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Atoms,
Molecules,
and Ions
Chapter 2
Atoms, Molecules,
and Ions
Chemistry, The Central Science, 10th edition
Theodore L. Brown; H. Eugene LeMay, Jr.;
and Bruce E. Bursten
Atoms,
Molecules,
and Ions
Atomic Theory of Matter
The theory that atoms
are the fundamental
building blocks of
matter reemerged in
the early 19th century,
championed by John
Dalton.
Atoms,
Molecules,
and Ions
Dalton’s Postulates
1. Each element is composed of
extremely small particles called atoms.
Atoms,
Molecules,
and Ions
Dalton’s Postulates
2. All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of all other elements.
Atoms,
Molecules,
and Ions
Dalton’s Postulates
3. Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions.
Atoms,
Molecules,
and Ions
Dalton’s Postulates
4. Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.
Atoms,
Molecules,
and Ions
Law of Constant Composition Joseph Proust (1754–1826)
• Also known as the law of definite
proportions.
• The elemental composition of a pure
substance never varies.
Atoms,
Molecules,
and Ions
Law of Multiple Proportions • In chemisty the law of multiple proportions is one of the basic
laws and a major tool of chemical measurement (stoichiometry)
• It states that when elements combine they do so in a ratio of
small whole numbers. For example, carbon and oxygen react to
form CO or CO2, but not CO1.8.
Atoms,
Molecules,
and Ions
Atoms,
Molecules,
and Ions
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.
Atoms,
Molecules,
and Ions
Atomic Structure
• Discovery of Electrons:
J J Thomson ( in 1897)
He gave the charge to mass ratio of
electrons.
He also showed that the nature of the
cathode ray did not depend on the
material of the cathode.
Atoms,
Molecules,
and Ions
Atoms,
Molecules,
and Ions
Conclusions drawn so far:
1. Cathode ray consists of negatively
charged particles and electrons are
constituents of all matter.
2. The charge on electrons is found to be
1.602 x 10 -19 coulombs.
Atoms,
Molecules,
and Ions
Millikan Oil Drop Experiment
Once the charge/mass
ratio of the electron
was known,
determination of either
the charge or the mass
of an electron would
yield the other.
Atoms,
Molecules,
and Ions
Millikan Oil Drop Experiment
Robert Millikan
(University of Chicago)
determined the charge
on the electron in
1909.
Atoms,
Molecules,
and Ions
• Now since a negative particle was
discovered it was definite that the atom
would also have an equal positive
charge.
• Then at the time the most reasonable
explanation seemed to be a plum
pudding model
Atoms,
Molecules,
and Ions
Atoms,
Molecules,
and Ions
• Rutherford explained the existence of a
focused positively charged nucleus in
the atom.
Atoms,
Molecules,
and Ions
Atoms,
Molecules,
and Ions
Atoms,
Molecules,
and Ions
The Nuclear Atom
• Rutherford postulated a very small, dense nucleus with the electrons around the outside of the atom.
• Most of the volume of the atom is empty space.
Atoms,
Molecules,
and Ions
Radioactivity:
• The spontaneous emission of radiation
by an atom.
• First observed by Henri Becquerel.
• Also studied by Marie and Pierre Curie.
Atoms,
Molecules,
and Ions
Radioactivity
• Three types of radiation were discovered by
Ernest Rutherford:
particles
particles
rays
Atoms,
Molecules,
and Ions
• Dalton Atomic theory
• J J Thomson Electrons and their charge to mass ratio
• Millikan Charge on the electron and later
the mass
• Henry Becquerel Radioactivity
• Rutherford α β and γ radiation
Gold leaf experiment to show the presence
of nucleus and coined the word proton
• James Chadwick Neutrons
Atoms,
Molecules,
and Ions
A. particles are scattered equally across a range of
deflection angles due to the high density of the foil
nuclei.
B. Most particles pass through the foil without being
deflected, because most of the volume of the atoms that
comprise the foil is empty space.
C. Most particles are scattered at acute angles as they
pass close to the foil nuclei.
D. Most particles are deflected in a backwards direction
from the foil due to the high density of the foil atom
nuclei.
