Download Molecules and Molecular Compounds

Chemistry
Second Edition
Julia Burdge
Lecture PowerPoints
Jason A. Kautz
University of Nebraska-Lincoln
2
Atoms, Molecules, and
Ions
Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Atoms, Molecules, and Ions
2.1 The Atomic Theory
2.7 Ions and Ionic Compounds
2.2 The Structure of the Atom
Atomic Ions
Discovery of the Electron
Polyatomic Ions
Radioactivity
Formulas of Ionic Compounds
The Proton and the Nucleus
Naming of Ionic Compounds
Nuclear Model of the Atom
Hydrates
The Neutron
Familiar Inorganic Compounds
2.3 Atomic Number, Mass Number,
and Isotopes
2.4 The Periodic Table
2.5 The Atomic Mass Scale and
Average Atomic Mass
2.6 Molecules and Molecular
Compounds
Molecules
Molecular Formulas
Naming Molecular Compounds
Empirical Formulas
2.1 The Atomic Theory
In 1808, John Dalton formulated a precise definition of matter that we call
atoms:
1) Elements are composed of extremely small particles called atoms. All
atoms of a given element are identical. The atoms of one element are
different from the atoms of all other elements.
2) Compounds are composed of atoms of more than one element. In any
given compound the same types of atoms are always present in the
same relative numbers.
3) A chemical reaction rearranges atoms in chemical compounds; it does
not create or destroy them.
The Atomic Theory
In the reaction below:
All the oxygen molecules appear identical to one another (hypothesis 1).
The compound CO2 forms when each carbon atoms combines with two
oxygen atoms (hypothesis 2).
All atoms present before the reaction are also present after the reaction
(hypothesis 3).
The Atomic Theory
According to Proust’s law of definite proportions, different samples of
a given compound always contain the same elements in the same mass
ratio.
Sample
Mass of O (g)
Mass of C (g)
Ratio (g O : g C)
123 g carbon dioxide
89.4
33.6
2.66:1
50.5 g carbon dioxide
36.7
13.8
2.66:1
88.6 g carbon dioxide
64.4
24.2
2.66:1
The Atomic Theory
According to the law of multiple proportions, if two elements can
combine to form more than one compound with each other, the masses
of one element that combine with a fixed mass of the other element are
in ratios of small whole numbers.
2
=
1
O to C ratio in CO2
2
=
O to C ratio in CO
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2.2 The Structure of the Atom
Based on Dalton’s atomic theory, an atom is the basic unit of an
element that can enter into a chemical combination.
The Structure of the Atom
When metal plates are connected to a high-voltage source, the
negatively charged plate, or cathode, emits an invisible ray.
The cathode ray is drawn to the anode.
Cathode
(-)
Anode
(+)
The Structure of the Atom
Cathode rays may be deflected by magnetic or electric fields.
Particles are negatively charged and are known as electrons.
The Structure of the Atom
J. J. Thomson determined the charge to mass ratio of an electron:
charge : mass = 1.76 × 108 C/g
C stands for coulomb which is the derived SI unit for charge
The Structure of the Atom
R. A. Millikan measured the charge of an electron with great precision.
charge
1.6022  1019 C
28
mass of an electron =
=
=
9.10

10
g
8
charge / mass
1.76  10 C/g
The Structure of the Atom
Three types of decay particles produced by radioactive decay include:
Alpha (α) rays; positively charged
Beta (β) rays; negatively charge
Gamma (γ) rays; no charge; very high energy waves
The Structure of the Atom
Ernest Rutherford used α
particles to prove the structure
of atoms.
The majority of particles
penetrated the gold foil
undeflected.
Sometimes, α particles were
deflected at a large angle.
Sometimes, α particles bounced
back in the direction from which
they had come.
The Structure of the Atom
Rutherford proposed a new model for
the atom:
Positive charge is concentrated in the
nucleus
The nucleus accounts for most of an
atom’s mass and is an extremely
dense central core within the atom
A typical atomic radius is
about 100 pm
A typical nucleus has a
radius of about 5 x 10–3 pm
1 pm = 1 x 10–12 m
The Structure of the Atom
Protons are positively
charged particles found in
the nucleus.
Neutrons are electronically
neutral particles found in the
nucleus.
Neutrons are slightly larger
than protons.
2.3 Atomic Number, Mass Number, and Isotopes
All atoms can be identified by the number of protons and neutrons they
contain.
The atomic number (Z) is the number of protons in the nucleus
The mass number (A) is the total number of protons and neutrons.
Mass number
(number of protons + neutrons)
Atomic number
(number of protons)
A
Z
X
Elemental symbol
Atomic Number, Mass Number, and Isotopes
Most elements have two or more isotopes, atoms that have the same
atomic number but different mass numbers.
