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 fundamental units of matter, composed of three primary 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

• Elements are organized in the periodic table by atomic number (number of protons).

• The periodic table helps predict element properties and chemical behavior.

Example: Hydrogen has atomic number 1, meaning it has 1 proton.

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) forms via ionic bonding; 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 indicate the precision of a measured quantity. The number of significant digits reflects the certainty of the measurement and affects how results are reported in calculations.

• 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 useful for identifying substances and predicting whether an object will float or sink in a fluid.

• Formula:

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

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

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