Transcript AP Chemistry Chapter 7

Unit 6
Periodicity
History of the PT
• Dimitri Mendeleev (1836-1907)
– Russian chemistry professor
•
In writing a textbook of general chemistry, he compiled vast
quantities of data on the elements. He realized as he examined the
data that the chemical properties of the elements repeated themselves
when the elements were placed in order of atomic mass. Based on
his realization, Mendeleev arranged the elements in order of
increasing atomic mass, and in such a way that elements with similar
chemical properties fell in the same column. He published a
primitive version of today’s periodic table in 1869. It contained the
62 elements that had been discovered at that time.
Mendeleev’s
Periodic Table
Dmitri Mendeleev
Genius of Mendeleev’s Work
• Left spaces for elements
not yet discovered.
• He predicted that some
still-unknown elements
must exist to fit in the
holes.
Inductive vs. Deductive Reasoning
• Inductive reasoning is the use of detailed facts
to form a general principle or model (going
from specific to general). How did Mendeleev
use inductive reasoning?
• Deductive reasoning is the use of a general
principle or model to draw specific inferences
(going from general to specific). How did
Mendeleev use deductive reasoning?
Mendeleev’s Periodic Table
• Contained 1 inconsistency.
– He placed the elements in order of atomic mass
• Forced to break pattern a couple times to preserve the
patterns he had discovered.
Henry Moseley
• Shortly after Rutherford’s discovery of the
proton in 1911, Henry Moseley (1887-1915)
did experiments with x-rays to determine the
number of protons in various elements.
When Moseley arranged the elements of
Mendeleev’s periodic table according to
increasing atomic number and not atomic
mass, the inconsistencies associated with
Mendeleev's table were eliminated. The
modern periodic table is based on Moseley's
arrangement by atomic number. At age 28,
Moseley was killed in action during World
War I. As a direct result, Britain adopted the
policy of exempting scientists from fighting
in wars.
Periodic Law
• From Mendeleev’s and Moseley’s work comes the
Periodic Law: The properties of the elements are
periodic functions of their atomic numbers.
• What this means is that if we arrange the elements in
order of increasing atomic number, we will periodically
encounter elements that have similar chemical and
physical properties. These elements appear in the same
vertical column (group).
Modern Russian Table
Stowe Periodic Table
A Spiral Periodic
Table
“Mayan”
Periodic
Table
Period
The Periodic Table
Group or Family
Group or
family
Period
Irregular conformations of Cr and Cu
Chromium steals a 4s electron to half
fill its 3d sublevel
Copper steals a 4s electron to FILL
its 3d sublevel
Nonmetals
Metals
Hydrogen
• The hydrogen square sits atop Family 1, but it is
not a member of that family. Hydrogen is in a class
of its own.
• It’s a gas at room temperature.
• It has one proton and one electron in its one and
only energy level.
• Hydrogen only needs 2 electrons to fill up its
valence shell.
The Properties of a Group:
the Alkali Metals
Group 1 (s-block)
Easily lose valence electron
(Reducing agents)
React violently with water
ns1 configuration
silvery apperance
soft (cut w/ a knife)
Most Reactive!
Not found as free elements.
React with halogens to form
salts
Alkali Metals
• The alkali family is found in
the first column of the
periodic table.
• Atoms of the alkali metals
have a single electron in
their outermost level, in
other words, 1 valence
electron.
• They are shiny, have the
consistency of clay, and are
easily cut with a knife.
Alkali Metals
• They are the most
reactive metals.
• They react violently with
water.
• Alkali metals are never
found as free elements in
nature. They are always
bonded with another
element.
Alkaline Earth Metals
• They are never found uncombined in nature.
• They have two valence electrons.
• Alkaline earth metals include magnesium and calcium,
among others.
Transition Metals
• Transition Elements
include those elements in
the B families.
• These are the metals you
are probably most familiar:
copper, tin, zinc, iron,
nickel, gold, and silver.
