Measurement and Unit Conversions

Metric System and Conversion Factors

Understanding the metric system and how to convert between units is essential in chemistry. The metric system uses prefixes to indicate multiples or fractions of base units.

• Common Prefixes: kilo (k), centi (c), milli (m), micro (μ), nano (n)

• Conversion Factors: Used to convert from one unit to another (e.g., liters to milliliters, kilograms to milligrams).

Example Conversions:

• Liters to milliliters: $1\ \text{L} = 1000\ \text{mL}$

• Kilograms to milligrams: $1\ \text{kg} = 1,000,000\ \text{mg}$

• Nanometers to meters: $1\ \text{nm} = 1 \times 10^{-9}\ \text{m}$

• Millimeters to meters: $1\ \text{mm} = 1 \times 10^{-3}\ \text{m}$

Significant Figures: Always report answers with the correct number of significant figures based on the data provided.

Specific Heat and Calorimetry

Calculating Heat Transfer

Specific heat is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius.

• Formula: $q = SH \times m \times \Delta T$

• Variables:

  • $q$ = heat (calories or joules)

  • $SH$ = specific heat (cal/g°C or J/g°C)

  • $m$ = mass (g)

  • $\Delta T$ = change in temperature ($T_{final} - T_{initial}$)

Example: Calculate the heat required to raise the temperature of 156 g of aluminum from 21.9°C to 128°C, given $SH = 0.220$ cal/g°C.

• $\Delta T = 128 - 21.9 = 106.1\ ^\circ\text{C}$

• $q = 0.220 \times 156 \times 106.1$

Atomic Structure and Electron Configuration

Subatomic Particles and Atomic Number

Atoms consist of protons, neutrons, and electrons. The atomic number is the number of protons in the nucleus, which defines the element.

• Protons: Positively charged particles in the nucleus

• Neutrons: Neutral particles in the nucleus

• Electrons: Negatively charged particles in orbitals around the nucleus

• Mass Number: Sum of protons and neutrons

Electron Configuration and Orbital Diagrams

Electron configuration describes the arrangement of electrons in an atom's orbitals.

• Order of Filling: 1s, 2s, 2p, 3s, 3p, 4s, 3d, etc.

• Box Diagrams: Visual representation of electrons in orbitals, showing paired and unpaired electrons.

Example: For sodium (Na, atomic number 11):

• Electron configuration: $1s^2\ 2s^2\ 2p^6\ 3s^1$

Ions and Ionic Compounds

Formation of Ions

Ions are formed when atoms gain or lose electrons to achieve a stable electron configuration.

• Cations: Positively charged ions (loss of electrons)

• Anions: Negatively charged ions (gain of electrons)

Lewis Structures and Ionic Bonding

Lewis structures show the arrangement of valence electrons. Ionic bonds form when electrons are transferred from one atom to another.

• Example: Na transfers an electron to Br, forming Na+ and Br-.

Table: Formation of Ions

Naming and Writing Formulas for Ionic Compounds

Rules for Naming Ionic Compounds

Ionic compounds are named by stating the cation first, followed by the anion. The formula must balance the charges.

• Example: Potassium fluoride: K+ and F- combine to form KF.

Chemical Bonding and Molecular Structure

Lewis Dot Structures and Molecular Geometry

Lewis dot structures represent valence electrons as dots around the element symbol. Molecular geometry describes the shape of molecules based on the number of bonded atoms and lone pairs.

• Bonded Atom Groups: Number of atoms directly bonded to the central atom

• Lone Pairs: Non-bonding pairs of electrons on the central atom

• Shape: Determined by VSEPR theory (e.g., bent, tetrahedral, linear)

• Polarity: Molecules are polar if they have an uneven distribution of charge

Table: Molecular Geometry and Polarity

Properties of Matter and Classification

States of Matter and Physical vs. Chemical Changes

Matter exists as solids, liquids, or gases. Physical changes do not alter the chemical identity, while chemical changes result in new substances.

• Physical Change: Melting, boiling, dissolving

• Chemical Change: Burning, rusting, reacting

Mixtures and Pure Substances

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

• Heterogeneous Mixture: Non-uniform composition (e.g., salad)

Density and Calculations

Density Formula and Applications

Density is the mass per unit volume of a substance.

• Formula: $d = \frac{m}{v}$

• Units: g/mL, g/cm3

Example: If a liquid has a mass of 17.2 g and a volume of 25.0 mL, its density is:

• $d = \frac{17.2}{25.0} = 0.688\ \text{g/mL}$

Additional Info

• Temperature conversions: $K = ^\circ\text{C} + 273$; $^\circ\text{F} = \frac{9}{5} ^\circ\text{C} + 32$; $^\circ\text{C} = \frac{5}{9} (^\circ\text{F} - 32)$

• Significant figures are important in all calculations.

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