1.1 Atoms and Molecules Study Guide

CHAPTER 1

Strand 1: Matter and Energy

Chapter Outline

1.1 ATOMS AND MOLECULES (8.1.1)

1.2 PROPERTIES OF MATTER (8.1.2)

1.3 CHEMICAL REACTIONS (8.1.3)

1.4 NATURAL VS SYNTHETIC MATERIALS (8.1.4)

1.5 STATES OF MATTER (8.1.5)

1.6 CONSERVATION OF MASS (8.1.6)

1.7 DEVICES AFFECTING PHASE CHANGE (8.1.7)

 

The physical world is made of atoms and molecules. Even large objects can be viewed as a combination of small particles. Energy causes particles to move and interact physically or chemically. Those interactions create a variety of substances. As molecules undergo a chemical or physical change, the number of atoms in that system remains constant. Humans use energy to refine natural resources into synthetic materials.

 

1.1 Atoms and Molecules (8.1.1)

Explore this Phenomenon

 

1. What do these three things have in common??
2. What are some similarities and differences in the objects?
3. Are these items made of atoms or molecules?
4. What are the similarities and differences between atoms and molecules?

 

1.1 Atoms and Molecules (8.1.1)

Develop a model to describe the scale and proportion of atoms and molecules. Emphasize developing atomic models of elements and their numbers of protons, neutrons, and electrons, as well as models of simple molecules. Topics like valence electrons, bond energy, ionic complexes, ions, and isotopes will be introduced at the high school level. (PS1.A)

In this section, focus on the scale and proportion of atoms and molecules and how they can be understood at various scales by using models to study systems that are too small to observe directly.

 

Models

Model: Larger or smaller representation of an item or system to be studied

• Based on all know experimental evidence about the item
• Allow scientists to study objects that are too complex and difficult to study in reality

• Limitations:
  • Simple representations
    • Only deal with small portion
  • May not predict real behavior accurately
    • More detail put in, more accurate the model

 

What Are Atoms?

What do you, stars, and a speck of dust have in common? What do a carbon atom, a diamond, and a pencil have in common? The answer is that everything is made of atoms. Atoms are the building blocks of matter. They are what makes up all solids, liquids, and gases. Atoms are extremely small, so small that they cannot be seen by the naked eye. The radius of an atom is well under 1 nanometer, which is one-billionth of a meter. If a size that small is hard to imagine, consider this: trillions of atoms would fit inside the period at the end of this sentence.

Atom: smallest amount of an element that still retains the characteristics of that element

• atoms are the building blocks of all matter (everything is made of atoms)

 

History of the Atom

The history of our understanding of the atom is a classic example of how scientific knowledge changes over time. As one thinker builds on another thinker’s ideas and as technology advances, our understanding of how the world works becomes more and more accurate. Consider the following timeline of how people have modeled the atom.

• Around 450 B.C., the Greek philosopher Democritus introduced the idea of the atom. However, the idea was essentially forgotten for more than 2000 years.
• In 1800, John Dalton re-introduced the atom. He provided evidence for atoms and developed atomic theory. His theory was essentially correct.
• In 1897, J.J. Thomson discovered electrons. He proposed the plum pudding model of the atom. In this model, negative electrons are scattered throughout a "sea" of positive charge.
• In 1911, Ernest Rutherford discovered the nucleus. He later discovered protons as well. Rutherford thought that electrons randomly orbit the nucleus.
• Niels Bohr and Ernest Rutherford, in 1913, represented the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around it, much like planets orbit the sun in the solar system.
• A little later, building on the thoughts of Bohr, Erwin Schrodinger took the understanding of the atom in a new direction when he developed the electron cloud model. The cloud model represents a sort of history of where the electron has probably been and where it is likely to be going. Imagine that as the electron moves it leaves a trace of where it was. This collection of traces quickly begins to resemble a cloud; the electron cloud.

 

Parts of an Atom

Although atoms are very tiny, they consist of even smaller particles. There are three main types of particles that make up all atoms and they are as follows.

