Summary
Highlights
Know how the number of valence electrons, determined by an element's group number, affects the charges of ions they form. For example, Group 1 forms +1 ions, Group 17 forms -1 ions. Apply the octet rule to predict ionic charges and derive empirical formulas for ionic compounds, such as MgCl2 for magnesium and chloride, and Al2S3 for aluminum and sulfide.
Learn to convert between moles and grams using atomic mass for elements and compounds. For instance, 10.00 grams of carbon dioxide converts to 0.2272 moles. Also, convert particles to moles using Avogadro's number (6.022 x 10^23 particles per mole). For example, 0.2272 moles of carbon dioxide equates to 1.368 x 10^23 molecules.
Understand how to read a mass spectrum graph to determine the relative abundance of an element's isotopes. By analyzing the mass and abundance of isotopes (e.g., 107 amu at 52% and 109 amu at 48%), you can estimate the average atomic mass and identify the element, such as silver in the provided example.
An empirical formula is the simplest whole-number ratio of atoms in a compound. To find it from percent composition (e.g., 40.05% sulfur and 59.95% oxygen), convert percentages to grams, then to moles, and divide by the smallest mole value to get the subscript ratios. This illustrates the law of definite proportions.
Understand that practical samples often contain impurities, making them mixtures, not pure substances. By analyzing the percentage of a common ion (e.g., chloride in various chloride compounds), you can determine the purity of a sample. A deviation from the expected percent mass indicates impurities.
Master writing electron configurations for elements, like scandium (1s2 2s2 2p6 3s2 3p6 4s2 3d1), and identify valence electrons and sublevels. Use Coulomb's Law (charge and distance) to explain the forces holding electrons to the nucleus. Greater charge leads to stronger attraction, while greater distance leads to weaker attraction, meaning valence electrons are easiest to remove.
Interpret PES graphs by labeling peaks with sublevels (1s, 2s, 2p, etc.) in increasing energy. The relative heights of the peaks correspond to the number of electrons in each sublevel. For example, a PES graph ending with 4s2 indicates the element is calcium.
Understand general periodic trends: ionization energy and electronegativity increase towards the top-right, while atomic radius increases towards the bottom-left. These trends are explained by effective nuclear charge (for left-to-right comparisons) and distance of valence electrons from the nucleus (for up-down comparisons). For ions, more positive charge means smaller size, and more negative charge means larger size due to electron repulsion.