Key Concepts in Atoms and Chemical Reactions

Definition of Matter:
- Anything with mass that occupies space.
- Composed of elements, approximately 92 naturally occurring.
Elements:
- Pure substances made of a single type of atom.
- Example: Gold consists entirely of gold atoms, each exhibiting gold's properties.
Periodic Table:
- Organized chart that shows elements arranged by atomic number.
- Arrangement reveals patterns related to atomic structure.
- Predictive nature, example: Mendeleev predicted undiscovered elements based on patterns.

Conductivity: Ability of a substance to conduct heat/electricity.
Ductile: Property allowing a substance to be drawn into wires (e.g., copper).
Malleable: Ability to be hammered or pressed into shapes without breaking (e.g., aluminum foil).
Ion: Atom that has gained or lost electrons, resulting in a charge.
Inert: Refers to noble gases that do not readily react with other elements.
Metals, Nonmetals, Metalloids:
- Metals: Good conductors, tend to lose electrons.
- Nonmetals: Poor conductors, tend to gain electrons.
- Metalloids: Exhibit properties of both metals and nonmetals (e.g., silicon).

Basic Structure:
- Nucleus: Contains protons (positive charge) and neutrons (neutral charge).
- Electrons: Negatively charged particles located in the electron cloud surrounding the nucleus.
Atomic Mass:
- Calculated as the sum of protons and neutrons. Electrons are negligible in mass when calculating atomic mass.
Atomic Number:
- Defined by the number of protons in the nucleus. In a neutral atom, this equals the number of electrons.
Isotopes:
- Variants of the same element that differ in neutron number, resulting in different atomic masses.
- May be stable or unstable (radioactive). Used in scientific applications (e.g., tracing in animal migration).

Groups and Periods:
- Groups (Columns):
- Number of valence electrons informs about chemical properties.
- Similar properties within each group (e.g., alkali metals, halogens, noble gases).
- Periods (Rows):
- Indicates the highest energy level with electrons.
- Higher elements in the same period have more electron shells.

Stability and Bonding:
- Atoms bond to achieve full outer electron shells, like noble gases.
- Cations: Positive ions formed when metals lose electrons.
- Example: Sodium (Na) loses one electron to form Na⁺.
- Anions: Negative ions formed when nonmetals gain electrons.
- Example: Nitrogen (N) gains three electrons to become N³⁻.

Ionic Bonds:
- Formed by the transfer of electrons from metals to nonmetals. Oppositely charged ions attract.
- Example: Sodium chloride (NaCl) from Na (cation) and Cl (anion).
Covalent Bonds:
- Involve the sharing of electrons between nonmetals. Typically result in weaker bonds than ionic bonds.
- Example: Water (H₂O), where hydrogen and oxygen share electrons.
Binary Compounds:
- Formed from two different elements. Naming rules depend on bond types (ionic/covalent).
- Ionic: Name metal first, followed by nonmetal whose name ends in -ide.
- Covalent: Use prefixes to indicate the amount of each element.

Law of Conservation of Matter:
- Matter cannot be created or destroyed in chemical reactions; only rearranged.
Recognizing Chemical Changes: Signs of chemical reactions include temperature changes, light emission, gas production, and precipitate formation.
Types of Chemical Reactions:
- Synthesis: A + B → AB (two or more reactants forming a product).
- Decomposition: AB → A + B (one compound breaking down).
- Single Replacement: AB + C → AC + B (one element replaces another).
- Double Replacement: AB + CD → AD + CB (two compounds exchange partners).
Balancing Equations:
- Requires equal numbers of each type of atom on both sides, achieved using coefficients.
- Reflects conservation of atoms and mass in reactions.

Understanding the organization of the periodic table and bond types informs about the reactions and properties of materials.
This knowledge provides a foundation for broader topics in chemistry and physics.