Exploring the Periodic Table
Inside the squares
The word periodic means a regular, repeated pattern. In the modern periodic table the properties of the
elements repeat in each period --or row --of the table. Since Mendeleev’s time new discoveries have required a
few changes in the periodic table. The most important came in the 1900’s when scientists learned about atomic
numbers. Also, new elements were added as they were discovered.
The periodic table has grown to include over 100 elements. Once you understand how the periodic table is
organized you can predict an element’s properties from its position in the table.
Each element on the table is placed within its own box. Included within that box are several pieces of
information about that particular element.
1. Its symbol.
2. Its atomic number.
3. Its atomic mass
The boxes are arranged on the table by atomic number, which
represents the number of protons within the nucleus of that
particular type of atom. For instance, the atomic number of
hydrogen is one. That means that every atom of hydrogen has
one proton in its nucleus. Helium, which is number two has
two protons, lithium which is number three has three protons
and so on.
The atomic symbol for each element is also unique to that element. Elements get their names in a variety of
ways. If a scientist discovers an element, they are awarded the privilege of naming that element. Elements
have been named after mythical characters, places, properties of the element, or the name of a scientist. Each
element’s name follows a specific rule for the way its symbol is written. Symbols can be 1, 2, or 3 letters long.
If the symbol is a single letter, it is always capitalized. If there is a second or 3rd letter they are always lower
case letters. For example: Boron (5) is B, Lithium (3) is Li, and Ununbium (112) is Uub. If an element is
shown with 3 letters it means that scientists have not agreed on a permanent name for that element.
The atomic mass represents the average mass of all the different types of
that particular type of atom. You see, not all the atoms of a particular
element have the same number of particles in them. Sometimes they have
different numbers of neutrons in their nucleus. These other types of
atoms are still the same kind of atom, because of the number of protons in
their nucleus; they just have a few more neutrons, so they have a little
different mass. For example, there are several different kinds of carbon
atom. They all have the exact same number of protons, 6, but they have
either 6, 7, or 8 neutrons in their nucleus. They are known as carbon 12,
carbon 13, or carbon 14. The atomic mass equals the average of the mass
of all the particles that are in their nuclei. These types of elements have a
special name, isotopes. Despite the differences in the number of particles, and the masses, all the isotopes of an
element react the same way chemically.
Organization of the Periodic Table
An element’s properties can be predicted from its location in the periodic table. As you look at elements across
a row, or down a column, the properties change in a predictable way. This predictability is one reason the table
is so useful to scientists.
The main body of the table is arranged
into 18 vertical columns and 7 horizontal
rows. The elements in a column are
called a group. Groups are also known
as families. Notice that each group is
numbered from 1 to 18 starting from the
left. The group is given a family name
based on the first element in the column.
Group 14, for example is the carbon
family; Group 15 is the nitrogen family.
The elements in each group, or family, have similar characteristics. The elements in Group1are all metals that
react violently with water. The metals in Group 11 all react with water slowly or not at all. Group 17 elements
react violently with elements from Group 1, while Group 18 elements rarely react at all.
Each horizontal row across the table is called a period. A period contains a series of different types of elements
from different families. Unlike the elements in a family, the elements in a period have very different properties.
In fact, as you move across a period from left to right those properties not only change, they change according
to a pattern.
In the 4th period for example the elements change from very reactive metals such as potassium and calcium to
very unreactive metals such as nickel and copper, to metalloids and nonmetals such as arsenic and bromine.
The last element in a period is always a very unreactive gas.
As you can see, there are 7 periods of elements. Each horizontal row of elements has
the same number of energy levels that contain its electrons. In row 1 they have 1
energy level, in row 2 they have 2 levels, in row 3 they have 3 and so on. The chlorine
atom to the right is in the 3rd row because its atoms are spread among its 3 energy
levels, or orbitals.
The periodic table works so well because it is based on the structure of atoms,
especially the valence electrons. Valence electrons are those that are in the outermost
shell or orbital of an atom. In the chlorine atom there are 7 valence electrons.
You know that from one element to the next, the atomic number increases by one. That means that an element
has one more valence electron than the element to its left. Since the first element of a period has one valence
electron the number of valence electrons in a row of 8 increases from 1 to 8. As a result, the properties across a
period change in a regular way.
By contrast, the elements in a family all have the same number of valence electrons. The elements of Group 1
all have 1 valence electron; Group 2 has 2 and so on. Because the valence electrons within a family are the
same, the elements in that group have similar properties.
Name ______________________________________________ Per. _____ Date ______________________
EXPLORING THE PERIODIC TABLE
1.
What is an isotope?
2. How many isotopes are there for the element carbon? _________________
3. Describe what all isotopes of an element have in common.
4. What is a valence electron?
5. How many valence electrons are there in the element chlorine? ______________
6. How many valence electrons are there in the element hydrogen? ______________
7. How many valence electrons are in the element calcium? _______________
8. How are elements arranged on the periodic table?
9. What does the atomic number of an element represent?
10. Why is the periodic table a useful tool for a scientist??
11. Describe how a group and a period are different.
12. How many groups and periods are there in the periodic table?
a. groups _____________________________
b. periods _____________________________
13. What do the elements that are last in each period have in common?
14. Describe how the elements change as you move from left to right across a period.
15. Describe the rules for writing atomic symbols.
a.
b.
c.
d.
16. What does the atomic mass represent?
17. What is another name for an orbital?
18. Use the term valence electrons to describe what all members of a family have in common.
19. Each element on the table has its own box. What information is usually given in the box that represents
an element?
a.
b.
c.
20. Describe what the elements in group 1 have in common.
21. What do the elements in group 11 have in common?
22. What do the elements in group 18 have in common?