Subatomic Particles. 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.
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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
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
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
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
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
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
X • Copper-63 • Cu • Copper-65 • Cu Isotope Symbols