Atoms and Elements

Subatomic Particles

Atoms are composed of three fundamental subatomic particles: protons, neutrons, and electrons. Each has distinct properties that determine the structure and behavior of atoms.

• Protons: Positively charged particles found in the nucleus. Relative mass ≈ 1 amu.

• Neutrons: Neutral particles (no charge) also located in the nucleus. Relative mass ≈ 1 amu.

• Electrons: Negatively charged particles found in orbitals surrounding the nucleus. Relative mass ≈ 0.0005 amu (much lighter than protons or neutrons).

Example: A carbon atom (C) has 6 protons, 6 neutrons (in its most common isotope), and 6 electrons.

Isotopes

Isotopes are atoms of the same element (same number of protons) that have different numbers of neutrons, resulting in different mass numbers.

• Example: Carbon-12 (12C) and Carbon-14 (14C) are isotopes of carbon.

Atomic Symbols

Atomic symbols represent the composition of atoms and ions, showing atomic number (Z), mass number (A), and charge.

• General format: AZXcharge

• Example: 2311Na+ represents a sodium ion with mass number 23, atomic number 11, and a +1 charge.

Atomic Mass Unit (amu) and Average Atomic Mass

The atomic mass unit (amu) is defined as 1/12 the mass of a carbon-12 atom. The average atomic mass of an element is the weighted average of the masses of its naturally occurring isotopes.

• Formula:

• Example: Chlorine has two main isotopes: Cl-35 and Cl-37. If their abundances are 75% and 25%, respectively, the average atomic mass is calculated accordingly.

Chemical Formulas and Molecules

Molecular and Empirical Formulas

Molecular formulas show the exact number of each type of atom in a molecule, while empirical formulas show the simplest whole-number ratio of atoms.

• Example: Glucose: Molecular formula = C6H12O6; Empirical formula = CH2O

The Periodic Table

Periodic Law and Organization

The periodic law states that the properties of elements are periodic functions of their atomic numbers. The periodic table is organized into periods (rows) and groups (columns) based on recurring chemical properties.

• Periods: Horizontal rows (numbered 1–7)

• Groups: Vertical columns (numbered 1–18 or with group names such as alkali metals, halogens, etc.)

Matter and Its Properties

Definition and States of Matter

Matter is anything that has mass and occupies space. It exists in three primary physical states:

• Solid: Definite shape and volume

• Liquid: Definite volume, takes the shape of its container

• Gas: No definite shape or volume; expands to fill its container

Physical vs. Chemical Properties and Changes

• Physical properties: Can be observed without changing the substance's identity (e.g., melting point, density).

• Chemical properties: Describe a substance's ability to undergo chemical changes (e.g., flammability, reactivity).

• Physical change: Alters form but not composition (e.g., melting ice).

• Chemical change: Alters the chemical composition (e.g., rusting iron).

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., density, boiling point).

Measurement and Calculations

Measurement Process

Every measurement consists of three parts: a number, a unit, and an indication of uncertainty.

• Uncertainty: All measurements have some degree of uncertainty, often reflected in the last significant digit.

Significant Figures and Rounding

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

• Rules: For addition/subtraction, round to the least number of decimal places; for multiplication/division, round to the least number of significant figures.

Unit Conversions and Dimensional Analysis

Unit conversions use dimensional analysis to convert between different units of measurement.

• Example: Converting 10.0 inches to centimeters using the conversion factor 1 inch = 2.54 cm.

• Temperature conversions:

Mass, Moles, and Number of Particles

• Mole: The amount of substance containing Avogadro's number () of particles.

• Conversions:

Electromagnetic Radiation and Atomic Structure

Properties of Electromagnetic Waves

• Wavelength (\(\lambda\)): Distance between two consecutive peaks.

• Frequency (\(\nu\)): Number of cycles per second (Hz).

• Amplitude: Height of the wave from the center line.

• Speed of light (c): m/s

• Relationship:

Energy of Electromagnetic Radiation

• Planck's equation:

• Where: J·s (Planck's constant)

Bohr Model of the Hydrogen Atom

The Bohr model describes electrons in quantized orbits around the nucleus, explaining the line spectra of hydrogen.

• Ground state: Lowest energy level

• Excited state: Higher energy levels

• Energy transitions: When electrons move between levels, photons are emitted or absorbed.

• Bohr equation: J

Photon Energy and Wavelength

• Energy of a photon:

Quantum Numbers

Four quantum numbers describe the properties of electrons in atoms:

• Principal (n): Energy level (n = 1, 2, 3, ...)

• Angular momentum (l): Shape of orbital (l = 0 to n-1)

• Magnetic (ml): Orientation of orbital (ml = -l to +l)

• Spin (ms): Electron spin (+1/2 or -1/2)

Classification of Elements and Chemical Bonds

Metals, Nonmetals, and Metalloids

• Metals: Good conductors, malleable, ductile, shiny; found on the left and center of the periodic table.

• Nonmetals: Poor conductors, brittle, dull; found on the right side of the periodic table.

• Metalloids: Properties intermediate between metals and nonmetals; found along the staircase line.

Chemical Bonds

• Ionic bonds: Formed between metals and nonmetals via transfer of electrons.

• Covalent bonds: Formed between nonmetals via sharing of electrons.

• Metallic bonds: Involve a 'sea' of delocalized electrons among metal atoms.