This document discusses the structure and properties of atoms. It explains that atoms are made up of protons, neutrons, and electrons. Protons and neutrons are located in the nucleus, while electrons move around the nucleus in different energy levels. Atoms become ions when they gain or lose electrons, acquiring a positive or negative charge. Other properties discussed include atomic number, atomic mass, isotopes, and atomic mass units.

1. Inside an Atom

3.  All matter is made up of one or more
elements
 Element: substance that cannot be broken
down into smaller substances
Examples: Hydrogen, Carbon, Oxygen
 Atom: the smallest unit of an element

4. Parts of an Atom
 Proton – positive charge (+)
 Neutron – neutral (no charge)
 Electron – negative charge (-)

5.  Protons and neutrons are found in the
nucleus in the center of the atom
 Electrons are moving rapidly in a
cloud around the nucleus
 Different energy levels around the nucleus
 Electrons may “hang out” in these levels
 Valence electrons – those that are farthest
from the nucleus and most loosely held

7. Properties of Atoms
 An atom is neutral when it has an equal
number of protons (+) and electrons (-).
 Sometimes when one atom reacts with
another atom, it gains or loses an electron
giving it a positive or negative charge
 This charged particle is called an ION

8.  If an atom loses an electron (-), it now
has a positive charge (cation)
 If an atom gains an electron (-), it now
has a negative charge (anion)
Properties continued…

9. More Properties
 Atomic Number – number of protons
 Identifies and determines the element
 Carbon: atomic # 6
 Sodium: atomic # 11
 Gold: atomic # 79
 Atomic mass – average mass of one
atom of an element

10. Atomic Mass Unit (amu)
 SI unit used to measure the mass of
particles in atoms
 Protons and Neutrons = 1 amu
 Approximately 2000 Electrons = 1 amu
 Almost all of an atom’s mass is in the
nucleus

11. Isotopes
 The number of protons for a certain
atom never changes, but sometimes
an atom may have different numbers
of neutrons
 Mass Number – sum of protons and
neutrons

12. Hydrogen Isotopes