Atoms,
Molecules,
and Ions
Subatomic Particles
• Protons and electrons are particles that have a
charge.
• Protons and neutrons have essentially the same
mass.
• The mass of an electron is so small we ignore it.
Atoms,
Molecules,
and Ions
Symbols of Elements
Elements are symbolized by one or two
letters.
Atoms,
Molecules,
and Ions
Atomic Number
All atoms of the same element have the same
number of protons:
The atomic number (Z)
Atoms,
Molecules,
and Ions
Atomic Mass
The mass of an atom in atomic mass units
(amu) is the total number of protons and
neutrons in the atom.
Atoms,
Molecules,
and Ions
Isotopes:
• Atoms of the same element with different masses.
• Isotopes have different numbers of neutrons.
11
6 C 12
6 C 13
6 C 14
6 C
Atoms,
Molecules,
and Ions
Isotopes of Hydrogen
Atoms,
Molecules,
and Ions
Question:
Which among the following represent a set of isotopes? Atomic nuclei
containing
I. 20 protons and 20 neutrons.
II. 21 protons and 19 neutrons.
III. 22 neutrons and 18 protons.
IV. 20 protons and 22 neutrons.
V. 21 protons and 20 neutrons.
Answer
A) I, II, III
B) III, IV
C) I, V
D) I, IV and II, V
E) No isotopes are indicated.
Atoms,
Molecules,
and Ions
138Ba atom has :
(a) 56 protons, 56 electrons, and 82 neutrons
(b)56 protons, 82electrons, and 82 neutrons
(c) 82 protons, 56 electrons, and 82 neutrons
(d)56 protons, 56 electrons, and 56 neutrons
Atoms,
Molecules,
and Ions
Average Mass
• The unit for atomic mass is amu
• Because in the real world we use large
amounts of atoms and molecules, we
use average masses in calculations.
• Average mass is calculated from the
isotopes of an element weighted by
their relative abundances.
Atoms,
Molecules,
and Ions
Naturally occurring chlorine is 75.78% 35Cl, which has an atomic mass of
34.969 amu, and 24.22% 37Cl, which has an atomic mass of 36.966 amu.
Calculate the average atomic mass (that is, the atomic weight) of chlorine
75.78% = 0.7578 and 24.22% = 0.2422,
Average atomic mass = (0.7578)(34.969 amu) + (0.2422)(36.966 amu)
= 26.50 amu + 8.953 amu
= 35.45 amu
Three isotopes of silicon occur in nature: 28Si (92.23%), which has an
atomic mass of 27.97693 amu; 29Si (4.68%), which has an atomic mass of
28.97649 amu; and 30Si (3.09%), which has an atomic mass of 29.97377
amu. Calculate the atomic weight of silicon.
Answer: 28.09 amu
Atoms,
Molecules,
and Ions
Atoms,
Molecules,
and Ions
The extra mass of 0.0989436 u represents
the mass converted into energy when the
fundamental particles combine in forming
the atom.
This energy, called the binding energy,
can be calculated with Einstein’s equation,
E = mc2, where m is the mass
converted into energy, and c is the speed
of light in a vacuum.
Atoms,
Molecules,
and Ions
Modern Periodic Table
• A systematic
catalog of
elements.
• Elements are
arranged in order
of atomic number.
Atoms,
Molecules,
and Ions
Mendeleev’s table as published in 1869, with many gaps
and uncertainties
Atoms,
Molecules,
and Ions
Atoms,
Molecules,
and Ions
Periodicity
When one looks at the chemical properties of
elements, one notices a repeating pattern of
reactivities.
Atoms,
Molecules,
and Ions
Periodic Table
• The rows on the
periodic chart are
called periods.
• Columns are called
groups.
• Elements in the same
group have similar
chemical properties.
Atoms,
Molecules,
and Ions
Groups
These five groups are known by their names.
Atoms,
Molecules,
and Ions
Periodic Table
Nonmetals are on
the right side of the
periodic table (with
the exception of H).
