General Chemistry: Atomic Structure, Periodicity, Compounds, and Calculations – Study Guide

Properties of Elements and Compounds

Chemical vs. Physical Properties

Understanding the distinction between chemical and physical properties is fundamental in chemistry. Physical properties can be observed without changing the substance's identity, while chemical properties describe a substance's ability to undergo chemical change.

• Physical Properties: Malleability, melting point, color, density.

• Chemical Properties: Reactivity with acids, ability to rust, flammability.

• Example: Tin dissolving in hydrochloric acid is a chemical property because it involves a chemical reaction.

Units and Conversions

Metric Conversions

Converting between metric units is a common skill in chemistry, especially for measurements of length, mass, and volume.

• 1 kilometer (km) = 1,000,000 micrometers (μm)

• Conversion Example: $6.0\ \text{km} = 6.0 \times 10^6\ \mu\text{m}$

Temperature and Energy Calculations

Temperature Conversions

Temperature can be measured in Celsius (°C) or Kelvin (K). The Kelvin scale is the SI unit for temperature.

• Conversion Formula: $K = ^\circ C + 273.15$

• Example: $-78.5^\circ C = 194.7\ K$

Density and Volume Calculations

Density Determination

Density is the mass per unit volume of a substance and is calculated using:

• Formula: $\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

• Units: g/cm3 or g/mL

• Example: If a 114 g metal raises water from 25.00 mL to 42.50 mL, the volume is $42.50 - 25.00 = 17.50$ mL. Density = $\frac{114\ g}{17.50\ mL} = 6.51\ g/mL$

Speed of Light and Communication

Radio Wave Travel Time

Radio waves travel at the speed of light. The time for a signal to travel a certain distance is:

• Formula: $\text{Time} = \frac{\text{Distance}}{\text{Speed}}$

• Speed of light: $3.0 \times 10^8\ \text{m/s}$

• Example: For Mars at $9.9 \times 10^{10}$ m, $\text{Time} = \frac{9.9 \times 10^{10}}{3.0 \times 10^8} = 330\ \text{s} \approx 5.5\ \text{minutes}$

Atomic Structure and Electron Configuration

Subatomic Particles

Atoms consist of protons, neutrons, and electrons. Ions have different numbers of electrons compared to protons.

• Example: Al3+ has 13 protons and 10 electrons.

Electron Configuration

Electron configuration describes the arrangement of electrons in an atom's orbitals.

• Example: The ground-state configuration for Cl is $1s^2 2s^2 2p^6 3s^2 3p^5$

• Transition metals and ions: Remove electrons from the highest principal quantum number first when forming cations.

Orbital Diagrams and Subshells

• d subshell: Contains 5 orbitals, each can hold 2 electrons, for a total of 10 electrons.

• Example: Nitrogen's orbital diagram: $1s^2 2s^2 2p^3$ (with three unpaired electrons in 2p).

Periodic Table Trends

Ionization Energy

Ionization energy is the energy required to remove an electron from a gaseous atom.

• Trends: Increases across a period, decreases down a group.

• Successive Ionization Energies: Large jumps indicate removal from a new shell.

Ionic and Atomic Radii

• Order of Ionic Radius: For isoelectronic species, more protons = smaller radius.

• Example: $O^{2-} > F^- > Na^+ > Mg^{2+}$

Compounds and Nomenclature

Formulas and Names

• Binary Ionic Compounds: Metal + nonmetal, e.g., NaCl, CaCl2

• Covalent Compounds: Nonmetal + nonmetal, e.g., CO2, NH3

• Acids: Hydrochloric acid (HCl), hydrobromic acid (HBr), etc.

• Polyatomic Ions: Know common ions like sulfate (SO42-), phosphate (PO43-), etc.

Empirical and Molecular Formulas

• Empirical Formula: Simplest whole-number ratio of atoms.

• Molecular Formula: Actual number of atoms in a molecule.

• Example: If empirical formula is CH and molar mass is 78 g/mol, molecular formula is C6H6 (benzene).

Stoichiometry and Molar Mass

Molar Mass Calculations

• Formula: $\text{Molar mass} = \sum (\text{atomic mass} \times \text{number of atoms})$

• Example: Acetaminophen (C8H9NO2): $8 \times 12.01 + 9 \times 1.01 + 1 \times 14.01 + 2 \times 16.00 = 151\ g/mol$

Percent Composition

• Formula: $\%\ \text{element} = \frac{\text{mass of element in 1 mol}}{\text{molar mass}} \times 100$

• Application: Used to determine empirical and molecular formulas.

Light and Quantum Mechanics

Wavelength, Frequency, and Energy

• Relationship: $c = \lambda \nu$ where $c$ is speed of light, $\lambda$ is wavelength, $\nu$ is frequency.

• Energy of a photon: $E = h\nu$

• Planck's constant: $h = 6.63 \times 10^{-34}\ \text{J s}$

• Example: For $\lambda = 468\ nm$, $\nu = \frac{3.0 \times 10^8}{468 \times 10^{-9}} = 6.41 \times 10^{14}\ Hz$

de Broglie Wavelength

• Formula: $\lambda = \frac{h}{mv}$

• Application: Used to calculate the wavelength of particles with mass.

Quantum Numbers and Electron Transitions

• Principal Quantum Number (n): Indicates energy level.

• Electron Transitions: Energy emitted/absorbed when electrons move between levels.

• Rydberg Equation: $E = -R_H \left( \frac{1}{n_f^2} - \frac{1}{n_i^2} \right )$ where $R_H = 2.18 \times 10^{-18}\ J$

Periodic Table and Electron Configuration Practice

Sample Electron Configurations

• Transition Elements: d-block elements, partially filled d subshells.

• Alkali and Alkaline Earth Ions: Lose s electrons to form +1 or +2 ions.

• Halide Ions: Gain one electron to complete p subshell.

Valence Electrons

• Definition: Electrons in the outermost shell, important for chemical bonding.

• Example: Tin (Sn) has 4 valence electrons.

Tables

Successive Ionization Energies

The following table shows the successive ionization energies (kJ/mol) for an element R:

1st	2nd	3rd	4th	5th	6th
737	1450	7732	10540	13630	17995

• Purpose: Identifying the group of the element based on large jumps in ionization energy.

• Interpretation: A large jump between 2nd and 3rd suggests two valence electrons (alkaline earth metal).

Additional info:

• Some questions require knowledge of periodic trends, quantum mechanics, and chemical nomenclature.

• Practice with electron configurations, empirical/molecular formulas, and stoichiometry is essential for exam preparation.