Chemistry - Matter

chemistry

Prof. J. Peña

Complutense University of Madrid

Structure & diversity of matter

structure & diversity of matter

UCM - Faculty of Education

Matter?

Aggregations?

Transitions?

Funny theory

Boiling point...

Essentials of Chemistry

What is matter?

UCM - Faculty of Education

Essentials of Chemistry

aggregation states

UCM - Faculty of Education

Essentials of Chemistry

transition of aggregation states

UCM - Faculty of Education

Essentials of Chemistry

kinetic-molecular theory

UCM - Faculty of Education

Theory?

Essentials of Chemistry

boiling and melting points

UCM - Faculty of Education

Essentials of Chemistry

General properties (which are extensive) refer to properties that depend on the amount of matter present, like mass and volume. These properties cannot be used to identify or distinguish between different substances because they change based on the quantity of the substance.

Density is the amount of matter (mass) within the volume it occupies and allows us to differentiate between objects that occupy the same volume but have different masses. Density(ρ) = mass/volume. The most commonly used units of density are g/cm³ and kg/m³.

Examples: Metals such as iron (Fe), copper (Cu), gold (Au); carbon (C) in its forms as diamond and graphite; and sodium chloride (NaCl).Many metals, typically solid, can be melted, and if heated to even higher temperatures, they can become gaseous.

The boiling and melting points are physical properties that can be measured or observed without altering the composition and identity of the substance.

Chemical changes, on the other hand, can only be observed in chemical reactions.

This theory suggests that matter is composed of a large number of small particles (which can be represented as small spheres, although this is simply a model) in continuous motion, between which there are forces of attraction.

The motion of these particles is related to the temperature of the matter.

Examples: Oxygen (O₂), nitrogen (N₂), hydrogen (H₂), carbon dioxide (CO₂), chlorine (Cl₂), ammonia (NH₃), and methane (CH₄).In the gaseous state, the matter tends to occupy the maximum possible volume, taking the shape of the container that holds it.

All matter has mass, the most noticeable effect of which is due to gravitational interaction. Even gases have weight. This can be demonstrated by weighing a car or bicycle tire before and after filling it with air. In the International System of Units, the unit of mass is the kilogram (kg).

Examples: Water (H₂O), ethyl alcohol (C₂H₅OH), mercury (Hg), and gasoline.Liquids have a fixed volume but take the shape of their container. This is because the molecules in a liquid are closely packed but can move around each other, allowing the liquid to flow and conform to the shape of its container.

In the liquid state, the vibrations are strong enough that the particles leave their fixed positions and slide past one another. Liquids have a variable shape (conforming to the container that holds them) and a fixed volume (one liter of water occupies the same volume in a jug, bottle, or divided among glasses).

Specific properties (which are intensive) refer to properties that do not depend on the amount of matter. Examples include density, boiling point, and melting point. These are useful for identifying and distinguishing different substances because they are intrinsic to the material itself, regardless of its size or amount.

Matter can exist in different states of aggregation: solid, liquid, and gas . Initially, one might think that substances like iron are always solid, water is always liquid, and air is always gas, but this is not the case. Matter can transition from one state to another depending on temperature and pressure, with each state being characteristic of a specific temperature and pressure.

It is important not to overlook the effect of pressure:

• Butane gas, when "trapped" under high pressure in a cylinder at room temperature, is in a liquid state, but when it is released and the pressure decreases, it turns into a gas. To explain phenomena like this, the kinetic-molecular theory has been proposed

In addition to the classic states of aggregation of matter—gas, liquid, and solid—we also have plasma, which is a gas composed of charged particles (ions), consisting almost entirely of positive ions (ions⁺) and electrons (e⁻). Plasma forms at very high temperatures (approximately 10,000 K).

In the solid state, the particles are closely packed, allowing only small vibrational movements. If energy is added to the system, the temperature increases, causing these vibrational movements to intensify, leading to the expansion of the solid.

In the gaseous state, if more energy is added to the system, resulting in a temperature increase, the particles move so vigorously that they begin to "escape" the forces of attraction and move in such a way that they tend to occupy a larger volume. In the gaseous state, the matter tends to occupy the maximum possible volume, taking the shape of the container that holds it.

Among the three states of matter, it is possible to transition from one to another through the gain or loss of energy. This involves either increasing or decreasing the forces of attraction between particles.

• Starting with a solid, if energy is supplied (which is reflected in a temperature increase), the particles' agitation increases until it eventually transitions to a liquid (melting).
• If energy continues to be added, it will become a vapor (vaporization). Conversely, if a gas is cooled (loss of energy), the agitation of its particles decreases, and it turns into a liquid (condensation or liquefaction).
• Further cooling will result in the substance becoming a solid (solidification). Additionally, certain solids can transition directly to a gas (sublimation) and from a gas to a solid (reverse sublimation).

Matter occupies space, even in a gaseous state. If you press the plunger of a syringe while blocking the exit, you can significantly reduce the interior volume, but not completely, as air occupies volume. In the International System of Units, the recommended unit of volume is the cubic meter (m³) and its submultiples.