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Development of the Modern
Periodic Table
The periodic table evolved over time as
scientists discovered more useful ways
to compare and organize the elements.
¥ In the 1700s, Lavoisier compiled a list of all
the known elements of the time.
Development of the Modern
Periodic Table
¥  The 1800s brought large amounts of information and scientists
needed a way to organize knowledge about elements.
¥  John Newlands proposed an arrangement where elements were
ordered by increasing atomic mass.
¥  Newlands noticed when the elements were arranged by
increasing atomic mass, their properties repeated every eighth
element.
¥  Meyer and Mendeleev both demonstrated a connection between
atomic mass and elemental properties.
¥  Mendeleev published the first periodic table
¥  He left blank spaces for elements that had yet to be discovered
Development of the Modern
Periodic Table
¥ Moseley rearranged the table by increasing
atomic number, and resulted in a clear
periodic pattern.
¥ Periodic repetition of chemical and physical
properties of the elements when they are
arranged by increasing atomic number is
called periodic law.
Development of the Modern
Periodic Table
¥ The modern periodic table contains boxes
which contain the element's name, symbol,
atomic number, and atomic mass.
Development of the Modern
Periodic Table
¥ Columns of elements are called groups.
¥ Rows of elements are called periods.
¥ Elements in groups 1-8 possess a wide variety of
chemical and physical properties and are called the
representative elements.
¥ Elements in groups 3b-12b are known as the
transition metals.
Development of the Modern
Periodic Table
¥ Elements are classified as metals,
non-metals, and metalloids.
¥ Metals are elements that are generally shiny when
smooth and clean, solid at room temperature, and
good conductors of heat and electricity.
¥ Alkali metals are all the elements in group 1 except
hydrogen, and are very reactive.
¥ Alkaline earth metals are in group 2, and are also
highly reactive.
Development of the Modern
Periodic Table
¥ Non-metals are elements that are generally
gases or brittle, dull-looking solids, and poor
conductors of heat and electricity.
¥ Group 7 is composed of highly reactive
elements called halogens.
¥ Group 8 gases are extremely unreactive and
commonly called noble gases.
Development of the Modern
Periodic Table
¥ Metalloids have physical and chemical
properties of both metals and non-metals,
such as silicon and germanium.
Bell Ringer Question
¥ Identify the group number, period number,
and family name of the following elements:
¥ Calcium
¥ Fluorine
Classification of the Elements
Elements are organized into different
blocks in the periodic table according to
their electron configurations.
¥ All group 1 elements have one valence
electron.
Classification of the Elements
¥ The trend continues among each of the other
main group elements (group 2 elements have
2 valence electrons, and group 3 elements
have 3 valence electrons!)
Periodic Trends
Trends among elements in the periodic
table include their size and their ability
to lose or attract electrons
¥ Trend 1 - Atomic Radius is a measure of the size of
an atom
Periodic Trends
¤  Atomic Radius – The distance between the
nucleus of two like atoms. Basically, the atomic
radius is a measure of the size of an atom.
¤  Atomic Radius INCREASES down a group – new
energy levels are being added which contributes
to larger size.
Each energy level further
away from nucleus
Periodic Trends
¥ Atomic Radius DECREASES across a period.
Why????
¥ This is puzzling because protons, neutrons,
and electrons are all INCREASING across a
period, one would expect the atom would be
larger.
Periodic Trends
¥ Electrons are filling an energy level as you move to
the right across a period. Meanwhile, the nucleus is
increasing in its positive charge. The electrons
become MORE ATTRACTED to the nucleus…they
squeeze in and make a more compact atom.
¥ Class example – What is your natural behavior
toward people you are more attracted to? You MOVE
CLOSER! To those who are less attractive? You
MOVE FURTHER AWAY!
¥ Electrons are people too!!!
Periodic Trends
Periodic Trends
¥ Ionic Radius
¥ Ions that have LOST electrons to become
POSITIVE get SMALLER (nucleus is more
attractive to each electron)
¥ Ions that have GAINED electrons to become
NEGATIVE get LARGER (nucleus is less attractive
to each electron)
Periodic Trends
Periodic Trends
¥ Ionization Energy – Energy required to
remove an electron from an atom.
¥ The key to understanding ionization energy to
determine the “happiness” of the electron.
The HAPPIER the electron is in its current
location, the MORE ENERGY REQUIRED to
remove it (the higher the ionization energy).
Periodic Trends
¥ Ionization energy INCREASES across a period,
and DECREASES down a group.
¥ Elements at the left of the periodic table have
very “unhappy” electrons. It is easy to
remove one. Elements at the right of the
periodic table have electrons that are much
harder to remove, because they are “happy”
where they are.
Periodic Trends
¥ Happiness is mostly determined by whether
removing electrons helps get 8 valence
electrons!!!
¥ Remember…Alkali Metals have ONE OUTER
ELECTRON! If they lose it, the outer energy
level goes away! This leaves 8 electrons in
its new outer level!
Periodic Trends
¥ Class Example – Dictionary read with your
dad. Are you happy or unhappy? How much
energy does it take to remove you? Front
row at favorite concert with your dad. Are
you happy or unhappy? How much energy
does it take to remove you?
¥ Electrons are people too!!!
Periodic Trends
¥ Elements at the bottom of the periodic table have
electrons that are more “unhappy” than the elements
at the top of the periodic table.
¥ Elements at the bottom of the periodic table are
larger (greater atomic radius, remember the trend!)
because they have more energy levels. Those
electrons in the outer energy levels are attracted to
the nucleus. BUT…all the other electrons are in their
way! This is why they are unhappy!
¥ In chemistry we call this the SHIELDING EFFECT
Periodic Trends
¥ Class Example – Concert in the front row…
how much energy does it take to remove
you? Concert in the last row…how much
energy does it take to remove you?
¥ Electrons are people too!!!
Periodic Trends
¥ The octet rule states that atoms tend to gain,
lose or share electrons in order to acquire a
full set of eight valence electrons.
¥ The octet rule is useful for predicting what
types of ions an element is likely to form.
Periodic Trends
¥ The electronegativity of an element
indicates its relative ability to attract electrons
in a chemical bond.
¥ Electronegativity decreases down a group
and increases left to right across a period.
¥ This is the same trend as ionization energy!
¥ Atoms with electrons that are happy (hard to
lose) are more likely to invite additional
electrons (easy to gain) to join the fun
Periodic Trends