ABCs of Atoms and Elements
Is all matter the same?
You already know the answer must be NO. There are many different kinds of matter.
Different kinds of matter are made up of atoms of different kinds of elements. Elements are substances that cannot be
further broken down into simpler substances. Hydrogen is hydrogen. Gold is gold.
You are probably familiar with many elements because most of them can be found in nature. There are 118 named
elements, at least 90 of them are naturally-occurring. The rest have been synthesized (made) by scientists. All of these
elements have a name (like hydrogen) and a symbol (like H).
Why so many?
Think of what the world would be like if there WEREN’T that many! The more elements there are, the more possible
combinations there are in the end, which means more matter. How is one element different from another? The most
basic answer is that each element is made up of only one kind of atom. A sample of gold is made up of only gold atoms.
The Indivisible Atom
Now that we mentioned atoms, it’s time to figure out what atoms are. To do that, we need only to look as far as the
nearest pile of paper clips.
Try this:
1. Divide your pile of paper clips into two equal piles.
2. Divide each of the smaller piles into two equal piles.
3. Keep dividing the piles equally until you are down to a pile containing only one paper clip. Can that one paper
clip still hold papers together? YES!
4. Bend the paper clip in half and then make it straight again. Repeat this action until the paper clip breaks into
two parts. Can half of the paper clip still hold papers together? NO!
When you get to the point where the paper clip no longer holds paper together, you can no longer call it a paper clip. If
you do the same thing with any element, you will reach a point where you can to an indivisible part that has the same
properties of the element, like the single paper clip. This indivisible part is called an atom.
But HOW are the atoms of different elements, well…different?
Ah, yes…an excellent question. In order to describe how atoms are different from each other, you must first know the
parts of the atom.
Atoms are made up of subatomic particles. The three main subatomic particles are the proton, neutron, and electron.
Protons and neutrons are located in the center area of the atom called a nucleus, and have almost all the mass of the
atom.
Electrons are located outside the nucleus. They are much tinier than protons or neutrons, and move very fast. So fast,
in fact, that we can usually only describe their location as a general area, instead of trying to pinpoint an exact spot. If
you took a snap shot of the area around a nucleus every second for, let’s say, 5 minutes, you would get a picture that
looks a bit like the following illustration.
The large dot in the middle is the nucleus. The small dots around the nucleus are the places where a single electron has
shown up over the past five minutes. These past locations define the general area where an electron is likely to be
found. It is called an electron cloud, but its proper name is an orbital.
Protons have a positive (+) charge, electrons have a negative (-) charge, and neutrons have no charge. Keep in mind
that the number of protons does not change under normal circumstances, but the number of electrons can and does.
With this information, we can look again at our question from the beginning of this chapter.
How are the atoms of one element different from the atoms of another element?
The atoms of each element have a different number of protons. Said another way, the protons in an atom’s nucleus give
it its unique identity as an element. All atoms of hydrogen (H) have one proton. All atoms of gold (Au) have 79 protons.
The number of protons contained in the nucleus of each element has another name: the atomic number.
Lots of elements on “The Table”
With about 118 elements to choose from, how do we keep track of them all? You could say we put them “all on the
table”… but in this case we don’t mean where you have dinner. We mean the Periodic Table of Elements. How are
elements arranged on the table? It’s all in the numbers.
Each rectangle on the table represents an element and contains several very important pieces of information:
Element Symbol: To avoid having to write down each chemical name over and over, the Periodic Table introduces a
“nick name”, a kind of abbreviation, for each element. Every element has a one-letter, or two-letter abbreviation. For
example, carbon is abbreviated as “C”. Sometimes the latters are different from what you would predict because they
are abbreviations of the Latin name of the element, not the English name. This is the case with gold (Au). The symbol
Au comes from the Latin word for gold, “aurum.”
Atomic Number: This is the number of protons in the nucleus of an atom of that element. It is also the number of
electrons in an uncharged (balanced) atom of the element. The atomic number is located about the element symbol.
Atomic Mass: This is the average total mass of the protons, neutrons, and electrons, of an atom of a specific element.
The atomic mass is located below the element symbol.