1
1
2
1
3
1
hydrogen
deuterium
tritium
1 proton
0 neutrons
1 proton
1 neutron
1 proton
2 neutrons
H
H
H
Isotopes of the same element exhibit similar chemical properties, forming
the same types of compounds and displaying similar reactivities.
Atomic Number, Mass Number, and Isotopes
How many protons neutrons and electrons are in an atom of boron-10?
Solution:
Atomic number (Z) = 5
Mass number (A) = 10
Protons = 5 (atomic number)
Electrons = 5 (same number of protons and electrons in an atom)
Neutrons = 5 (mass number – atomic number; 10 – 5 = 5)
10
5
B
2.4 The Periodic Table
The periodic table is a chart in which elements having similar chemical
and physical properties are grouped together.
The Periodic Table
Elements are grouped in horizontal rows called periods.
Vertical columns are called groups or families.
The Periodic Table
Elements can be categorized as metals, nonmentals or metalloids.
Metals are good conductors
of heat and electricity.
Nonmetals are poor
conductors of heat or
electricity.
Metalloids have
Intermediate properties.
2.5 The Atomic Mass Scale and Average Atomic Mass
The most direct way to measure molecular mass is in a mass
spectrometer.
The Atomic Mass Scale and Average Atomic Mass
The Atomic Mass Scale and Average Atomic Mass
Atomic mass is the mass of an atom in atomic mass units (amu).
1 amu = 1/12 the mass of a carbon-12 atom
The atomic weight on the periodic table represents the average mass of the
naturally occurring mixture of isotopes.
Isotope
Isotopic mass
(amu)
Natural
abundance (%)
12C
12.00000
98.93
13C
13.003355
1.07
Average mass (C) = (0.9893)(12.00000 amu) + (0.0107)(13.003355 amu)
Average mass (C) = 12.01 amu
The Atomic Mass Scale and Average Atomic Mass
The atomic mass and natural abundances of the two stable isotopes of
copper are given below. Calculate the average atomic mass.
Isotope
Isotopic mass
(amu)
Natural
abundance (%)
63Cu
62.929599
69.17
65Cu
64.927793
30.83
Solution:
Average mass (Cu) = (0.6917)(62.929599 amu) + (0.3083)(64.927793 amu)
Average mass (Cu) = 63.55 amu
2.6 Molecules and Molecular Compounds
A molecule is a combination of at least two atoms in a specific arrangement
held together by chemical forces (chemical bonds).
A molecule may be an element or a compound.
Diatomic molecules contain two atoms and may be either heteronuclear
or homonuclear.
Polyatomic molecules contain more than two atoms.
Molecules and Molecular Compounds
A chemical formula denotes the
composition of the substance.
A molecular formula shows the exact
number of atoms of each element in a
molecule.
A structural formula shows not only
the elemental composition, but also
the general arrangements.
Molecules and Molecular Compounds
Binary molecular compounds are substances that consist of just two
different elements.
Nomenclature:
1) Name the first element that appears in the formula
2) Name the second element that appears in the formula, changing
its ending to –ide.
Examples:
HCl
hydrogen chloride
HI
hydrogen iodide.
Molecules and Molecular Compounds
Greek prefixes are used to denote the number of atoms of each element
present.
Examples:
SO2
sulfur dioxide
CO
carbon monoxide
N2O5
dinitrogen pentoxide
The prefix mono- is generally omitted for the first element.
Molecules and Molecular Compounds
Name the following binary molecular compounds:
(a) Cl2O
(b) SiCl4
Solution:
(a) Cl2O
dichlorine monoxide
(b) SiCl4
silicone tetrachloride
Molecules and Molecular Compounds
Write the formula for the following compounds
(a) carbon disulfide
(b) dinitrogen trioxide
Solution:
(a) CS2
(b) N2O3
Molecules and Molecular Compounds
One definition of an acid is a substance that produces hydrogen ions (H+)
when dissolved in water.
HCl is an example of a binary compound that is an acid when dissolved
in water.
To name these types of acids:
1) remove the –gen ending from hydrogen
2) change the –ide ending on the second element to –ic.
hydrogen chloride + –ic acid → hydrochloric acid
Molecules and Molecular Compounds
A compound must contain at least one ionizable hydrogen atom to be
an acid upon dissolving.
Examples:
HF
hydrofluoric acid
HCl
hydrochloric acid
HBr
hydrobromic acid
HI
hydroiodic acid
Molecules and Molecular Compounds
Organic compounds contain
carbon and hydrogen, sometimes
in combination with other atoms.
