The Periodic Table and Periodic law
In the 1700’s Lavoisier compiled a list of all known elements of the time.
See table 1
The 1800’s brought large amounts of information and scientists
needed a way to organize knowledge about elements
John Newlands proposed an arrangement were elements are ordered
by increasing atomic mass.
Newlands noticed when elements are arranged by increasing atomic
mass, their properties repeated every eight element.
Meyer and Mendeleev both demonstrated a connection between
atomic mass and elemental properties.
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 the
Contributions to the classification of elements. See Table 6.2
The modern periodic table contains boxes which contain the elements name,
symbol, atomic number, and atomic mass. See fig
Columns of elements are called groups.
Rows of elements are called periods
Elements in groups 1, 2, and 13 -18 possess a wide variety of
chemical and physical properties and are called the representative
Elements in groups 3 – 12 are known as the transition metals.
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
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.
The transition elements are divided into transition metals and inner
The two sets of inner transition metals are called the lanthanide
series and actinide series and are located at the bottom of the periodic
Non-metals are elements that are generally gases, or brittle, dull
looking solids, and poor conductors of heat and electricity.
Group 17 is composed of highly reactive elements called halogens.
Group 18 gases are extremely unreactive and commonly called noble
Metalloids have physical and chemical properties of both metals and
non-metals such as silicon and germanium.
Main idea – Elements are arranged into different blocks in the periodic
table according to their electron configurations.
Organizing the elements by electron configuration
Recall electrons in the highest principle energy level are called
All group 1 elements have one valence electron. See table 6.3
The energy level of an element’s valence electrons indicates the
period on the periodic table in which it is found.
The number of valence electrons for elements in group 13 – 18 is
ten less than their group number
The s-, p-, d-, and f- block Elements
The shape of the periodic table becomes clearer if it is divided into
blocks representing the atom’s energy sublevel being filled with
S-block elements consist of group 1 and 2, and the element helium.
Group 1 elements have a partially filled s orbital with one electron.
Group 2 elements have a completely filled s orbital with two electrons
After the s orbital is filled, valence electrons occupy the p-orbital
Groups 13 – 18 contain elements with completely or partially filled p
orbitals. See table 6.4
The d-block contains the transition metals and is the largest block
There are exceptions, but d-block elements usually have filled
outermost s orbital, and filled or partially filled d-orbital.
The five d orbitals can hold 10 electrons, so the d-block spans ten
groups on the periodic table.
The f-block contains the inner transition metals.
f-block elements have filled or partially filled outermost s orbitals and
filled or partially filled 4f and 5f orbitals.
The 7f orbitals hold 14 electrons, and the inner transition metals span
Main Idea Trends among elements in the periodic table include their size
and ability to lose or attract electrons.
Atomic size is a periodic trend influenced by electron configuration.
For metals, atomic radius is half the distance between adjacent nuclei
in a crystal of the element.
For elements that occur as molecules, the atomic radius is half the
distance between nuclei of identical atoms.
There is a general decrease in atomic radius from left to right, caused
by increasing positive charge in the nucleus.
Valence electrons are not shielded from the increasing nuclear charge
because no additional electrons come between the nucleus and
Atomic radius generally increases as you move down a group.
The outermost orbital size increases down a group, making the atom
An ion is an atom or bonded group of atoms with a positive or
When atoms lose electrons and form positively charged ions, they
always become smaller for two reasons:
The lose of a valence electron can leave an empty outer orbital
resulting in a small radius
Electrostatic repulsion decrease allowing the electrons to be pulled
closed to the radius.
When atoms gain electrons, they can become larger, because the
addition of an electron increases electrostatic repulsion.
The ionic radii of positive ions generally decrease from left to right,
beginning with group 15 or 16.
Both positive and negative ions increase in size moving down a group.
Ionization energy is defined as the energy required to remove an
electron from a gaseous atom.
The energy required to remove the first electron is called the first
Removing the second electron requires more energy, and is called the
second ionization energy.
Each successive ionization requires more energy, but it is not a steady
The ionization at which the large increase in energy occurs is related
to the number of valence electrons.
First ionization energy increases from left to right across a period
First ionization energy decreases down a group because the atomic
size increases and less energy is required to remove an electron farther
from the nucleus.
The octet rule states that atoms tend to gain, lose or share electrons in
order to acquire a full set of eight valance electrons.
The octet rule is useful for predicting what type of ions an element is
likely to form.
The electronegativity of an element indicates its relative ability to
attract electrons in a chemical bond.
Electronegativity decreases down a group and increase from left to
right across a period.