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Atoms, Molecules and Ions
Chapter 2
3 Lectures
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Chapter 2 Topics
Atoms, Molecules and Ions
• Chemical laws
1) Law of Conservation of mass
2) Law of definite Proportion
3) Law of Multiple Proportions
•Dalton’s Atomic Theory
•Early Atom Characterization
•Atomic number, mass number & Isotopes
•Introduction to periodic Table
•Molecules and Ions
•Chemical Formulas
•Chemical nomenclature
•Introduction to Organic Compounds
Dr. Ali Bumajdad
Chemical laws
1) Law of Conservation of mass
In any chemical reaction mass neither created nor destroyed
•What is the benefit of this law?
balancing chemical equation
Mg + O2
MgO
What about the second O !!!
Dr. Ali Bumajdad
2) Law of definite Proportion
Different pure samples of a compound always contain the same
elements in the same proportion by mass
50000 grams of water
H:O mass ratio 1:8
5 grams of water
H:O mass ratio 1:8
•What is the benefit of this law?
e.g. In a sample of H2O that have 3.00 g of H it should have 24.0 g of O because
3 1

24 8
e.g. If I have 3.00 g of H and 8.00 g of O and they react, does the reaction
proceeds until all chemicals react?
No, 2.00 g of H remain unreacted
Q) A sample of NaCl contains 23.0 g of Na and 35.5 g of Cl,
In a different sample of NaCl, how many grams of Na
would be combined with 71.0 g of Cl.
Mass of Na = 46.0 g
3) Law of Multiple Proportions
When two elements, A and B, form more than one compound, If the
masses of one element are the same in the two samples, then the
masses of the other element are in a ratio of small whole numbers.
Dr. Ali Bumajdad
•What is the benefit of this law?
Q)
In a sample of 2.33 g of CO we find
1.33 g of O combined with
1.00 g of C
In a sample of 3.66 g of CO2 we find
2.66 g of O combined with
1.00 g of C
Show that the data support the law of Multiple proportions
2.66 2 A ratio of

1.33 1
small whole numbers
Dr. Ali Bumajdad
Q) (Not very Important)
What is the ratio of masses of O that are combined with 1.00 g of N in the
compounds NO and N2O3
Here we need to use both law of definite proportion and law
of multiple proportions
? g O 16.0 g O
in NO

 1.14 g of O
1g N 14.0 g N
? g O 48.0 g O
in N 2O3

 1.71g of O
1g N 28.0 g N
1.71g 1.5 3



1.14 g 1.0 2
Dr. Ali Bumajdad
Dalton’s Atomic Theory(1808)
Dr. Ali Bumajdad
Dalton’s Atomic Theory(1808)
1. Elements are composed of extremely small
particles called atoms. All atoms of a given
element are identical, having the same size,
mass and chemical properties.
2. Compounds are composed of atoms of more
than one element. The relative number of atoms
of each element in a given compound is always
the same.
3. Chemical reactions only involve the
rearrangement of atoms. Atoms are not created or
destroyed in chemical reactions.
Dr. Ali Bumajdad
Early Atom Characterization
The electron discovery
•J.J. Thomson (English physicist, 1856-1940)
•Studied the electrical discharges in evacuated
tubes called ‘Cathode-ray tubes’
•1906 Nobel Prize in Physics
Dr. Ali Bumajdad
Cathode Ray Tube
Glass tube evacuated from air
Cathode
-
Anode
+
High Voltage
He Found particles transfer from Cathode to
Anode  it must be negative particles
E

B
L
• In 1897 He measured mass/charge of e- and
found it to be -1.76 × 108 C/g using
e/m = E  / B L (not Important)
• Thomson said ‘since e- can be produced from
different metals then all atoms must contains e-’
• It is known that atoms are neutral. Because of
that Thomson assumed that atoms also contain
positive charges. He assumes atoms as a cloud
of +ve charge with – ve electrons dispersed in it.
