Matter, Measurements, and Basic Chemical Concepts

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.

Pure Substances and Mixtures

Pure substances have a fixed composition and distinct properties. They are classified as:

• Elements: Substances that cannot be broken down into simpler substances by chemical means. Examples: Oxygen (O2), Gold (Au).

• Compounds: Substances composed of two or more elements chemically combined in fixed proportions. Examples: Water (H2O), Carbon dioxide (CO2).

Mixtures (not detailed in the original notes) are physical combinations of two or more substances and can be separated by physical means. Additional info: Mixtures can be homogeneous (uniform composition) or heterogeneous (non-uniform composition).

Atomic Structure and the Periodic Table

Structure of the Atom

Atoms are the basic units of matter, consisting of three fundamental 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 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.

Chemical Bonding

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 the formation of 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, a metal) and chlorine (Cl, a nonmetal). Water (H2O) forms via covalent bonding between hydrogen and oxygen atoms.

Measurements 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 (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.

• Rules: 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.

Density

Density is a physical property defined as mass per unit volume. It is calculated using the formula:

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

• d: Density (e.g., g/cm3 or kg/m3)

• m: Mass

• V: Volume

Example: If a sample has a mass of 10.0 g and a volume of 2.0 cm3, its density is $d = \frac{10.0\ \mathrm{g}}{2.0\ \mathrm{cm}^3} = 5.0\ \mathrm{g/cm}^3$.