Matter, Measurement, and Atomic Structure: General Chemistry Study Notes

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, each with distinct 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

• 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 group (vertical column) have similar chemical properties.

• Atomic Number (Z): Number of protons in the nucleus; unique to each element.

• Mass Number (A): Total number of protons and neutrons in the nucleus.

Chemical Bonding

Ionic and Covalent Bonds

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

• Ionic Bonds: Formed by the transfer of electrons from a metal to a nonmetal, resulting in oppositely charged ions that attract each other.

• Covalent Bonds: Formed when two nonmetal atoms share one or more pairs of electrons.

Example: Sodium chloride (NaCl) forms via ionic bonding, while water (H2O) forms via 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): Length

• Kilogram (kg): Mass

• Second (s): Time

• Kelvin (K): Temperature

• Mole (mol): Amount of substance

Significant Figures

Significant figures (sig figs) indicate the precision of a measured quantity. The number of significant figures in a measurement includes all certain digits plus the first uncertain digit.

• When multiplying or dividing, the result should have as many significant figures as the measurement with the fewest significant figures.

• When adding or subtracting, the result should have as many decimal places as the measurement with the fewest decimal places.

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 10.0 g and a volume of 2.0 mL, its density is $d = \frac{10.0\ \mathrm{g}}{2.0\ \mathrm{mL}} = 5.0\ \mathrm{g/mL}$.