You might find it odd that the Periodic Table does not specifically list the number of neutrons contained in each
element’s atomic nucleus. Well, it IS there…only you have to do one small calculation to find it. Subtract the atomic
number (the number of protons) from the atomic mass (average mass of protons, neutrons, and electrons), and round
your answer to the nearest whole number. CONGRATULATIONS, you have much found the number of neutrons!
The Periodic Table also tells us what kind of matter each element is by putting them together into these three general
categories: metals, nonmetals, and metalloids. Each of these categories is found in a specific area of the Periodic Table.
Each column of elements, called groups or families, contains elements with similar physical properties.
Grouping the Elements
The Periodic Table is divided into Groups (sometimes called families). These are the vertical columns of the table. Each
Group has its own number. Group 1 is on the left of the table and Group 18 is on the right. Elements in the same Group
have similar chemical properties, and react similarly to other elements in the same group.
Metals make up the majority of the elements on the Periodic Table, more than 75%! They are located on the left side of
the Table, and in the center. Elements in Group 1 are called Alkali Metals. Hydrogen is the only exception – it is a gas at
room temperature, and is considered a nonmetal. The alkali metals are the most chemically reactive metals on the
Periodic Table. Group 2 metals are called Alkaline Earth Metals. The block of elements in the center of the Table
(Groups 3 – 12) are called Transition Metals. Group 13 also contains metals. Here are a few properties of metals:
 They have a metallic shine, or luster
 They are usually solid at room temperature
 They are malleable, meaning they can be hammered, pounded, or pressed into different shapes without
breaking
 They are ductile, meaning they can be drawn (pulled) into thin sheets or wires without breaking
 They are good conductors of heat and electricity
Nonmetals are on the right side of the Periodic Table, in Groups 14 – 18. There are only about 18 elements that fall into
this category. Nonmetals are usually gases, or dull, brittle solids at room temperature. Some examples of nonmetals
are hydrogen (H), helium (He), carbon (C), nitrogen (N), oxygen (O), fluorine (F), and neon (Ne). Here are a few
important properties of nonmetals:
 They rarely have metallic luster/shine
 They are usually gases at room temperature
 Nonmetallic solids are neither malleable nor ductile
 They are poor conductors of heat and electricity
The halogens are a group of elements that are all non-metals. They are found in Group 17. The halogens react easily
with many other elements. In particular, halogens chemically react with alkali metals to form salts like NaCl (sodium
chloride). Group 18 also contains non-metals, called noble gases. They do not usually react with any other elements,
another way of saying that they don’t usually react with other elements is to say they are “inert”, which is a chemical
property.
The elements diagonally between the metals and the nonmetals are called metalloids. There are 7 elements that fall
into this category. They are boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te), and
polonium (Po). Metalloids have properties of both metals and nonmetals. One important property is that most
metalloids are semiconductors. That means that, at certain temperatures they conduct electricity very well; at other
temperatures, they do not. Metalloids are frequently used in computer chips.
These are general categories that allow us to group elements by their physical properties. The Periodic Table may also
be used to discover important information about the chemical properties of the elements. It tells us how the elements
“like” to combine with other elements. This combining of atoms is called bonding. The process of reorganizing atoms
into different bonding clusters (called molecules) is what happens in a chemical reaction. The number of protons and
neutrons in a chemical reaction does not change, but the number of electrons does. We will look at chemical reactions
later.
1. Which of the following is the heaviest?
a. Electron
b. Proton
c. Neutron
d. Nucleus
2. Neutral (no charge) lithium has three protons. During a chemical reaction, one electron is removed/lost. How
many protons does lithium have now? BE CAREFUL WHEN ANALYZING YOUR ANSWER
a. 3
b. 4
c. 1
d. cannot be determined
3.
a.
b.
c.
d.
Which of the following is a positive ion?
Lithium (Li), with 3 protons and 2 electrons
Neon (Ne), with 10 protons and 13 electrons
Oxygen (O), with 8 protons and 10 electrons
Fluorine (F), with 9 protons and 10 electrons
4.
a.
b.
c.
d.
Orbitals contain ___
Thousands of fast-moving electrons
A few fast-moving protons
A few fast-moving electrons
Many nuclei
5.
a.
b.
c.
d.
The nucleus of an atom is ____.
Always positively charged
Always negatively charged
Always neutrally charged
Sometimes an ion charge