Atoms, Isotopes, and Radioactivity: Chapter 2 Study Notes

Atoms and Their Components

Elements and Atomic Structure

All matter is composed of atoms, which are the fundamental building blocks of elements. Each element is defined by a particular type of atom, distinguished by its number of protons.

• Element: A pure substance consisting of only one type of atom.

• Atom: The smallest unit of an element that retains its chemical properties.

• Example: Diamond (pure carbon), graphite (carbon in a different structure), and the lead in a pencil (graphite) are all forms of the element carbon.

Subatomic Particles

Structure of the Atom

Atoms are made up of three primary subatomic particles: protons, neutrons, and electrons. These particles differ in charge, location, and mass.

• Proton (p or p+): Positively charged, found in the nucleus.

• Neutron (n or n0): Uncharged (neutral), found in the nucleus.

• Electron (e-): Negatively charged, orbits the nucleus.

Subatomic Particle	Symbol	Electrical Charge	Relative Mass
Electron	e-	1−	0.0005 (1/2000)
Proton	p or p+	1+	1
Neutron	n or n0	0	1

Atomic Mass Unit (amu)

Definition and Application

The atomic mass unit (amu) is a standard unit of mass used to express atomic and molecular weights. It is defined as one-twelfth the mass of a carbon-12 atom.

• 1 amu: Approximately the mass of one proton or one neutron.

• Example: Carbon-12 has 6 protons and 6 neutrons, so its mass is about 12 amu.

Atomic Number and Mass Number

Identifying Elements and Isotopes

Atoms of different elements have different numbers of protons, neutrons, and electrons. The atomic number and mass number are key identifiers.

• Atomic Number (Z): Number of protons in the nucleus; unique to each element.

• Mass Number (A): Total number of protons and neutrons in the nucleus.

• Neutral Atom: Number of protons equals number of electrons.

• Formula: $\text{Mass Number} = \text{Number of Protons} + \text{Number of Neutrons}$

• Example: For carbon: $^{12}_{6}\text{C}$, atomic number = 6, mass number = 12.

Isotopes and Atomic Mass

Isotopic Variations

Isotopes are atoms of the same element that have different numbers of neutrons, resulting in different mass numbers.

• Isotope: Atoms with the same number of protons but different numbers of neutrons.

• Example: Carbon has three common isotopes: carbon-12, carbon-13, and carbon-14.

• Notation: $^{12}_{6}\text{C}$, $^{13}_{6}\text{C}$, $^{14}_{6}\text{C}$

• Neutron Calculation: $\text{Number of Neutrons} = \text{Mass Number} - \text{Atomic Number}$

Periodic Table Reference

Using the Periodic Table

The periodic table organizes elements by atomic number and provides information about their properties, including atomic mass and group classification.

• Groups: Vertical columns indicating elements with similar chemical properties.

• Periods: Horizontal rows indicating increasing atomic number.

• Application: The periodic table can be used to determine the number of protons, neutrons, and electrons for each element.

*Additional info: Some context and explanations have been expanded for clarity and completeness, including definitions, formulas, and examples relevant to GOB Chemistry students.*