Introduction to Chemistry: Practice Exam Study Guide

Study Guide - Smart Notes

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Significant Figures and Scientific Notation

Understanding Significant Figures

Significant figures are the digits in a measurement that are known with certainty plus one digit that is estimated. They are crucial for reporting scientific data accurately.

Definition: Significant figures reflect the precision of a measured or calculated quantity.
Example: The number 0.0250 has three significant figures: 2, 5, and the trailing zero (since it is after a decimal point).
Scientific Notation: Used to express very large or very small numbers in a compact form. For example, 325.00 in scientific notation is .

Rules for Significant Figures

All nonzero digits are significant.
Zeros between nonzero digits are significant.
Leading zeros are not significant.
Trailing zeros in a decimal number are significant.

States of Matter and Their Properties

Physical Properties of Gases, Liquids, and Solids

Matter exists in three primary phases: solid, liquid, and gas. Each phase has distinct physical properties.

Gases: Indefinite volume and shape; easily compressed.
Liquids: Definite volume but indefinite shape; not easily compressed.
Solids: Definite volume and shape; difficult to compress.
Example: Gases are the most difficult to contain due to their indefinite volume.

Chemical and Physical Changes

Distinguishing Chemical and Physical Changes

Chemical changes result in the formation of new substances, while physical changes do not alter the chemical identity of a substance.

Chemical Change: Burning paper is an example, as it produces new substances (ash, gases).
Physical Change: Evaporation of gasoline is a physical change; the chemical composition remains the same.

Atomic Structure and Elements

Atomic Number, Mass Number, and Isotopes

Atoms consist of protons, neutrons, and electrons. The atomic number is the number of protons in an atom, and the mass number is the sum of protons and neutrons.

Atomic Number: Oxygen has an atomic number of 8.
Mass Number: For isotopes, mass number = protons + neutrons.
Isotope Notation: , where A is mass number, Z is atomic number, and X is the element symbol.
Example: A neutral atom of Ne-21 contains 10 protons and 11 neutrons, but only 10 electrons.

Periodic Table and Element Classification

Groups, Periods, and Element Types

The periodic table organizes elements by increasing atomic number and groups elements with similar properties into columns.

Metals: Elements with properties such as conductivity, malleability, and luster.
Nonmetals: Elements that are generally poor conductors and may be gases, liquids, or brittle solids.
Transition Elements: Found in the center of the periodic table; often form colored compounds and have variable oxidation states.
Alkali Metals: Group 1 elements, highly reactive.
Halogens: Group 17 elements, very reactive nonmetals.

Ions and Ionic Compounds

Formation and Properties of Ions

Ions are formed when atoms gain or lose electrons. Ionic compounds consist of positive and negative ions held together by electrostatic forces.

Cations: Positively charged ions (loss of electrons).
Anions: Negatively charged ions (gain of electrons).
Example: Sodium (Na) loses one electron to form Na+; chlorine (Cl) gains one electron to form Cl-.
Ionic Compound: NaCl (sodium chloride) is formed from Na+ and Cl-.

Chemical Formulas and Nomenclature

Writing and Naming Compounds

Chemical formulas represent the types and numbers of atoms in a compound. Nomenclature rules help name compounds systematically.

Ionic Compounds: Composed of metals and nonmetals; named by cation first, then anion.
Molecular Compounds: Composed of nonmetals; prefixes indicate the number of each atom.
Example: CO2 is carbon dioxide; Na2S is sodium sulfide.

Polyatomic Ions and Common Charges

Important Polyatomic Ions

Polyatomic ions are charged species composed of two or more atoms covalently bonded.

Name	Formula
Acetate	CH3COO-
Sulfate	SO42-
Nitrate	NO3-
Ammonium	NH4+
Phosphate	PO43-

Unit Conversions and Useful Constants

Common Unit Conversions

Unit conversions are essential for solving chemistry problems. Use conversion factors to change from one unit to another.

Length: 1 kilometer = 0.6214 mile; 1 meter = 39.37 inches
Mass: 1 kilogram = 2.205 pounds
Volume: 1 liter = 1000 milliliters

Temperature Conversions

Sample Calculations

Density and Volume

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

Formula:
Example: If the density of titanium is 4.50 g/cm3 and the mass is 3.7 g, then cm3.

Significant Figures in Calculations

When multiplying or dividing, the answer should have the same number of significant figures as the measurement with the fewest significant figures.
When adding or subtracting, the answer should have the same number of decimal places as the measurement with the fewest decimal places.

Classification of Elements and Compounds

Metals vs. Nonmetals

Metals: Calcium, Lead
Nonmetals: Oxygen, Arsenic, Phosphorous

Ionic vs. Molecular Compounds

Compound	Type
SrCl2	Ionic
CS2	Molecular
LiClO4	Ionic
PbS	Ionic

Periodic Table Reference

Organization and Use

The periodic table is a fundamental tool for understanding element properties, trends, and relationships.

Groups (columns) contain elements with similar chemical properties.
Periods (rows) indicate increasing atomic number.
Transition metals are found in the center block.

Useful Information and Constants

1 cal = 4.184 J
Density of water = 1.00 g/mL
C (water) = 4.184 J/goC

Summary Table: Common Polyatomic Ions

Name	Formula
Acetate	CH3COO-
Carbonate	CO32-
Nitrate	NO3-
Sulfate	SO42-
Phosphate	PO43-
Ammonium	NH4+

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard introductory chemistry curriculum.