Reading – Elements and the Periodic Table

Essential Question: What is an element, and how are elements organized in the periodic table?

Do you remember when you first learned to write your name? It may have been a

VERY challenging exercise! Before you could manage something complicated like Aiden or

Hayley or Elizabeth, you first had to learn how to make each individual letter! Letters are

the building blocks for words, which are the building blocks for paragraphs, essays, and

novels. In English, just 26 letters can be combined into over 200,000 different words.

Elements are the building blocks of matter in the same way

that letters are the building blocks of words. Building matter

is similar to building words except instead of starting with 26

letters, we start with 118 elements. These elements can be

arranged in billions of different combinations to make all the

matter that exists!

An element is a pure substance, made of only one type of atom. An element cannot

be broken into anything simpler by any natural

means. All the atoms of a given element have the

same number of protons in their nucleus. Helium is

an element, so in a helium balloon all of the atoms

would be helium atoms, and they would all have 2

protons in their nucleus. Gold is an element, so in a

sample of gold all of the atoms would be gold atoms,

and they would all have 79 protons in their nucleus.

We always write our alphabet in the same order. The letters in our language are

organized alphabetically. The 118 elements in our universe are arranged in a chart called

the periodic table. This table is organized according to the number of protons in each

element’s nucleus. (Remember – the atomic number tells you the number of protons in an

atom’s nuclueus) Hydrogen, with only one proton, is the first element on the table. The

second element has two protons, the third element 3

protons, and so on until you reach the 118th element,

which has 118 protons! Because protons make up a

big part of the mass of the atom, the periodic table is

also organized by atomic mass, with the lightest

elements at the beginning and the heaviest at the end.

You read the periodic table from left to right and from top to bottom, so helium is our

lightest element and ununoctium is the heaviest.

Today, we see the periodic table as mainly organized based on number of protons.

But the person who first designed the periodic table didn’t even know what a proton was!

Back in 1868, a scientist named Dmitri Mendeleev arranged the elements based on atomic

mass, and based on properties. A property of matter is a

characteristic that can be used to describe it. For example, if you

were to describe helium you might say it was a gas (at room

temperature), that it is colorless, odorless, that it is very light, that

it’s not flammable and that it has a strange effect on vocal cords! All

of these things are properties of helium. If you tried to describe

gold, you would come up with a very different list of properties. You

might say that it was a solid (at room temperature), that it is yellow

in color, shiny, bendable, very dense, and soft relative to other

metals. These are all properties of gold.

Mendeleev used the known properties of the elements to group similar elements

together. He began arranging them into groups called families that all share similar

properties. For example, Helium, Neon, Argon, Krypton, and Xenon, which are all on the far

right side of the table, are members of a family called the noble gases. They are all

colorless and odorless, gases at room temperature, and they are all non-reactive, which

means that they don’t bond with other elements to form molecules. On the other side of the

table you’ll find Lithium, Sodium, Potassium, Cesium, and Rubidium. Members of this

family, the Alkali metals, are mostly soft, silvery metals that conduct electricity and are

HIGHLY reactive, meaning they easily bond with other elements to form compounds. In

fact, it is rare to find these elements by themselves in nature.