Ionic Compounds and Their Properties

Chapter 2: Atoms, Molecules, and Ions

• This chapter introduces atomic theory and subatomic particles.
• Early Greek philosophers proposed the concept of the atom, believing it to be the smallest indivisible unit.
• John Dalton's atomic theory, developed in the early 1800s, organized the earlier discoveries into a more structured model.
• Dalton's theory was based on several laws:
  • Law of constant composition: compounds always contain the same elements in the same proportions. Examples include H₂O, CO, and CO₂. This law was discovered by Joseph Proust.
  • Law of conservation of mass: the total mass of substances present at the end of a chemical process is the same as the mass of substances present before the process took place. This was discovered by Antoine Lavoisier.
  • Law of multiple proportions: if two elements form more than one compound, the masses of one element that combine with a given mass of the other are in the ratio of small whole numbers. This was discovered by John Dalton. Example: CO vs. CO₂.

2.1 Atomic Theory of Matter

• Greek philosophers like Democritus envisioned "atomos" (uncuttable) as fundamental particles making up all matter.
• Experiments in the 18th and 19th centuries led to Dalton's organized model of atoms.

Postulates of Dalton's Atomic Theory

• Each element is made up of extremely small particles called atoms.
• All atoms of a given element are identical in mass and other properties but differ from atoms of other elements.
• Atoms of one element cannot be changed into atoms of another element by chemical reactions.
• Atoms of different elements combine in simple whole-number ratios to form chemical compounds.

2.2 Discovery of Subatomic Particles

• Dalton's model viewed atoms as indivisible. But further discoveries revealed subatomic particles.
• Electrons, discovered by J.J. Thomson in 1897, are negatively charged particles found in atoms.
• Radioactivity, discovered by Henri Becquerel, demonstrates the atom's internal complexity and energy content.
• Marie and Pierre Curie also studied radioactivity.
• The nucleus, a tiny, dense, positively charged central core of the atom, and protons (positively charged) and neutrons (neutral) were discovered by Ernest Rutherford.

2.3 Modern View of Atomic Structure

• Rutherford's gold foil experiment proved the existence of a dense, positively charged nucleus within the atom.
• Most of the atom is empty space.
• Atoms have a size of 1-5 Å (or 100-500 pm).
• Atoms are made up of protons, neutrons, and electrons.

Subatomic Particles

• Protons (+1), electrons (-1) have charges, while neutrons are neutral.
• Protons and neutrons are approximately the same mass; electrons have much less mass.

Atomic Number

• The atomic number identifies an element. It represents the number of protons within an atom's nucleus.
• The number of protons equals the number of electrons in a neutral atom.

Atoms of an Element

• Elements are represented by one or two-letter symbols (e.g., C for carbon).
• Atomic number (number of protons) is written as a subscript before the symbol.
• Mass number (protons + neutrons) is written as a superscript before the symbol.
• Isotopes: atoms of the same element with different numbers of neutrons but the same number of protons. Example: ¹²C, ¹³C, ¹⁴C.

2.4 Atomic Mass Unit (amu)

• Atoms have extremely small masses, and a scale using atomic mass units (amu) is used.
• The atomic mass unit is relative to the mass of carbon-12 (¹²C), which is assigned a mass of exactly 12 amu. One amu is equal to 1.66054 × 10⁻²⁴ g

Atomic Weight

• Since the isotopes ratios naturally exist, atomic weight is the average mass of an atom based on relative isotopes abundance.
• It is determined by averaging the mass of an element's various isotopes with their relative abundance in nature.

Atomic Weight Measurement

• Mass spectrometry is used to measure atomic and molecular weights, and the abundance of isotopes. Isotopes have similar chemical properties, but different masses.

2.5 Periodic Table

• The periodic table organizes elements by atomic number (number of protons) and similar properties.
• Elements are arranged in periods (rows) and groups (columns).
• Elements in the same group have similar chemical properties, and have a repeating pattern of chemical behavior.

Reading the Periodic Table

• Atomic number is listed above the element symbol.
• Atomic weight is listed below the element symbol.