Dr. Ali Bumajdad
The electron charge and mass discovery
British
Millikank’s e- charge = -1.60 x 10-19 C
Thomson’s charge/mass of e- = -1.76 x 108 C/g
Millikank’s e- mass = 9.10 x 10-28 g
Dr. Ali Bumajdad
•R. A. Millikan (1868-1953) measured e- charge and
mass of e•1923 Nobel Prize in Physics
•He sprayed oil with atomizer
• Some of these small drops fall dawn from the upper
small hole
•He determine the mass of oil drop from its velocity
•Next he ionized the chamber gas using X-ray source
Dr. Ali Bumajdad
•Some of these charge adhere to the oil droplets by
controlling the voltage across the plates, the negatively
charge droplets slow down
• At certain voltage the oil drop can be suspended
• At this point
m×g = q ×E
•Now q can be found
•He found always q = n × small charge
where n is an integer
• This small charge were found to be -1.60 × 10-19C
•He said this is the charge of e•Then he used e- × (m / e-) to find m
French
The discovery of radiation
A.H. Becquerel
(1845-1923)
Nobel Prize in 1901
(e.g. Uranium: emit radiation
spontaneously)
Alpha,  = particles with +2 charge (i.e. 2 ×1.60 x 10-19 C)
Beta, 
= high speed eDr. Ali Bumajdad
Gamma,  = high energy light (no charge)
The discovery proton and nucleus
• Rutherford (1871-1937) tested
Thomson Model
• He directed  particles at a thin
Sheet of metal
a) If there were no big deflection then
Thomson model correct
b) If there were big deflection then
Thomson model wrong
New Zealand
but did most of his
work in England
Nobel prize 1908
He found some  particles not only deflected but even
scattered or bounced back
• So he assume a new model:
- most of the atom are empty space
- the atom’s +ve charge are concentrated in the center
 particle velocity ~ 1.4 x 107 m/s
(~5% speed of light)
1. atoms positive charge is concentrated in the nucleus
2. proton (p) has opposite (+) charge of electron (-)
3. mass of p is 1840 x mass of e- (1.67 x 10-24 g)
Rutherford’s Model of
the Atom
- Atomic radius ~ 100 pm = 1 x 10-10 m
- nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m
- P + ve charge = e –ve charge = 1.6 × 10-19 C
- N are neutral and its mass  mass of P 1.67 x 10-24 g
Mass of atom  mass of nucleus
-Nucleus are very dense (a pea have a mass of 250
million tons)  in chemistry e is more important that P
mass p = mass n = 1840 x mass e-
Atomic number, mass number & Isotopes
•Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
• Atomic number (Z) = number of protons in nucleus
•Isotopes: atoms of the same element has the same number of P
but different numbers of N
Mass Number
A
ZX
Atomic Number
1
1H
235
92
2
1H
U
Element Symbol
(D)
238
92
3
1H
U
(T)
Dr. Ali Bumajdad
Q)
How many protons, neutrons, and electrons are in
14
6C ?
6 protons, 8 (14 - 6) neutrons, 6 electrons
Q)
11
How many protons, neutrons, and electrons are in 6 C ?
6 protons, 5 (11 - 6) neutrons, 6 electrons 16
Q)
How many protons, neutrons, and electrons are in O-2 ?
8 protons, 8 (16 - 8) neutrons, 10 electrons
Sa. Ex. 2.2:
Atom has an atomic number of 9 and a mass of 19.
What is it symbol? How many e’s and N’s does it contain?
F, 9 electrons,10 (19 - 9) neutrons,
Dr. Ali Bumajdad
Q)
How many protons and electrons are in
27 3+
13 Al
?
13 protons, 10 (13 – 3) electrons
Q)
How many protons and electrons are in
78 234 Se
34 protons, 36 (34 + 2) electrons
?
Introduction to periodic Table
monatomic
diatomic
Noble Gas
Halogen
Group
Alkali Earth Metal
Alkali Metal
Period
•Groups: Vertical columns, element having similar
physical and chemical properties
•Periods: Horizontal rows
•Metals: Good conductor of heat and electricity,
malleability (can be hammered), ductility (can be
wired), shiny, tend to lose e- to form +ve ions, form
ionic bond with non-metals
•Non-Metals: Poor conductor of heat and electricity,
can not be hammered, can not be wired, not shiny,
tend to gain e- to form -ve ions, form ionic bond with
metals and covalent bond with nonmetal
•Metalloid: Intermediate properties between metals
•and non-metals
Molecules and Ions
A molecule is an aggregate of two or more atoms in a
definite arrangement held together by chemical bonds
H2
H2O
NH3
CH4
A diatomic molecule contains only two atoms
H2, N2, O2, Br2, HCl, CO
A polyatomic molecule contains more than two atoms
O3, H2O, NH3, CH4
A Covalent bond bond formed by sharing of e-( nonmetalnon-metal)
An Ionic bond bond formed by attraction between ions
Dr. Ali Bumajdad
(metal  non-metal)
An ion is an atom, or group of atoms, that has a net
positive or negative charge.
cation – ion with a positive charge
If a neutral atom loses one or more electrons
it becomes a cation.
