Introduction to Matter: States, Elements, and Compounds

• Matter is anything in the Universe that has mass and takes up space
• Matter exists in different states, most commonly as solids, liquids, gases, and plasma
• Matter is composed of atoms, which are the smallest units of an element that retain its chemical properties
• Atoms are made up of protons, neutrons, and electrons

States of Matter

• Solids have a definite shape and volume because their constituent particles are tightly packed and have strong intermolecular forces
• Liquids have a definite volume but take the shape of their container; their particles are close together but can move past each other
• Gases have no definite shape or volume and expand to fill their container; their particles are widely separated and move randomly
• Plasma is an ionized gas with high energy

Elements and Compounds

• Elements are pure substances consisting of only one type of atom, and cannot be broken down into simpler substances by chemical means
• About 118 elements are known, each identified by its atomic number (number of protons in the nucleus)
• Elements are organized in the periodic table based on their atomic number and chemical properties
• Compounds are substances formed by the chemical combination of two or more elements in a fixed ratio
• The properties of compounds are usually different from those of their constituent elements
• Compounds can be broken down into simpler substances or elements by chemical reactions

Mixtures

• Mixtures are combinations of two or more substances that are physically combined but not chemically bonded
• Mixtures can be homogeneous, with uniform composition throughout (e.g., saltwater), or heterogeneous, with non-uniform composition (e.g., salad)
• The components of a mixture retain their individual properties
• Mixtures can be separated by physical means, such as filtration, evaporation, distillation, or magnetism

Properties of Matter

• Matter can be described by its physical and chemical properties
• Physical properties are those that can be observed or measured without changing the substance's composition (e.g., color, density, melting point, boiling point)
• Chemical properties describe how a substance reacts with other substances or changes its composition (e.g., flammability, acidity, reactivity)
• Intensive properties do not depend on the amount of substance (e.g., temperature, pressure, density)
• Extensive properties depend on the amount of substance (e.g., mass, volume)

Changes in Matter

• Physical changes alter the form or appearance of matter but do not change its chemical composition (e.g., melting, freezing, boiling, tearing)
• Chemical changes involve the rearrangement of atoms and molecules to form new substances with different properties (e.g., burning, rusting, cooking)
• Chemical reactions are processes that involve the breaking and forming of chemical bonds
• Chemical equations represent chemical reactions using chemical formulas and symbols
• The law of conservation of mass states that matter cannot be created or destroyed in a chemical reaction; it is only transformed

Mass and Weight

• Mass is a measure of the amount of matter in an object and is constant, regardless of location
• Weight is the force of gravity acting on an object's mass and can vary depending on the gravitational field
• The SI unit of mass is the kilogram (kg)

Volume

• Volume is the amount of space that matter occupies
• The SI unit of volume is the cubic meter (m³), but liters (L) and milliliters (mL) are commonly used
• Volume can be measured directly with graduated cylinders or calculated from dimensions for regular shapes

Density

• Density is the mass per unit volume of a substance and is an intensive property
• Density is calculated using the formula: density = mass / volume (ρ = m/V)
• Density is typically expressed in units of grams per cubic centimeter (g/cm³) or kilograms per cubic meter (kg/m³)
• Density can be used to identify substances and predict whether an object will float or sink in a fluid

Energy and Matter

• Energy is the ability to do work
• Energy can exist in various forms, including kinetic, potential, thermal, chemical, and electromagnetic
• The law of conservation of energy states that energy cannot be created or destroyed but can be converted from one form to another
• Energy changes often accompany changes in matter (e.g., chemical reactions release or absorb energy)
• Exothermic processes release energy to the surroundings, while endothermic processes absorb energy from the surroundings

Measurement and Units

• Measurements in science involve both a numerical value and a unit
• The International System of Units (SI) is the standard system of measurement used in science, based on seven base units: meter (m) for length, kilogram (kg) for mass, second (s) for time, ampere (A) for electric current, kelvin (K) for temperature, mole (mol) for amount of substance, and candela (cd) for luminous intensity
• SI units can be modified with prefixes to indicate multiples or fractions of the base units (e.g., kilo-, milli-, centi-)
• Accuracy refers to how close a measurement is to the true or accepted value
• Precision refers to how reproducible a measurement is
• Significant figures indicate the number of digits in a measurement that are known with certainty plus one estimated digit

Atoms and Molecules

• Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in specific energy levels or orbitals
• The number of protons determines the element's identity (atomic number)
• Isotopes are atoms of the same element with different numbers of neutrons, resulting in different mass numbers
• Molecules are formed when two or more atoms are held together by chemical bonds
• Chemical formulas represent the types and numbers of atoms in a molecule (e.g., H₂O for water)
• Molecular compounds are formed from nonmetal atoms sharing electrons through covalent bonds
• Ionic compounds are formed from ions (charged atoms or molecules) held together by electrostatic forces through ionic bonds