From Atoms to Water

In order to understand how any biological system works, from your body to something as complex as a forest, you need to have a basic understanding of chemistry. Basically, biology is the study of how living organisms process matter and energy. We will cover energy in a later module, but for now, let’s talk about matter.

We first begin with the structure of the basic building block of matter – the atom.

Structure of an Atom

Ask Yourself?

  • Where are each of the subatomic particles located in an atom?
  • What are the charges on each of these particles?
  • Why would the number of protons and electrons in an atom be equal?

Quiz:

When you are ready, take the interactive quiz below:

Take the Quiz: Atomic Structure

Understanding the Periodic Table

Now that we have defined the basic structure of an atom, it is important to recognize that atoms vary in the number of protons, electrons and neutrons that they contain. Of these three subatomic particles, it is the number of protons that identify to which element that the atom belongs. For example, all carbon (C) atoms have 6 protons, and all nitrogen atoms have 7 (protons). In other words, the number of protons is constant in all atoms of an element. We will see that this not the case for both neutrons and electrons.

We can arrange the elements in a chart, called the periodic table, based on the number of protons in their nucleus. A quick summary of the periodic table is provided in the animation below.

 

Questions:

1.  Explain the differences between an atom of chlorine and an atom of sodium.

2.  Why is the periodic table based on the number of protons and not the other subatomic particles (electrons or neutrons)?

When you are ready, take the interactive quiz below:

Take the Quiz: The Periodic Table

What is an Isotope?

Recall from the previous video that the atomic mass is equal to the number of protons and neutrons in the nucleus of an atom. While the number of protons is constant between the atoms of an element, the number of neutrons can vary. Since neutrons are neutral, increasing or decreasing their number does not have a significant influence on the chemical reactivity of the atom. However, it does affect the overall mass of the atom.

Atoms with the same number of protons, but a different number of neutrons, are said to be isotopes of each other. There is a misconception that all isotopes are radioactive (or unstable), but that is not the case for every isotope. Almost all elements have a number of isotopes, only a few of which may be unstable and radioactive.

The video below explore the concept of an isotope in greater detail.

Questions:

1. Why aren’t electrons included in the atomic mass of at atom?

2. What would be the difference between oxygen with an atomic mass of 16 and oxygen with an atomic mass of 18?

When you are ready, take the interactive quiz below:

Take the Quiz: Isotopes

Overview of Chemical Bonds

Now we need to turn our attention to the processes that combine atoms to form compounds and molecules. To understand why chemical bonds are formed, we need to go back to the structure of the atom and examine what happens to the electrons in the outer energy shell of the atom. These are called the valence electrons, and the number of valence electrons basically determines the chemical reactivity of an atom.

Atoms form chemical bonds to stabilize their valence energy shell. The video below explores this process and the two types of chemical bonds that may result.

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Take the Quiz: Chemical Bonding

Hydrogen Bonds

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Take the Quiz: Polarity and Hydrogen Bonds

The Importance of Electronegativity

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Take the Quiz: Electronegativity

The Properties of Water

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Take the Quiz: Properties of Water

The pH Scale

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Take the Quiz: Acids and Bases