Classification of Matter, States, and Atomic Structure: Study Notes for General, Organic, and Biological Chemistry

Classification of Matter

Types of Matter

Matter is anything that has mass and occupies space. It can be classified based on its composition and properties into pure substances and mixtures.

• Pure Substances: Have a constant composition and distinct properties. They can be further divided into:

  • Elements: Substances that cannot be broken down into simpler substances by chemical means. Each element is made up of one kind of atom.

  • Compounds: Substances composed of two or more elements chemically combined in fixed ratios.

• Mixtures: Combinations of two or more substances in which each retains its own identity and properties. Mixtures can be separated by physical means and are not combined in fixed proportions.

  • Homogeneous Mixtures (Solutions): Have uniform composition throughout (e.g., salt water, air).

  • Heterogeneous Mixtures: Do not have uniform composition and may contain visibly different parts (e.g., sand in water, salad).

States of Matter

Physical States and Their Properties

Matter exists in three primary physical states: solid, liquid, and gas. Each state has distinct characteristics based on the arrangement and movement of particles.

Characteristic	Solid	Liquid	Gas
Shape	Definite	Takes shape of container	Takes shape of container
Volume	Definite	Definite	Fills container
Arrangement of particles	Fixed, very close	Random, close	Random, far apart
Interaction between particles	Very strong	Strong	Essentially none
Movement of particles	Very slow	Moderate	Very fast
Examples	Ice, salt, iron	Water, oil, vinegar	Water vapor, helium, air

Physical and Chemical Properties and Changes

Physical Properties and Changes

Physical properties are characteristics that can be observed or measured without changing the substance's chemical identity. Physical changes alter the form or appearance of matter but do not change its composition.

• Examples of physical changes: melting, boiling, chopping, shredding, dissolving.

• Physical changes are often reversible.

Chemical Properties and Changes

Chemical properties describe a substance's ability to undergo changes that transform it into different substances. Chemical changes result in the formation of one or more new substances with new properties.

• Examples of chemical changes: combustion, rusting, digestion, rotting, baking a cake.

• Chemical changes are usually not reversible by simple physical means.

Atomic Structure

Subatomic Particles

Atoms are the basic building blocks of matter. Each atom consists of a nucleus (containing protons and neutrons) and an electron cloud.

• Protons (p+): Positively charged particles found in the nucleus.

• Neutrons (n): Neutral particles found in the nucleus.

• Electrons (e–): Negatively charged particles found in the electron cloud surrounding the nucleus.

Electrostatics

Electrostatic forces govern the interactions between charged particles:

• Like charges repel each other.

• Opposite charges attract each other.

Elements and the Periodic Table

Elements and Symbols

Elements are pure substances that cannot be broken down into simpler substances. Each element is represented by a unique chemical symbol, usually derived from its English or Latin name (e.g., H for hydrogen, Au for gold).

• Some elements are monoatomic (e.g., He), diatomic (e.g., O2), or polyatomic (e.g., S8).

The Periodic Table

The periodic table organizes elements by increasing atomic number and groups elements with similar chemical properties into columns called groups or families. Rows are called periods.

• Metals are found on the left and center, nonmetals on the right, and metalloids along the zigzag line.

• Group 1A: Alkali metals (e.g., Na, K)

• Group 2A: Alkaline earth metals (e.g., Mg, Ca)

• Group 7A: Halogens (e.g., F, Cl, Br)

• Group 8A: Noble gases (e.g., He, Ne, Ar)

Atomic Number, Mass Number, and Isotopes

Atomic Number (Z)

The atomic number is the number of protons in the nucleus of an atom and determines the identity of the element.

• Each element has a unique atomic number.

• In a neutral atom, the number of electrons equals the number of protons.

Mass Number (A) and Isotopes

The mass number is the total number of protons and neutrons in the nucleus. Isotopes are atoms of the same element with different numbers of neutrons (and thus different mass numbers).

• Isotope notation: $^A_ZX$ where X is the element symbol, A is the mass number, and Z is the atomic number.

• Number of neutrons = Mass number (A) – Atomic number (Z)

Formulas of Compounds

Chemical Formulas

A chemical formula shows the types and numbers of atoms in a compound. Compounds always have elements combined in fixed ratios.

• Example: NaCl (sodium chloride) has a 1:1 ratio of sodium to chlorine atoms.

• Example: H2O (water) has a 2:1 ratio of hydrogen to oxygen atoms.

Temperature and Measurement

Temperature Scales

Temperature is a measure of how hot or cold an object is. The three main temperature scales are Celsius (°C), Kelvin (K), and Fahrenheit (°F).

• Celsius: Water freezes at 0°C and boils at 100°C.

• Kelvin: Absolute zero is 0 K; water freezes at 273.15 K and boils at 373.15 K.

• Fahrenheit: Water freezes at 32°F and boils at 212°F.

Temperature Conversions

• Kelvin to Celsius: $K = ^\circ C + 273.15$

• Celsius to Kelvin: $^\circ C = K - 273.15$

• Celsius to Fahrenheit: $^\circ F = (^\circ C \times \frac{9}{5}) + 32$

• Fahrenheit to Celsius: $^\circ C = (^\circ F - 32) \times \frac{5}{9}$

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