Atoms This goes in the Chemistry section of your binder.

An atom is the smallest particle of an element that has the chemical properties of that element.

A single atom is not visible to the eye. Therefore most substances are made of millions or billions of atoms.

The element Hydrogen (H) #1 on the periodic table, accounts for 90% of the total mass of the universe.

Only 1% of the atoms on Earth are Hydrogen (H) and most of those are combined with oxygen to form water, H 2 O

Look at the circle graph on page D 10. Answer the ?s in your notes.

1. How does the Oxygen (O) on Earth compare the O in humans? 2. What element is the 2 nd highest in humans? On Earth? 3. Why do you think there is a higher percentage of (H) in the human body than on Earth? 4. Humans are mostly composed of what 4 elements? 5. Earth is mostly composed of what 4 elements?

Atoms are made of smaller particles (sub-atomic); electrons protons neutrons

Match the charge with the particle: (+) electron (N) neutral proton (-) neutron

A proton is a positively charged particle. A neutron is an uncharged particle. Where are both particles located in an atom?

Neutrons and protons have approximately the same mass. (+) and (N) are grouped together in the center of an atom, called the nucleus.

Electrons are negatively charged particles that move around the nucleus. (-) are much smaller than protons, they are 1/2000 of a proton or neutron. (-) move around the nucleus of an atom so quickly their exact positions cannot be determined. Therefore (-) are considered a “cloud” around the nucleus.

Electrons are attracted to the positively charged protons. Atoms that have = numbers of protons and electrons are said to be neutral.

Go to page D 20

Atoms are identified by their number of protons. That # is called the atomic #.

For example: C=Carbon Atomic # 6 Means 6 protons

Find Chlorine on page D 20 What is the atomic # for Cl? How many (+)?

The total number of (+) + (N) is called the atomic mass. Remember, most of the mass of an atom is found where?

The number of (+) is = to the # of (-). The number of (+) is not always = to the # of (N).

Look at Carbon again on page D 20. The atomic mass is the number below the element symbol. What is the atomic mass of C?

When working with atomic mass, you round off the number. (We will tell you what to round to according to each activity.)

What is the atomic # of O? What is the atomic mass of O? How many protons does O have?

To find the # of neutrons, you subtract atomic # from atomic mass.

How many neutrons in O?

Find the atomic # Find the atomic mass # of (+) # of (N) # of (-) in the following elements 1. Ne 2. N 3. Li 4. K 5. Au 6. Hg 7. Sn 8. S 9. Cl 10. Ca