Atoms are made up of three types of subatomic particles, and lots of empty space

• "sub" = below/beneath/less than
• "atomic" = related to atoms
• "particle" = small portion of matter
  • subatomic particle = particle smaller than an atom

 

At the center of an atom is a nucleus made up of two types of particles called protons and neutrons.

• Protons have a positive electrical charge. The number of protons in the nucleus determines what element the atom is.
  • + charge
• Neutrons are about the same mass as protons but have no charge.
  • 0 charge
• Electrons , much smaller than protons or neutrons , have a negative electrical charge, move at nearly the speed of light, and orbit the nucleus at certain distances, depending on their energy.
  • - charge

 

Protons and neutrons have almost the same mass as each other.

• proton mass = neutron mass = 1 amu (atomic mass unit)
• An electron is only .054% of the mass of a neutron.
• The protons and neutrons make up most of the atom’s mass.

 

For a fun way to learn about atomic particles, watch this video! Mr Parr Song on Atomic Particles:

https://www.youtube.com/watch?v=Qfcmzxhga-U

 

The model in the previous figure shows how these particles are arranged in an atom. At the center of the atom is a dense area called the nucleus, where all the protons and neutrons are clustered closely together. The protons and neutrons make up almost all of the mass of an atom. The electrons have almost no mass and are constantly moving around the nucleus. Because the protons and electrons have opposite electric charges, they attract each other; negative electrons are attracted to the positive nucleus. This force of attraction keeps electrons constantly moving through the otherwise empty space around the nucleus. The number of protons in a neutral atom equals the number of electrons. This makes atoms neutral in charge because the positive and negative charges “cancel out.”

Using our knowledge of an atom, what is accurate and inaccurate about the model shown? The model is very useful in showing us the parts of the atom and their approximate locations. What it fails at is to show the correct scale of atom. For example, the nucleus of an atom is one trillionth the size of the whole atom. The rest of the atom is mostly empty space. Although this model is not completely accurate, we will frequently see and use it because making an accurate model is impractical given the size and scale of this book.

 

Go to the following video link to understand the relative size of the atom and nucleus.

http://go.uen.org/aZc

For a virtual lab on building an atom go to:

https://phet.colorado.edu/en/simulation/build-an-atom

 

What is an Element?

An element is the basic substance that cannot be simplified.  They are found in nature.

• example: gold, oxygen, nitrogen, sodium, chlorine, etc
• The known elements are listed on a periodic table

 

Elements

In ancient times, people thought the elements were fire, earth, water, and air, but we now have a much better understanding of elements. Think back again to you and a speck of dust. We know that we are both made of atoms but it is important to understand that not all atoms are the same. All atoms have the same structure, in that they are made of protons, neutrons, and electrons. What makes one atom different than another atom is that they have different numbers of protons. Atoms with different numbers of protons are called elements; each element has its own unique number of protons in its atoms. Elements are pure substances —such as nickel, hydrogen, and helium—that make up all kinds of matter. Examine the next figures. A helium atom has two protons, whereas a lithium atom has three protons. Go to the following link for a video to further learn about what elements are. http://go.uen.org/aZd

 

Molecules

There are only 118 known elements, but there are millions of different substances in our everyday lives. How do we get millions of substances from just 118 elements? When two or more atoms combine, it makes a molecule. Molecules make up the millions of things our universe is made of. One of the most common molecules we have on Earth is water . It is made of two atoms of hydrogen (H) and one atom of oxygen (O).

Other common examples of molecules are carbon dioxide which is made of two carbon atoms and one oxygen atom (CO 2 ), salt which is made of one atom of sodium and one atom of chlorine (NaCl) and sugar (C 6H12O6) which is made of six carbons, twelve hydrogens, and six oxygens.

 

Putting It Together

Using your knowledge of atoms and molecules, see how your answers have changed.

1. What do these three things have in common?
2. What are some similarities and differences in the objects?
3. Are these items made of atoms of molecules?
4. What are the similarities and differences between atoms and molecules?