X Unit 10:
The Periodic Table
History of the Periodic Table
Antoine Lavoisier (1743 – 1794)
– Published Elements of Chemistry in 1789
• Included a list of “simple substances”
(which we now know to be elements)
• Formed the basis for the modern list of
elements
– Only classified substances as
metals or nonmetals
History of the Periodic Table
Johann Döbereiner (1780 – 1849)
– Classified elements into “triads”
• Groups of three elements with related
properties and weights
• Began in 1817 when he realized Sr was
halfway between the weights of Ca and Ba
and they all possessed similar traits
– Döbereiner’s triads:
• Cl, Br, I
• Ca, Sr, Ba
 S, Se, Te
 Li, Na, K
History of the Periodic Table
John Newlands (1837 – 1898)
– Law of Octaves (1863)
• Stated that elements repeated their chemical
properties every eighth element
• Similar to the idea of octaves in music
History of the Periodic Table
Dmitri Mendeleev (1834 – 1907)
– Russian chemist (“The father of the periodic table”)
– Arranged elements based on accepted atomic
masses and properties that he observed
– Listed elements with similar
characteristics in the same
family/group
• Left blank spots for predicted
elements (Ted-Ed Video)
Dmitri Mendeleev (1834 – 1907)
Dmitri Mendeleev (1834 – 1907)
Property
Mendeleev’s
Observed Properties
Prediction for “ekaof Germanium
silicon” in 1871
(discovered in 1886)
Atomic Weight
72
72.59
Density
(g/cm3)
Melting Point
(°C)
Color
Formula of
oxide
5.5
5.35
High
947
Dark gray
Grayish white
XO2
GeO2
History of the Periodic Table
Henry Moseley (1887 – 1915)
– English physicist
– Arranged elements based on increasing atomic
number
• Remember: atomic number = # of p+ in nucleus
– Periodic table looked similar to
Mendeleev’s design since as
atomic number increases, so
does the atomic mass
Periodic Law
• Periodic – occurring at regular intervals
– Relates to trends on the periodic table of
elements
• Modern Periodic Law
– When elements are arranged in order of
increasing atomic number, there is a
periodic repetition of their properties
• Just like Mendeleev suspected!!
Reading the Periodic Table
•Periods - “Horizontal Rows”
•Groups (or Families) - “Vertical Columns”
Reading the Periodic Table
• Valence electrons are periodic!
• Notice the similarities
– Ex.) Write the noble gas configurations for:
• F [He]2s22p5
7 valence electrons
• Cl [Ne]3s23p5
7 valence electrons
• Br [Ar]4s23d104p5
7 valence electrons
• I [Kr]5s24d105p5
7 valence electrons
– GROUPS have similar valence electron
configurations!
Groups of Elements
• Group 1 = Alkali Metals
– Located in Group 1 (except Hydrogen)
– Extremely reactive
• Want to lose 1 e- to become “noble gas-like”
• Group 2 = Alkaline Earth Metals
– Also very reactive
– Both Group 1 & 2 occur naturally as
compounds not elements
Groups of Elements
• Group 17 = Halogens
– Very active nonmetals
• Want to gain 1 e- to become like a noble gas
Groups of Elements
• Group 18 = Noble Gases
– Sometimes called “inert gases” since they
generally don’t react
• Mainly true, but not always (Kr, Xe will
react sometimes)
• Have a full valence shell (8 e-)
Mythbusters Noble Gas Demo
Groups of Elements
• Transition Metals
– Located in the center of the Periodic Table
– 10 elements wide (“d” orbitals)
– Semi-reactive, valuable, crucial to many life
processes
• Lanthanides and Actinides
– Located at the bottom of the Periodic Table
– 14 elements wide (“f” orbitals)
– Some are radioactive, though not all
– Lanthanides = Period 6 (4f)
– Actinides = Period 7 (5f)
Alkali Metals =
Alkaline Earth Metals =
Transition metals =
Metalloids =
Halogens =
Noble Gases =
Lanthanides =
Actinides =
Periodic Properties & Trends
• Electronegativity
– Ability of an atom to pull e- towards itself
– Increases going up and to the right
• Across a period  more protons in nucleus =
more positive charge to pull electrons closer
• Down a group  more electrons to hold onto =
element can’t pull e- as closely
Periodic Properties & Trends
• Atomic Radius
– Distance between the nucleus and the
furthest electron in the valence shell
– Increases going down and to the left
• Down a group  more e- = larger radius
• Across a period  elements on the right can pull
e- closer to the nucleus (more electronegative) =
smaller radius
• *Remember*
– LLLL  Lower, Left, Large, Loose
Periodic Properties & Trends
• Ionization Energy
– Energy required to remove an e- from the
ground state
– 1st I.E. = removing 1 e-, easiest
– 2nd I.E. = removing 2 e-, more difficult
– 3rd I.E. = removing 3 e-, even more difficult
• Ex.) B --> B+ + e• Ex.) B+ --> B+2 + e• Ex.) B+2 --> B+3 + e-
I.E. = 801 kJ/mol
I.E.2 = 2427 kJ/mol
I.E.3 = 3660 kJ/mol
Periodic Properties & Trends
Ionization Energy
• Increases going up and to the right
– Down a group  more e- for the nucleus to
keep track of = easier to rip an e- off
– Across a period  elements on the right
can hold electrons closer (more
electronegative) = harder to rip an e- off
Periodic Properties & Trends
• Metallic Character
– How “metal-like” an element is
• Metals lose e-
– Most Metallic: Cs, Fr
– Least: F, O
– Increases going down and to the left
Think about where the metals & nonmetals are
located on the periodic table to help you remember!
Periodic Properties & Trends
• Ionic Radius
– Radius of an atom when e- are lost or
gained different from atomic radius
– Ionic Radius of Cations
• Decreases when e- are removed
– Ionic Radius of Anions
• Increases when e- are added
Sizes of Ions
+
Li,152 pm
3e and 3p
Li + , 78 pm
2e and 3 p
• CATIONS are SMALLER than the
atoms from which they are formed.
• Size decreases due to increasing he
electron/proton attraction.
Sizes of Ions
F, 71 pm
9e and 9p
F- , 133 pm
10 e and 9 p
• ANIONS are LARGER than the atoms
from which they are formed.
• Size increases due to more electrons
in shell.
Overall Periodic Trends
Property
Group Trend
Period Trend
Atomic Radius
Increases going
down
Increases to the left
Increases going up
Increases to the
right
Increases going up
Increases to the
right
Increases going
down
Increases to the left
Ionization Energy
Electronegativity
Metallic Character
Practice:
Rank the elements from lowest to highest…
Electronegativity - C, F, Mg
Atomic Radius - Ir, Re, Bi
Metallic Character - Rb, Mn, P
Ionization Energy - B, Ga, In
Summary of Periodic Trends