Introductory Chemistry:
A Foundation
Elements, Atoms & Ions
FOURTH EDITION
by Steven S. Zumdahl
University of Illinois
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Chapter 4
1
Elements
• Aims: To learn about the relative abundances of the
elements, learn the names of elements
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2
Table 4.1: Distribution (Mass Percent) of the 18
Most Abundant Elements in the Earth's Crust,
Oceans, and Atmosphere
• Over 114 known, of which 88 are found in nature
– others are man-made
• Abundance is the percentage found in nature
– oxygen most abundant element (by mass) on earth and in
the human body
– the abundance and form of an element varies in different
parts of the environment
• Each element has a unique symbol
• The symbol of an element may be one letter or two
– if two letters, the second is lower case
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Table 4.2: Abundance of elements in the
human body
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The Symbols for the Elements
• Aim: to learn the names/symbols for some
of the elements
• You need to know the elements in Table 4.3
for Quiz #3!!
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Table 4.3: The names and symbols of the
most common elements
• Aims:
Dalton’s Atomic Theory
– Learn Dalton’s Atomic Theory
– Learn Law of Constant Composition
– In the 18th century, scientists studying the nature of
things agreed upon the following things:
• Most natural materials are mixtures of pure substances
• Pure substances are either elements or combinations of
elements
• A given compound always contains the same proportions (by
mass) of the elements. e.g., water always contains 8 g of
oxygen for every 1 g of hydrogen. This principle is known as
the Law of Constant Composition. It means a given
compound always has the same composition.
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Figure 4.1: John Dalton
(1766-1844)
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Dalton’s Atomic Theory
1. Elements are composed of atoms
An English scientist and
teacher was aware of these
observations and formulated
an explanation.
2. All atoms of a given element are identical
His explanation became
known as Dalton’s Atomic
Theory
3. Atoms of a given element are different from those of
any other element
– tiny, hard, unbreakable, spheres
– all carbon atoms have the same chemical and physical
properties
– carbon atoms have different chemical and physical properties
than sulfur atoms
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Dalton’s Atomic Theory
10
Dalton’s Atomic Theory
4. Atoms of one element combine with atoms of
other elements to form compounds.
– Law of Constant Composition
• all samples of a compound contain the same proportions
(by mass) of the elements
– Chemical Formulas
5. Atoms are indivisible in a chemical process.
– all atoms present at beginning are present at the end
– atoms are not created or destroyed, just rearranged
– atoms of one element cannot change into atoms of
another element
• cannot turn Lead into Gold by a chemical reaction
• Describe the proportions of elements in a compound
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• Aims:
Formulas Describe Compounds
Formulas
– Learn how a formula describes a compounds composition
– Learn how to write formulas
• a compound is a distinct substance that is composed
of atoms of two or more elements
• Formulas describe the compound by describing the
number and type of each atom in the simplest unit of
the compound
Rules for Writing Formulas
• each element represented by its letter symbol
• the number of atoms of each element is written to the
right of the element as a subscript
– if there is only one atom, the 1 subscript is not written
• polyatomic groups are placed in parentheses
– if more than one
• If subscript is one (1), then it is not written
– molecules or ions
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Figure 4.2: Dalton pictured compounds as collections of
atmosphere NO, NO2, and N2O are represented
Structure of the Atom
• Aims:
– Learn the internal parts of the atom
– Understand Rutherford’s experiment to
characterize the atom’s structure
• Dalton’s theory explained compounds as a
collection of atoms. But what were the
atoms themselves like?
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16
Are Atoms Really Unbreakable?
The Nature of the Atom
• Many scientists pondered the nature of the atom in
the 1800s
• Physicist J.J. Thomson showed that atoms of any
kind can emit tiny negative particles. Therefore
all atoms must contain these tiny, negative particle
known as electrons
• Since J.J. Thomson knew that atoms are neither
positively or negatively charged, he concluded
that there must also be positive particles present in
the atom to balance the charge to 0 (zero)
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• J.J. Thomson investigated a beam called a cathode ray
• he determined that the ray was made of tiny negatively
charged particles we call electrons
• his measurements led him to conclude that these
electrons were smaller than a hydrogen atom
• if electrons are smaller than atoms, they must be pieces
of atoms
• if atoms have pieces, they must be breakable
• Thomson also found that atoms of different elements
all produced these same electrons
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Thomson’s Plum Pudding Model
The Electron
Thomson concluded from his studies:
1. Atom breakable!!
2. Atom has structure
3. Electrons suspended in a positively charged electric field
– must have positive charge to balance negative charge
of electrons and make the atom neutral
4. mass of atom due to electrons
5. atom mostly “empty” space
• Tiny, negatively charged particle
• Very light compared to mass of atom
– 1/1836th the mass of a H atom
• Move very rapidly within the atom
– compared size of electron to size of atom
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Figure 4.3: The
plum pudding
model
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Figure 4.4: Ernest
Rutherford (1871-1937)
A physicist, who found that
something was deflecting
the α-particles he was
studying
He set up an experiment to
find out what it was…
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Figure 4.5: Rutherford’s experiment on αparticle bombardment of metal foil
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Rutherford’s Gold Foil Expt
• How can you prove something is empty?
