8th Grade Science Final Exam Flashcards
Properties and Building Blocks of Matter
Identification of Unknown Substances: * Specific properties used to identify unknown substances include: * Color * Density * Hardability * Melting points * Boiling points
The Building Blocks of Matter: * Atoms: These are the fundamental basic building blocks of all matter. They are composed of three subatomic particles: * Protons: Found within the nucleus; they carry a positive electrical charge. * Neutrons: Found within the nucleus; they carry no charge (neutral). * Electrons: Located on the outside of the nucleus; they carry a negative electrical charge. * Elements: These are different types of atoms. An element is a pure substance that cannot be broken down. * Molecules: These consist of two or more atoms joined together.
Chemical Symbols vs. Formulas: * Symbol: Acts as an abbreviation for an element. * Chemical Formula: Shows the specific elements contained in a compound and the ratio of atoms present.
Electrical Neutrality of Atoms: * The electrical charge on an atom is zero or neutral because the positive charge from the protons is exactly equal to the negative charge from the electrons. The charges balance each other out.
Anatomy of an Atom (Volume and Mass): * Volume: The majority of an atom's volume is made up of electrons. They move constantly in a large, fuzzy "cloud" around the center. * Mass: Electrons have almost no mass compared to the heavy particles (protons and neutrons) found in the nucleus. Consequently, the nucleus contains the bulk of the mass while electrons provide the volume.
States of Matter and Phase Changes
Solid State: * Particles in a solid are packed closely together in a fixed and tight arrangement. * Particles vibrate in place rather than moving around from one position to another.
Liquid State: * Particles are free to move, which explains why liquids have no definite shape. * Despite the movement, liquids maintain a definite volume.
Gaseous States (Temperature and Pressure): * If the temperature of a gas is increased while the volume is kept constant, the pressure will increase.
Energy and Matter Transitions: * Adding Energy: Increases particle movement and causes them to spread apart. This facilitates changes from solids to liquids or gases. * Removing Energy: Causes particles to slow down and cluster together. This results in phase changes like condensation or freezing.
The Periodic Table of Elements
Historical Development (Dmitri Mendeleev): * In , Mendeleev organized the known elements by atomic mass and chemical properties. * He used cards for each element and noticed a repeating pattern of properties. * Organization: Elements were arranged in order of increasing atomic mass. He left gaps in the table for elements that had not yet been discovered.
Structure and Information: * Each square of the periodic table contains: 1. Atomic number 2. Element name 3. Element symbol 4. Atomic mass * Groups: These are the vertical columns. Elements in the same group have similar properties because they have the same number of valence electrons. * Overview: Pointing to any element at random makes it most likely to be a metal, as metals constitute approximately of all known elements.
Reactivity Trends: * Metals on the left side are generally more reactive than those on the right because they readily lose electrons to form positive ions. * Metals on the right side are less likely to lose electrons because their outer shells are filled or almost filled. * General Trend: Reactivity in metals increases moving down a group and from right to left across a period.
Chemical Bonds and Compounds
Valence Electrons: These are the electrons in an atom's outermost shell. During chemical bond formation, they are either shared between atoms or transferred from one atom to another.
Chemical Reactivity: Driven by an element's drive to achieve a full, stable outer electron shell.
Ions and Ionic Bonds: * Ions: Atoms or groups of atoms that have acquired a net electrical charge by gaining or lost electrons. * Cations: Positively charged (often metals that lost electrons). * Anions: Negatively charged (often nonmetals that gained electrons). * Ionic Bonds: Formed through the electrostatic attraction between oppositely charged ions. * Writing Formulas/Names: The total positive and negative charges must balance perfectly to zero (electrically neutral). * Properties: High melting/boiling points, hard and brittle crystalline structures, and high solubility in water.
Covalent Bonds and Molecular Compounds: * Covalent Bond: Formed by the electrostatic attraction between positively charged nuclei and shared pairs of valence electrons. They involve two non-metals sharing electrons. * Writing Formulas/Names: Uses numerical prefixes to indicate the number of atoms ("di-", "tri-", "tetra-"), and the second element name ends in "-ide." * Properties: Low melting/boiling points, poor electrical conductivity, lower water solubility, and softer structures. * Polarity: Unequal sharing occurs when some atoms pull more strongly on shared electrons than others, creating slight electrical charges in the molecule.
