1.1  Moles and Molar Mass     Go to Topic Page

• • One cannot count particles directly while performing laboratory work. Thus, there must be a connection between the masses of substances reacting and the actual number of particles undergoing chemical changes. (SPQ-1.A.1) 

  • Avogadro’s number (NA = 6.022 x 1023 particles/mole) provides the connection between the number of moles in a pure sample of a substance and the number of constituent particles (or formula units) of that substance. (SPQ-1.A.2)   

  •  Expressing the mass of an individual atom or molecule in atomic mass units (amu) is useful because the average mass in amu of one particle (atom or molecule) or formula unit of a substance will always be numerically equal to the molar mass of that substance in grams. Thus, there is a quantitative connection between the mass of a substance and the number of particles that the substance contains. (SPQ-1.A.3)  

1.2  Mass Spectroscopy of Elements    Go to Topic Page

• • The mass spectrum of a sample containing a single element can be used to determine the identity of the isotopes of that element and the relative abundance of each isotope in nature. (SPQ-1.B.1)  

  • The average atomic mass of an element can be estimated from the weighted average of the isotopic masses using the mass of each isotope and its relative abundance (SPQ-1.B.2)  

1.3  Elemental Composition of Pure Substances    Go to Topic Page

• • Some pure substances are composed of individual molecules, while others consist of atoms or ions held together in fixed proportions as described by a formula unit. (SPQ-2.A.1)  

  • According to the law of definite proportions, the ratio of the masses of the constituent elements in any pure sample of that compound is always the same. (SPQ-2.A.2)  

  • The chemical formula that lists the lowest whole number ratio of atoms of the elements in a compound is the empirical formula. (SPQ-2.A.3) 

1.4  Composition of Mixtures     Go to Topic Page

• • While pure substances contain molecules or formula units of a single type, mixtures contain molecules or formula units of two or more types, whose relative proportions can vary. (SPQ-2.B.1)  

  • Elemental analysis can be used to determine the relative numbers of atoms in a substance and to determine its purity (SPQ-2.B.2)  

1.5  Atomic Structure and Electron Configuration     Go to Topic Page

• • The atom is composed of negatively charged electrons and a positively charged nucleus that is made of protons and neutrons (SAP-1.A)

  • Coulomb’s law is used to calculate the force between two charged particles. (SAP-1.A.2) 

  • In atoms and ions, the electron can be thought of as being in “shells (energy levels)” and “subshells (sublevels)” as described by the electron configuration. Inner electrons are called core electrons, and outer electrons are called valence electrons. The electron configuration is explained by quantum mechanics, as delineated in the Aufbau principle and exemplified in the periodic table of the elements. (SAP-1.A.3) 

  • The relative energy required to remove an electron from different subshells of an atom or ion or from the same subshell in different atoms or ions (ionization energy) can be estimated through a qualitative application of Coulomb’s law. This energy is related to the distance from the nucleus and the effective (shield) charge of the nucleus. (SAP-1.A.4)

1.6  Photoelectron Spectroscopy     Go to Topic Page

• • The energies of the electrons in a given shell can be measured experimentally with photoelectron spectroscopy (PES). The position of each peak in the PES spectrum is related to the energy required to remove an electron from the corresponding subshell, and the height of each peak is (ideally) proportional to the number of electrons in that subshell.  (SAP-1.B.1) 

1.7  Periodic Trends     Go to Topic Page

• The organization of the periodic table is based on the recurring properties of the elements and explained by the pattern of electron configurations and the presence of completely or partially filled shells (and subshells) of electrons in atoms.  (SAP-2.A.1)  

WRITING THE ELECTRON CONFIGURATION OF ELEMENTS THAT ARE EXCEPTIONS TO THE AUFBAU PRINCIPLE WILL NOT BE ASSESSED ON THE AP EXAM. Rationale: The mere rote recall of the exceptions does not match the goals of the curriculum revision. 

• Trends in atomic properties within the periodic table (periodicity) can be qualitatively understood through the position of the element in the periodic table, Coulomb’s law, the shell model, and the concept of shielding/effective nuclear charge. These properties include:   (SAP-2.A.3) 

a. Ionization energy 

b. Atomic and ionic radii 

c. Electron affinity 

d. Electronegativity.

1.8  Valence Electrons and Ionic Compounds     Go to Topic Page

• • The likelihood that two elements will form a chemical bond is determined by the interactions between the valence electrons and nuclei of elements. (SPQ-2.B.1)  

  • Elements in the same column of the periodic table tend to form analogous compounds (SPQ-2.B.2) 

  • Typical charges of atoms in ionic compounds are governed by their location on the periodic table and the number of valence electrons. (SPQ-2.B.3)