The Structure of the Atom and the Periodic Table: Study Notes

Chapter 2: The Structure of the Atom and the Periodic Table

Composition of the Atom

The atom is the fundamental building block of matter and the smallest unit of an element that retains its chemical properties. Understanding atomic structure is essential for studying chemical behavior.

• Atom: The basic structural unit of an element.

• Atomic models: Historical models include the Billiard Ball (Dalton), Plum Pudding (Thomson), Planetary (Rutherford), Bohr, and Electron Cloud (Schrödinger).

• Example: The Bohr model depicts electrons in fixed orbits around the nucleus, while the electron cloud model describes regions of probability for electron location.

Electrons, Protons, and Neutrons

Atoms consist of three primary subatomic particles: protons, neutrons, and electrons. Their arrangement and properties determine the atom's identity and behavior.

• Protons: Positively charged particles located in the nucleus.

• Neutrons: Uncharged (neutral) particles also found in the nucleus.

• Electrons: Negatively charged particles that move rapidly in the space surrounding the nucleus.

• Nucleus: The small, dense, positively charged center of the atom containing protons and neutrons.

Characteristics of Atomic Particles

Each subatomic particle has distinct properties that influence atomic structure and chemical reactions.

• Electrons: Negatively charged, located outside the nucleus, move rapidly in a large volume of space.

• Charge balance: Protons and electrons have charges equal in magnitude but opposite in sign.

• Neutral atom: Has equal numbers of protons and electrons.

Selected Properties of the Three Basic Subatomic Particles

The following table summarizes the charge and mass of electrons, protons, and neutrons.

Particle	Charge	Mass (amu)	Mass (grams)
Electron (e-)	-1	5.486 × 10-4	9.1094 × 10-28
Proton (p+)	+1	1.007	1.6726 × 10-24
Neutron (n)	0	1.009	1.6750 × 10-24

Symbolic Representation of an Element

Elements are represented using their atomic number, mass number, and chemical symbol.

• Atomic number (Z): Number of protons in the atom.

• Mass number (A): Sum of protons and neutrons.

• Symbolic notation: $^A_Z X$ where X is the elemental symbol, A is the mass number, and Z is the atomic number.

Atomic Calculations

Calculating the number of subatomic particles is fundamental for understanding isotopes and ions.

• Mass number: $ext{Mass number} = ext{number of protons} + ext{number of neutrons}$

• Number of neutrons: $ext{Number of neutrons} = ext{mass number} - ext{atomic number}$ $ext{Number of neutrons} = A - Z$

Determining the Composition of an Atom

To find the number of protons, neutrons, and electrons in an atom, use the atomic number and mass number.

• Example: For $^{11}_5 B$ (Boron): Protons = 5, Neutrons = 6, Electrons = 5 (if neutral)

• Example: For $^{56}_{26} Fe$ (Iron): Protons = 26, Neutrons = 30, Electrons = 26 (if neutral)

Isotopes

Isotopes are atoms of the same element with different masses due to varying numbers of neutrons.

• Isotopes: Same number of protons, different number of neutrons.

• Example: Hydrogen has three isotopes: $^1_1 H$ (protium), $^2_1 H$ (deuterium), $^3_1 H$ (tritium).

Additional info:

• Isotopes are important in fields such as radiochemistry and medical imaging.

• Atomic mass is a weighted average of all naturally occurring isotopes.