Science 8 Reviewer - 3rd Periodical PDF

**SCIENCE 8 REVIEWER** **[Lesson 1. Matter]** Matter - Pertains to all substances and materials from which the physical universe is composed. - anything that has mass and occupies space. - Examples: Air, water, rocks, and food Atoms - the smallest particle of an element that retains its che...

**SCIENCE 8 REVIEWER** **[Lesson 1. Matter]** Matter - Pertains to all substances and materials from which the physical universe is composed. - anything that has mass and occupies space. - Examples: Air, water, rocks, and food Atoms - the smallest particle of an element that retains its chemical properties. Element - A substance made up of only one type of atom. - cannot be broken down into simpler substances by chemical means. JOHN DALTON - formulated the idea that the world around us is made of large numbers of identical and very small particles called molecules. **Phases of Matter:** **1. SOLID** -- particles tightly packed.. - the state of matter with a definite shape and volume. Classification of Solids according to the attractive forces: - Molecular solids- A type of solid held together by same kind of forces that hold liquid together. This force is the weakest among the types that hold solids together. Ex. Candle wax and ice - Metallic solids - A type of solid held together by metallic bond which involves electron sharing throughout the body of the metal. Ex. Iron, gold, copper and zinc - Ionic solids - Held together by ionic bond. These force are much stronger than the ones in molecular solids. Ex. Sodium chloride or table salt. - Covalent network solid - Are giant covalent substances held together by covalent bond. Ex. Diamond **2. LIQUID - Intermediate phase between solid and gas.** **- The type of matter that has no fixed shape but has a fixed volume.** **Properties of Liquid:** \- Cohesion and surface tension \- Adhesion and cohesion \- Capillary action \- Viscosity \- Evaporation \- Volatility and vapor pressure **3. GAS - moves very quickly because of the empty space surrounding them.** **- This is the reason why gas can easily be compressed.** **- Gases occupy more space than solids and liquids.** **- A gas fills the entire volume of its container because its particles are in constant, random motion, spreading out to evenly occupy all available space. The weak or negligible intermolecular forces allow gas particles to move freely and independently, driven by their kinetic energy, ensuring they distribute throughout the container.** **4. PLASMA - made up of electrically charged particles, hot ionized gas where electrons break free.** **- Ex. Lightning, aurorae, neon signs, solar wind, Earth's ionosphere, stars including the Sun, tail of a comet, interstellar cloud.** **5. BOSE-EINSTEIN CONDENSATE - A state of a dilute gas of bosons cooled to temperatures close to absolute zero, or the lower limit of the thermodynamic scale.** **6. FERMIONIC CONDENSATE - Are atoms that merge at super low temperatures to form a single object that behave like a wave.** **PHASE CHANGES:** - **Melting is a phase change from solid to liquid through the application of heat.** - **Boiling/Evaporation is a phase that converts liquid into gas.** - **Condensation is a change of phase from gas or vapor to liquid.** - **Freezing/Solidification is a change of phase from liquid to solid.** - **Sublimation is a process of changing solid to gas directly without passing through the liquid phase.** **Lesson 2: Physical and Chemical Changes** **PHYSICAL CHANGES** - is a change in the form or appearance of a substance, but its composition remains the same. - include color, volume, shape, and phase changes. - Example: Melting ice, tearing paper, dissolving sugar in water. Physical Property - the state of matter with a definite shape and volume. **CHEMICAL CHANGES** - A chemical change is a change where a new substance is formed with different properties. - Example: Burning wood, rusting iron, baking a cake - **Sign/Indicators of Chemical Changes:** 1\. Color changes 2\. Gas production (bubbles/fizzing) 3\. Odor change 4\. Temperature or light change \- Example: Vinegar and baking soda reaction, rusting of metal **Difference:** **Physical change** **Chemical change** ---------------------------- ------------------------------------------ do not form new substances form new substances. are usually reversible usually irreversible affect physical properties involve changes in chemical composition. **[Lesson 2. Atoms and Molecules:]** Matter - Everything around us is made up of matter. - Matter has mass and takes up space. Atoms - smallest unit of matter that retains the properties of an element. - Composed of protons, neutrons, and electrons. - Protons (+), Electrons (-), Neutrons (neutral or no charge) MOLECULES - Two or more atoms bonded together. - Example: Oxygen molecule (O₂), Water molecule (H₂O). Difference between Atom and Molecule **Aspect** **Atoms** **Molecules** --------------- ----------------- --------------------------------------- Smallest unit element Compound/element Composition Single particle Two or more atoms Examples Hydrogen (H) Water molecule (H~2~O), Oxygen (O~2~) - **Atoms** are the basic building blocks of matter, and **molecules** are formed when two or more atoms bond together chemically. **Molecules** form through covalent bonds (sharing electrons) or ionic bonds (transferring electrons). For example, water (H₂O) is a molecule formed by covalent bonds between hydrogen and oxygen. Molecules are essential for life because they make up biological structures (e.g., proteins, carbohydrates) and facilitate biochemical processes like energy transfer (e.g., ATP). These molecules enable life-sustaining reactions and form the basis of all living organisms. **Types of Chemical Bonding:** - Covalent Bonds: Atoms share electrons. - Ionic Bonds: Transfer of electrons between atoms. - Example: NaCl (Ionic), H₂ (Covalent). IMPORTANCE OF ATOMS & MOLECULES: - Basis of all matter in the universe. - Foundation of chemical reactions. - Essential in biology, physics, and chemistry. PERIODIC TABLE: Elements are arranged by increasing atomic number. - Groups: Columns with similar properties. - Periods: Rows that indicate energy levels. FUN FACTS: There are over 118 known elements. - The human body is made up of trillions of atoms. - Water is the most abundant molecule on Earth. - Gold atoms can be stretched into thin wires. **ATOMIC STRUCTURE:** - Nucleus - center of the atom, contains protons and neutrons. - Electrons - tiny particles that orbit the nucleus. **Subatomic Particles:** 1\. **Protons** - Positively charged particles. (+1) \- Located in the nucleus. \- Determines the element's identity (atomic number). 2**. Neutrons** - Neutral charge or no charge. \- Located in the nucleus. \- Contributes to atomic mass. 3\. **Electrons** - Negatively charged (-1). \- Move in orbitals around the nucleus. \- Involved in chemical reactions. Atomic Number (Z): Number of protons in the nucleus. Mass Number (A): Total number of protons and neutrons. - Example: Carbon - Atomic Number 6, Mass Number 12. **\*How to identify the no. of protons, neutrons and electrons in an element?** 1\. **Number of Protons:** \- the number of protons is the same as the atomic number of the element. Ex. Carbon (c), atomic number is 6, so it has 6 protons. 2\. **Number of Electrons:** \- in neutral atom, the number of electrons is equal to the number of protons (atomic number) If the atom is an ion: - **A positive charge (+)** means the atoms has lost electrons. - **A negative charge (-) means the atoms has gained electrons.** **Example: C^3-\ has^ more electrons than protons, so it has 9 electrons.** 3\. **Number of Neutrons:** \- To find the number of neutrons, use this formula: Number of Neutrons = Mass number -- atomic number **Example: For Carbon, the atomic mass is 12** - **Neutrons = 12 (mass no.) -- 6 (protons) = 6 neutrons** Summary Table for Carbon (C) ------------------------------ -------- Subatomic Particle Number Protons 6 Neutrons 6 Electrons 6