1. Subatomic Particles

2. An atom is the smallest part of an element that retains the same chemical properties as the element. • The nucleus is the central part of an atom. It is made up of protons and neutrons and contains most of the atom’s mass. • The nucleus was discovered by Ernest Rutherford in 1911. Atoms

3. Protons (p+) • Positively charged particles found in nucleus. • Mass of 1 atomic mass unit (AMU). • Discovered by Ernest Rutherford in 1911. • Neutrons (n0) • Neutral particles found in nucleus. • Mass of 1 atomic mass unit (AMU). • Discovered by James Chadwick in 1932. • Electrons (e-) • Negative particles found in nucleus. • Negligible mass. • Discovered by J.J. Thomson in 1897. Subatomic Particles

4. The number of protons in an atom • Can be found by looking at the top of each box on the periodic table • In a neutral atom, the number of electrons is the same as the number of protons Atomic Number

5. The number of protons and neutrons added together. • Usually seen after the element name or symbol (carbon – 13). Mass number is NOT found on the periodic table. • Mass Number = p+ + no • How would you find the neutrons if you knew the protons and mass number? • Neutrons = mass number – protons Mass Number

6. How many protons, neutrons, and electrons are in a neutral atom of: fluorine – 20. • Protons = 9 (from periodic table) • Neutrons = 11 (20 – 9) • Electrons = 9 (electrons = protons) • Isotopes of the same elements have: • Same number of protons & electrons and atomic number. • Different number of neutrons and therefore a different mass number. Example

7. Atoms of the SAME element, with different numbers of neutrons • Example: • Copper – 63 • (29 p+, 34 no, 29 e-) • Copper – 65 • (29 p+, 36 no, 29 e-) Isotopes

8. X • Copper-63 • Cu • Copper-65 • Cu Isotope Symbols