PO4)4 is made of
Pb(4+) and PO4(3-); its name is: a, lead
phosphate; b, lead (IV) phosphate; c,
RQ2-13: Previous Material
Review 3
   When naming a compound made of non-metals,
first name the nonmetal found in the: a, leftmost;
b, rightmost position in a row, or in the : a,
lowest; b, highest position in a column of the
periodic table, followed by the first part of the name
of the other non-metal ending with the suffix: a,
“ite”; b. “ate”; c,“ide”.
   The use of prefixes to show repeats of atoms in a
formula is needed only for naming: a, ionic
compounds; b, covalent; c, both ionic and
covalent compounds, except when the non metal is
used once and is named: a, first; b, last
RQ2-13 B
   In line with the correct answer to the
previous question, the name of C3As4 is: a,
tetraarsenic tricarbide ;b. tricarbon
tetrarsenide; c. carbon arsenide, and the
name of SiO is: a, silicon oxide; b,
monosilicon monoxide; c. silicon monoxide
2.8. Formula – Structure
Connection.
 Tool: Microscopic Representation, used
to convert a formula into the structure of the
molecule it represents
 Convention:

* Circle = atom
* Arrow head: negative ON
* Arrow tail: positive ON
 To build a structure, connect atoms with
arrow heads to atoms with arrow tails
RQ2-12B: Previous
Material Review
   The following convention is used in the process to
build the structure of a molecule from its formula and
the ON’s of its atoms:
   * Atoms are represented by: a, circles; b, arrow
heads; c, arrow tails
   * Positive charges are represented by: a, circles; b,
arrow heads; c, arrow tails
   In order to build the structure of a molecule,
connect: a, atoms with arrow tails to atoms
with arrow tails and likewise for atoms with
arrow heads; b, atoms with arrow tails to
atoms with arrow heads
RQ2-12B: Previous
Material Review
   In the formula Li2SO3, the ON’S of the atoms are +1,
+4, and -2 respectively. Which atom is connected to
which in the molecule?
   a. O is connected to S and Li is connected to O.
Atoms with positive ON’s must be connected to
atoms with negative ON’s.
   b. Li is connected to S and O is connected to O.
Atoms with positive ON’s must be connected to
atoms with positive ON’s, and vice versa
   c. Li is connected to Li and O is connected to O.
That is what the formula shows.
RQ2-12C
   http://www.abac.edu/bmiburo/CHEM1211/Ch
em%201211%20Graphics/GC1Sp8T1RVMicSt
r1.htm
   Examine the two possible structures of
LiClO4. Which one is the correct one?
   1. A, because all the atoms have the
correct ON’s
   2. B, because all the atoms have the
correct ON’s
   3. Neither, because they both have the
wrong ON’s
RQ2-12D
   http://www.abac.edu/bmiburo/CHEM1211/Chem
%201211%20Graphics/GC1Sp8T1RVMicStr2.ht
m
   Which one of H2PO4(-) or H2SO4 is represented
by the structure in the above link?
   a. H2PO4(-). It shows a loose connection with a
negative charge.
   b. H2SO4. It shows a loose connection with a
negative charge.
   c. None of the above. The ON of the central
atom is +5.
RQ2-13B: Previous
Material Review
   When naming an ionic compound
containing a transition metal, in addition to
the name, it is necessary to indicate the: a,
atomic weight; b, mass number; c,
oxidation number of the: a, metal, b,
non-metal; c, both the metal and the non-
metal
   The use of prefixes to show repeats of
atoms in a formula is needed only for
naming: a, ionic compounds; b, covalent;
c, both ionic and covalent compounds

```
To top