Na
11 protons
11 electrons
Na+
11 protons
10 electrons
anion – ion with a negative charge
If a neutral atom gains one or more electrons
it becomes an anion.
Cl
17 protons
17 electrons
Cl-
17 protons
18 electrons
Dr. Ali Bumajdad
A monatomic ion contains only one atom
Na+, Cl-, Ca2+, O2-, Al3+, N3A polyatomic ion contains more than one atom
OH-, CN-, NH4+, NO3-
Some Common Polyatomic Ions
Name
Symbol
Charge
bicarbonate
(or hydrogen carbonate)
HCO3- (e.g. NaHCO3)
-1
bisulfate (or hydrogen sulfate)
HSO4- (e.g. NaHSO4)
-1
chlorate
ClO3- (e.g. NaClO3)
-1
cyanide
CN- (e.g. NaCN)
-1
dihydrogen phosphate
H2PO4- (e.g. NaH2PO4)
-1
hydroxide
OH- (e.g. NaOH)
-1
Nitrate
NO3- (e.g. NaNO3)
-1
nitrite
NO2- (e.g. NaNO2)
-1
perchlorate
ClO4- (e.g. NaClO4)
-1
permanganate
MnO4- (e.g. KMnO4)
-1
carbonate
CO32- (e.g. Na2CO3)
-2
hydrogen phosphate
HPO42- (e.g. Na2HPO4)
-2
peroxide
O22- (e.g. H2O2)
-2
sulfate
SO42- (e.g. H2SO4)
-2
sulfite
SO32- (e.g. H2SO3)
-2
phosphate
PO43- (e.g. H3PO4)
-3
ionic compounds consist of a combination of cations
and an anions
• The sum of the charges on the cation(s) and anion(s) in each
formula unit must equal zero
The ionic compound NaCl
Formula of Ionic Compounds
2 x +3 = +6
3 x -2 = -6
Al2O3
Al3+
1 x +2 = +2
Ca2+
2 x +1 = +2
Na+
O22 x -1 = -2
CaBr2
Br1 x -2 = -2
Na2CO3
CO32-
Chemical Formulas
Empirical Formula Molecular Formula Structural Formula
Show simplest-whole Show exact number
number ratio
H2O
H2O
CH2O
C6H12O6
O
O3
NH2
N2H4
Show :
1) Exact number
2) How atoms are
bonded to one another
Dr. Ali Bumajdad
- Chemical nomenclature: the naming of chemical compounds.
- We must first distinguish between organic and inorganic compounds.
- Organic compounds contain carbon (C), usually in combination with elements
such as hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S).
- All other compounds are classified as inorganic compounds.
For convenience, some carbon-containing compounds such as: carbon monoxide
(CO), carbon dioxide (CO2), carbon disulfide (CS2), cyanide group (CN-), carbonate
(CO32-) and bicarbonate (HCO3-) groups are considered to be inorganic
compounds.
- We can divide inorganic compounds into four categories:
1. ionic compounds, 2. molecular compounds, 3. acids and bases, and
4. hydrates
Chemical Nomenclature: Ionic Compounds
- Ionic Compounds are:
1. Often a metal (+ve - start) and a nonmetal (-ve - end)
2. Anion (nonmetal), add “-ide” to element name
3. Many ionic compounds are binary compounds: compounds formed
from just two elements e.g. NaCl.
4. Some ionic compounds are ternary compounds: compounds consist
of three elements e.g. LiOH.
