Science 7th Grade Second Midterm Study Guide 2026

Assessment Context and General Information

The academic evaluation for the second midterm of the 2026 school year at the Colegio Bilingüe Boca del Monte is overseen by Professor Maricela Guerrero V. This evaluation, scheduled for September 8, 2026, is specifically designed for the seventh-grade Science (Ciencias) students under a Significant Adaptation (Adecuación Significativa) framework. The curriculum focuses on fundamental physics and chemistry concepts, encompassing measurement systems, properties of matter, and the physical transitions of substances.

Unit Conversion and Applied Measurement in Daily Life

The application of conversion factors is a critical skill for performing accurate measurements in various everyday scenarios. Students are expected to master the techniques required to transition between different units within two primary measurement categories: length ($L$) and mass ($m$). Length conversions involve determining distances or dimensions using standardized scales, while mass conversions involve calculating the quantity of matter within an object.

In addition to standardized scientific units, the study of measurement includes the use of non-conventional units. These are informal or traditional units of measure that do not belong to the International System of Units but are still prevalent in certain cultural or practical contexts. Understanding both conventional and non-regulated systems ensures a comprehensive grasp of how physical properties are quantified and communicated globally.

Calculation and Application of Body Mass Index (IMC)

The Body Mass Index, known in Spanish as Índice de Masa Corporal ($IMC$), is a standardized calculation used to evaluate an individual's physical mass in proportion to their height. This indicator provides essential data for identifying weight-related health categories, such as underweight, healthy weight, or overweight.

The calculation is performed using the following mathematical relationship:

$IMC = \frac{\text{masa}}{\text{estatura}^2}$

To yield a correct result, the mass must be recorded in kilograms ($kg$) and the stature (height) must be recorded in meters ($m$). The resulting value is an essential tool for assessing nutritional status and physical well-on health benchmarks.

Fundamental Concepts and Properties of Matter

Matter is scientifically defined as any substance that possesses mass and occupies physical space (volume). To analyze the physical world, one must distinguish between the physical and chemical properties of substances. This distinction relies on the concept that a physical property describes the substance as it is, while a chemical property describes how a substance changes into something else.

Physical properties are characteristics that can be observed or measured without altering the chemical composition of the substance. These are further divided into qualitative properties, which describe qualities that are often measured by the senses rather than numbers. Key examples include:

1. Fragility: The tendency of a material to break, crumble, or shatter easily when subjected to force, rather than deforming or bending.
2. Elasticity: The physical ability of a material to return to its original form and dimensions after the external forces causing deformation are removed.

Chemical properties represent the internal capacity of a substance to undergo specific transformations that result in new substances with different identities. These properties are only observable during a chemical reaction.

Differentiation Between Mass, Weight, and Volume

Clarifying the distinctions between mass, weight (peso), and volume is essential for scientific literacy, as each represents a different physical quantity and requires specific instrumentation.

Mass refers to the total amount of matter contained in an object. It remains constant regardless of the object's location in the universe. The standard units of measurement for mass are the kilogram ($kg$) and the gram ($g$), and it is measured using a balance (balanza).

Weight (peso) is the measure of the gravitational force acting upon an object's mass. Because it depends on gravity, an object's weight can change depending on its location (e.g., on Earth versus the Moon). The standard unit for weight is the Newton ($N$), and it is measured using a dynamometer (dinamómetro).

Volume represents the amount of three-dimensional space an object occupies. For liquid substances, common units include the liter ($L$) and milliliter ($mL$), often measured with a graduated cylinder (probeta). For solid objects, volume is often expressed in cubic centimeters ($cm^3$) or cubic meters ($m^3$).

States of Aggregation and Molecular Characteristics

Matter exists in four primary states of aggregation, which are defined by the energy levels and behavior of the molecules within the substance. These states are solid, liquid, gaseous, and plasma.

At the molecular level, the solid state is characterized by particles that are tightly packed in a regular, fixed pattern. These particles have low kinetic energy and only vibrate in place, resulting in a definite shape and volume. Examples include ice, rocks, and wood.

The liquid state features particles that are close together but lack a fixed arrangement. They have sufficient energy to slide over one another, allowing the liquid to flow and take the shape of its container while maintaining a definite volume. Examples include water and oil.

In the gaseous state, particles are far apart and move rapidly in random directions. They possess high kinetic energy and minimal intermolecular attraction, leading to no definite shape or volume as they expand to fill any container. Examples include steam and oxygen.

The plasma state is an ionized gas that occurs at very high temperatures. It consists of a sea of free electrons and positive ions, making it highly conductive of electricity. It is the most common state of matter in the universe, found in stars and lightning.

Phase Changes and Daily Life Examples

Matter can transition from one state to another through the gain or loss of thermal energy. These transitions are known as changes of state and are observed frequently in daily life:

1. Fusion: The process of a solid turning into a liquid due to the addition of heat. A daily example is the melting of an ice cube into liquid water.
2. Solidification: The process of a liquid becoming a solid as it loses heat. An example is the freezing of liquid water into ice.
3. Evaporation: The transition from a liquid to a gaseous state, occurring when molecules gain enough energy to escape the liquid surface. Examples include water boiling or clothes drying in the sun.
4. Condensation: The process by which a gas loses energy and turns back into a liquid. This is commonly seen when water vapor in the air touches a cold surface, such as the dew on grass in the morning or the droplets on a cold soda can.