chapter 1 lec 1

CHAPTER 1: Chemistry – The Study of Change

Introduction to Chemistry

Chemistry is known as the central science because it studies matter and the changes it undergoes, impacting fields from medicine to materials science. Success in chemistry requires critical thinking, not rote memorization, and consistent study habits.

• Chemistry: The study of matter and its transformations.

• Applications: Food, pharmaceuticals, energy, new materials (e.g., semiconductors, LCDs, diamond coatings).

• Critical thinking is essential for problem-solving in chemistry.

The Scientific Method

The scientific method is a systematic approach to research and problem-solving in chemistry.

1. Define the problem

2. Perform experiments: Make careful observations and record data (qualitative or quantitative).

3. Formulate a hypothesis: A tentative explanation for observations.

4. Formulate a law: A concise statement (verbal or mathematical) describing a consistent relationship.

5. Develop a theory: A unifying principle explaining a body of facts, not yet a law.

Phases and Classification of Matter

Definition and Types of Matter

Matter is anything that occupies space and has mass. It can be classified as substances or mixtures.

• Substance: Matter with definite composition and distinct properties (e.g., copper, water).

• Mixture: Combination of two or more substances retaining their individual identities.

• Mass: Measure of the amount of matter.

• Weight: Force gravity exerts on an object; varies with location (e.g., moon vs. earth).

Classification of Matter

• Pure Substance: Constant composition; can be an element or compound.

• Element: Cannot be separated into simpler substances by chemical means (e.g., Cu, H).

• Compound: Composed of two or more elements chemically united in fixed proportions (e.g., H2O, CuSO4).

• Mixture: Variable composition; can be separated by physical means.

Types of Mixtures

• Homogeneous Mixture: Uniform composition throughout (e.g., salt water, air).

• Heterogeneous Mixture: Non-uniform composition; components are visibly distinct (e.g., sand and iron filings).

States of Matter

• Solid: Rigid, definite shape.

• Liquid: Fluid, takes shape of container, flows.

• Gas: Fluid, expands to fill container.

• States can be interconverted without changing chemical composition (e.g., ice → water → steam).

Physical and Chemical Properties

Physical Properties

Physical properties can be measured without changing the substance's composition.

• Examples: Color, melting point, boiling point, viscosity, density.

• Measurement does not alter the substance (e.g., measuring gold's density leaves gold unchanged).

Chemical Properties

Chemical properties are observed only during a chemical change.

• Example: Iron reacts with hydrochloric acid to form iron(II) chloride and hydrogen gas.

$\mathrm{Fe(s) + 2HCl(aq) \rightarrow FeCl_2(aq) + H_2(g)}$

Extensive vs. Intensive Properties

• Extensive Properties: Depend on the amount of matter (e.g., mass, volume).

• Intensive Properties: Independent of the amount of matter (e.g., temperature, density).

Elements, Compounds, and Ions

Element Symbols and Groups

Element symbols are one or two letters; the first is always capitalized.

• Group 1 (Alkali Metals): H, Li, Na, K, Rb, Cs (form +1 cations).

• Group 2 (Alkaline Earth Metals): Be, Mg, Ca, Sr, Ba (form +2 cations).

• Group 7A/17 (Halogens): F, Cl, Br, I (form -1 anions).

• Group 6A/16: O, S, Se, Te (form -2 anions).

• Group 5A/15: N, P, As (form -3 anions).

• Group 4A/14: C, Si, Ge (can form -4 anions).

Compounds

• Composed of two or more elements chemically united in fixed proportions.

• Cannot be separated by physical means; have unique properties.

• Examples: C2H5OH (ethyl alcohol), CuCl2, KMnO4, CO2.

Ions

An ion is an atom or group of atoms with a positive or negative charge, formed by loss or gain of electrons.

• Cations: Positively charged, formed by loss of electrons (e.g., Na+, Ca2+).

• Anions: Negatively charged, formed by gain of electrons (e.g., Cl-, O2-).

• Monatomic ions: Single atom ions (e.g., Fe2+, Br-).

• Polyatomic ions: Groups of atoms bonded together with a net charge (e.g., NH4+, SO42-).

Common Polyatomic Ions

Name	Formula/Charge	Name	Formula/Charge
Ammonium	NH4+	Hydronium	H3O+
Mercury(I)	Hg22+	Mercury(II)	Hg2+
Azide	N3-	Chromate	CrO42-
Perchlorate	ClO4-	Dichromate	Cr2O72-
Chlorate	ClO3-	Phosphate	PO43-
Chlorite	ClO2-	Hydrogen Phosphate	HPO42-
Hypochlorite	ClO-	Dihydrogen Phosphate	H2PO4-
Cyanide	CN-	Oxalate	C2O42-
Carbonate	CO32-	Hydroxide	OH-
Hydrogen Carbonate	HCO3-	Nitrate	NO3-
Peroxide	O22-	Nitrite	NO2-
Hydrogen Sulphate	HSO4-	Permanganate	MnO4-
Phosphite	PO33-	Sulfate	SO42-
Hydrogen Phosphite	HPO32-	Sulfite	SO32-
Thiocyanate	SCN-

Measurements and Calculations

Scientific Notation

Scientific notation is used to express very large or small numbers conveniently.

