GOB Chemistry: Fundamental Concepts and Problem-Solving Study Guide

Measurement and Significant Figures

Decimal Places and Significant Digits

Accurate measurement and reporting of data are essential in chemistry. Significant figures reflect the precision of a measurement, while decimal places indicate the number of digits to the right of the decimal point.

• Significant Figures: All nonzero digits are significant; zeros between nonzero digits and trailing zeros in the decimal portion are also significant.

• Example: 0.0015 mL has three decimal places and two significant digits.

Scientific Notation and Metric Prefixes

Scientific notation expresses numbers as a product of a coefficient and a power of ten. Metric prefixes denote specific powers of ten.

• centi- means $10^{-2}$.

• Example: 1 centimeter (cm) = $1 \times 10^{-2}$ meters.

Elements, Periodic Table, and Chemical Symbols

Element Classification

The periodic table organizes elements by atomic number and properties. Alkaline Earth metals are found in Group 2.

• Example: Calcium (Ca) is an Alkaline Earth metal in the fourth period.

Chemical Symbols

Each element is represented by a unique one- or two-letter symbol.

• Example: The symbol for Copper is Cu.

Temperature and Unit Conversions

Temperature Scales

Temperature can be measured in Celsius, Fahrenheit, or Kelvin. The Kelvin scale is the SI unit for temperature.

• Conversion: $K = ^\circ F + 459.67 \times \frac{5}{9}$

• Example: -208°F = 140 K

Volume and Density Calculations

Density is mass per unit volume. To find volume from mass and density:

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

• Example: 125 g acetone at 0.791 g/mL: $\frac{125}{0.791} = 158$ mL

Atomic Structure and Isotopes

Protons, Neutrons, and Electrons

Atoms consist of protons, neutrons, and electrons. Isotopes have the same number of protons but different numbers of neutrons.

• Example: $^{23}_{11}$Na has 11 protons and 12 neutrons.

Electron Configuration

Valence electrons are the outermost electrons and determine chemical reactivity.

• Example: Bromine has seven valence electrons.

Mixtures, Compounds, and Chemical Changes

Types of Matter

Matter can be classified as elements, compounds, or mixtures.

• Heterogeneous mixture: Composition is not uniform throughout (e.g., chicken soup).

• Pure substance: Uniform composition (element or compound).

Chemical vs. Physical Changes

Chemical changes result in new substances; physical changes do not.

• Example of chemical change: Meat spoils after being removed from the refrigerator.

• Example of physical change: Ice melts.

Nuclear Chemistry

Radioactive Decay and Nuclear Reactions

Radioactive isotopes decay at characteristic rates, measured as half-life.

Isotope	Half-life
Carbon-14	5730 Years
Phosphorus-32	14 days

• Carbon-14 decays the slowest and is the most stable.

Nuclear Equations

Nuclear reactions involve changes in the nucleus, such as electron capture or positron emission.

• Electron capture: $^{196}_{80}\text{Hg} + e^- \rightarrow ^{196}_{79}\text{Au}$

• Positron emission: $^{40}_{19}\text{K} \rightarrow ^{40}_{18}\text{Ar} + e^+$

Properties of Substances

Physical vs. Chemical Properties

Physical properties can be observed without changing the substance's identity. Chemical properties describe a substance's ability to undergo chemical changes.

• Example of physical property: Ammonia is a gas at room temperature.

• Example of chemical property: Ammonia reacts with acids to form ammonium chloride.

Problem Solving and Calculations

Significant Figures in Calculations

When performing calculations, the result should be reported with the correct number of significant figures.

• Example: $41.73 - 17.81283 = 23.92$ (rounded to two decimal places)

Volume Calculations

To find the volume of a rectangular solid:

• Formula: $\text{Volume} = \text{length} \times \text{width} \times \text{height}$

• Example: $9.876 \text{ cm} \times 3.21 \text{ cm} \times 1.2 \text{ cm} = 38 \text{ cm}^3$ (rounded to two significant figures)

Subatomic Particles

Charge and Identity

Subatomic particles include protons, neutrons, and electrons.

• Proton: Positive charge

• Neutron: No charge

• Electron: Negative charge

Metals, Nonmetals, and Metalloids

Classification

Elements are classified based on their properties.

• Metals: Good conductors, malleable, ductile (e.g., Barium)

• Nonmetals: Poor conductors, brittle (e.g., Nitrogen)

• Metalloids: Properties intermediate between metals and nonmetals

Electron Dot Structures

Valence Electrons

Electron dot structures (Lewis structures) represent valence electrons as dots around the element symbol.

• Example: Aluminum (Al) has three valence electrons, best represented by three dots around the symbol.