Transcript Slide 1

Spencer L. Seager
Michael R. Slabaugh
www.cengage.com/chemistry/seager
Chapter 3:
Electronic Structure
and the Periodic Law
Jennifer P. Harris
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.
QUANTUM MECHANICAL MODEL
• According to the quantum mechanical model of electron behavior,
the precise paths of electrons moving around the nucleus cannot be
determined accurately.
• Instead of circular orbits, the location and energy of electrons
moving around the nucleus is specified using the three terms shell,
subshell, and atomic orbital.
SHELL
• The location of electrons in a
shell is indicated by assigning a
number n to the shell and all
electrons located in the shell.
• The value of n can be 1, 2, 3, 4,
etc.
• The higher the n value, the higher
is the energy of the shell and the
contained electrons.
SUBSHELL
• Each shell is made up of one
or more subshells that are
designated by a letter from
the group s, p, d, or f.
• The number of the shell to
which a subshell belongs is
combined with the letter of
the subshell to clearly
identify subshells.
• For example, a p subshell
located in the fourth shell
(n = 4) would be designated
as a 4p subshell.
SUBSHELL (continued)
• The number of subshells located in a shell is the same as the
number of the shell. Thus, shell number 3 (n = 3) contains three
subshells, designated 3s, 3p, and 3d.
• Electrons located in a subshell are often identified by using the
same designation as the subshell they occupy. Thus, electrons in
a 3d subshell are called 3d electrons.
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.
ATOMIC ORBITALS (continued)
•Atomic orbitals are designated by
the same number and letter used to
designate the subshell to which they
belong. Thus, an s orbital located in
a 2s subshell would be called a 2s
orbital.
•All s subshells consist of a single s
orbital.
•All p subshells consist of three p
orbitals.
•All d subshells consist of five d
orbitals.
•All f subshells consist of seven f
orbitals.
ATOMIC ORBITALS (continued)
• According to the quantum mechanical model, all types of atomic
orbitals can contain a maximum of two electrons.
• Thus, a single d orbital can contain a maximum of 2 electrons, and
a d subshell that contains five d orbitals can contain a maximum
of 10 electrons.
ATOMIC ORBITAL SHAPES
• Atomic orbitals of different types have different shapes.
ENERGY OF ELECTRONS
• Electron energy increases with increasing n value. Thus, an
electron in the third shell (n = 3) has more energy than an electron
in the first shell (n = 1).
• For equal n values but different orbitals, the energy of electrons in
orbitals increases in the order s, p, d and f. Thus, a 4p electron has
more energy than a 4s electron.
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
ELECTRONIC CONFIGURATIONS
• Electronic configurations give details of the arrangements of
electrons in atoms.
• The notation used to represent electronic configurations is
1s22s22p6…, where the occupied subshells are indicated by their
identifying number and letter such as 2s and the number of
electrons in the subshell is indicated by the superscript on the
letter. Thus, in the example above, the 2s2 notation indicates that
the 2s subshell contains two electrons.
SUBSHELL FILLING ORDER
• Electrons will fill subshells in the order of increasing energy of the
subshells. Thus, a 1s subshell will fill before a 2s subshell.
• The order of subshell filling must obey Hund's rule and the Pauli
exclusion principle.
HUND'S RULE
• According to Hund's rule, electrons will not join
other electrons in an orbital of a subshell if an
empty orbital of the same energy is available in
the subshell.
• Thus, the second electron entering a p subshell
will go into an empty p orbital of the subshell
rather than into the orbital that already contains
an electron.
PAULI EXCLUSION PRINCIPLE
• Electrons behave as if they spin on an axis.
• According to the Pauli exclusion principle, only electrons spinning
in opposite directions (indicated by ↑ and ↓) can occupy the same
orbital within a subshell.
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
FILLING ORDER (continued)
• The filling order for any number
of electrons is obtained by
following the arrows in
the diagram.
• Shells are represented
by large rectangles.
• Subshells are represented
by small colored rectangles.
• Orbitals within the subshells
are represented by circles.
FILLING ORDER MEMORY AID
• The diagram provides a compact way to remember the subshell
filling order.
• The correct order is given by
following the arrows from top to
bottom of the diagram, going
from the arrow tail to the head,
and then from the next tail to
the head, etc.
• The maximum number of
electrons each subshell can
hold must also be remembered:
s subshells can hold 2,
p subshells can hold 6,
d subshells can hold 10,
and f subshells can hold 14.
FILLING ORDER & PERIODIC TABLE
• Notice the order of subshell filling matches the order of the
subshell blocks on the periodic table, if the fill occurs in the order
of increasing atomic numbers.
ELECTRON CONFIGURATION EX.
• The following electronic configurations result from the correct use
of any of the diagrams given earlier.
• Magnesium, Mg, 12 electrons: 1s22s22p63s2
• Silicon, Si, 14 electrons: 1s22s22p63s23p2
• Iron, Fe, 26 electrons: 1s22s22p63s23p64s23d6
• Gallium, Ga, 31 electrons: 1s22s22p63s23p64s23d104p1
NOBLE GAS CONFIGURATIONS
• With the exception of helium, all noble gases (group VIIIA) have
electronic configurations that end with completely filled s and p
subshells of the highest occupied shell. These configurations are
called noble gas configurations.
• Noble gas configurations can be used to write electronic
configurations in an abbreviated form in which the noble gas
symbol enclosed in brackets is used to represent all electrons found
in the noble gas configuration.
NOBLE GAS CONFIGURATION EX.
• Magnesium: [Ne]3s2
(The symbol [Ne] represents the electronic configuration of neon,
1s22s22p6.)
• Iron: [Ar]4s23d6
(The symbol [Ar] represents the electronic configuration of argon,
1s22s22p63s23p6.)
• Gallium: [Ar]4s23d104p1
(The symbol [Ar] represents the electronic configuration of argon,
1s22s22p63s23p6.)
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.
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.