Atoms,
Molecules,
and Ions
Periodic Table
Metalloids border
the stair-step line
(with the exception
of Al and Po).
Atoms,
Molecules,
and Ions
Periodic Table
Metals are on the left side of the chart.
Note that there are more metals than nonmetals
Atoms,
Molecules,
and Ions
The element __________ is the most similar to strontium (Sr) in chemical
and physical properties.
A) Li B) At C) Cs D) Rb E) Ba
Atoms,
Molecules,
and Ions
Chemical Formulas
H2O, CO2, CO, CH4,
H2O2,O2
The subscript to the right
of the symbol of an
element tells the number
of atoms of that element
in one molecule of the
compound.
Atoms,
Molecules,
and Ions
Molecular Compounds
Molecular compounds
are composed of
molecules and almost
always contain only
nonmetals.
Atoms,
Molecules,
and Ions
Diatomic Molecules
These seven elements occur naturally as
molecules containing two atoms.
Atoms,
Molecules,
and Ions
Allotropes
• Many elements like C, O and S exist in
more than one form in nature.
Oxygen :
dioxygen O2 - colorless
ozone O3 - blue
Atoms,
Molecules,
and Ions
Carbon:
• Diamond - an extremely hard, transparent crystal, with the carbon atoms arranged in a tetrahedral lattice. A poor electrical conductor. An excellent thermal conductor.
• Graphite - a soft, black, flaky solid, a moderate electrical conductor. The C atoms are bonded in flat hexagonal lattices, which are then layered in sheets.
• amorphous carbon
• fullerenes including "buckyballs", such as C60, and carbon nanotubes
Atoms,
Molecules,
and Ions
• Carbon Nanotube
Atoms,
Molecules,
and Ions
Phosphorus:
White phosphorus - crystalline solid P4
Red phosphorus - polymeric solid
Atoms,
Molecules,
and Ions
Sulfur
• Plastic (amorphous) sulfur - polymeric solid
• Rhombic sulfur - large crystals composed of
S8 molecules
• Monoclinic sulfur - fine needle-like crystals
• Other ring molecules such as S7 and S12
Atoms,
Molecules,
and Ions
Types of Formulas
• Molecular formulas give the exact
number of atoms of each element in
a compound.
• Empirical formulas give the lowest
whole-number ratio of atoms of each
element in a compound.
Atoms,
Molecules,
and Ions
__________ are found uncombined, as monatomic species in nature.
A) Noble gases
B) Halogens
C) Alkali metals
D) Alkaline earth metals
E) Chalcogens
Atoms,
Molecules,
and Ions
Types of Formulas
• Structural formulas show the
order in which atoms are
bonded.
• Perspective drawings also
show the three-dimensional
array of atoms in a
compound.
Atoms,
Molecules,
and Ions
Ions
• When atoms lose or gain electrons, they
become ions.
Cations are positive and are formed by elements
on the left side of the periodic chart.
Anions are negative and are formed by elements
on the right side of the periodic chart.
Atoms,
Molecules,
and Ions
Beryllium
• The chemistry of Beryllium is
dominated by its tendency to lose an
electron to form Be2+. As this ion is so
small it is highly polarizing to the
neighboring atom, to the extent that its
compounds are mostly covalent.
Atoms,
Molecules,
and Ions
• Polyatomic ions
• The ions that contain more than one
atom. These can be cations or anions
• NH4+ , CO3
2-
• Within the polyatomic ion the elements
are covalently linked. But they have an
overall charge.
Atoms,
Molecules,
and Ions
Poly atomic ions:
1. Only two cations:
NH4+ and H3O
+
2. Anions are many
In most chemical reactions the polyatomic
ions will move as a whole.
Atoms,
Molecules,
and Ions
Ionic Bonds
Ionic compounds (such as NaCl) are
generally formed between metals and
nonmetals.
Atoms,
Molecules,
and Ions
Atoms,
Molecules,
and Ions
______ form ions with a 2+ charge when
they react with nonmetals.
A) Alkali metals
B) Alkaline earth metals
C) Halogens
D) Noble gases
E) None of these choices
Atoms,
Molecules,
and Ions
All ionic compounds are crystalline
solids with high melting points.