Metal
Nonmetal + ide
BaCl2
barium chloride
K2O
potassium oxide
Mg(OH)2
magnesium hydroxide
KNO3
potassium nitrate
Ionic Compounds
The cation (+ve): Transition metal
- Transition metal (can have multiple charges) ionic compounds:
1. indicate charge on metal with Roman numerals (I, II, III, IV, V, VI, VII)
FeCl2
2 Cl- -2 so Fe is +2
iron(II) chloride
FeCl3
3 Cl- -3 so Fe is +3
iron(III) chloride
Cr2S3
3 S-2 -6 so Cr is +3 (6/2)
chromium(III) sulfide
Ionic Compounds
The Anion (-ve)
Look at the charge!
Name the following compounds:
(a)Cu(NO3)2
contain both metal and nonmetal atoms, copper(II) nitrate
(b) KH2PO4
contain both metal and nonmetal atoms, potassium dihydrogen phosphate
(c) NH4ClO3
ammonium group, which bears a positive charge. So NH4ClO3 is also an
ionic compound, ammonium chlorate
Strategy Note that the compounds in (a) and (b) contain both
metal and nonmetal atoms, so we expect them to be ionic
compounds.
There are no metal atoms in (c) but there is an ammonium
group, which bears a positive charge. So NH4ClO3 is also an
ionic compound.
Our reference for the names of cations and anions is Table 2.3.
Keep in mind that if a metal atom can form cations of different
charges (see Figure 2.11), we need to use the Stock system.
Solution
(a)The nitrate ion (
) bears one negative charge, so the
copper ion must have two positive charges. Because copper
forms both Cu+ and Cu2+ ions, we need to use the Stock system
and call the compound copper(II) nitrate.
(b)The cation is K+ and the anion is
(dihydrogen
phosphate). Because potassium only forms one type of ion
(K+), there is no need to use potassium(I) in the name. The
compound is potassium dihydrogen phosphate.
(c) The cation is
(ammonium ion) and the anion is
The compound is ammonium chlorate.
.
Write chemical formulas for the following compounds:
(a)mercury(I) nitrite
Hg2(NO2)2
(b)cesium sulfide
Cs2S
(c)calcium phosphate
Ca3(PO4)2
Strategy
We refer to Table 2.3 for the formulas of cations and anions.
Recall that the Roman numerals in the Stock system provide
useful information about the charges of the cation.
Solution
(a)The Roman numeral shows that the mercury ion bears a +1
charge. According to Table 2.3, however, the mercury(I) ion is
diatomic (that is,
) and the nitrite ion is
. Therefore,
the formula is Hg2(NO2)2.
(b)Each sulfide ion bears two negative charges, and each
cesium ion bears one positive charge (cesium is in Group 1A,
as is sodium). Therefore, the formula is Cs2S.
(c) Each calcium ion (Ca2+) bears two positive charges, and
each phosphate ion (
) bears three negative charges.
To make the sum of the charges equal zero, we must adjust
the numbers of cations and anions:
3(+2) + 2(−3) = 0
Thus, the formula is Ca3(PO4)2.
Chemical Nomenclature: Molecular compounds
-
Molecular compounds: Nonmetals or nonmetals +
metalloids
1. Common examples: H2O, NH3, CH4
2. Element furthest to the left in a period and
closest to the bottom of a group on periodic
table is placed first in formula
3. If more than one compound can be formed from
the same elements, use prefixes to indicate
number of each kind of atom
4. Last element name ends in -ide
Chemical Nomenclature: Molecular compounds
HI
hydrogen iodide
NF3
nitrogen trifluoride
SO2
sulfur dioxide
N2Cl4
dinitrogen tetrachloride
NO2
nitrogen dioxide
N2O
dinitrogen monoxide
- Exceptions to the use of Greek prefixes are molecular compounds containing
hydrogen.
- Traditionally, many of these compounds are called either by their common,
nonsystematic names or by names that do not specifically indicate the number
of H atoms present:
Name the following molecular compounds:
(a) SiCl4
silicon tetrachloride
(b) P4O10
tetraphosphorus decoxide
Strategy
We refer to Table 2.4 for prefixes.
In (a) there is only one Si atom so we do not use the prefix
“mono.”
Solution
(a)Because there are four chlorine atoms present, the
compound is silicon tetrachloride.
(b)There are four phosphorus atoms and ten oxygen atoms
present, so the compound is tetraphosphorus decoxide. Note
that the “a” is omitted in “deca.”