– The Plum Pudding model postulated that the atom was an
empty cloud of positive charge with electrons scattered
through it
• If the Plum Pudding Model was correct, the α-particles
would fly right through his gold foil (like a bullet
through a piece of paper)
– Rutherford expected the α-particles to fly through the foil
with at most a minor deflection
• But some particles experienced large deflections!!
• Therefore the Plum Pudding Model is not correct!
• α-particles have a mass of 4 amu & charge of +2 c.u.
• gold has a mass of 197 amu & is very malleable
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– The large deflections were due to positive particles hitting a
positively charged nucleus
23
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Figure 4.6: (a) The results that the metal foil
experiment would have yielded if the plum pudding
model had been correct; (b) Actual results
Rutherford’s Results
• Over 98% of the α particles went straight through
• About 2% of the α particles went through but
were deflected by large angles
• About 0.01% of the α particles bounced off the
gold foil
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Rutherford’s Nuclear Model
26
Structure of the Nucleus
• The nucleus was found to be composed of two kinds of
particles
• Some of these particles are called protons
1. The atom contains a tiny dense center called the
nucleus
– the volume is about 1/10 trillionth the volume
of the atom
2. The nucleus is essentially the entire mass of the
atom
3. The nucleus is positively charged
– the amount of positive charge of the nucleus
balances the negative charge of the electrons
4. The electrons move around in the empty space of
the atom surrounding the nucleus
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– charge = +1
– mass is about the same as a hydrogen atom
• Since protons and electrons have the same amount of
charge, for the atom to be neutral there must be equal
numbers of protons and electrons
• The other particle is called a neutron
– has no charge
– has a mass slightly more than a proton
27
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The Modern Atom
The Modern Concept of the Atom
• We know atoms are composed of three main
pieces - protons, neutrons and electrons
• Aim:
– To understand the main features of subatomic particles
Particle
Electron
Proton
Neutron
Relative Mass
1
1836
1839
Relative Charge
11+
0 (none)
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• The nucleus contains protons and neutrons
• The nucleus is only about 10-13 cm in diameter
• The electrons move outside the nucleus with an
average distance of about 10-8 cm
– therefore the radius of the atom is about 105 times
larger than the radius of the nucleus
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Figure 4.9: A nuclear
atom viewed in cross
section
Components of Atoms
• If all atoms are composed of the same components
(electrons, protons, and neutrons) …Why do
different atoms have different chemical
properties??
• The answer is the number and arrangement of the
electrons
– Electrons account for most of the “volume” of an atom
– Electrons are the part of the atom that intermingle with
other atoms, so the number and arrangement of
electrons affect chemical behavior
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Bohr’s Model
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The Orbits or Shells (Bohr)
• We’ll Talk about this more in Chapter 10…
• Planetary Model
– Based upon the orbits of our solar system.
• Also talk more about this in Chapter 10
• So there are these orbits around the nucleus of the atom
where the electrons are.
• The first orbit can only hold 2 electrons.
• All other orbits can hold 8 electrons.
– Octet Rule
• Not a 100% correct model, but good enough
to explain some concepts.
• Atoms will arrange themselves in order to obtain 8 electrons.
• Except: hydrogen and helium
• Valence Orbit: the outer most orbit
– This is the orbit that is used to create ion and is used in bonding.
– The electrons in this orbit are called valence shell electrons.
– So it is kind of important…
• Bohr’s model can only be used for the first 3 periods in the
periodic table.