Atoms,
Molecules,
and Ions
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.
Atoms,
Molecules,
and Ions
Common Cations
Atoms,
Molecules,
and Ions
Common Anions
Atoms,
Molecules,
and Ions
Inorganic Nomenclature
• Write the name of the cation.
• If the anion is an element, change its
ending to -ide; if the anion is a
polyatomic ion, simply write the name of
the polyatomic ion.
Atoms,
Molecules,
and Ions
If the cation can have more than one possible charge,
write the charge as a Roman numeral in
parentheses.
This happens in the case of transition metals.
The other metals will have only a fixed charge.
Atoms,
Molecules,
and Ions
The 7th group elements are called
A) Alkali metals
B) Alkaline earth metals
C) Halogens
D) Noble gases
E) None of these choices
Atoms,
Molecules,
and Ions
Atoms,
Molecules,
and Ions
Which of the following is a transition metal and will have more than
one kind of ion.
A. Na
B. F
C. Fe
D. Al
E. Cs
Atoms,
Molecules,
and Ions
Patterns in Oxyanion Nomenclature
• When there are two oxyanions involving
the same element:
The one with fewer oxygens ends in -ite
• NO2− : nitrite; SO3
2− : sulfite
The one with more oxygens ends in -ate
• NO3− : nitrate; SO4
2− : sulfate
Atoms,
Molecules,
and Ions
indicating that a chemical compound contains a high proportion of a specified element: peroxide ; perchloride. indicating that a chemical element is in a higher than usual state of oxidation: permanganate ; perchlorate
Atoms,
Molecules,
and Ions
•
ClO − : hypochlorite
ClO2− : chlorite
ClO3− : chlorate
ClO4− : perchlorate
Atoms,
Molecules,
and Ions
Anions derived by adding H+ to the oxy
anion:
• CO32- and HCO3
-
Carbonate and hydrogen carbonate
• PO43- , H2PO4
-
Phosphate and dihydrogen phosphate
Atoms,
Molecules,
and Ions
Acid Nomenclature
• If the anion in the acid
ends in -ide, change
the ending to -ic acid
and add the prefix
hydro- :
HCl: hydrochloric acid
HBr: hydrobromic acid
HI: hydroiodic acid
Atoms,
Molecules,
and Ions
Acid Nomenclature
• If the anion in the acid
ends in -ate, change
the ending to -ic acid:
HClO3: chloric acid
HClO4: perchloric acid
Atoms,
Molecules,
and Ions
Acid Nomenclature
• If the anion in the acid
ends in -ite, change
the ending to -ous
acid:
HClO: hypochlorous
acid
HClO2: chlorous acid
Atoms,
Molecules,
and Ions
Other than this you need to know the names of
Acetic acid,
phosphoric acid,
chlorous acid and
hypochlorous acid for now
Atoms,
Molecules,
and Ions
When a metal and a nonmetal react, the __________ tends to lose
electrons and the __________
tends to gain electrons.
A) metal, nonmetal
B) nonmetal, metal
C) nonmetal, nonmetal
D) metal, metal
E) None of the above, these elements share electrons .
Atoms,
Molecules,
and Ions
Covalent Compounds
• Covalent compounds are formed
between two nonmetals.
• Covalent compounds can be solids,
liquids or gases at room temperature.
Atoms,
Molecules,
and Ions
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.)
Atoms,
Molecules,
and Ions
Nomenclature of Binary
Compounds
• The ending on the more
electronegative element is
changed to -ide.
CO2: carbon dioxide
CCl4: carbon tetrachloride
Atoms,
Molecules,
and Ions
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
Atoms,
Molecules,
and Ions
The correct name for N2O5 is __________.
A) nitric oxide
B) nitrogen pentoxide
C) nitrogen oxide
D) nitrous oxide
E) dinitrogen pentoxide
Atoms,
Molecules,
and Ions
The correct name for CaH2 is
A) calcium hydride
B) hydrocalcium
C) calcium dihydride
D) calcium dihydroxide
E) calcium hydroxide