Organization of the Periodic Table

• Rows are called periods, and columns are called groups.
• Elements in the same group share similar physical and chemical properties, due to their similar electron configurations.

Periodicity - Rows

• Elements in a row exhibit repeating properties and reactivities.

Groups - Columns

• Groupings have named groups like Alkali metals, Alkaline earth metals, Chalcogens, Halogens, and Noble gases, these groups have related chemical properties.

2.6 Molecules and Molecular Compounds

• A chemical formula uses subscripts to represent the number of each kind of atom in a molecule.
• Molecular Compounds are made up of molecules almost always consisting of nonmetals.
• Diatomic molecules occur naturally as molecules with two atoms. Examples include H₂, N₂, O₂, F₂, Cl₂, Br₂, and I₂

Types of Formulas

• An empirical formula gives the lowest whole number ratio of atoms.
• A molecular formula shows the exact number of atoms.

Picturing Molecules

• Structural formulas (2D) display the order of attachment, not their shape.
• Perspective drawings, ball-and-stick models, and space-filling models represent three-dimensional shape.

2.7 Ions and Ionic Compounds

• Ions are formed when atoms gain or lose electrons.
• Cations are positively charged ions (formed by metals).
• Anions are negatively charged ions (formed by nonmetals except noble gases).
• Ionic compounds generally form between metals and nonmetals. Transfer of electrons results in oppositely charged ions that attract each other.

Ionic Compounds

• Ionic compounds are formed from charged particles called ions.
• Oppositely charged ions attract, forming an ionic lattice structure.
• Only empirical formulas are used to represent ionic compounds.

2.8 Naming Inorganic Compounds

• Chemical nomenclature is the system of naming compounds.
• Names of ions (cations and anions) are essential to memorize.
• Rules exist for naming ionic compounds, acids, and binary molecular compounds.

Common Cations

• Table 2.4 List of common cations with their charges and names including groups 1-A and 2-A elements. The transition metals are also included.

Common Anions

• Table 2.5 List of common anions with their charges and names. The anions included in this table are monatomic anions like chloride or bromide. Polyatomic anions are also listed like perchlorate or phosphate.

Polyatomic Ions

• Some groups of atoms act as ions and are called Polyatomic ions.

Writing Inorganic Formulas

• The charges of the ions will determine the ratio of one element to another, the subscript for each element.

Naming Inorganic Compounds

• Cations are named first, followed by anions.
• Transition metals (having more than one ionic charge) require Roman numerals in parentheses.
• Polyatomic ions have specific names. The rule for nonmetals such as chlorine is to change the ending to ide in the anion name.

Patterns in Oxyanion Nomenclature

• Oxyanions (polyatomic anions containing oxygen) follow naming patterns based on the number of oxygen atoms.
• The ion with fewer oxygen atoms ends in -ite. The ion with more oxygen atoms ends in -ate. These are also referred to as oxyanions.

Inorganic Acid Nomenclature

• Acids with -ide ending of the anion name is changed to -ic acid with the prefix hydro- put before the name.
• Acids with -ite ending of the anion name is changed to -ous acid.
• Acids with -ate ending of the anion name is changed to -ic acid.

Nomenclature of Binary Molecular Compounds

• The element farther to the left on the periodic table or lower in the same group is usually named first.
• Prefixes are used to denote the numbers of atoms of each element. Examples are mono, di, tri....

2.9 Some Simple Organic Compounds

• Organic chemistry is the study of carbon compounds and its branches for nomenclature.
• Hydrocarbons (compounds with C and H) are alkanes.
• The names follow prefixes based on the number of carbon atoms. (Example meth-, eth-, prop-...) followed by the suffix -ane in the name.

Nomenclature of Alcohols

• Alcohols are hydrocarbons with -OH groups.
• Their names are derived from the alkane by adding the suffix -ol to it.

Nomenclature Isomers: Alcohols

• Isomers are compounds that have the same chemical formula but different structures.
• Isomers are formed when the atoms are arranged differently but with the same molecular formula.