Transcript The Periodic Table

The 19th Century……The Good
Life?
Typical chemist’s responsibilities during the
middle of the 19th century:
• Learn the properties of more than 60 elements
• Learn the properties of all known compounds
• “Best Guess” atomic mass of the elements
Different chemists using different atomic
masses for the same element. Not
good!
Chapter 6: The Periodic Table
• Scientist Stanislao Cannizzaro discovered a method for
accurately determining the atomic masses of the
elements.
Russian chemist, Dmitri Mendeleev
sought to arrange the elements using
both the atomic masses and properties of
each.
• when the elements were arranged in
order of increasing atomic mass, certain
similarities occurred periodically.
• his procedure produced the first periodic table of the
elements.
• his periodic table even predicted existence of
undiscovered elements and left blanks to account for
these elements.
Mendeleev’s Periodic Table
•Mendeleev’s Periodic Table
• Mendeleev arranged
elements with similar
properties in the
same row.
• Henry Moseley later recognized that the
atomic number, not atomic mass, is the
basis for the organization of the periodic
table.
• periodic law: the physical and chemical
properties of the elements are periodic
functions of their atomic numbers.
The Modern Periodic Table
• the elements are arranged in order of their atomic
numbers so that elements with similar properties fall in
the same column, or group.
• the elements are also arranged into periods, or
horizontal rows of elements.
AlkalineEarth
metals
Transition
metals
Halogens
Li
Na
K
Alkali
metals
Inner Transition Metals
Noble
Gases
Blocks (Magic) of the Periodic Table
Periodic Properties
1. Atomic Radius: defined as one-half the distance
between the nuclei of two identical atoms chemically
bonded together.
Trends:
Atomic
Radius
• Atomic radius decreases
from left to right across a
period.
Caused by the increasing
positive charge of the
nucleus at similar energy
levels!
• Atomic radius increases
down a group.
2. Ionization Energy: the energy required to
remove an electron from a neutral atom
(producing an ion).
Trend:
• IE increases from left to
right across a period.
 Due to increasing
nuclear charge.
 Noble gases do not lose
electrons easily (low
reactivity).
• IE generally decreases down the groups.
 Electrons are in higher energy levels (further
from the nucleus), thus easily removed.
3. Electron Affinity
• the energy change (released) that occurs when an
electron is acquired by a neutral atom.
EA
• think of EA as the “desire” or “liking” of electrons.
Trends:
• EA increases left to right
across a period.
• EA decreases from top to
bottom in a group.
4. Ionic Radius
• when an atom gains/loses electrons it becomes an ion.
Cation: positive ion (losing electrons)
Anion: negative ion (gaining electrons)
5. Electronegativity: a measure of the ability of an atom
in a chemical compound to attract electrons.
•
Fluorine is the most electronegative element.
Trend:
• Electronegativity increases from left to right within
a period.
• Electronegativity decreases from top to bottom
within a group.
Practice Time!