BackChapter 2: The Structure of the Atom and the Periodic Table – Study Notes
Study Guide - Smart Notes
Tailored notes based on your materials, expanded with key definitions, examples, and context.
Composition of the Atom
Definition and Structure of the Atom
The atom is the fundamental structural unit of an element. It is the smallest unit that retains the chemical properties of that element.
Atom: The basic building block of matter, unique to each element.
Chemical Properties: Characteristics that determine how an element reacts with other substances.
Models of the Atom: Over time, several models have been proposed, including the Billiard Ball (Dalton), Plum Pudding (Thomson), Planetary (Rutherford), Bohr, and Electron Cloud (Schrödinger) models.
Example: The Bohr model depicts electrons in fixed orbits around the nucleus, while the Electron Cloud model describes regions of probability for electron location.
Subatomic Particles
Electrons, Protons, and Neutrons
Atoms consist of three primary subatomic particles: protons, neutrons, and electrons.
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 a large volume of space outside 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.
Electrons: Negatively charged, located outside the nucleus, move rapidly in a relatively large space.
Charge Magnitude: Protons and electrons have charges equal in magnitude but opposite in sign.
Neutral Atom: Has equal numbers of protons and electrons, resulting in no net electrical charge.
Selected Properties of Subatomic Particles
The following table summarizes the charge and mass of the three basic subatomic particles:
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 |
Atomic Number, Mass Number, and Symbolic Representation
Symbolic Representation of an Element
Elements are represented using their atomic number (Z), mass number (A), and elemental symbol (X):
Atomic Number (Z): Number of protons in the nucleus.
Mass Number (A): Sum of protons and neutrons.
Symbolic Notation:
Atomic Calculations
To determine the composition of an atom, use the following relationships:
Mass number:
Number of neutrons:
Number of neutrons:
Number of neutrons:
Isotopes
Definition and Properties of Isotopes
Isotopes are atoms of the same element that have different masses due to varying numbers of neutrons.
Same number of protons (same atomic number).
Different number of neutrons (different mass number).
Example: Hydrogen has three isotopes: , (deuterium), and (tritium).
Isotope | Protons | Neutrons | Electrons |
|---|---|---|---|
1 | 0 | 1 | |
1 | 1 | 1 | |
1 | 2 | 1 |
Additional info: Isotopes of an element have nearly identical chemical properties but may differ in physical properties such as mass and radioactivity.
