Protons neutrons
atomic symbol
atomic number
chemical element
Atoms are tiny pieces of matter that make up all the substances around you. All atoms
contain one or more positively charged particles called
, which are
found in an atom's nucleus. In many atoms, the nucleus also contains
which have no electrical charge. There are also small, negatively
charged particles called electrons found outside the nucleus. Together, these three types
of particles make up the structure of atoms.
The number of protons in an atom is the atom's
When two atoms
have the same atomic number, they are are classified as the same
All known chemical elements are listed in the periodic table, where they are arranged by
atomic number. The periodic table contains information about each element, often
including a short version of the element's full name called its

What happens to energy in an open system?

The earth's moon is unusually large. two popular theories of the moon's origin include the "sister world" hypothesis, which states that the moon formed from the same materials as the earth, near enough to the earth that they fell into orbit around each other. a second theory is the "capture" hypothesis, in which the moon formed elsewhere in the solar system, and the earth's gravity pulled it into its orbit. studies of what the moon is made of indicate that some of its materials had to come from the earth or from the same area of the solar system where the earth had formed. at the same time, the moon does not contain much of the material that makes up the earth's core, so the moon could not have formed from the same materials as the earth. how do the two facts above affect the described theories of the moon's origin? a. they show that scientists will never agree on where the moon came from. b. they show that more experiments on moon formation need to be done. c. they show that no theory accounts for the existence of the moon. d. they show that neither theory is complete and entirely correct.

Which is the layer underground where all empty spaces are filled with a combination of air and water ?