Chemistry Concepts in Stoichiometry and Solutions

Stoichiometry

• The limiting reactant determines the amount of product formed in a reaction
• The percent yield is calculated by dividing the actual yield by the theoretical yield and multiplying by 100%
• The actual yield is the amount of product obtained in a reaction
• The theoretical yield is the maximum amount of product that can be formed from a given amount of reactants

Solutions

• Molarity is the number of moles of solute dissolved in one liter of solution
• The mass of solute can be calculated from the molarity, molecular weight, and volume
• The number of moles of solute can be calculated by dividing the mass of solute by the molar mass

Quantum Numbers

• The four quantum numbers (n, l, ml, ms) describe the state of an electron in an atom
• The principal quantum number (n) describes the electron shell and its average distance from the nucleus
• The azimuthal quantum number (l) describes the shape of the orbital and its subshell
• The magnetic quantum number (ml) describes the orientation of the orbital
• The spin quantum number (ms) describes the spin of the electron

Pauli Exclusion Principle

• No two electrons in the same atom can have the same set of four quantum numbers
• This means that each orbital can only hold a maximum of two electrons, which have opposite spins
• The spin magnetic moments of these two electrons cancel each other out

Electron Configuration

• The electron configuration of an atom is the way in which electrons are arranged in the atom
• The ground-state electrons occupy the shells in order of increasing value of n and then in order of increasing value of l
• The orbital diagram represents each orbital with a dash and the electron with an arrow pointing up (↑) or down (↓) to represent its spin

VSEPR Theory

• The VSEPR theory predicts the shapes of molecules by considering the repulsion between electron pairs in the valence shell
• Nonbonding electrons occupy an equatorial position in SF4 to minimize repulsion
• Nonbonding electrons occupy equatorial positions in ClF3 to result in a T-shaped molecule
• The triiodide (I3-) ion has a linear shape because the nonbonding electrons occupy equatorial positions

Hybridization

• The type of hybridization taking place within the atomic orbitals of the interacting atoms can predict the molecular geometry
• Hybridization combines atomic orbitals to form new hybrid orbitals

Chemical Bonding

• Atoms bond to achieve a more stable state
• This stable state is often achieved when the valence shell is filled with electrons or when the octet rule is satisfied (eight valence electrons)
• Atoms can achieve stability by gaining, losing, or sharing electrons via bonds

Ions and Ionic Bonds

• Ions are charged particles formed by gaining or losing electrons
• Cations are positive ions formed by losing electrons
• Anions are negative ions formed by gaining electrons
• Ionic bonds are formed by the electrostatic attraction between oppositely charged ions

Formulas of Compounds

• The chemical formula of a compound indicates the relative number of atoms of each element in the compound
• The molecular formula gives the number of atoms of each type in a single molecule of the compound
• The empirical formula gives the simplest whole number ratio of atoms in a compound
• Ionic compounds are composed of ions held together by electrostatic attraction and are not molecular
• Their formulas represent the simplest ratio of ions in the compound

Periodic Law

• The periodic law states that the properties of elements recur periodically when arranged in order of increasing atomic number
• Mendeleev's periodic table organized elements so that similar elements appeared in vertical columns called groups
• Mendeleev predicted the properties of missing elements based on his periodic table, which later led to the discovery of those elements
• The discovery of noble gases expanded the periodic classification of elements
• The atomic number, determined using X-rays, was found to be a more fundamental property than atomic weight for classifying elements
• Moseley's discovery of X-ray spectra provided evidence for the atomic number being a fundamental property of elements, solving the problem of elements misplaced based on atomic weight alone