CHEM 1050 Exam 1 Study Guide: Matter, Measurement, Atoms, and Compounds

Chemistry Basics: Matter and Measurement

Periodic Table: Groups, Periods, Metals, and Nonmetals

The periodic table organizes elements by increasing atomic number and groups them based on similar properties.

• Groups: Vertical columns; elements in the same group have similar chemical properties.

• Periods: Horizontal rows; elements in the same period have the same number of electron shells.

• Metals: Located on the left and center; typically shiny, malleable, and good conductors.

• Nonmetals: Located on the right; often dull, brittle, and poor conductors.

• Chemical Formulas: Indicate the number and type of atoms in a compound (e.g., H2O has 2 hydrogen and 1 oxygen atom).

Physical vs. Chemical Changes

Understanding the difference between physical and chemical changes is fundamental in chemistry.

• Physical Change: Alters the form or appearance but not the composition (e.g., melting ice).

• Chemical Change: Produces new substances (e.g., burning wood).

• Reactants: Substances present before a chemical reaction.

• Products: Substances formed as a result of a chemical reaction.

• Balancing Equations: Ensures the same number of atoms for each element on both sides of the equation.

Example: Balancing the reaction for water formation:

$2H_2 + O_2 \rightarrow 2H_2O$

Significant Figures and Measurement

Accurate measurement and reporting are essential in chemistry.

• Significant Figures: Digits in a measurement that are known with certainty plus one estimated digit.

• Certain Digits: Digits definitely known from the measurement device.

• Uncertain Digits: The last digit, estimated by the observer.

• Rules for Significant Figures: Apply when adding, subtracting, multiplying, or dividing measurements.

• Rounding: Values are rounded to the correct number of significant figures based on calculation rules.

• Scientific Notation: Expresses numbers as a product of a coefficient and a power of ten (e.g., $3.2 \times 10^4$).

• Prefixes: Common metric prefixes include micro- ($\mu$), milli- (m), centi- (c), deci- (d), kilo- (k).

• Dimensional Analysis: Method for converting units using conversion factors.

Example: Converting 5.0 cm to meters:

$5.0\ \text{cm} \times \frac{1\ \text{m}}{100\ \text{cm}} = 0.050\ \text{m}$

Volume and Density Calculations

Volume and density are key physical properties used to characterize substances.

• Volume by Water Displacement: The volume of a solid is found by the change in water level when the solid is submerged.

• Density: The mass per unit volume of a substance.

Formula:

$\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

Unit Conversion in Health Contexts

Unit conversions are essential for dosage calculations in health-related fields.

• Dosage Calculations: Use dimensional analysis to convert between units (e.g., mg to g).

Example: Converting 500 mg to grams:

$500\ \text{mg} \times \frac{1\ \text{g}}{1000\ \text{mg}} = 0.5\ \text{g}$

Atoms and Radioactivity

Structure of the Atom

Atoms are the basic units of matter, composed of subatomic particles.

• Protons: Positively charged, located in the nucleus.

• Neutrons: Neutral, located in the nucleus.

• Electrons: Negatively charged, orbit the nucleus.

Atomic Data and Symbolic Notation

Atomic properties can be determined from periodic table data.

• Atomic Number (Z): Number of protons.

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

• Charge: Difference between protons and electrons.

• Symbolic Notation: Represents an atom as $^A_Z\text{X}$ where X is the element symbol.

Example: Carbon-14: $^{14}_6\text{C}$

Mass Number vs. Atomic Mass; Isotopes

Understanding atomic mass and isotopes is important for interpreting chemical properties.

• Mass Number: Total number of protons and neutrons in an atom.

• Atomic Mass: Weighted average mass of all isotopes of an element (found on the periodic table).

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

Compounds: How Elements Combine

Valence Electrons and the Octet Rule

Valence electrons determine how atoms interact and form compounds.

• Valence Electrons: Electrons in the outermost shell; involved in bonding.

• Octet Rule: Atoms tend to gain, lose, or share electrons to achieve eight valence electrons.

• Main Group Elements: Groups 1, 2, and 3A–8A; their valence electrons can be determined from their group number.

Ions: Cations and Anions

Atoms form ions to achieve stable electron configurations.

• Ion: An atom or molecule with a net charge due to loss or gain of electrons.

• Cation: Positively charged ion (loss of electrons).

• Anion: Negatively charged ion (gain of electrons).

• Noble Gas Configuration: Atoms gain or lose electrons to match the electron configuration of noble gases.

• Electron Transfer Reactions: Show how atoms gain or lose electrons to form ions.

Example: Sodium (Na) loses one electron to become Na+:

$\text{Na} \rightarrow \text{Na}^+ + e^-$

Chlorine (Cl) gains one electron to become Cl-:

$\text{Cl} + e^- \rightarrow \text{Cl}^-$

Table: Main Group Elements and Their Likely Charges

Group	Valence Electrons	Likely Charge	Example Element
1 (1A)	1	+1	Na
2 (2A)	2	+2	Mg
3A	3	+3	Al
5A	5	-3	N
6A	6	-2	O
7A	7	-1	Cl
8A	8	0	Ne

Additional info: Table inferred from periodic trends and main group element behavior.