General Chemistry: Matter, Measurement, and Atomic Structure

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 physical states:

• Solid: Has a definite shape and volume; particles are closely packed in a fixed arrangement.

• Liquid: Has a definite volume but takes the shape of its container; particles are close but can move past one another.

• Gas: Has neither definite shape nor volume; particles are far apart and move freely.

Classification of Matter

• Pure Substance: Matter with a fixed composition and distinct properties. Examples include elements and compounds.

• Element: A pure substance that cannot be broken down into simpler substances by chemical means. Examples: Oxygen (O2), Gold (Au).

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

Example: Table salt (NaCl) is a compound, while iron (Fe) is an element.

Atomic Structure and the Periodic Table

Structure of the Atom

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

• Protons: Positively charged particles located in the nucleus.

• Neutrons: Neutral particles (no charge) also located in the nucleus.

• Electrons: Negatively charged particles that orbit the nucleus in electron clouds or shells.

The nucleus contains most of the atom's mass, while electrons occupy most of its volume.

The Periodic Table

• The periodic table organizes elements by increasing atomic number (number of protons).

• Elements in the same column (group) have similar chemical properties.

Example: Hydrogen (H) has atomic number 1; Carbon (C) has atomic number 6.

Chemical Bonds

Ionic and Covalent Bonds

Chemical bonds are forces that hold atoms together in compounds. The two main types are:

• Ionic Bonds: Formed when electrons are transferred from a metal to a nonmetal, resulting in oppositely charged ions that attract each other.

• Covalent Bonds: Formed when two atoms (usually nonmetals) share one or more pairs of electrons.

Example: Sodium chloride (NaCl) is formed by ionic bonding; water (H2O) is formed by covalent bonding.

Measurement in Chemistry

SI Units

The International System of Units (SI) is the standard for scientific measurements. Key SI base units include:

• 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 quantity. The number of significant figures reflects the certainty in the measurement.

• All nonzero digits are significant.

• Zeros between nonzero digits are significant.

• Leading zeros are not significant; trailing zeros are significant only if there is a decimal point.

Example: 0.00450 has three significant figures.

Density

Density is a physical property defined as mass per unit volume. It is useful for identifying substances and converting between mass and volume.

• Formula: $d = \frac{m}{V}$

• Where d is density, m is mass, and V is volume.

Example: If a sample has a mass of 10 g and a volume of 2 mL, its density is $d = \frac{10\ \mathrm{g}}{2\ \mathrm{mL}} = 5\ \mathrm{g/mL}$.