Atomic Mass Number

The Periodic Table is an organizational tool used by scientists to place elements into different categories.

Elements are the building blocks of matter, each having different chemical and physical properties.

Today, we will be looking at what atoms are composed of, and how we describe those atoms.

The atomic number is the number of protons in the element.

The atomic mass is the number of protons and neutrons in one atom of that element.

All elements are electrically neutral, meaning they have ZERO NET CHARGE. This means that the number of protons (positive charges) are equal to the number of neutrons (negative charges)

The element Helium (He) has an Atomic Number of 2. This means that all Helium atoms have exactly two protons.

Since the atom is electrically neutral, that means the atom also has exactly two electrons.

How do we determine how many neutrons there are in an atom?

Atomic Mass = Protons + Neutrons

We round the atomic mass to the nearest whole number, 4

Since we already determined that Helium has two protons, that means: 4=2+Neutrons

There must be 2 Neutrons in one atom of Helium

What is the Atomic Number?

What is the Atomic Mass?

How many protons are in a Lithium Atom?

How many electrons are in a Lithium Atom?

What is the rounded Atomic Mass?

How many neutrons are in a Lithium Atom?

What is the Atomic Number? 3

What is the Atomic Mass? 6.941

How many protons are in a Lithium Atom? 3

How many electrons are in a Lithium Atom? 3

What is the rounded Atomic Mass? 7

How many neutrons are in a Lithium Atom? 7-3=4