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34
Isotopes
Isotopes
• All atoms of an element have the same number of protons
• The number of protons in an atom of a given element is
the same as the atomic number
• Aims:
• Learn the following terms
–
–
–
–
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– found on the Periodic Table
Isotope
Atomic number
Mass number
Understand the symbols used to describe atoms
• Atoms of an element with different numbers of neutrons
are called isotopes
• All isotopes of an element are chemically identical
– undergo the exact same chemical reactions
• Isotopes of an element have different masses
• Isotopes are identified by their mass numbers
– mass number = protons + neutrons
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Figure 4.10: Two isotopes of sodium
Symbols and Calculations
Mass Number = # protons + # Neutrons
Atomic number = # protons
• You should be able to do the following:
• Interpret a symbol for an isotope (Ex 4.2)
• Write a symbol for an isotope (Ex 4.3)
• Calculate a mass number (Ex 4.4)
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Elements
Figure 4.11: The periodic table
• Arranged in a pattern called the Periodic Table
• Position on the table allows us to predict properties of
the element
• Metals
– about 75% of all the elements
– lustrous, malleable, ductile, conduct heat and
electricity
• Nonmetals
– dull, brittle, insulators
• Metalloids
– also know as semi-metals
– some properties of both metals & nonmetals
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Figure 4.11: The periodic table
The Modern Periodic Table
Group
• Elements with similar chemical and
physical properties are in the same column
• Columns are called Groups or Families
• Rows are called Periods
• Each period shows the pattern of properties
repeated in the next period
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Period
41
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Figure 4.12: The elements classified as metals
and nonmetals
The Modern Periodic Table
• Main Group = Representative Elements
– “A” columns
• Transition Elements
– all metals
• Bottom rows = Inner Transition Elements =
Rare Earth Elements
– metals
– really belong in Period 6 & 7
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Metalloids
43
• Noble Metals
• Ag, Au, Pt
• all solids at room
temperature
• least reactive metals
• found in nature
uncombined with
other atoms
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Figure 4.14: Gaseous nitrogen and oxygen contain
diatomic (two-atom) molecules
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Figure 4.13:
Argon gas
consists of a
collection of
separate argon
atoms
Important Groups
• Group 8 = Noble Gases
• He, Ne, Ar, Kr, Xe, Rn
• all colorless gases at room
temperature
• very non-reactive, practically
inert
• found in nature as a
collection of separate atoms
uncombined with other
atoms
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Figure 4.15: The decomposition of two water molecules (H2O) to
form two hydrogen molecules (H2) and an oxygen molecule (O2)
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Figure 4.16: (a) Sodium chloride (table salt) can be
decomposed to the elements sodium metal and
chlorine gas (b)
Important Groups - Halogens
• Group 7A = Halogens
• very reactive
nonmetals
• react with metals to
form ionic compounds
• HX all acids
• Fluorine = F2
– pale yellow gas
• Chlorine = Cl2
– pale green gas
• Bromine = Br2
– brown liquid that has lots of
brown vapor over it
– Only other liquid element at
room conditions is the metal
Hg
• Iodine = I2
– lustrous, purple solid
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Figure 4.17: In solid metals, the spherical atoms are
packed closely together
Allotropes
• Many solid nonmetallic elements can exist
in different forms with different physical
properties, these are called allotropes
• the different physical properties arise from
the different arrangements of the atoms in
the solid
• Allotropes of Carbon include
– diamond
– graphite
– buckminsterfullerene
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Figure 4.18a: The three solid elemental (allotropes)
forms of carbon
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Figure 4.18b: The three
solid elemental
(allotropes) forms of
carbon
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Figure 4.18c: The three solid elemental (allotropes)
forms of carbon
Electrical Nature of Matter
• Most common pure substances are very poor conductors
of electricity
– with the exception of metals and graphite
– Water is a very poor electrical conductor
• Some substances dissolve in water to form a solution that
conducts well - these are called electrolytes
• When dissolved in water, electrolyte compounds break
up into component ions
– ions are atoms or groups of atoms that have an electrical charge
(c) Buckminsterfullerene
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Figure 4.20: (a) Pure water does not conduct a
current; (b) Water containing a dissolved salt
conducts electricity
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Ions
• ions that have a positive charge are called cations
– form when an atom loses electrons
• ions that have a negative charge are called anions
– form when an atom gains electrons
• ions with opposite charges attract
– therefore cations and anions attract each other
• moving ions conduct electricity
• compound must have no total charge, therefore we
must balance the numbers of cations and anions in a
compound to get 0 total charge
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Figure 4.19: The ions formed by selected members
of Groups 1, 2, 3, 6, and 7
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Atomic Structures of Ions
• Metals form cations
• For each positive charge the ion has 1 less electron than the
neutral atom
– Na = 11 e-, Na+ = 10 e– Ca = 20 e-, Ca+2 = 18 e-
• Cations are named the same as the metal
sodium
Na → Na+ + 1esodium ion
calcium
Ca → Ca+2 + 2e- calcium ion
• The charge on a cation can be determined from the Group
number on the Periodic Table for Groups IA, IIA, IIIA
– Group 1A ⇒ +1, Group 2A ⇒ +2, (Al, Ga, In) ⇒ +3
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Figure 4.21b: Solid sodium chloride highly
magnified.
Figure 4.21a: The
arrangement of
sodium ions (Na+)
and chloride ions
(Cl-) in the ionic
compound sodium
chloride.
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Atomic Structures of Ions
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Figure 4.7: Schematic of a cathode ray tube
• Nonmetals form anions
• For each negative charge the ion has 1 more electron
than the neutral atom
– F = 9 e-, F- = 10 e– P = 15 e-, P3- = 18 e-
• Anions are named by changing the ending of the name
to -ide
fluorine
F + 1e- → F- fluoride ion
oxygen
O + 2e- → O2oxide ion
• The charge on an anion can be determined from the
Group number on the Periodic Table
– Group 7A ⇒ -1, Group 6A ⇒ -2
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Figure 4.8: A CRT being used to display
computer graphics
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