The Periodic Table of Elements

First 18 Elements

MS Word Version

The first 18 elements show all of the basic 8 “groups” in the Periodic Table of Elements. In fact most of the matter of the known universe is made up of these 18 elements and the first element, hydrogen, makes up more than 90% of all matter.

The most important piece of information on the Periodic Table is the atomic number. The atomic number tells you how many protons can be found in each atom’s nucleus. (It also tells you the number of electrons for each atom because the number of electrons is always equal to the number of protons.) An element is really defined by the number of protons in the nuclei of its atoms. Carbon’s Atomic Number is 6 because a carbon atom has 6 protons in its nucleus. If you could remove a proton from a carbon atom, that atom would no longer be carbon – it would be an atom of Boron.

1 I

The First 18 Elements on a simplified Periodic Table of Elements

8 VIII

1

1 H

2 II

3 III

4 IV

5 V

6 VI

7 VII

2 He

2

3 Li

4 Be

5 B

6 C

7 N

8 O

9 F

10 Ne

3

11 Na

12 Mg

The ten rows of elements below are known as “transition metals” because they follow different electron rules.

13 Al

14 Si

15 P

16 S

17 Cl

18 Ar

4

K

Ca

Sc

TI

V

Cr

Mn

Fe

Co

Mi

Cu

Zi

Ga

Ge

As

Se

Br

Kr

5

Rb

Sr

Y

Zr

Nb

Mo

Tc

Ru

Rh

Pd

Ag

Cg

In

Sn

Sb

Te

I

Xe

6

Cs

Ba

La

Hf

Ta

W

Re

Os

Ir

Pt

Au

Hg

Tl

Pb

Bi

Po

At

Rn

Any table is organized into vertical columns and horizontal rows.

The rows of the Periodic Table are known as “Periods”. The row number tells you how many electron shells (energy levels) are possible for each atom in that row. Elements in the first period have only one shell. Elements in the second period have 2 shells - and so on. Carbon (element 6) is in the second period because carbon atoms have two electron shells.

The columns of the Periodic Table are known as “Groups”. The group number tells you how many electrons are in that atom’s outermost shell. The number of electrons in an atom’s outermost shell determines how it can bond with other atoms to form molecules. Carbon is in Group 4 because carbon has 4 electrons in its outermost shell. In the last group (Group 8) the elements all have full outer shells.

The elements in the lower center of this table are “transition metals” because they have their own electron rules. Complete “Periodic Tables” also include two other sets of special elements that are usually shown below the main table.

	1 I							8 VIII
1	1 H Hydrogen 1.00794	2 II	3 III	4 IV	5 V	6 VI	7 VII	2 He Helium 4.002602
2	3 Li Lithium 6.941	4 Be Beryllium 9.012182	5 B Boron 10.811	6 C Carbon 12.0107	7 N Nitrogen 14.00674	8 O Oxygen 15.9994	9 F Fluorine 18.9984032	10 Ne Neon 20.1797
3	11 Na Sodium 22.989770	12 Mg Magnesium 24.3050	13 Al Aluminum 26.981538	14 Si Silicon 28.0855	15 P Phosphorus 30.973761	16 S Sulfur 32.066	17 Cl Chlorine 35.4527	18 Ar Argon 39.948

A Periodic Table of Elements will often include another number, the “Atomic Mass” of an element. The Atomic Mass is a multiple of the mass of a proton which physicists arbitrarily[1] set at 1. This helps tell you how many neutrons each atom usually contains because subtracting the number of protons (the Atomic Number) gives you the average mass of the neutrons. The Atomic Mass is usually not a whole number for two reasons. First, a neutron actually has slightly more mass than a proton (a neutron has a mass slightly higher than 1). Another reason is that the atoms of any element are identical except that sometimes they may have a different number of neutrons. Remember, the number of protons in an atom DEFINES what element it is. The number of neutrons can vary. This has to be “averaged in.”

Different atoms of the same element are called isotopes. Carbon always has 6 protons – or it wouldn’t be carbon. The Atomic Mass of carbon is slightly over 12. This means that most carbon atoms have 6 neutrons. Carbon12 is the most common isotope of carbon. It has 6 neutrons. Carbon 13 is an isotope of carbon with 7 neutrons (6 protons + 7 neutrons = an Atomic Mass of 13). Carbon 14 is a radioactive form of carbon that has eight neurons. Most of the first 18 elements usually have an equal number of protons and neutrons, but you can see that Argon could be an exception.

More complex Periodic Tables have more detailed information on the electron configurations and sub-orbits. They may also include information like boiling points and melting points. Sometimes they are color coded to show various “families” of elements.

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[1] The word “arbitrarily” means “for no justifiable reason”. It is not literally true that scientists were being “arbitrary” when they set the mass of a proton at 1 because doing that makes the math as easy as possible.