Properties and Changes in Matter
Defining Matter: Anything that has mass and takes up space.
Physical vs. Chemical Properties: * Physical Property: Characteristics that can be observed without changing the substance into another substance. * Chemical Property: Characteristics that describe the ability of a substance to change into different substances.
Mass vs. Weight: * Mass: The amount of matter in an object; it remains constant regardless of location in the universe. * Weight: The force of gravity pulling on mass; it changes based on the gravitational pull of the location.
Volume: * The amount of space occupied by matter. * Measured using the International System of Units. * The standard unit is the cubic meter ().
Density: * Determined by the ratio of mass to volume. *
Physical vs. Chemical Changes: * Physical Change: Any change altering the form or appearance of matter without producing a new substance. * Chemical Change: A change that produces one or more new substances. Occurs when bonds break and new ones form.
Mixtures: Combinations of two or more substances that are physically combined rather than chemically bonded, allowing substances to retain their individual properties.
Energy and Chemical Reactions
Chemical Energy: Potential energy stored inside the bonds holding atoms together. Chemical changes rearrange these atoms, breaking old bonds and forming new ones to release or absorb energy.
Forms of Energy: * Thermal: Internal energy created by the random, vibrating movement of atoms and molecules. * Chemical: Stored in chemical bonds. * Electrical: Caused by the movement of electrons from one atom to another. * Nuclear: Stored in the nucleus of an atom, holding protons and neutrons together.
Chemical Equations: Contain information regarding the "how much" (quantities), the action, and the "what" (substances involved).
Law of Conservation of Mass: In a closed system, mass is neither created nor destroyed during chemical reactions or physical changes. Total mass of reactants equals the total mass of products.
Motion, Forces, and Newton's Laws
Motion and Distance: * An object is in motion if it changes position relative to a reference point. * Distance is measured using SI units.
Speed and Velocity: * Speed: Calculated by dividing distance by time. * Velocity: A vector quantity that includes both speed and the specific direction of movement.
Acceleration: * Occurs when an object speeds up, slows down, or changes direction. * Calculation: * Free Fall: Objects accelerate during free fall because gravity acts as an unbalanced force.
Motion Graphs: * Distance vs. Time: Plots distance traveled over time. * Acceleration vs. Distance: Shows how acceleration changes based on location. * Speed-versus-time: Also used to analyze accelerating objects.
Forces: * Defined as a push or pull exerted on an object. * Balanced Forces: Do not change an object's motion. * Unbalanced Forces: Result in a net force and cause a change in motion.
Friction: The force surfaces exert on each other when rubbing. Factors include how hard the surfaces push together and the types of surfaces involved.
Gravity: Factors affecting gravitational force are the masses of the objects and the distance between them.
Newton's Laws of Motion: 1. First Law: An object at rest remains at rest and an object in motion remains in motion at a constant velocity unless acted upon by an unbalanced force. 2. Second Law: Acceleration depends on the object's mass and the net force acting on it. 3. Third Law: If one object exerts a force on another, the second object exerts a force of equal strength in the opposite direction on the first.
Momentum: * Calculation: * Law of Conservation of Momentum: In the absence of outside forces, the total momentum of interacting objects does not change.
Work, Power, and Machines
Work: * Performed when a force acts on an object and causes it to move in the direction of that force. * Calculation:
Power: * The rate at which work is done or energy is transferred. * Calculation:
Machines: * Machines make work easier by changing how force is applied to a task. * Mechanical Advantage (MA): Calculated by comparing output force to input force or the ratio of distances. * Efficiency: Calculated as: * Simple Machines: There are six kinds: 1. Inclined plane 2. Wedge 3. Screw 4. Lever 5. Wheel and axle 6. Pulley * Ideal Mechanical Advantage (IMA): Ratio of input distance to output distance. * Compound Machines: Made up of two or more simple machines.
Energy Principles: * Different forms of energy work together to form power. * Energy Transformations: Can be single or multiple transformations. * Law of Conservation of Energy: Energy cannot be created or destroyed.