• They are good conductors
of heat and electricity.
Transition Metals
• The compounds of
transition metals are
usually brightly colored
and are often used to
color paints.
• Transition elements
have 1 or 2 valence
electrons, which they
lose when they form
bonds with other
atoms. Some transition
elements can lose
electrons in their nextto-outermost level.
Boron Family
• The Boron Family is named
after the first element in the
family.
• Atoms in this family have 3
valence electrons.
• This family includes a
metalloid (boron), and the rest
are metals.
• This family includes the most
abundant metal in the earth’s
crust (aluminum).
Carbon Family
• Atoms of this family have 4
valence electrons.
• This family includes a nonmetal (carbon), metalloids,
and metals.
• The element carbon is called
the “basis of life.” There is
an entire branch of chemistry
devoted to carbon
compounds called organic
chemistry.
Nitrogen Family
• The nitrogen family is named
after the element that makes up
78% of our atmosphere.
• This family includes non-metals,
metalloids, and metals.
• Atoms in the nitrogen family have
5 valence electrons. They tend to
share electrons when they bond.
• Other elements in this family are
phosphorus, arsenic, antimony,
and bismuth.
Oxygen Family
• Atoms of this family have 6
valence electrons.
• Most elements in this family
share electrons when forming
compounds.
• Oxygen is the most abundant
element in the earth’s crust. It
is extremely active and
combines with almost all
elements.
Halogen Family
• The elements in this family
are fluorine, chlorine,
bromine, iodine, and astatine.
• Halogens have 7 valence
electrons, which explains why
they are the most active nonmetals. They are never found
free in nature.
• Halogen atoms only need to
gain 1 electron to fill their
outermost energy level.
• They react with alkali metals
to form salts.
Noble Gases
• Noble Gases are colorless gases
that are extremely un-reactive.
• One important property of the
noble gases is their inactivity.
They are inactive because their
outermost energy level is full.
• Because they do not readily
combine with other elements to
form compounds, the noble
gases are called inert.
• The family of noble gases
includes helium, neon, argon,
krypton, xenon, and radon.
• All the noble gases are found in
small amounts in the earth's
atmosphere.
Rare Earth Elements
• The thirty rare earth
elements are composed of
the lanthanide and actinide
series.
• One element of the
lanthanide series and most
of the elements in the
actinide series are called
trans-uranium, which
means synthetic or manmade.
Properties of Metals
 Metals are good
conductors of heat and
electricity
 Metals are malleable
 Metals are ductile
 Metals have high tensile
strength
 Metals have luster
Examples of Metals
Potassium, K
reacts with
water and
must be
stored in
kerosene
Copper, Cu, is a relatively soft
metal, and a very good electrical
conductor.
Zinc, Zn, is
more stable
than potassium
Mercury, Hg, is the only
metal that exists as a
liquid at room temperature
Properties of Nonmetals
Carbon, the graphite in “pencil lead” is a great
example of a nonmetallic element.
 Nonmetals are poor conductors of heat and
electricity
 Nonmetals tend to be brittle
 Many nonmetals are gases at room
temperature
Examples of Nonmetals
Sulfur, S, was
once known as
“brimstone”
Graphite is not the only
pure form of carbon, C.
Diamond is also carbon;
the color comes from
impurities caught within
the crystal structure
Microspheres
of phosphorus,
P, a reactive
nonmetal
Properties of Metalloids
Metalloids straddle the
border between metals
and nonmetals on the
periodic table.
 They have properties of both metals and
nonmetals.
Metalloids are more brittle than metals, less
brittle than most nonmetallic solids
 Metalloids are semiconductors of electricity
 Some metalloids possess metallic luster
Silicon, Si – A Metalloid
 Silicon has metallic luster
 Silicon is brittle like a nonmetal
 Silicon is a semiconductor of
electricity
Other metalloids include:





Boron, B
Germanium, Ge
Arsenic, As
Antimony, Sb
Tellurium, Te
Electron Shielding
Shielding electrons:
electrons in the
energy levels
between the nucleus
and the valence
electrons. They are
called "shielding"
electrons because
they "shield" the
valence electrons
from the force of
attraction exerted by
the positive charge in
the nucleus.