• Format: $a \times 10^n$ where $a$ is a number with one integer to the left of the decimal.

• Positive exponent: Decimal moved left (large numbers).

• Negative exponent: Decimal moved right (small numbers).

Example: 0.002456 g = $2.456 \times 10^{-3}$ g

Operations with Scientific Notation

• Add/Subtract: Exponents must be the same before performing the operation.

• Multiply: Add exponents.

• Divide: Subtract exponents.

Examples:

• Add: $3.245 \times 10^2 + 1.456 \times 10^4 = 3.245 \times 10^2 + 145.6 \times 10^2 = 148.845 \times 10^2 = 1.48845 \times 10^4$

• Multiply: $4.550 \times 10^{-2} \times 3.245 \times 10^{-3} = 1.476475 \times 10^{-4}$

• Divide: $4.550 \times 10^{-2} \div 3.245 \times 10^{-3} = 1.402157164 \times 10^1$

Significant Figures

Significant figures indicate the precision of a measurement. The last digit is always uncertain.

• Non-zero digits are always significant.

• Zeros between non-zero digits are significant (e.g., 12.005302 has 8 sig. figs).

• Leading zeros are not significant (e.g., 0.001234 has 4 sig. figs).

• Trailing zeros are significant if there is a decimal point (e.g., 3.400 has 4 sig. figs).

• Trailing zeros in numbers without a decimal may or may not be significant; scientific notation clarifies this.

Rules for Calculations with Significant Figures

• Addition/Subtraction: Answer cannot have more digits to the right of the decimal than the number with the fewest.

• Multiplication/Division: Answer is limited by the number with the fewest significant figures.

Examples:

• Add: $1.2345 + 38.2 + 0.02234 = 39.5$ (3 sig. figs)

• Multiply: $12.345 \times 38.2 \times 0.02234 = 10.5$ (3 sig. figs)

• Divide: $1.24678 \div (22.16 \times 1.220) = 0.04612$ (4 sig. figs)

Units and Conversions

SI Units

• Length: meter (m)

• Mass: gram (g)

• Temperature: Celsius (°C)

• Amount of substance: mole (mol)

Common Multipliers

• Kilo: $1 \text{ kg} = 1000 \text{ g}$

• Milli: $1 \text{ mL} = 0.001 \text{ L}$

• Micro: $1 \mu\text{g} = 1 \times 10^{-6} \text{ g}$

• Nano: $1 \text{ ng} = 1 \times 10^{-9} \text{ g}$

Conversion Factors

• $1 \text{ foot} = 12 \text{ inches}$

• $1 \text{ inch} = 2.54 \text{ cm}$

• $5280 \text{ ft} = 1 \text{ mile}$

• $453 \text{ g} = 1 \text{ lb}$

Temperature Conversions

• Celsius to Kelvin: $K = ^\circ C + 273.15$

• Celsius to Fahrenheit: $^\circ F = \frac{9}{5} \times ^\circ C + 32$

Example: $38.1^\circ C$ to Kelvin: $38.1 + 273.15 = 311.25 \text{ K}$ $38.1^\circ C$ to Fahrenheit: $\frac{9}{5} \times 38.1 + 32 = 100.6^\circ F$

Density

• Density: Ratio of mass to volume.

$\text{Density} = \frac{\text{mass}}{\text{volume}}$

Example: Calculate volume if density is $1.345 \text{ g/mL}$ and mass is $14.62 \text{ g}$: $\text{Volume} = \frac{\text{mass}}{\text{density}} = \frac{14.62}{1.345} = 10.87 \text{ mL}$ (rounded to correct sig. figs)

Dimensional Analysis

Dimensional analysis uses conversion factors to solve unit conversion problems.

• Example: Convert $1252 \text{ in}$ to cm: $1252 \times \frac{2.54 \text{ cm}}{1 \text{ in}} = 3180 \text{ cm}$ (rounded to correct sig. figs)

Summary Table: Classification of Matter

Type	Description	Examples
Element	Cannot be separated by chemical means	Cu, H, O
Compound	Two or more elements chemically united	H2O, CuSO4
Homogeneous Mixture	Uniform composition	Air, salt water
Heterogeneous Mixture	Non-uniform composition	Sand and iron filings

Key Takeaways

• Chemistry requires understanding, not memorization.

• Matter is classified as elements, compounds, and mixtures.

• Physical and chemical properties help distinguish substances.

• Measurements must be precise, using correct significant figures and units.

• Dimensional analysis and scientific notation are essential tools for calculations.