Ions and Chemical Formulas

• A formula unit represents the simplest ratio of ions needed to cancel charges in an ionic compound.
• The oxidation number of an ion corresponds to its charge.
• Oxidation number is equal to the number of electrons transferred from an atom to form the ion.
• Monatomic ions consist of a single atom.
• Examples of monatomic ions include Ti+3, Ti+2, Fe+2, Fe+3, Au+, and Au+3.
• Polyatomic ions are composed of multiple atoms bonded together.
• Examples of polyatomic ions include NH4+, NO2-, CO3-2, and SO4-2.

Chemical Formulas

• For binary ionic compounds, the chemical symbol of the cation is written first, followed by the anion.
• Subscripts are added to the chemical symbols to indicate the ratio of ions needed to achieve a neutral charge in the compound.
• For polyatomic ionic compounds, the polyatomic ion is enclosed in parentheses, and a subscript is added outside to indicate its quantity.
• The subscripts within a polyatomic ion's chemical formula cannot be altered, as it acts as a single unit.

Ionic Compound Names

• Binary ionic compounds are named by stating the name of the metal first, followed by the name of the nonmetal with the suffix "-ide."
• Roman numerals after a metal's name indicate its oxidation number, distinguishing between different oxidation states.
• Polyatomic ionic compounds are named by stating the metal or polyatomic metal first, followed by the nonmetal or polyatomic nonmetal/oxyanion, considering the number of oxygen atoms.
• Oxyanions are elements, often nonmetals, bonded to one or more oxygen atoms. The suffix "-ite" indicates the oxyanion with fewer oxygen atoms, while "-ate" indicates the oxyanion with more oxygen atoms.

Lesson 4

• The electron sea model proposes that metal cations in a metallic solid contribute electrons to a sea where they move freely.
• Delocalized electrons are not bonded to a specific atom and move freely throughout the metal structure.
• A metallic bond results from the attraction between cations and the sea of electrons.
• Metals generally have high melting and boiling points, but melting points are lower because the cations and electrons are mobile. It requires much more energy to separate the atoms at boiling point.
• Metals are malleable and ductile because their cations are mobile but strongly attracted to the electrons, preventing easy removal.
• The movement of electrons around positive metallic cations allows electric current and fluidity, making metals thermally and electrically conductive.
• The more delocalized electrons, the greater the strength and hardness of the metal.
• Metal alloys are mixtures of elements that exhibit metallic properties.
• Alloys are made because metallic bonds easily introduce other elements into their lattice, leading to a wide range of commercial applications.
• Interstitial alloys form when smaller atoms fill the spaces between the larger atoms in a metal crystal lattice.
• Substitutional alloys occur when some atoms of the original metal are replaced by another metal of similar atomic size.