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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, H2O
1. How does the Oxygen (O) on Earth compare the O in humans?2. What element is the 2nd 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?
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.
The total number of (+) + (N) is called the atomic mass.
Remember, most of the mass of an atom is found where?
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.)