Write chemical formulas for the following molecular compounds:
(a)carbon disulfide
CS2
(b) disilicon hexabromide
Si2Br6
Strategy
Here we need to convert prefixes to numbers of atoms (see
Table 2.4).
Because there is no prefix for carbon in (a), it means that there
is only one carbon atom present.
Solution
(a)Because there are two sulfur atoms and one carbon atom
present, the formula is CS2.
(b) There are two silicon atoms and six bromine atoms present,
so the formula is Si2Br6.
Chemical Nomenclature: acids
- An acid: a substance that yields (produces) hydrogen ions (H+) when dissolved
in water. Formulas for acids contain one or more hydrogen atoms as well as an
anionic group. Anions whose names end in “-ide” form acids with a “hydro-”
prefix and an “-ic” ending, as shown in Table 2.5 .
-For example: HCl gas and HCl in water, dissolved in water (H3O+ and Cl−),
hydrochloric acid
- Oxoacids: are acids that contain hydrogen, oxygen, and another element (the
central element).
- The formulas of oxoacids are usually written with the H first, followed by the
central element and then O. We use the following five common acids as our
references in naming oxoacids:
-Often two or more oxoacids have the same central atom but a different
number of O atoms.
- Starting with our reference oxoacids whose names all end with “-ic,” we
use the following rules to name these compounds.
1. Addition of one O atom to the “-ic” acid: The acid is called “per . . . -ic” acid.
Thus, adding an O atom to HClO3 changes chloric acid to perchloric acid, HClO4.
2. Removal of one O atom from the “-ic” acid: The acid is called “-ous” acid. Thus,
nitric acid, HNO3, becomes nitrous acid, HNO2.
3. Removal of two O atoms from the “-ic” acid: The acid is called “hypo . . . -ous”
acid. Thus, when HBrO3 is converted to HBrO, the acid is called hypobromous
acid.
Naming oxoacids and oxoanions.
The rules for naming oxoanions, anions of oxoacids, are as follows:
1. When all the H ions are removed from the “-ic” acid, the anion’s name ends with
“-ate.” For example, the anion CO32- derived from H2CO3 is called carbonate.
2. When all the H ions are removed from the “-ous” acid, the anion’s name ends
with “-ite.” Thus, the anion ClO2- derived from HClO2 is called chlorite.
3. The names of anions in which one or more but not all the hydrogen ions have
been removed must indicate the number of H ions present. For example, consider
the anions derived from phosphoric acid:
Table 2.6 gives the names of the oxoacids and oxoanions that contain chlorine.
Name the following oxoacid and oxoanion:
(a)H3PO3
reference acid, phosphoric acid (H3PO4). This is
phosphorous acid
(b)
The parent acid is HIO4. has one more O atom than our
reference iodic acid (HIO3), it is called periodic acid.
Therefore, the anion derived from HIO4 is called periodate.
Strategy To name the acid in (a), we first identify the reference
acid, whose name ends with “ic,” as shown in Figure 2.15.
In (b), we need to convert the anion to its parent acid shown in
Table 2.6.
Solution
(a)We start with our reference acid, phosphoric acid (H3PO4).
Because H3PO3 has one fewer O atom, it is called phosphorous
acid.
(b)The parent acid is HIO4. Because the acid has one more O
atom than our reference iodic acid (HIO3), it is called periodic
acid. Therefore, the anion derived from HIO4 is called
periodate.
Naming Bases
A base: a substance that yields hydroxide ions (OH-) when dissolved in water. Some
examples are:
Ammonia (NH3), a molecular compound in the gaseous or pure liquid state, is
also classifi ed as a common base.
Hydrates
- Hydrates: are compounds that have a specific number of water molecules
attached to them.
- For example, in its normal state, each unit of copper(II) sulfate has five
water molecules. The systematic name for this compound is copper(II) sulfate
pentahydrate, and its formula is written as:
CuSO4.5H2O.
Organic chemistry: is the branch of chemistry that deals with carbon compounds
Table 2.8 shows the names, formulas, and molecular models of the first ten
straight-chain alkanes, in which the carbon chains have no branches. Note that
all the names end with - ane .
- The chemistry of organic compounds is largely
determined by the functional groups. For example,
when an H atom in methane is replaced by a hydroxyl
group (-OH), an amino group (-NH2), and a carboxyl
group (-COOH).
- All will be discussed in chapter 24