Inside an Atom

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. Properties continued… • 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)

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