Transcript The modern period table

The modern periodic table
• The modern periodic table arranges elements
by atomic number.
– Hydrogen (atomic number 1), because of its
many unique properties, is placed at the
top of the table in a cell by itself.
– Helium (atomic number 2) is placed at the
top of the right-hand column above the
other noble gases.
– Hydrogen and helium form the first series
or period row).
•The Element name and symbol
are given for each element on P.T.
• The number at the
top of each cell
represents the
atomic number of the
element.
– The atomic number is
the number of
protons.
The number at the bottom
represents the average atomic
mass of all the types of atoms of
that element (isotopes).
– Atomic mass (atomic weight) - The
average mass of atoms of an
element, calculated using the
relative abundance of isotopes in a
naturally-occurring element.
• mass number = # of protons + # of
neutrons
Periods- Each of the rows is considered to be a
different period
 In the periodic table, elements have something in
common if they are in the same row.
 All of the elements in a period have the same
number of atomic orbitals.
 Every element in the top row (the first period) has
one orbital for its electrons.
 All of the elements in the second row (the second
period) have two orbitals for their electrons. It goes
down the periodic table like that.
 At this time, the maximum number of electron
orbitals or electron shells for any element is seven.
Groups
• The vertical columns are
known as groups or
families. There are 18
groups going from left to
right.
– The elements are grouped
together by their chemical
properties.
– The chemical properties
are based on their electron
configuration.
– Every element in a group
will have the same # of
Valence electrons.
More about groups
• The first column (group) is called the alkali metals.
• The second column (group) is called the alkali earth
metals.
• Groups 3-11 are the transition elements. Their
common characteristics include:
– They are all metals
– Most have more than one oxidation state
(possible valence electrons)
– Most form colored ions
• The 7th column is Halogens.
• The noble gases have 8 valence electrons (except
helium (2 valence electrons for a full shell) and tend
not to react with other elements.
Electrons
• The elements with 1 (alkali metals) or 2 valance
electrons (alkali earth metals) are metals.
– They are unstable and will form cations (positive ions) by
losing those electrons to reach the stable state of the noble
gases.
• Elements with 7 valance electrons (halogens) are
nonmetals
– will form anions (negative ions) by gaining electrons to
become stable.
Electrons are the part of the atom
that reacts with other atoms
• Electron configurations
explain the recurrence of
physical and chemical
properties.
• If the outer shell has 4 or less
electrons, the element will
give up electrons in a
chemical reaction.
• If the outer shell has more
than 4 electrons, the element
usually accepts electrons
during a reaction.
General principles
• An atom has the same number of protons as it
does electrons to be neutral.
• The electrons exists outside the nucleus in
orbitals (levels of energy).
• The outer electrons, those involved in chemical
reactions, are known as the valence electrons.
• Reactivity increases from top to bottom in a
group of metals but decreases from top to
bottom in the nonmetals.
Metals, non metals, metalloids
Metals, non metals, metalloids
• A metal is an element that readily loses
electrons to form positive ions (cations) and
has metallic bonds between metal atoms
– metals tend to be lustrous, ductile,
malleable, and good conductors of
electricity
Non-metals are most of the
elements in groups 14-16 of
the periodic table.
• Non-metals are not able to conduct electricity or heat very
well.
• Unlike metals, non-metallic elements are very brittle, and
cannot be rolled into wires or pounded into sheets.
• The non-metals exist in two of the three states of matter at
room temperature: gases (such as oxygen) and solids (such as
carbon).
• The non-metals have no metallic luster, and do not reflect
light. They have oxidation numbers of ±4, -3, and -2.
Metalloids are the elements found along the
stair-step line that distinguishes metals from nonmetals
• Metalloids have properties of both
metals and non-metals.
– Some of the metalloids, such as silicon
and germanium, are semi-conductors.
This means that they can carry an
electrical charge under special
conditions.
• They can be shiny or dull and their
shape is easily changed.
• Metalloids typically conduct heat and
electricity better than nonmetals but
not as well as metals.