Introduction to Chemistry: Study Guide and Electron Configuration Reference

Study Guide for Test 1: Introduction to Chemistry

Steps Involved in the Scientific Method

The scientific method is a systematic approach used in scientific study. It involves making observations, forming hypotheses, conducting experiments, and drawing conclusions.

• Observation: Gathering data and noticing phenomena.

• Hypothesis: Proposing a tentative explanation or prediction.

• Experiment: Testing the hypothesis through controlled procedures.

• Analysis: Interpreting data and results.

• Conclusion: Determining whether the hypothesis is supported or refuted.

Significant Figures

Significant figures are the digits in a measurement that are known with certainty plus one estimated digit. They are important for expressing the precision of measurements and calculations.

• Rules for Single Numbers: All nonzero digits are significant; zeros between nonzero digits are significant; leading zeros are not significant; trailing zeros are significant only if there is a decimal point.

• Rules for Calculations: In multiplication/division, the result should have as many significant figures as the measurement with the fewest significant figures. In addition/subtraction, the result should have as many decimal places as the measurement with the fewest decimal places.

Example: 0.00450 has three significant figures.

Conversion Factor Problems

Conversion factors are ratios used to express a quantity in different units.

• Simple Conversion Factor Problems: Involve a single step, such as converting centimeters to meters.

• Complex (Multi-step) Conversion Factor Problems: Require multiple steps, such as converting inches to kilometers.

Example: To convert 5.0 cm to meters: $5.0\ \text{cm} \times \frac{1\ \text{m}}{100\ \text{cm}} = 0.050\ \text{m}$

Temperature Conversion Calculations

Temperature can be converted between Celsius, Fahrenheit, and Kelvin using specific formulas.

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

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

Density Calculations

Density is the mass per unit volume of a substance.

• Formula: $\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

Example: If a block has a mass of 10 g and a volume of 2 cm3, its density is $\frac{10\ \text{g}}{2\ \text{cm}^3} = 5\ \text{g/cm}^3$.

Components of an Atom

An atom consists of three main subatomic particles: protons, neutrons, and electrons.

• Proton (p+): Positively charged, found in the nucleus.

• Neutron (n0): Neutral, found in the nucleus.

• Electron (e-): Negatively charged, found in electron clouds around the nucleus.

Components of an Isotope

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

• Same number of protons (atomic number)

• Different number of neutrons (mass number varies)

Calculation of Atomic Mass Unit (amu) Given Abundance

The average atomic mass of an element is calculated using the relative abundance and mass of each isotope.

• Formula: $\text{Average Atomic Mass} = \sum (\text{Fractional Abundance} \times \text{Isotopic Mass})$

Example: If an element has two isotopes: 75% with mass 10 amu and 25% with mass 11 amu, average mass = $(0.75 \times 10) + (0.25 \times 11) = 10.25$ amu.

Electron Configuration

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

• Quantum Number: Numbers that describe the properties of atomic orbitals and the properties of electrons in orbitals (principal, angular momentum, magnetic, and spin quantum numbers).

• Electron Configuration of Neutral Atom/Ion: Distribution of electrons among the atom's orbitals, following the Aufbau principle, Pauli exclusion principle, and Hund's rule.

• Noble Gas Notation: Shorthand using the previous noble gas to represent core electrons.

Example: Sodium (Na): $1s^2 2s^2 2p^6 3s^1$

Names and Symbols of Elements

Each element is represented by a unique one- or two-letter symbol. The first letter is always capitalized, the second (if present) is lowercase.

• Example: Hydrogen (H), Carbon (C), Sodium (Na), Iron (Fe)

Percent Mass Calculations

Percent mass is the percentage by mass of each element in a compound.

• Formula: $\%\ \text{mass} = \frac{\text{mass of element in 1 mol of compound}}{\text{molar mass of compound}} \times 100\%$

Example: In H2O, percent mass of H = $\frac{2.02}{18.02} \times 100\% = 11.2\%$

Electron Configuration Reference Tables

Table 1: Electron Configurations of Selected Elements

Element	Atomic Number	Electron Configuration
Sodium	11	1s2 2s2 2p6 3s1
Bromine	35	1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
Calcium	20	1s2 2s2 2p6 3s2 3p6 4s2
Iron	26	1s2 2s2 2p6 3s2 3p6 4s2 3d6
Fluorine	9	1s2 2s2 2p5
Chromium	24	1s2 2s2 2p6 3s2 3p6 4s1 3d5
Potassium	19	1s2 2s2 2p6 3s2 3p6 4s1
Krypton	36	1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6
Hydrogen	1	1s1
Carbon	6	1s2 2s2 2p2

Table 2: Electron Configurations and Shell Occupancy

Element	Atomic Number	Electron Configuration
Sodium	11	1s2 2s2 2p6 3s1 (1e in 3rd shell)
Lithium	3	1s2 2s1 (1e in 2nd shell)
Beryllium	4	1s2 2s2 (2e in 2nd shell)
Magnesium	12	1s2 2s2 2p6 3s2 (2e in 3rd shell)
Boron	5	1s2 2s2 2p1 (1e in 2p)
Aluminum	13	1s2 2s2 2p6 3s2 3p1 (1e in 3rd shell)
Carbon	6	1s2 2s2 2p2
Silicon	14	1s2 2s2 2p6 3s2 3p2 (2e in 3rd shell)
Oxygen	8	1s2 2s2 2p4
Sulfur	16	1s2 2s2 2p6 3s2 3p4 (4e in 3rd shell)
Fluorine	9	1s2 2s2 2p5
Chlorine	17	1s2 2s2 2p6 3s2 3p5 (7e in 3rd shell)
Helium	2	1s2 (FULL OUTER SHELL)
Neon	10	1s2 2s2 2p6 (FULL OUTER SHELL)
Argon	18	1s2 2s2 2p6 3s2 3p6 (FULL OUTER SHELL)

Additional info: The tables above provide a reference for electron configurations, which are essential for understanding atomic structure and periodic trends in chemistry.