General Chemistry MCAT Review
Chapter 1: Atomic Structure
1.1 : Subatomic Particles
• 3 subatomic particles: protons, neutrons and electrons
• Protons: found in the nucleus of an atom
o Charge: +1e or +1
o Mass of 1 amu
▪ Atomic mass unit (amu): a unit of mass defined as 1/12 of the ma...
General Chemistry MCAT Review
Chapter 1: Atomic Structure
1.1 : Subatomic Particles
• 3 subatomic particles: protons, neutrons and electrons
• Protons: found in the nucleus of an atom
o Charge: +1e or +1
o Mass of 1 amu
▪ Atomic mass unit (amu): a unit of mass defined as 1/12 of the mass
of a carbon-12 atom
o Atomic number (Z): number of proteins found in an atom of that element
▪ Unique identifier for each element
• Neutrons: found in the nucleus of an atom
o No charge (neutral)
o Mass is slightly larger than proton 1 amu
o Neutrons + protons = nucleus
• Every atom has a mass number (A): sum of protons and neutrons in the
atom’s nucleus
o A given element can have a variable number of neutrons SO mass
number can vary
• Isotopes: atoms that share an atomic number but have different mass numbers
o Differ in number of neutrons
• Convention for atom: Mass number on top of atomic number
• Electrons: move through the space surrounding the nucleus and are
associated with varying levels of energy
o Charge equal to magnitude of proton but with the opposite sign (negative)
▪ -1e or -1
o Mass of electron 1/2000 of a proton
o The electrostatic force of attraction between unlike charges of the proton and
electron is far greater than the gravitation force of attraction based on their
respective masses
o Electrons move around the nucleus at varying distance, which corresponds to
varying levels of electrical potential energy
▪ Closer to nucleus = lower energy levels
▪ Further from nucleus (higher electron shell) = higher energy
o Valence electrons: electrons that are the farthest from the nucleus
▪ Have the strongest interactions with the environment
▪ Weakest interactions with the nucleus
▪ More likely involved in bonds with other atoms since they experience
the least electrostatic pull from their nucleus
▪ Determines reactivity of an atom
▪ The sharing or transferring of valence electrons in bonds allows
elements to fill their highest energy level to increase stability
• Neutral state: protons = electrons
• Cation: positively charged atom that lost electrons
• Anion: negatively charged atom that gained electrons
, 1.2 : Atomic Mass vs Atomic Weight
• Atomic mass (in amu): the sum of protons and neutrons
o Nearly equal to its mass number
o Varies from one isotope to another because of variation in number of
neutrons
o Isotopes are referred to by the name of the element followed by mass
number
▪ EX: Carbon-12
▪ Hydrogen has 3 isotopes with proper names:
• Protium = 1 proton (1 amu)
• Deuterium = 1 proton & 1 neutron (2 amu)
• Tritium = 1 proton & 2 neutrons (3 amu)
▪ Because isotopes have the same number of protons and electrons,
they generally exhibit similar chemical properties
• Atomic weight: weighted average of different isotopes
o Constant and is reported on the periodic table
o Calculate atomic weight:
▪ Atomic weight = (atomic mass x % abundance) + (atomic mass x %
abundance) + (atomic mass x % abundance) + ….
o Half-life corresponds to stability and helps determine the relative proportions
of different isotopes
o The utility of atomic weight is that it represents both the mass of the
“average” atom of an element in amu AND the mass of one mole of
the element in grams
o Mole: a number of “things” (atoms, ions, molecules) = Avogadro’s
number (6.02 x 1023)
1.3 : Rutherford, Planck and Bohr
• Ernest Rutherford provided experimental evidence that an atom has a dense,
positively charged nucleus that accounts for only a small proportion of the atom’s
volume
• Max Planck developed the first quantum theory, proposing that energy emitted as
electromagnetic radiation from matter comes in discrete bundles called quanta
• The energy of a quantum is given by the Planck relation:
o E = hf
▪ E: energy
▪ h: 6.626 X 10-34 Planck’s constant
▪ f: frequency of radiation
• Bohr used the work of Rutherford and Planck to develop his model of the electronic
structure of the hydrogen atom
o Assumed that the hydrogen atom has a central proton around which
an electron travels in a circular orbit
o Postulated that the centripetal force acting on the electron as it
revolved around the nucleus was created by the electrostatic force
between the positively charged proton and the negatively charged
electron
o Incorporated Planck’s quantum theory in his model and placed restrictions on
the possible values of angular momentum
o Predicted that the possible values of angular momentum of an
electron orbiting around a hydrogen nucleus could be given by:
▪ nh
L= 2 π
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