General Chemistry 1: Fundamental Concepts and Classification of Matter

Matter is defined as anything that occupies space and volume.
The classification of matter is a foundational topic in general chemistry, involving the study of the bases, states, and properties of substances.

There are four distinct states or phases of matter, characterized by their shape, volume, and energy levels.

Solid:
- A solid has a definite shape and a definite volume.
- The volume and shape of a solid are independent of the container holding it.
- For example, a solid cube retains its shape whether it is placed in a hand, thrown in the air, or placed in a container, provided it doesn't break.
Liquid:
- A liquid has a definite volume but an indefinite shape.
- The shape of a liquid is dependent upon the container holding it.
- If a liquid, such as a bottle of water, is poured onto the floor or into a glass, the volume remains the same, but the liquid spreads out or adapts to the new shape of its environment.
Gas:
- A gas has both an indefinite shape and an indefinite volume.
- Both the shape and volume of a gas depend entirely on the container.
- Gas particles expand to fill the space available to them. This is demonstrated by spraying perfume from an aerosol; the gas expands and can eventually be smelled on the opposite side of a room.
Plasma:
- Plasma is the fourth state of matter, defined as a highly energetic state.
- It shares some similarities with gases but is not identical to them.
- Common examples of plasma include fire, lightning, and electrical sparks.

In scientific contexts, mass and weight are distinct concepts, despite being used interchangeably in daily conversation.

Mass:
- Mass is the amount of matter contained within an object.
- Commonly, people refer to weight when they mean mass (e.g., saying a person weighs $200\,lbs$ is technically referring to the person's mass).
Weight:
- Weight is the force that mass exerts upon a surface.
- It is calculated using the formula for force: $F = m \times a$
- For a body at rest, acceleration ( $a$ ) is replaced by the force of gravity ( $g$ ), resulting in: $W = m \times g$
Gravitational Variations:
- An object has the same mass whether it is on Earth or the Moon because the amount of matter does not change.
- An object's weight on the Moon is significantly less than on Earth because the gravity of the Moon is less. This explains why astronauts jump easily on the lunar surface; they are less strongly attracted to the surface than on Earth.

Law of Conservation of Mass: Mass is conserved throughout all chemical and physical changes. Matter cannot be created or destroyed.
- Example: If a log of wood is burned and all products are collected (including the consumed oxygen, ashes, and gaseous products), the total initial mass will be identical to the total final mass.
- The inability to create matter "out of nowhere" is why magical tricks appear spectacular or unnatural; science dictates that stuff must come from somewhere.
Law of Conservation of Energy: Energy is neither created nor destroyed; it can only be transformed from one form to another.
Mass-Energy Equivalence in Nuclear Chemistry:
- In nuclear chemistry, the law of conservation of mass has a unique caveat regarding the nucleus of an atom (which contains protons and neutrons).
- The mass of an intact nucleus is slightly less than the combined sum of the individual protons and neutrons that compose it.
- This "missing" mass is transformed into the energy required to hold the nucleus together.

A pure substance consists of only one type of matter and has a constant composition.

Elements:
- An element is a pure substance that cannot be broken down into simpler substances by chemical means.
- Any chemical reaction performed on an element will result in a more complex substance, never a simpler one.
- Example: Coal is pure carbon ( $C$ ). Burning it creates carbon monoxide ( $CO$ ) or carbon dioxide ( $CO_2$ ), which are more complex compounds containing carbon and oxygen.
- There are more than $100$ known elements, $90$ of which occur naturally. Elements may be found in nature in their pure state or within ores (oxide or fluorite minerals) from which they must be extracted (e.g., iron is extracted from iron oxide).
- Dozens of elements have been synthesized in laboratories, some daily in hospitals for medicinal and radiologic tests.
Compounds:
- A compound is a pure substance made of two or more different elements that are chemically bonded together.
- Compounds can be decomposed into their constituent elements or into simpler compounds.
- The properties of a compound are often radically different from the properties of the elements that form it.
- Examples and Nomenclature:
  - Water ( $H_2O$ ), systematically known as dihydrogen oxide.
  - Glucose ( $C_6H_{12}O_6$ ).
  - Silver chloride ( $AgCl$ ).

A mixture is a combination of two or more substances that can be separated by physical means.

Physical Separation Methods:
- Filtration: Separating a solid from a liquid (e.g., water and sand).
- Evaporation: Removing a liquid to leave behind a dissolved solid (e.g., boiling water away to reclaim sodium chloride, or table salt).
- Distillation: A process to collect both the liquid and the dissolved solid by evaporating and then condensing the liquid.
Heterogeneous Mixtures:
- The composition varies from point to point, and components are visible to the naked eye.
- Examples: Greek salad (tomatoes, olives, lettuce are distinct), sand and water.
Homogeneous Mixtures (Solutions):
- The composition is uniform throughout, meaning the eye cannot differentiate between the various parts.
- Solutions are not exclusively liquids:
  - Liquid Solutions: Kool-Aid, coffee.
  - Gas Solutions: Air (a uniform mixture of oxygen, nitrogen, carbon dioxide, carbon monoxide, and argon).
  - Solid Solutions: Dental fillings (a blend of zinc and mercury).

The Atom:
- The atom is the smallest unit of an element that retains the properties of that element.
- The word comes from the Greek atomos, meaning "indivisible."
- Philosophical concepts of the atom date back to the 5th century BCE in Greece, but scientific evidence was not established until the 19th century when John Dalton performed experiments to support the atomic hypothesis.
- Metaphor: If money is the element, the penny is the atom—it is the smallest repeating unit that makes up the whole.
The Molecule:
- A molecule consists of two or more atoms bonded together.
- Molecules are the units for covalent compounds and some elements.
- Elements in the Molecular State: Some elements exist naturally as diatomic or polyatomic molecules rather than individual atoms.
  - Hydrogen: $H_2$
  - Oxygen: $O_2$
  - Phosphorus: $P_4$
  - Sulfur: $S_8$
- Molecules in Compounds: These consist of different types of atoms.
  - Water ( $H_2O$ ): Two hydrogen atoms (white) and one oxygen atom (red).
  - Carbon Dioxide ( $CO_2$ ): One carbon atom (black) and two oxygen atoms (red).
  - Glucose ( $C_6H_{12}O_6$ ): A more complex molecular structure.