Chemistry Study Notes Overview

Chemistry Study Notes

• Chemistry Definition: The study of matter and its interactions. It focuses on atoms, elements, compounds, and reactions.

Matter

• Matter Definition: Anything with mass and volume. Examples include books, water, air, and people.
• States of Matter:
• Solid: Definite shape and volume.
• Liquid: Definite volume, takes shape of container.
• Gas: No definite shape or volume.
• Plasma: High-energy state, found in stars and lightning.
• Phase Changes: Changes from one state to another (e.g., melting, freezing). Chemical identity stays the same.

Mass and Weight

• Mass: Amount of matter in an object (kg). Doesn't change with location.
• Weight: Force of gravity on an object's mass (N). Changes with gravity.
• Weight Formula: Weight = Mass × Gravity.
• Earth's Gravity: Approximately 9.8 m/s².
• Moon's Gravity: Approximately 1.6 m/s².

Physical vs. Chemical Changes

• Physical Change: Changes form/appearance, not substance identity. Often reversible (e.g., melting ice, cutting paper).
• Chemical Change: Creates new substances with new properties. Often not reversible (e.g., burning wood, rusting iron).

Atoms and Subatomic Particles

• Atom: Smallest unit of an element with the element's properties.
• Subatomic Particles:
• Proton (+): Positive charge, in the nucleus.
• Neutron (0): No charge, in the nucleus.
• Electron (-): Negative charge, orbits the nucleus.
• Element Identity: Determined by the number of protons (atomic number).
• Atomic Mass: Sum of protons and neutrons. (Atomic Mass ≈ Protons + Neutrons)
• Isotopes: Atoms of the same element with different neutron numbers (e.g., Carbon-12 and Carbon-14).
• Ions: Atoms with a different number of electrons than protons, resulting in a net electrical charge.

Periodic Table and Valence Electrons

• Valence Electrons: Outermost electrons, affect element bond behavior.
• Noble Gases (Group 18): Full valence shells, very stable and unreactive.

Chemical Bonds

• Ionic Bond: Between metal and non-metal, electron transfer. Example: NaCl (sodium chloride).
• Covalent Bond: Between non-metals, electron sharing. Example: H₂O (water).
• Metallic Bond: Between metal atoms, electrons freely move.
• Hydrogen Bond: Weak bond between polar molecules, crucial for water's properties.

Surface Tension

• Surface tension: Liquid property caused by hydrogen bonds creating a "skin."

Density

• Density Formula: Density = Mass ÷ Volume.
• Units: g/cm³ or kg/m³.
• Floating/Sinking: Objects with density less than water float; greater density sinks.

Key Concepts Summary

• Chemistry studies matter’s properties and changes.
• Matter exists in various states (solid, liquid, gas, plasma).
• Physical changes differ from chemical changes.
• Atomic structure affects element properties (e.g., isotopes, ions).
• Bonds create compounds, with varied types (ionic, covalent, metallic, hydrogen) determining properties.
• Density is a measure of mass per unit volume.

Test Review Tips

• Memorize definitions (matter, mass, weight, density, physical/chemical changes).
• Practice formulas (weight = mass × gravity, density = mass ÷ volume).
• Differentiate between physical and chemical changes.
• Understand differences in types of bonding.
• Review atomic structure and the Periodic Table.
• Understand that noble gases are generally non-reactive.

Extra Practice Questions Solutions

• Question 1: Both have the same weight on Earth.
• Question 2:
• Baking bread - Chemical change
• Freezing water - Physical change
• Burning paper - Chemical change
• Question 3: Density is 2 g/cm³.
• Question 4:
• NaCl - Ionic bond
• CO₂ - Covalent bond
• Question 5:
• Atomic number 8 - 8 protons
• Mass number 16 - 8 neutrons (16 - 8)