Chemistry in Our Lives

What is Chemistry?

Chemistry is the study of the composition, structure, properties, and reactions of matter. Matter refers to all substances that make up our world, from the air we breathe to the materials we use daily.

• Matter: Anything that has mass and occupies space.

• Application: Chemistry helps us understand the materials and processes that are fundamental to life and technology.

The Scientific Method

The scientific method is a systematic approach used by scientists to explore observations, answer questions, and solve problems.

1. Make Observations: Gather information using the senses or instruments.

2. Form a Hypothesis: Propose a tentative explanation or prediction.

3. Design Experiments: Test the hypothesis through controlled experiments.

4. Draw a Conclusion: Analyze data and determine if the hypothesis is supported.

Chemistry and Measurements

Calculating Percentages

Percentages are used to express proportions in chemistry, such as concentration or yield.

• Formula:

• Example:

Identifying Place Values and Scientific Notation

Scientific notation expresses very large or small numbers using powers of ten. The coefficient must be between 1 and 10.

• Example:

• Positive exponent: Large numbers; Negative exponent: Small numbers.

Significant Figures

Significant figures (SFs) in a measured number include all certain digits plus one estimated digit. The rules for counting significant figures depend on the position of zeros.

• Nonzero digits: Always significant.

• Zeros: May or may not be significant depending on their position.

Rounding Off: When rounding, retain only as many significant figures as justified by the measurement.

Metric and SI Prefixes

The metric system uses prefixes to indicate multiples or fractions of units.

• Kilo- (k):

• Centi- (c):

• Milli- (m):

• Micro- (\mu):

• Nano- (n):

Unit Conversions and Density

Units can be converted by squaring or cubing both the number and the unit for area and volume. Density determines whether an object will sink or float in water.

• Density:

• Objects denser than water sink; less dense objects float.

Matter and Energy

Classification of Matter

Matter can be classified as pure substances or mixtures.

• Pure Substance: Consists of one type of atom or molecule (e.g., elements like silver, compounds like H2O).

• Mixture: Physical combination of two or more substances.

• Homogeneous Mixture (Solution): Uniform composition (e.g., air, seawater).

• Heterogeneous Mixture: Non-uniform composition (e.g., oil and water, cookie with raisins).

Physical and Chemical Properties and Changes

• Physical Property: Observed without changing the substance's identity (e.g., melting point).

• Chemical Property: Describes the ability to change into a new substance (e.g., flammability).

• Physical Change: Alters physical properties, not composition (e.g., melting ice).

• Chemical Change: Produces new substances (e.g., rusting iron).

Energy: Kinetic and Potential

Energy is the capacity to do work. It exists as kinetic (motion) or potential (position/composition).

• Kinetic Energy: Energy of motion.

• Potential Energy: Stored energy due to position or composition.

Temperature and Heat Calculations

• Boiling Point: F = 212°F, C = 100°C, K = 373 K

• Freezing Point: F = 32°F, C = 0°C, K = 273 K

• Conversions:

  • Fahrenheit to Celsius:

  • Celsius to Fahrenheit:

  • Celsius to Kelvin:

• Specific Heat (SH): , where is heat, is mass, is temperature change.

• Heat Equation:

Atoms and Elements

Structure of the Atom

Atoms consist of a nucleus (protons and neutrons) and electrons in surrounding energy levels.

• Protons: Positive charge (+)

• Neutrons: No charge

• Electrons: Negative charge (−)

• Atomic Number (Z): Number of protons

• Mass Number (A): Protons + Neutrons

• In a neutral atom: Number of protons = number of electrons

Isotopes

Isotopes are atoms of the same element with different numbers of neutrons.

• Atomic Symbol: Mass number (upper left), atomic number (lower left)

• Example: and

• Atomic Mass Calculation: Weighted average of isotopic masses and abundances.

Classification of Elements

• Metals: Shiny, malleable, good conductors; left of zigzag line.

• Nonmetals: Dull, poor conductors; right of zigzag line.

• Metalloids: Properties of both; along zigzag line.

• Groups:

  • Alkali Metals (1A): Soft, shiny, 1 valence electron

  • Alkaline Earth Metals (2A): 2 valence electrons

  • Halogens (7A): 7 valence electrons

  • Noble Gases (8A): 8 valence electrons (except He: 2)

Electronic Structure of Atoms and Periodic Trends

Electromagnetic Radiation

Electromagnetic radiation includes radio waves, visible light, and more. All travel at the speed of light ().

• Wavelength (λ): Distance between wave crests or troughs.

• Frequency (ν): Number of waves passing a point per second.

• Relationship:

• Visible Light: 400–700 nm (violet to red)

• Energy: Higher frequency = higher energy

Atomic Spectra

Atomic spectra show discrete lines, indicating quantized energy levels in atoms. White light contains all visible wavelengths.

Valence Electrons and Periodic Trends

• Valence Electrons: Electrons in the outermost energy level; determine chemical properties.

• Group Number: Indicates number of valence electrons for main group elements.

• Electron Configuration: Example for argon: (8 valence electrons in 3rd shell)

• Atomic Size: Determined by distance of valence electrons from nucleus; trends down a group and across a period.

Ionic and Molecular Compounds

Ionic and Covalent Bonds

• Ionic Bonds: Transfer of electrons from metals to nonmetals, forming cations and anions (e.g., NaCl).

• Covalent Bonds: Sharing of electrons between nonmetals (e.g., H2O, C3H8).

Writing Formulas and Naming Compounds

• Charge Balance: Total positive and negative charges must equal zero in ionic compounds.

• Polyatomic Ions: Groups of atoms with a charge (e.g., sulfate SO42−, sulfite SO32−).

• Naming:

  • Metal first, then nonmetal (ending in -ide).

  • Roman numeral for metals with multiple charges (e.g., lead(II) sulfate).

  • Polyatomic ions retain their names (ending in -ate or -ite).

• Example: Magnesium phosphide: Mg3P2 (from Mg2+ and P3−)

Cations and Anions

• Cation: Positively charged ion (e.g., Na+, Mg2+).

• Anion: Negatively charged ion (e.g., Cl−, O2−).

• Formation: Metals lose electrons (cations); nonmetals gain electrons (anions).

Bonding and Properties of Solids and Liquids

Lewis Structures and Bonding Patterns

Lewis structures represent valence electrons as dots around element symbols, showing bonding and lone pairs.

• Ionic Compounds: Show transfer of electrons (e.g., NaCl: Na+ and [Cl]−).

• Typical Bonding Patterns: Nonmetals form predictable numbers of bonds (e.g., oxygen forms two, nitrogen three).