genchem

Matter

Composed of two or more types of substances, classified into mixtures and pure substances.

Heterogeneous Mixtures

Particles are distributed non-uniformly, e.g., salad, sand in water.

Homogeneous Mixtures

Particles are uniformly distributed, e.g., saltwater, air.

Pure Substances

Have a definite composition and distinct properties, including elements and compounds.

Elements

Simplest form of matter that cannot be broken down into simpler substances.

Compounds

Consist of two or more elements chemically united in fixed proportions, e.g., water (H2O).

Intensive Properties

Do not depend on the amount of matter, e.g., density, boiling point.

Extensive Properties

Depend on the amount of matter, e.g., mass, volume.

Physical Change

Change that does not alter the chemical composition, e.g., melting ice.

Chemical Change

Atoms rearrange to form new substances with different properties, e.g., rusting iron.

Significant Figures

Crucial in scientific measurements to convey precision.

Spatula

Flat, scoop-like tool for transferring solid chemicals.

Beaker

Cylindrical glass container for mixing and heating liquids.

Funnel

Cone-shaped tool for channeling liquids into containers.

Graduated Cylinder

Tall, narrow glass tube with calibrated markings for precise liquid measurement.

Volumetric Flask

Used for measuring and dispensing specific volumes of liquids.

Triple Beam Balance

Instrument for measuring mass, consists of three beams for precision.

Analytical Balance

Designed for measuring small masses in the sub-milligram range, enclosed to prevent interference.

Centrifuge

Used to separate particles suspended in a liquid based on density and size.

Fume Hood

Ventilation device to limit exposure to hazardous fumes.

Reagent Bottle

Containers for storing chemicals, usually made of glass with a stopper.

Pipette Technique

Place the pipette tip above the beaker bottom, hold it with one hand, and use the other to operate the aspirator.

Measuring Mass

Use a watch glass to measure solids, transferring them with a spatula to a balance.

Parallax Error

Occurs when the measurement scale is not viewed perpendicularly, leading to inaccurate readings.

Systematic Error

Consistent errors due to faulty equipment or flawed experimental design, which can skew results.

Random Error

Unpredictable errors that occur without a pattern, often minimized through repeated trials.

Percent Yield

A measure of the efficiency of a reaction, calculated as: [ \text{Percent Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100\% ]

Theoretical Yield

The maximum amount of product expected from a reaction based on stoichiometry.

Actual Yield

The amount of product actually obtained from a reaction, which can be less than the theoretical yield due to various factors.

Filtration Process

A method used to separate solids from liquids, leaving sediment behind in the filter paper.

Atomism

The theory that all matter is composed of small, indivisible particles called atoms, proposed by Democritus in the 5th century BC.

Solid Sphere Model

Proposed by John Dalton in 1803, it states that atoms are indivisible solid spheres and compounds are combinations of different types of atoms.

Plum Pudding Model

Proposed by J.J. Thomson in 1897, it describes the atom as a sphere of positive charge with negative electrons embedded within it.

Nuclear Model

Proposed by Ernest Rutherford in 1911, it states that the atom has a dense, positively charged nucleus with electrons moving around it in mostly empty space.

Planetary Model

Proposed by Niels Bohr in 1913, it describes electrons orbiting the nucleus in fixed, specific circular orbits, each with a defined energy level.

Quantum Model

Proposed by Erwin Schrödinger in 1926, it states that electrons do not move in fixed orbits and their locations can only be described as a cloud of probability around the nucleus.

Protons (p+)

Positively charged particles found in the nucleus, determining the atomic number (Z).

Neutrons (n0)

Neutral particles in the nucleus, contributing to atomic mass (A) but not charge.

Electrons (e-)

Negatively charged particles orbiting the nucleus, balancing the charge in neutral atoms.

Acidity Testing

Using litmus paper to test for acidity or basicity; red indicates acidic, blue indicates basic solutions.

pH Paper

Used to determine the pH level by comparing the color change to a provided scale.

Decantation

A method for separating liquids from solids by carefully pouring off the liquid, leaving the solid behind.

Quantum Mechanical Theory

Models of atoms that use the complex shape of orbits (electron clouds) based on probability rather than certainty.

Energy Levels

Fixed distances from the nucleus of an atom where electrons may be found, representing a fixed amount of energy.

Sublevels

Represented by the letters s, p, d, and f.

Bohr's Model

Describes the path electrons travel in fixed orbits around the nucleus.

