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 Model: 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