Download Objective - davis.k12.ut.us

Objective 1. Students will name who first created the periodic table and when it was created.
2. Students will describe the properties Mendeleev used to create the periodic table.
3. Students will define atomic mass, atomic mass unit, and atomic number.
4. Students will define valence electrons, proton number, and neutron number.
5. Students will name and describe the groups/families of the periodic table.
6. Students will use the periodic table to identify properties of elements.
IV. The Periodic Table
a. Dmitri Mendeleev created the first periodic table in 1869. He discovered that the elements
shared certain patterns and trends. He observed that the elements shared some chemical
and physical properties. Dmitri believed the properties that the elements shared were
important. Therefore, he wrote down all the properties he knew about elements on cards.
He used the properties of melting point, density, color, atomic mass and bonding power to
begin his template. The atomic mass of an element is the average mass of one atom of the
element. The bonding power of an element refers to the number of chemical bonds an
element can form. This was determined by how each element formed bonds with oxygen.
Mendeleev noticed that patterns appeared when the elements were arranged in order of
increasing atomic mass. As he put his cards in order he realized that everything was not
perfect and that there appeared to be blanks. He predicted that the blanks were for
undiscovered elements and even described their properties. Although today’s periodic table
is arranged by atomic number, it was due to Dmitri Mendeleev that we have a periodic table
at all.
b. The periodic table displays characteristics of the elements, such as; atomic mass, atomic
number, element symbol, element name, proton number and electron number. Since
protons, neutrons and electrons are so small, the atomic mass is measured using atomic
mass units. Atomic mass units measure the particles in an atom. The atomic number, a
unique property to each element, is the number of protons in the nucleus of the atom.
c. Each atom has protons, neutrons, and electrons. Proton number is equal to the atomic
number. The neutron number is the amount of neutrons in the nucleus in an atom. To
find the neutron number of an element, take the atomic number and subtract it from the
atomic mass. Atomic mass – atomic number = neutron number. Since some atoms have
different numbers of neutrons for the same element the final number must be rounded up
or rounded down. While all atoms have electrons, the valence electrons are the most
important. Valence electrons are electrons found in the outermost shell/level and are
involved in chemical bonding. Valence electrons are transferred or shared during chemical
bonding.
d. A period is a row across the periodic table. Elements in the same column of the periodic
table are called a group or family. Each family in the periodic table has its own
characteristic properties based on the number of valence electrons.
1. Group 1 is known as the alkali metal family. Alkali metals are very reactive and each
has only 1 valence electron.
2. Group 17 is known as the halogens. The halogens are very reactive nonmetals and
each has 7 valence electrons.
3. Group 18 is known as the noble gases. The noble gases are considered inert which
means they are not chemically reactive. Except for helium (which has two), the
noble gases have 8 valence electrons.