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NEAR EAST UNIVERSITY
ENGINEERING FACULTY
CHEM 101-GENERAL CHEMISTRY
INSTR : FİLİZ ALSHANABLEH
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CHAPTER 2
ATOMS & MOLECULES
 Atomic Structure and Mass
. Fundamental Concepts of Atom
. Atomic Number-Mass Number-Isotopes
 Ions
 Compounds and Chemical Bonds
. Chemical Formulas
. Chemical Bonding
 The Periodic Table
 Chemical Nomenclature
EARLY HISTORY OF CHEMISTRY



Greeks were the first to
attempt to explain why
chemical changes occur.
Alchemy dominated for
2000 years.

Several elements
discovered.

Mineral acids prepared.
Robert Boyle was the first
“chemist”.

Performed quantitative
experiments.
BP
250,000 : Homo Sapience – Stone Tools.
80,000 : Fire (Cooking)
10,000 : Farming, Neolithic Age
7,000 : Copper
6,000 : Wine
5,000 : Bronze
3,300 : Iron
2,400: Atomic Theory(Democritos)
2,000: (Alchemy)
500: Metallurgy (Bauer),
Alchemy (Paracelsus )
400: Modern Chemistry:
(Robert Boyle, Priestley
Lavoisier, Proust, Dalton …)
DALTON’S ATOMIC THEORY (1808)
 Each element is made up of tiny particles
called ATOMS.
 The atoms of a given element are identical;
the atoms of different elements are different
in some fundamental way or ways.
 Chemical compounds are formed when
atoms of different elements combine with
each other. A given compound always has
the same relative numbers and types of
atoms.
CONCEPT CHECK
Which of the following statements regarding
Dalton’s atomic theory are still believed to
be true?
I. Elements are made of tiny particles called atoms.
II. All atoms of a given element are identical.
III. A given compound always has the same relative
numbers and types of atoms.
IV. Atoms are indestructible.
EARLY EXPERIMENTS TO CHARACTERIZE THE ATOMS (I)
J. J. Thomson (1898—1903)



Postulated the existence of electrons using cathode-ray tubes .
Determined the charge-to-mass ratio of an electron.
The atom must also contain positive particles that balance
exactly the negative charge carried by particles that we now call
ELECTRONS.
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EARLY EXPERIMENTS TO CHARACTERIZE THE ATOMS(II)
Robert Millikan (1909)
 Performed experiments
involving charged oil
drops.
 Determined the
magnitude of the charge
on a single electron.
 Calculated the mass of the
electron.
EARLY EXPERIMENTS TO CHARACTERIZE THE ATOMS(III)
Ernest Rutherford (1911)
 Explained the nuclear atom.
 Atom has a dense center of positive charge called the NUCLEUS.
 Electrons travel around the nucleus at a relatively large distance.
EARLY EXPERIMENTS TO CHARACTERIZE THE ATOMS(IV)
THE MODERN VIEW OF ATOMIC STRUCTURE(I)
The atom contains:
 Electrons – found outside the nucleus; negatively
charged.
 Protons – found in the nucleus; positive charge equal
in magnitude to the electron’s negative charge.
 Neutrons – found in the nucleus; no charge; virtually
same mass as a proton.
The nucleus is:
 Small compared with the overall size of the atom.
 Extremely dense; accounts for almost all of the
atom’s mass.
THE MODERN VIEW OF ATOMIC STRUCTURE(II)
 Nuclear Atom Viewed in Cross Section
ATOMIC NUMBER AND MASS NUMBER
 Atomic Number (Z): The number of protons in a particular atom.
 Mass Number (A): The total number of protons and neutrons in the
nucleus of a particular atom.
 Atomic symbols
 Isotopes : Atoms of an element with same atomic number but
different mass number.
. Show almost identical chemical
properties
. In nature most elements contain
mixtures of isotopes.
ISOTOPES OF HYDROGEN:
ATOMIC MASSES(I)
 Atomic Mass Unit (amu) is the standard unit that is used for
indicating mass on an atomic scale. It is defined as one twelfth of
the mass of an unbound neutral atom of carbon-12.
 C-12 isotope with 6 proton and 6 neutron has a mass exactly 12amu
 Relative atomic masses ;
. H: 1.008amu
. He: 4.003amu
. O: 16.00amu
. Fe: 55.85amu
ATOMIC MASSES(II)
AVERAGE ATOMIC MASSES
Average Atomıc Mass of Carbon:
98.89% of 12 amu + 1.11% of 13.0034 amu =
natural abbundance
of C*12
exact number
natural abbundance
of C*12
(0.9889)(12 amu) + (0.0111)(13.0034 amu) =
= 12.01 amu
EXERCISE
An element consists of 62.60% of an isotope
with mass 186.956 amu and 37.40% of an
isotope with mass 184.953 amu.
 Calculate the average atomic mass and
identify the element.
 SOLN: (186.956x0.6260)+(184.953x0.3740)
= 186.2 amu
Rhenium (Re)
MOLECULES AND IONS(I)
 MOLECULE : Two or more atoms joined and acting as a unit.
 TYPES MOLECULES :
. Diatomic Molecule (contains only 2 atoms)
HCl, H2, O2, NaCl, CO, CO2 , H2O, Cl2
. Polyatomic Molecule (contains more than
2 atoms)
O3, H2SO4, SO3, P4, KMnO4
MOLECULES AND IONS(II)
 IONS : is a charged species formed from a neutral atom or molecule when electrons
are gained or removed from.
 Ion with a net (+)ve charge........ CATION
Na atom
11 proton
11 electron
Na + ion
11 proton
10 electron
 Ion with a net (-)ve charge........ ANION
Cl atom
17 proton
17 electron
Cl - ion
17 proton
18 electron
 TYPES IONS :
. Monatomic Ion (contains only 1 atom)
H+, Cl-, O2-, Na+, Fe2+ , N-3
. Polyatomic Ions (contains more than 1 atoms)
COMPOUNDS AND CHEMICAL FORMULAS
 CHEMICAL FORMULAS
. Empirical formula (the simplest formula)
. Molecular formula (the true formula)
CHEMICAL BONDING(I)
 Atoms combine to make compounds by forming CHEMICAL BONDS
 Three broad categories;
. Covalent Bonding
. Metallic Bonding
. Ionic Bonding
 COVALENT BONDS
. Bonds form between atoms by sharing electrons.
. Resulting collection of atoms is called a molecule.
CHEMICAL BONDING(II)
 Metallic Bonding
Bonds form between positively charged
İon cores and free valence electrons
 Ionic Bonding
Bonds form due to force of
attraction between oppositely
charged ions.
THE PERIODIC TABLE(I)
Groups or Families – elements in the same vertical columns; have similar chemical properties
Periods – horizontal rows of elements
THE PERIODIC TABLE(II)
 CLASSIFICATION OF ELEMENTS
I. Metals: Good conductor of heat & electricity, tends to form cations
II. Nonmetals: Poor conductor of heat & electricity, tends to form anions
III. Metalloids: Properties between those metals & nonmetals
NAMING COMPOUNDS
 Binary Compounds