Atomic
Radius
Definition: Half of the distance
between nuclei in covalently bonded
diatomic molecule
Radius decreases across a period
 Increased effective nuclear charge due to
decreased shielding
Radius increases down a group
 Each row on the periodic table adds a
“shell” or energy level to the atom
Table of
Atomic
Radii
Period Trend:
Atomic Radius
Ionic Radii
Cations
 Positively charged ions formed when
an atom of a metal loses one or
more electrons
 Smaller than the corresponding
atom
 Negatively charged ions formed
when nonmetallic atoms gain one
Anions
or more electrons
 Larger than the corresponding
atom
Ionic Radii
Cations
Positively charged ions formed when
an atom of a metal loses one or
more electrons
Smaller than the corresponding
atom
 Negatively charged ions formed
when nonmetallic atoms gain one
Anions
or more electrons
 Larger than the corresponding
atom
Graphic courtesy Wikimedia Commons user Popnose
Table
of Ion
Sizes
Ionization
Energy
Definition: the energy required to remove an
electron from an atom
 Tends to increase across a period
 As radius decreases across a period,
the electron you are removing is closer
to the nucleus and harder to remove
 Tends to decrease down a group
 Outer electrons are farther from the
nucleus and easier to remove
Ionization of Magnesium
Mg + 738 kJ  Mg+ + eMg+ + 1451 kJ  Mg2+ + eMg2+ + 7733 kJ  Mg3+ + e-
Periodic Trend:
Ionization
Energy
Trends in Electron Affinity
• electron affinity (electron-liking): the energy change that
accompanies the addition of an electron to an atom.
– *If energy is released in the process of adding an electron, EA is negative. A negative EA
means that the atom wants to gain the electron. The larger the negative number, the more it
wants to gain the electron. It is a favorable process. Nonmetal atoms have large negative EAs.
– *If energy is absorbed in the process of adding an electron, EA is positive. A positive EA
means that the atom does not want to gain the electron. The larger the positive number, the
more it does not want to gain the electron. It is an unfavorable process. Metal atoms have small
negative or positive EAs.
• group trend: EA decreases (less favorable/value is more +) going down a
group.
– It is harder to add the electron when it is farther from the nucleus. The nucleus can’t “grab onto
it” as well
• periodic trend: EA increases (more favorable/value is more - )
going across a period.
– This is due to nuclear charge - across a period, nuclear charge increases, so it becomes easier to
add an electron.
– Note that this periodic trend supports the idea that nonmetals have a much greater tendency to
gain electrons than metals do.
Electron Affinity
• Electron Affinity
– Increases UP and to the RIGHT
1
2
3
4
5
6
7
Electronegativity
Definition: A measure of the ability of an
atom in a chemical compound to attract
electrons
o Electronegativity tends to increase
across a period
o As radius decreases, electrons get
closer to the bonding atom’s nucleus
o Electronegativity tends to decrease
down a group or remain the same
o As radius increases, electrons are
farther from the bonding atom’s
nucleus
Electronegativity
A measure of the ability of an atom in a chemical
compound to attract electrons
Electronegativities tend to increase across
a period
Electronegativities tend to decrease down a
group or remain the same
Periodic Table of
Electronegativities
Periodic Trend:
Electronegativity
Summary of
Periodic Trends
Metallic Character
Group trend
• Metallic character increases as you move down a group.
This is because the distance from the nucleus is larger
(shielding effect). It is easier to lose an electron if the
electron is far from the nucleus.
Periodic Trend
• Metallic character decreases as you move left to right
across a period. This is mainly due to increasing
nuclear charge.
Summation of Periodic Trends