Orbital

Refers to the dimensional motion of an electron around the nucleus in three-dimensional motion, indicating where the electron is likely to be found.

Electron Configuration

The ways in which electrons are arranged around the nucleus of atoms.

Aufbau Principle

States that electrons fill lower-energy atomic orbitals before filling higher-energy ones.

Pauli's Exclusion Principle

States that an atomic orbital may describe at most two electrons.

Paired Electrons

To occupy the same orbital, two electrons must have opposite spins.

Hund's Rule

In the orbitals of the same subshell, electrons are filled singly first before pairing starts.

Orbital Filling Rules

1) The lowest energy orbitals are filled before the higher energy orbitals. 2) Each orbital gets one electron first before a second electron is added to the orbital. 3) Only 2 electrons, of opposite spins, can occupy each orbital.

Isoelectronic Species

Atoms, molecules, or ions that have the same number of electrons.

Alkali Metals

Highly reactive metals, especially with water. Soft, silvery, and have one valence electron (e.g., Lithium, Sodium, Potassium).

Alkaline Earth Metals

Reactive (but less than alkali metals), shiny, and have two valence electrons. They form basic (alkaline) solutions in water (e.g., Magnesium, Calcium).

Icosagens (Boron Group)

Contain both metals and a metalloid. They have three valence electrons and are used in materials like aluminum alloys and boron compounds (e.g., Boron, Aluminum).

Crystallogens (Carbon Group)

Diverse elements (nonmetals, metalloids, metals). They have four valence electrons and include essential elements like Carbon and Silicon.

Pnictogens (Nitrogen Group)

Five valence electrons, can form multiple oxidation states. Includes nonmetals (Nitrogen, Phosphorus), a metalloid (Arsenic), and metals.

Chalcogens (Oxygen Group)

Six valence electrons, reactive, and often form compounds with metals (oxides, sulfides). Includes Oxygen, Sulfur, and Selenium.

Halogens

Very reactive nonmetals with seven valence electrons. They form salts with metals (e.g., Fluorine, Chlorine, Iodine).

Noble Gases

Inert, stable gases with full valence shells. Rarely react with other elements (e.g., Helium, Neon, Argon).

Dobereiner's Triads

Grouped elements in threes where the middle element's mass ≈ average of the other two. Only worked for a few elements.

Newland's Law of Octaves

Arranged elements by increasing atomic mass; every 8th element had similar properties. Worked only for lighter elements.

Mendeleev's Periodic Table

Arranged elements by atomic mass and properties; left gaps for undiscovered elements and predicted them. Some placement issues remained.

Moseley's Modern Periodic Table

Based on atomic number, not mass. Gave the current table structure (7 periods, 18 groups) and solved Mendeleev's anomalies.

Transition Metals

Good conductors of heat and electricity. Can have different charges (variable oxidation states). Many form colored compounds (like Cu2+ = blue). Often used as catalysts in reactions.

Inner Transition Metals

Lanthanides: Shiny metals, used in magnets and electronics. Actinides: Mostly radioactive; many are man-made (like Uranium, Plutonium).

Atomic Size/Radius

The distance from the nucleus to the outermost electron. Atoms get bigger as they move from right to left and from up to down.

Ionization Energy

The ability of an element to remove an electron from itself. Increases as it moves from left to right and from down to up.

Electronegativity

The ability of an atom to pull shared electrons toward itself in a bond. Elements get stronger electronegativity as they move from left to right and from down to up.

Electron Affinity

Energy change when an atom gains an extra electron. Follows same trend or movement as Ionization Energy and Electronegativity.

Metallic Character

The ability/characteristic of an atom to act like a metal.

Chemical Nomenclature

The system of systematically naming chemical compounds. These are the rules and conventions that are followed.

Octet Rule

States that atoms tend to lose, gain, or share electrons to obtain 8 valence electrons. Followed to attain stability of electrons.

Chemical Formula

Notation that shows the number and type of atoms in a molecule. It expresses the bond's composition. Shows how many atoms of each element are present in a bond.

Ionic Bond

When atoms transfer electrons and become ions of different charge. Common between a metal (cation) and a nonmetal (anion).

Covalent Bond

When atoms share electrons to achieve a stable outer shell. Common between metals. Strongest and most common form of bond. Can be nonpolar covalent bond or polar covalent bond.

Nonpolar Covalent Bond

Electrons are equally shared.

Polar Covalent Bond

Electrons are unequally shared which creates different charges.