- [Instructor] We know that everything in the universe
is composed of atoms,
but not all atoms are the same.
There are many different types of atoms called elements,
each with a unique set of physical and chemical properties.
Many elements are probably familiar to you.
Oxygen and carbon, for example, are elements,
and so is gold.
Others may be less familiar
such as bismuth, xenon, and osmium.
A particular element is identified
by the number of protons in its atoms.
And the number of protons in the nucleus of an atom
is its atomic number, represented by the symbol Z.
For example, helium has an atomic number of two.
That means that every helium atom has two protons.
And here's another example, iron,
its atomic number is 26,
so every iron atom has 26 protons.
An element's atomic number can also tell us
the number of electrons in a neutral atom of an element.
Remember, equal and opposite charges cancel each other out
so to be neutral,
an atom must have an equal number of protons,
which have a charge of 1+,
and electrons, which have a charge of 1-.
This means that our helium atom must have two electrons
and our iron atom must have 26 electrons.
All of the known elements
are organized according to their atomic numbers
in the periodic table.
The periodic table lists the elements
in order of increasing atomic number
as you go from left to right and from top to bottom.
The elements are further organized into columns
based on their properties.
Elements in the same column
tend to have similar physical and chemical properties.
Every element is represented by a chemical symbol,
a unique one or two letter abbreviation
that appears below the element's atomic number
on the periodic table.
Many chemical symbols
are based on the English name for an element.
For example, the symbol for hydrogen is H,
and the symbol for aluminum is Al.
But some chemical symbols
are based on the Latin name for the element.
For example, the symbol for lead is Pb,
which actually comes from its Latin name plumbum.
Notice that whenever the chemical symbol
for an element has two letters,
the second letter is written in lowercase.
All of this information is contained
inside of each element's box on the periodic table.
For example, here's the box for the element nitrogen.
At the top of the box
is nitrogen's atomic number, which is seven.
Remember that this is equal
to the number of protons in each atom of nitrogen
as well as the number of electrons.
Below that is nitrogen's chemical symbol, N,
followed by its name.
Often, you'll also see another number
listed at the bottom of an elements box,
which has to do with atomic mass.
We'll cover details about this and another video.
What's neat about having
all of this information in one place
is that if we know one detail about an element,
either it's atomic number, chemical symbol, or a name,
we can often use the periodic table
to find out the other details.
Let's take a look at a few examples.
Say we have the element phosphorus,
what is its atomic number and chemical symbol?
Looking through the periodic table,
we can find phosphorus
and see that its atomic number is 15
and its chemical symbol is P.
Let's do another example.
Say we know the chemical symbol Hg,
what is this element's name
and how many protons does it have?
Here is the symbol Hg on the periodic table.
Its name is mercury,
and its atomic number is 80
so it has 80 protons.
Let's reveal.
The universe is made up
of different types of atoms called elements,
and these elements are organized by atomic number
in the periodic table.
So, the next time that you stare up at the starry sky,
you know that everything out there is made up of elements.