Elementa

I. Elements: The Building Blocks of Matter

• Definition: Elements are fundamental substances that cannot be broken down into simpler substances through chemical means.

  • "Elements are substances that cannot be broken down by chemical means into simpler substances."

• The Periodic Table: A summary of the elements and an essential chemistry tool, regularly updated with new discoveries.

  • Currently, there are 118 known elements.

  • "Today there are 118 known elements."

• Natural vs. Man-Made: The first 94 elements are found in nature; the rest have been synthesized.

  • "The first 94 elements have been found in nature and the rest have been man-made."

• Isotopes and Radioactivity: Most elements have at least one stable isotope, while others are radioactive.

  • Radioactive decay involves the nucleus splitting and emitting particles, and transforms one element into another.

  • "80 of the elements have at least one stable isotope while the remaining are radioactive…"

• Abundance in the Universe and Earth:

  • Hydrogen and helium are the most abundant elements, formed during the Big Bang.

  • Earth is mostly iron (approximately 89%), with silicon and oxygen dominating the surface.

  • The atmosphere is primarily nitrogen and oxygen; oceans are mostly hydrogen and oxygen (water).

• Life and Technology: Life relies on carbon and other key elements (oxygen, nitrogen, hydrogen), with carbon being an energy source.

• Standardization of Names and Symbols: IUPAC standardizes element names and symbols for global communication.

  • "The names and symbols of the elements are now standardized worldwide by the IUPAC."

• Historical Names and Symbols: Many symbols derive from Latin names used in international chemistry.

• Memorization of Names and Symbols: Students should be aware that some symbols differ from their English names (e.g., Fe for iron).

• Format of Chemical Symbols: The first letter of a symbol is capitalized, and the second is lowercase, avoiding confusion.

  • "Notice the format of the chemical symbols."

II. Atoms and the Organization of the Periodic Table

• Atomic Structure: Atoms consist of protons, neutrons, and electrons. The atomic number (number of protons) defines an element and its properties.

• Organization by Atomic Number: The periodic table arranges elements by increasing atomic number.

• Periods and Groups: Horizontal rows are periods (numbered 1-7), and vertical columns are groups with similar properties.

  • IUPAC numbering (1-18) is now standard.

• Neutral Atoms: In a neutral atom, protons equal electrons.

• Metals, Non-metals, and Metalloids: Divided by a metalloid line, metals are on the left, non-metals on the right, and metalloids along the line.

• Main Group, Transition, and Inner Transition Elements: Main group elements on the left and right, transition metals in the center, and inner transition metals at the bottom.

• Hydrogen's Position: Hydrogen is classified as a non-metal but behaves similarly to elements between boron and carbon.

• Group Names: Specific group names include:

  • Group 1A: Alkali metals

  • Group 2A: Alkaline earth metals

  • Group 7A: Halogens

  • Group 8A: Noble gases

• Importance of Periodic Table Divisions: Helps predict chemical behavior; metals form cations, and non-metals form anions.

• Diatomic Molecules: Elements such as nitrogen and oxygen exist as diatomic molecules.

• Allotropes: Elements can exist in different forms that have different properties (e.g., carbon as diamond or graphite).

• Importance of Memorization: Students should memorize element names and symbols, focusing on the first three rows and commonly encountered elements.

III. Ions: Charged Atoms and Molecules

• Formation of Ions: Ions are formed when atoms gain or lose electrons, resulting in a net charge.

• Cations and Anions:

  • Cations: Positively charged ions (loss of electrons).

  • Anions: Negatively charged ions (gain of electrons).

• Predicting Ion Formation: Metals form cations; non-metals form anions.

• Noble Gas Configuration: Ions tend toward a stable electron configuration similar to noble gases.

• Examples of Ion Formation:

  • Sodium (Na) loses an electron to form Na⁺.

  • Chlorine (Cl) gains an electron to form Cl⁻.

• Writing Ion Charges: Charges are written as superscripts; IUPAC prefers +/− for single charges.

• Main Group Ion Formation Patterns:

  • Group 1A: +1 cations

  • Group 2A: +2 cations

  • Group 7A: -1 anions

  • Group 6A: -2 anions

  • Group 5A: -3 anions

  • Aluminum typically forms +3 ions.

• Transition Metal Ion Formation: Transition metals can exhibit multiple oxidation states.

• Memorizing Ions: Students should memorize common ion symbols and charges.

IV. Chemical Bonding: Holding Atoms Together

• Definition of a Chemical Bond: An attractive force between atoms overcoming nuclear repulsion.

• Purpose of Bonding: Atoms bond to achieve a stable electron configuration, typically through closed shells.

• Types of Chemical Bonds:

  • Ionic Bonds: Involve electron transfer, creating oppositely charged ions.

  • Covalent Bonds: Involve electron sharing between atoms.

• Ionic Bond Formation Example: Sodium transfers its valence electron to sulfur, forming Na⁺ and S²⁻.

• Covalent Bond Formation Example: Hydrogen atoms share electrons achieving stable configurations.

• Molecules and Extended Arrays: Covalently bonded compounds form discrete molecules; ionic compounds form repeating arrays.

• Representing Chemical Compounds:

  • Space-filling models: Spheres represent atoms.

  • Ball-and-stick models: Sticks represent bonds.

  • Chemical formulas: Indicate types and proportions of atoms.

• Chemical Formulas and Proportions: Atoms combine in fixed ratios to form compounds.

• Subscripts and Parentheses: Indicate quantities and groupings of elements in formulas.

• Types of Chemical Formulas:

  • Molecular Formula: Exact number of atoms.

  • Empirical Formula: Simplest ratio of elements.

  • Structural Formula: Arrangement of atoms and bonds in a molecule.