Atoms, Elements, Molecules, and Compounds: Foundations of Chemistry

Chapter 4: Molecules and Elements

Examples of Medicinal Chemistry

Many compounds and elements play crucial roles in medicine. Understanding their chemical nature helps explain their function and application.

• Sodium nitrate (NaNO3): Used in food preservation, pharmaceuticals, and dermatological medicines.

• Sodium fluoride (NaF): Added to toothpaste and water to prevent tooth decay.

• Ferrous salt: Used in anemia medications.

• Lithium carbonate (Li2CO3): Used to treat bipolar disorder.

• Sodium chloride (NaCl): Used in general anesthetics and oxygen delivery systems.

Method: Using the Table of Elements

The periodic table is a guide for learning about the different types of elements, their properties, and their uses in medicine and other fields.

Application: Atoms and Elements

• Understanding what elements are, how they interact, and their properties is essential for studying medicinal chemistry and biology.

Atomic Theory

• Ancient Greek Model: Matter is composed of small, indestructible particles called atoms.

• Atoms: The smallest identifiable unit of an element.

• Atoms of a given element have unique properties that distinguish them from atoms of other elements.

• Atoms combine in simple, whole-number ratios to form compounds.

The Nuclear Model of the Atom

• The atom is composed of protons and neutrons (in the nucleus) and electrons (in the electron cloud).

• Electrons occupy most of the atom's volume.

• Protons and neutrons have similar masses (~1 amu), while electrons have much smaller mass.

Charge

• Protons and electrons both have electrical charge.

• Proton charge: +1; Electron charge: -1; Neutron: no charge.

• When protons and electrons combine in atoms, their charges cancel, resulting in a neutral atom.

• Electricity is the movement of electrical charge, often involving electrons.

The Periodic Table

• Arranges all known elements in order of increasing atomic number.

• Columns are called groups or families and contain elements with similar properties.

• Elements on the left are metals (tend to lose electrons in reactions).

• Elements on the upper right are nonmetals (tend to gain electrons).

• Elements between metals and nonmetals are called metalloids.

Atomic Number

• The atomic number (Z) is the number of protons in an atom's nucleus and defines the element.

Ions

• When an atom gains or loses electrons, it becomes an ion.

• Cations: Positively charged ions (loss of electrons).

• Anions: Negatively charged ions (gain of electrons).

• Cations and anions combine so that matter is charge neutral.

Isotopes

• Atoms of the same element with different numbers of neutrons are called isotopes.

• Isotopes are characterized by their mass number (A): $A = \text{number of protons} + \text{number of neutrons}$

• The atomic mass of an element is a weighted average of the masses of its isotopes.

Chapter 5: Molecules and Compounds

Definition

• Molecules: Two or more elements joined together (e.g., O2).

• Compounds: Two or more different elements joined together (e.g., CO, CO2).

Purpose

• Learn the different types of compounds: ionic, molecular/covalent, and be able to name them.

Application

• Understanding the different kinds of compounds is essential for predicting their properties and uses.

Chemical Principles

• Compounds have definite composition: the elements and their ratios are fixed in every sample.

• Chemical formulas indicate the elements present and the relative number of atoms of each.

Chemical Nomenclature

• The names of simple ionic compounds, molecular compounds, and acids can be written by examining their chemical formulas.

Formula Mass

• The formula mass of a compound is the sum of the atomic masses of all the atoms in its chemical formula.

• Formula mass calculation: $\text{Formula mass} = \sum (\text{number of atoms of each element} \times \text{atomic mass of element})$

Examples and Applications

• Example: The formula for potassium chloride is KCl. The formula for magnesium chloride is MgCl2. The formula for barium chloride is BaCl2.

• Example: The name of the ionic compound made of beryllium and chlorine is beryllium chloride.

Sample Table: Types of Elements and Their Properties

Type	Location on Periodic Table	Properties
Metals	Left side	Good conductors, malleable, tend to lose electrons
Nonmetals	Upper right	Poor conductors, brittle, tend to gain electrons
Metalloids	Between metals and nonmetals	Intermediate properties

Additional info: The notes include embedded multiple-choice questions (examples) to reinforce key concepts, such as identifying ions, isotopes, and chemical formulas. These are typical of introductory chemistry courses and help students apply theoretical knowledge to practical problems.