Transcript Development of the Periodic Table

CHAPTER 6
Chemical Periodicity
Development of the Periodic
Table



Scientists needed a way to organize and
refer to the growing number of known
elements
Categorize the elements according to
similarities in their physical and chemical
properties
Relationship between atomic structure and
properties of elements
Development of the Periodic
Table



Mendeleev listed the elements in vertical
columns in order of increasing atomic
mass
Regular recurrence of physical and
chemical properties
Blank spaces left where unknown elements
belonged, but able to predict their
properties
Development of the Periodic
Table


Moseley determined
atomic number of the
atoms of the
elements
Arranged the
elements by order of
atomic number
Modern Periodic Table



The horizontal rows of the periodic table are
called periods (organized by increasing atomic
number)
The vertical columns are called groups or families
(organized by chemical properties)
Periodic Law: when the elements are arranged in
order of increasing atomic number, there is a
periodic pattern in their physical and chemical
properties
Electron Configurations and
Periodicity


Electron plays the greatest part in
determining the physical and chemical
properties of an element
Elements can be classified into four
different categories based on their
electron configurations
Electron Configurations and
Periodicity
1.
The noble gases are elements in which the
outermost s and p sublevels are filled (group 0)
–
Called inert gases because they do not
partake in chemical reactions
–
Valence: outermost s and p orbitals
–
Octet: 8 electrons in valence shell
Electron Configurations and
Periodicity
The representative elements are elements
whose outermost s or p sublevels are only
partially filled (group A)
2.
–
–
–
–
Alkali metals: group 1A elements
Alkaline earth metals: groups 2A elements
Halogens: nonmetallic elements of group 7A
Group number = number of valence electrons
Electron Configurations and
Periodicity
3.
4.
The transition metals are elements
whose outermost s sublevel and the
nearby d sublevel contain electrons
(group B)
The inner transition metals are elements
whose outermost s sublevel and the
nearby f sublevel contain electrons
Electron Configurations and
Periodicity





S block: groups 1A and 2A and He
P block: groups 3A, 4A, 5A, 6A, 7A, and 0
except He
D block: transition metals
F block: inner transition metals
Period number corresponds to the
principal energy level
Periodic Trends in Atomic Size



The radius of atoms: atomic radii
Atomic size increases as you move down a
group of the periodic table and decreases
as you move form left to right across a
period
The shielding effect of these electrons
on the nucleus is constant within a period
Periodic Trends in Ionization
Energy


The energy that is required to overcome the
attraction of the nuclear charge and remove
an electron to create a positive atom is the
ionization energy
First ionization energy decreases as you move
down a group of the periodic table and
increases as you move form left to right
across a period
Periodic Trends in Ionic Size

Ionic radii is the size of an ion compared
to same neutral atom
–
–
Cations (positive ions) are smaller because of
the reduced energy level with the same
number of protons
Anions (negative ions) are larger because of a
reduced effective nuclear charge on outer
electrons
Periodic Trends in
Electronegativity


The electronegativity of an element is the
ability of an atom to attract electrons
within a bond
Electronegativity increases as you go
across a period form left to right and
decreases as you move down a group