(Chapter 18.1)

 

 

 

·       Atom—smallest piece of matter that still has the properties of the element.  Atoms are made up of subatomic particles called:

1.   Protons—they have an electrical charge of +1

2.   Neutrons—they do not have a charge

3.   Electrons—they have an electrical charge of -1

·       Protons and neutrons are in the nucleus of the atom; electrons surround the nucleus

·       Protons and Neutrons are made up of smaller particles called quarks

·       Scientists use scaled-up models to represent atoms

· Early models of the atom were solid spheres (no subatomic particles)

· Current model is called the electron cloud model: it shows electrons traveling in specific energy levels around the nucleus

·       Elements are abbreviated in scientific shorthand (ex. Ne for Neon)

 

                      (Chapter 18.2)

· Atomic Mass: composed mostly of protons and neutrons in the nucleus

·       The unit of measurement for atomic particles is the atomic mass unit (amu) which is one-twelfth the mass of a carbon atom containing six protons and six neutrons

·       Atomic number—the number of protons in an atom (this number identifies the element)

·       Mass number—the sum of the number of protons and neutrons in the nucleus of an atom

· Isotopes: atoms of the same element (same number of protons) with different numbers of neutrons (ex. Carbon-14, Uranium-238)

1.   Different isotopes have different properties

2.   Number of neutrons is equal to mass number minus atomic number

3.   Name of the element followed by mass number identifies the isotope

4.   Average Atomic Mass: the weighted-average mass of an element’s isotopes

5.   Average atomic mass is closest to the most abundant isotope