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.

Pure Substances and Mixtures

Matter can be classified based on its composition:

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

• Element: A substance that cannot be broken down into simpler substances by chemical means. Each element is made of one type of atom.

• Compound: Consists of two or more elements chemically combined in fixed proportions. Compounds can be broken down into elements by chemical reactions. Examples: water (H2O), carbon dioxide (CO2).

Atomic Structure and the Periodic Table

Structure of the Atom

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

• Protons: Positively charged particles located in the nucleus.

• Neutrons: Neutral particles also found 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 (column) have similar chemical properties.

Chemical Bonding

Ionic and Covalent Bonds

Atoms combine to form compounds through chemical bonds:

• 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) forms via ionic bonding between sodium (Na) and chlorine (Cl). Water (H2O) forms via covalent bonding between hydrogen and oxygen.

Measurement in Chemistry

SI Units

The International System of Units (SI) is used 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 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 performing calculations, the result should be reported with the correct number of significant figures based on the rules for addition, subtraction, multiplication, and division.

Density

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

• The formula for density is:

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

• 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 $d = \frac{10.0\ \mathrm{g}}{2.0\ \mathrm{mL}} = 5.0\ \mathrm{g/mL}$.