Physical Science - Chapter 3 

The Atom

3A: The Atomic Model

• $Subatomic Particles$: particles that are smaller than atoms
• Dalton suggested several properties of atoms:
  • Elements are made of atoms
  • Atoms are indivisible and cannot be destroyed
  • The atoms of an element are all alike
  • The atoms of one element are different from the atoms of all other elements, especially their masses
  • Atoms combine chemically in small, whole number ratios

The Discovery of the Electron

• $Law of Electrostatic Charges$: the law that states that opposite electrical charges attract each other, while like charges repel each other
• $Plum Pudding Mode$l: the atomic model suggested negatively charged material with embedded electrons
  • Thomson’s plum pudding model suggested negatively charged electrons embedded in a positive substance

The Nuclear Model

• $Alpha Particle$: a helium nucleus that is emitted from a nucleus when a radioactive isotope experiences alpha decay

• $Nuclear Model$: the atomic developed by Ernest Rutherford in which an atom is made up of a tiny, dense, positively charged central nucleus surrounded by negatively charged electrons

• $Quantum Mechanics$: the branch of physics that explores the behavior of matter and energy at the atomic and subatomic level

The Bohr Model

• $Bohr Model$: the atomic model developed by Niels Bohr in which electrons travel in distinct spherical regions called $energy levels$ at fixed distances from the nucleus
  • $Energy Level$: in the Bohr model of the atom; the regions located at fixed distances from the nucleus of an atom in which electrons are found

The Quantum-Mechanic Model

• $Quantum - Mechanic Model$: the currently accepted atomic model in which electrons are found in orbitals that are positioned around a nucleus that contains protons and (usually) neutrons
  • the key factor that drove the development of the new atomic models is ^^workability^^

3B: Atomic Structure

What is it like inside an atom?

• $Electrons$: the smallest of the main subatomic particles
• $Proton$: a subatomic particles located in the atom’s nucleus
• $Neutron$: carries no electrical charge

Properties of Atoms

$Atomic Number$: the unique number of protons in the atoms of each element

$Neutral Atom$: an atom with balanced electric charges

• Neutron

  • Relative mass: 1u
  • Actual mass: 1.6749 x 10^-27 kg
  • Symbol: n
  • Charge: 0

• Proton

  • Relative mass: 1u
  • Actual mass: 1.6726 x 10^-27 kg
  • Symbol: p+
  • Charge: +1e

• Electron

  • Relative mass: 1/1836u
  • Actual mass: 9.1094 x 10^-31
  • Symbol: e-
  • Charge: -1e

Mass Number

• $Isotopes$: atoms of the same element with differing numbers of neutrons

• $Mass Number$: the total number of particles found in the nucleus of a particular isotope of an element

• $Isotope Notation$: a symbol that distinguishes between different isotopes

• Ions

  • $Ion$: a charged atom or group of atoms that has gained or lost electrons, producing an unequal number of protons and electrons
  • $Anion$: a negatively charged ion
  • $Cation$: a positively charged ion

• $Atomic Mass$: the weighted average of the masses of all naturally occurring isotopes of that element