Spencer L. Seager
Michael R. Slabaugh
www.cengage.com/chemistry/seager
Chapter 3:
Electronic Structure
and the Periodic Law
Jennifer P. Harris
Chapter 3 Objectives
1. Locate elements in the periodic table on the basis of group and period designations. (Section 3.1;
Exercise 3.1-3.4)
2. Determine the number of electrons in designated subshells, or shells. (only a small part of Section 3.2)
3. Determine the number of valence shell electrons and the electronic structure for atoms, and relate this
information to the location of elements in the periodic table. (Section 3.3; Exercises 3.18-3.21)
4. Determine the following for elements: the electronic configuration of atoms, the number of unpaired
electrons in atoms, and the identity of atoms based on provided electronic configurations. (Section
3.4, part of page 76 only; Exercises - none)
5. Determine the shell and subshell locations of the distinguishing electrons in elements, and based on
their location in the periodic table, classify elements into the categories given in Figures 3.10
(representative element, transition element, inner‐transition, noble gas) and 3.12. (metal,
metalloid, nonmetal). (Section 3.5; Exercises 3.36 – 3.39)
6. Recognize property trends of elements within the periodic table, and use the trends to predict
selected properties of the elements. (Section 3.6; Exercises 3.40 - 3.45)
PERIODIC LAW
• This is a statement about the behavior of the elements when they
are arranged in a specific order.
• In its present form, the statement is:
Elements with similar chemical properties
occur at regular (periodic) intervals when
the elements are arranged in order of
increasing atomic numbers.
PERIODIC TABLE
• A periodic table is a tabular arrangement of the elements based on
the periodic law.
• In a modern periodic table, elements with similar chemical
properties are found in vertical columns called groups or families.
18 groups/families
7
periods
PERIODIC TABLE GROUP OR FAMILY
• A group or family is a vertical column of elements that
have similar chemical properties.
• Traditional designation uses a Roman numeral and a
letter (either A or B) at the top of the column.
• Modern (but not universally-used) designation uses only
a number from 1 to 18.
PERIODIC TABLE PERIOD
• A period is a horizontal row of elements arranged according to
increasing atomic numbers.
• Periods are numbered from top to bottom of the periodic table.
MODERN PERIODIC TABLE
• Elements 58-71 and 90-103 are not placed in their correct periods,
but are located below the main table.
GROUP & PERIOD IDENTIFICATION
• ELEMENTS AND THE PERIODIC TABLE
• Each element belongs to a group and period of the periodic
table.
• EXAMPLES OF GROUP AND PERIOD LOCATION FOR
ELEMENTS
• Calcium, Ca, element 20: group IIA (2), period 4
• Silver, Ag, element 47: group IB (11), period 5
• Sulfur, S, element 16: group VIA (16), period 3
BOHR THEORY
• Bohr proposed that the
electron in a hydrogen
atom moved in any one of
a series of circular orbits
around the nucleus.
• The electron could change
orbits only by absorbing or
releasing energy.
• This model was replaced
by a revised model of
atomic structure in 1926.
ATOMIC ORBITALS
• The last descriptor of the location and energy of an electron moving
around a nucleus is the atomic orbital in which the electron is
located.
• Each subshell consists of one or more atomic orbitals, which are
specific volumes of space around the nucleus in which electrons of
the same energy move.
RELATIONSHIP SUMMARY
CHEMICAL PROPERTIES
• The valence shell of an atom is the shell that contains electrons
with the highest n value.
• Atoms with the same number of electrons in the valence shell
have similar chemical properties.
Members of Group IIA(2)
magnesium
calcium
strontium
ELECTRON SHELL OCCUPANCY
•
What do magnesium and
calcium have in common?
2 electrons in valence shell
•
What predictions can be
made about the number of
electrons in strontium’s
valence shell?
Sr has similar chemical
properties to Mg and Ca,
so it likely has 2 electrons
in its valence shell.
•
What other element on this
chart has similar properties
to Mg, Ca, and Sr?
Beryllium
FILLING ORDER
• When it is remembered that each orbital of a subshell can hold a
maximum of two electrons, and that Hund's rule and the Pauli
exclusion principle are followed, the following filling order for the
first 10 electrons results:
H
He
Li
Be
B
C
N
Ne
ELEMENT CLASSIFICATION
• The periodic table can be used to classify elements in numerous
ways:
• by Distinguishing Electron.
• by status as Representative, Transition, or Inner-transition
Element.
• by status as Metal, Nonmetal, or Metalloid.
DISTINGUISHING ELECTRON
• The distinguishing electron is the last electron listed in the
electronic configuration of the element.
ELEMENT CLASSIFICATION
• Representative elements have an s or p distinguishing electron.
• Transition elements have an d distinguishing electron.
• Inner-transition elements have an f distinguishing electron.
METALS, METALLOIDS, & NONMETALS
PROPERTY TRENDS
• Properties of elements change in a systematic way within the
periodic table.
The Elements of Group VA(15)
arsenic antimony
nitrogen phosphorous
bismuth
• METALLIC AND NONMETALLIC PROPERTIES
• Most metals have the following properties: high thermal
conductivity, high electrical conductivity, ductility, malleability
and metallic luster.
• Most nonmetals have properties opposite those of metals and
generally occur as brittle, powdery solids or as gases.
METALLOIDS
• Metalloids are elements that form a diagonal separation zone between
metals and nonmetals in the periodic table. Metalloids have properties
between those of metals and nonmetals, and often exhibit some
characteristic properties of each type (semiconductors).
METALLIC PROPERTY TRENDS
• Elements in the same period of the periodic table become less
metallic and more nonmetallic from left to right across the period.
• Elements in the same group of the periodic table become more
metallic and less nonmetallic from top to bottom down the group.
ATOMIC SIZE TRENDS
• For representative elements in the same period, atomic size
decreases from left to right in the period.
• For representative elements in the same group, atomic size
increases from top to bottom down the group.
REPRESENTATIVE ELEMENT ATOMS
FIRST IONIZATION ENERGY TRENDS
• The first ionization energy is the energy required to remove one
electron from a neutral gaseous atom of an element.
• For representative elements in the same period, the general
trend is an increase from left to right across the period.
• For representative elements in the same group, the general trend
is a decrease from top to bottom down the group.
CHEMICAL REACTIVITY TRENDS
• Based on the photo, what is the trend for chemical reactivity with
ethyl alcohol in group 1A(1)?
lithium
sodium
potassium
• As the atomic number increases in group 1A(1), the chemical
reaction becomes more vigorous. The rate of gas formation and
the size of the bubbles indicate that reactivity increases from top to
bottom in this group.