Matter, Measurements, and Atomic Structure: General Chemistry Study Guide

Matter and Its Classification

Definition and States of Matter

Matter is defined as anything that has mass and occupies space. It exists in three primary states, each with distinct physical properties.

• Solid: Definite shape and volume; particles are closely packed and vibrate in place.

• Liquid: Definite volume but no definite shape; particles are less tightly packed and can flow past one another.

• Gas: No definite shape or volume; particles are far apart and move freely.

Classification of Matter

Matter can be classified based on its composition and properties.

• Pure Substance: Has a fixed composition and distinct properties.

• Element: A pure substance that cannot be broken down by chemical means. Examples: Hydrogen (H), Oxygen (O).

• Compound: A pure substance composed of two or more elements chemically combined. Examples: Water (H2O), Carbon Dioxide (CO2).

Example: Water is a compound because it consists of hydrogen and oxygen atoms chemically bonded.

Atomic Structure and the Periodic Table

Atoms and Subatomic Particles

Atoms are the basic units of matter, composed of three main subatomic particles:

• Proton: Positively charged particle located in the nucleus.

• Neutron: Neutral particle located in the nucleus.

• Electron: Negatively charged particle that orbits the nucleus.

The nucleus contains protons and neutrons, while electrons move in regions around the nucleus.

The Periodic Table

The periodic table organizes elements by their atomic number, which is the number of protons in the nucleus.

• Atomic Number: Determines the identity of an element.

• Organization: Elements are arranged in rows (periods) and columns (groups) based on similar properties.

Example: Carbon has an atomic number of 6, meaning it has 6 protons.

Chemical Bonds

Ionic and Covalent Bonds

Chemical bonds are forces that hold atoms together in compounds.

• Ionic Bond: Formed when electrons are transferred from a metal to a nonmetal, resulting in oppositely charged ions.

• Covalent Bond: Formed when atoms share pairs of electrons, typically between nonmetals.

Example: Sodium chloride (NaCl) is formed by an ionic bond between sodium (Na) and chlorine (Cl).

Measurements and Units

SI Units

The International System of Units (SI) is used for scientific measurements.

• Meter (m): Unit of length

• Kilogram (kg): Unit of mass

• Second (s): Unit of time

• Kelvin (K): Unit of temperature

• Mole (mol): Unit for amount of substance

Significant Figures

Significant figures indicate the precision of a measured value. The number of significant digits reflects the certainty in a measurement.

• Rules: All nonzero digits are significant; zeros between nonzero digits are significant; leading zeros are not significant; trailing zeros in a decimal number are significant.

Example: 0.00450 has three significant figures.

Density

Density is a physical property defined as mass per unit volume.

• Formula:

$d = \frac{m}{V}$

• Where: d = density, m = mass, V = volume

Example: If a substance has a mass of 10 g and a volume of 2 cm3, its density is $d = \frac{10}{2} = 5 \text{ g/cm}^3$.