General Chemistry Exam Study Guide: Atoms, Elements, Molecules, and Compounds

Equation Sheet and Reference Data

Potentially Useful Equations

This section provides key equations and constants commonly used in General Chemistry, essential for solving problems related to density, atomic mass, and mole calculations.

• Density Equation: Density (d) is defined as mass divided by volume.

$d = \frac{m}{v}$

• Atomic Mass Calculation: The atomic mass of an element is the weighted average of the masses of its isotopes, based on their natural abundance.

$\text{Atomic mass} = \sum (\text{fraction of isotope} \times \text{mass of isotope})$

• Avogadro's Number: The number of particles (atoms, molecules, ions) in one mole of a substance.

$6.022 \times 10^{23}$ particles = 1 mole

Periodic Table of the Elements

Reference Table

The periodic table organizes all known elements by increasing atomic number and groups elements with similar chemical properties. It is essential for identifying element symbols, atomic numbers, and common charges.

• Groups (Columns): Elements in the same group have similar chemical properties.

• Periods (Rows): Elements in the same period have the same number of electron shells.

• Metals, Nonmetals, Metalloids: The table distinguishes between these types based on their location and properties.

Chapter 1: Scientific Approach, Matter, and Measurement

Key Concepts

This chapter introduces the scientific method, classification of matter, physical and chemical properties, and measurement techniques.

• Scientific Approach: Involves forming hypotheses, conducting experiments, and developing theories and laws.

• States of Matter: Solid, liquid, and gas, each with distinct properties regarding shape and volume.

• Classification of Matter: Pure substances (elements and compounds) vs. mixtures (homogeneous and heterogeneous).

• Physical vs. Chemical Properties: Physical properties can be observed without changing the substance; chemical properties involve changes in composition.

• Law of Conservation of Energy: Energy cannot be created or destroyed, only transformed.

• Units of Measurement: SI prefixes (kilo-, milli-, centi-) and their meanings.

• Density Calculations: Use the density equation to relate mass and volume.

• Significant Figures: Important for maintaining precision in calculations.

• Dimensional Analysis: Used to convert between units using conversion factors.

Example: Calculating the density of a substance given mass and volume.

Chapter 2: Atoms and Elements

Key Concepts

This chapter covers atomic theory, structure of the atom, subatomic particles, isotopes, and the periodic table.

• Dalton's Atomic Theory: All matter is composed of atoms; atoms of each element are identical; atoms combine in simple ratios to form compounds.

• Subatomic Particles: Protons (positive charge), neutrons (neutral), electrons (negative charge).

• Isotopes: Atoms of the same element with different numbers of neutrons.

• Atomic Number (Z): Number of protons in the nucleus.

• Mass Number (A): Sum of protons and neutrons.

• Periodic Table Organization: Elements are arranged by increasing atomic number; groups and periods indicate chemical properties.

• Ion Formation: Atoms gain or lose electrons to form ions (cations and anions).

Example: Calculating the number of protons, neutrons, and electrons in an isotope.

$\text{Number of neutrons} = \text{Mass number} - \text{Atomic number}$

Chapter 3: Molecules and Compounds

Key Concepts

This chapter discusses chemical bonding, molecular and empirical formulas, naming compounds, and mole calculations.

• Ionic vs. Covalent Bonding: Ionic bonds form between metals and nonmetals; covalent bonds form between nonmetals.

• Empirical Formula: The simplest whole-number ratio of atoms in a compound.

• Molecular Formula: The actual number of atoms of each element in a molecule.

• Naming Compounds: Use systematic rules for naming ionic and covalent compounds, including polyatomic ions.

• Mole Concept: Relates mass, number of particles, and volume using Avogadro's number.

• Mass Percent and Empirical Formula Calculations: Use mass data to determine the simplest formula.

Example: Determining the empirical formula from percent composition.

Practice Exam Questions and Answers

Sample Questions

Below are representative questions covering the above topics, with answer key provided for self-assessment.

• Scientific Method: Identify true statements about experiments and hypotheses.

• States of Matter: Describe properties of solids, liquids, and gases.

• Significant Figures: Determine the correct number of significant figures in calculations.

• Atomic Structure: Calculate protons, neutrons, and electrons in isotopes.

• Periodic Table: Predict charges of ions based on group location.

• Mole Calculations: Convert between grams, moles, and number of atoms using Avogadro's number.

• Empirical and Molecular Formulas: Identify and calculate formulas from mass data.

• Naming Compounds: Write names and formulas for ionic and covalent compounds.

Answer Key Table

The following table provides the answer key for the practice exam questions:

Question	Answer
1	E
2	A
3	D
4	D
5	C
6	A
7	A
8	B
9	A
10	C
11	A
12	A
13	B
14	A
15	D
16	D
17	D
18	E
19	B
20	A
21	D
22	A
23	A
24	C
25	A
26	B
27	A
28	B
29	B
30	C
31	B
32	E
33	D
34	D
35	A
36	B
37	C
38	D
39	D
40	B
41	B
42	C
43	A
44	D
45	D

Additional Info

• Precision and Accuracy: Precision refers to the consistency of repeated measurements; accuracy refers to how close a measurement is to the true value.

• Systematic vs. Random Error: Systematic error consistently skews results in one direction; random error varies unpredictably.

• SI Prefixes: Common prefixes include kilo- ($10^3$), milli- ($10^{-3}$), centi- ($10^{-2}$).