Hydrocarbons contain only
carbon and hydrogen
The simplest hydrocarbons are
called alkanes.
Molecules and Molecular Compounds
Many organic compounds contain groups of atoms known as functional
groups.
Functional groups determine many of the chemical properties of a
compound.
Reactivity typically takes place at functional groups.
Molecules and Molecular Compounds
Molecules and Molecular Compounds
Molecular formulas give the exact number of each type of element in a
compound.
Empirical formulas give the simplest ratio of elements in a compound.
Compound
Molecular Formula Empirical Formula
water
H2O
H2O
hydrogen peroxide
H2O2
HO
benzene
C6H6
CH
Molecules and Molecular Compounds
Molecules and Molecular Compounds
Write the empirical formula for the following compound:
C8H10N4O2
Solution:
Step 1: The elements are in an 8:10:4:2 ratio, which may be simplified to
a 4:5:2:1 ratio (divide by the smallest number)
Empirical formula
C4H5N2O1
2.7 Ions and Ionic Compounds
An atomic ion or monatomic ion is one that consists of just one atom
with a positive or negative charge.
The loss of one or more electrons from an atom yields a cation.
Cations have a positive charge.
Na Atom
Na+ Ion
11 protons
11 protons
11 electrons
10 electrons
Ions and Ionic Compounds
An anion is an ion whose net charge is negative due to an increase in
the number of electrons.
Cl Atom
Cl– Ion
17 protons
17 protons
17 electrons
18 electrons
Ions and Ionic Compounds
Atoms can lose or gain more than one electron.
Ions and Ionic Compounds
A monatomic ion is named by changing the ending of the element’s name
to –ide.
Cl– is chloride
O2– is oxide
Some metals can form cations of more than one possible charge.
Fe2+ : ferrous ion [Fe(II)]
Fe3+ : ferric ion [Fe(III)]
Mn2+ : manganese(II) ion
Mn3+ : manganese(III) ion
Mn4+ : manganese(IV) ion
Ions and Ionic Compounds
Ions that consist of a combination
of two or more atoms are called
polyatomic ions.
Ions and Ionic Compounds
Formulas for ionic compounds are generally empirical formulas.
Ionic compounds are electronically neutral.
Ions and Ionic Compounds
In order for ionic compounds to be electronically neutral, the sum of the
charges on the cation and anion in each formula must be zero.
Aluminum oxide:
Al3+
O2–
Al2O3
Sum of charges:
2(+3) + 3(–2) = 0
Ions and Ionic Compounds
To name ionic compounds:
1) Name the cation
.
omit the word ion
use a Roman numeral if the cation can have more than one
charge
2) Name the anion
omit the word ion
Examples:
NaCN sodium cyanide
FeCl2
iron(II) chloride
FeCl3
iron(III) chloride
Ions and Ionic Compounds
Name the following ionic compounds
(a) Na2SO4
(b) Cu(NO3)2
(c) CuNO3
Solution:
(a) sodium sulfate
(b) copper(II) nitrate
(c) copper(I) nitrate
Ions and Ionic Compounds
Oxoanions are polyatomic anions that contain one or more oxygen
atoms and one atom of another element.
Starting with the oxoanions whose names end in –ate, the following can
be used to name other oxoanions in the same family:
1) The ion with one more O atom than the –ate ion is called
per . . . ate ion. (ClO-3 is chlorate; ClO-4 is perchlorate)
2) The ion with one less O atom than the –ate anion is called the
–ite ion. (ClO-2 is chlorite)
3) The ion with two fewer O atoms than the –ate ion is called the
hypo . . . ite ion (ClO- is hypochlorite)
Ions and Ionic Compounds
Oxoacids are acids that contain oxoanions.
1) An acid based on the –ate ion is called . . . ic acid
HClO3 is chloric acid
2) An acid based on the –ite ion is called . . . ous acid
HClO2 is chlorous acid
3) Prefixes in oxoanion names are retained in the name of the acid.
HClO4 is perchloric acid
HClO is hypochlorous acid
Ions and Ionic Compounds
Hydrates are compounds that have a specific number of water molecules
within their solid structure.
CuSO4 • 5 H2O
copper(II) sulfate pentahydrate
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Chapter Summary: Key Points
The Atomic Theory
Discovery of the Electron
Radioactivity
The Proton and the Nucleus
Nuclear Model of the Atom
The Neutron
The Periodic Table
Average Atomic Mass
Molecular Formulas
Naming Molecular Compounds
Empirical Formulas
Atomic Ions
Polyatomic Ions
Formulas of Ionic Compounds
Naming Ionic Compounds
Hydrates
Inorganic Compounds