Atoms and Elements

Introduction to Elements

Elements are the fundamental building blocks of all matter. Understanding their properties and organization is essential for studying biological systems in Anatomy & Physiology.

• Element: The simplest identifiable unit of an element is the atom.

• There are 118 known elements; 92 occur naturally, and 26 have been synthesized.

• All known elements are organized in the Periodic Table.

Periodic Table of the Elements

The periodic table arranges elements by increasing atomic number and groups them by similar chemical properties.

• Elements are classified into metals, nonmetals, and semimetals (metalloids).

• Each element has a unique name and symbol.

• Element names may derive from Latin, Greek, places, or people (e.g., Hydrogen from Greek for 'water former', Neobium for Alfred Nobel).

Element Symbols

Each element is abbreviated using a chemical symbol, typically one or two letters. The first letter is always capitalized.

• Symbols may be derived from English or Latin names (e.g., Na for sodium from Natrium).

• Examples: Au (Gold), Ag (Silver), Fe (Iron).

Chemical Formulas and Writing Formulas

Chemical Formulas

A chemical formula expresses the number and type of atoms in a molecule.

• Example: The chemical formula for sulfuric acid is .

Writing Chemical Formulas

The number of each type of atom is indicated by a subscript in the chemical formula.

• Example: has 2 hydrogen atoms and 1 oxygen atom.

• Example: (glucose) has 6 carbon, 12 hydrogen, and 6 oxygen atoms.

Interpreting Chemical Formulas

Parentheses and subscripts clarify atom composition in complex molecules.

• Example: contains 1 calcium, 2 oxygen, and 2 hydrogen atoms.

Types of Elements

Classification of Elements

Elements are divided into three main classes:

• Metals: Located on the left side of the periodic table; typically shiny, malleable, and good conductors.

• Nonmetals: Located on the right side; often dull, brittle, and poor conductors.

• Semimetals (Metalloids): Properties intermediate between metals and nonmetals.

Atomic Theory and Subatomic Particles

Dalton's Atomic Theory

John Dalton proposed that atoms are indivisible and combine in fixed ratios to form compounds.

• Atoms of an element are identical and different from those of other elements.

• Compounds contain atoms in small whole number ratios.

Subatomic Particles

Atoms are composed of three main subatomic particles:

• Proton: Positive charge (+1), located in the nucleus.

• Neutron: No charge (0), located in the nucleus.

• Electron: Negative charge (-1), located outside the nucleus.

Structure of the Atom

Atomic Structure

Atoms consist of a central nucleus containing protons and neutrons, surrounded by electrons.

• The nucleus is dense and contains most of the atom's mass.

• Electrons occupy regions called orbitals around the nucleus.

Atomic Mass, Mass Number, and Isotopes

Atomic Mass and Mass Number

The mass number is the total number of protons and neutrons in an atom. The atomic mass is the weighted average mass of all isotopes of an element.

• Mass number = number of protons + number of neutrons

• Atomic mass is measured in atomic mass units (amu).

Isotopes

Isotopes are atoms of the same element with different numbers of neutrons.

• All isotopes have the same atomic number but different mass numbers.

• Example: Hydrogen has three isotopes—protium (), deuterium (), and tritium ().

Weighted Average and Average Atomic Mass

The average atomic mass of an element is calculated using the weighted average of its isotopes.

• Weighted average formula:

• Example: If isotope A is 90% and isotope B is 10%, average mass =

Periodic Law and Trends

The Periodic Law

The periodic law states that the properties of elements recur in a predictable pattern when arranged by increasing atomic number.

• Periodic trends include atomic radius, ionization energy, and electronegativity.

Tables

Subatomic Particle Properties

The following table summarizes the properties of subatomic particles:

Isotope Example Table

Isotopes of Hydrogen:

Weighted Average Calculation Example

Example of calculating a weighted average (from grades):

Weighted average =

Atomic Notation

Atomic Notation Format

Atomic notation displays the number of protons, neutrons, and electrons in an atom:

• Format: , where is the mass number, is the atomic number, and is the element symbol.

• Example: for sodium.

Using Atomic Notation

Atomic notation helps determine the number of subatomic particles:

• Number of protons = atomic number ()

• Number of neutrons = mass number () - atomic number ()

• Number of electrons = atomic number () (for neutral atoms)

Summary

Understanding atoms, elements, and their organization is foundational for Anatomy & Physiology. These concepts explain the chemical basis of biological molecules and processes.