Composed of two elements
Ionic and covalent compounds included
 Binary Ionic Compounds

Metal—nonmetal
 Binary Covalent Compounds

Nonmetal—nonmetal
BINARY IONIC COMPOUNDS (TYPE I)





The cation is always named first and the anion second.
A monatomic cation takes its name from the name of the
parent element.
A monatomic anion is named by taking the root of the element
name and adding – ide .
Ionic compounds written by their imperical formula.
X 2+ + Y 2= X 2 Y 2 = XY
Examples:
KCl
Potassium chloride
MgBr2
Magnesium bromide
CaO
Calcium oxide
Examples of compounds containing polyatomic ions:
NaOH
Sodium hydroxide
Mg(NO3)2
Magnesium nitrate
(NH4)2SO4
Ammonium sulfate
BINARY IONIC COMPOUNDS (TYPE II)




Metals in these compounds form more than one type of
positive charge.
Charge on the metal ion must be specified.
Roman numeral indicates the charge of the metal cation.
Transition metal cations usually require a Roman numeral.
Examples:
CuBr
Copper(I) bromide
FeS
Iron(II) sulfide
Fe2S3
Iron(III) sulfide
PbO2
Lead(IV) oxide
BINARY COVALENT COMPOUNDS (TYPE III)

.
.
.
.
Formed between two nonmetals.
The first element in the formula is named first, using the element name.
The second element is named as if it were an anion.
Prefixes are used to denote the numbers of atoms present.
The prefix mono - is never used for naming the first element.
Prefixes Used to Indicate Number in Chemical Names
Examples:
CO2
Carbon dioxide
CO
Carbon monoxide
SF6
Sulfur hexafluoride
N2O4
Dinitrogen tetroxide
FLOWCHART FOR NAMING BINARY
COMPOUNDS
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EXERCISE
Which of the following compounds is named
incorrectly?
a) KNO 3
b) TiO 2
c) Sn(OH) 4
d) PBr 5
e) CaCrO 4
potassium nitrate
titanium(II) oxide
tin(IV) hydroxide
phosphorus pentabromide
calcium chromate
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