Study Notes on Atoms and Elements

Chapter 2: Atoms and Elements

Introduction to Atoms

  • In the early 1800s, John Dalton first described atoms.

  • Dalton's Atomic Theory:

    • The atom is the basic unit from which matter is constructed.

    • Current scientific consensus agrees that matter is indeed composed of atoms.

  • Atoms are complex structures made up of smaller subatomic particles:

    • Protons: positively charged particles.

    • Neutrons: neutrally charged particles.

    • Electrons: negatively charged particles.

Question on Subatomic Particles

  • Question: Which subatomic particle contributes the least to the mass of an atom?
    a. Proton
    b. Neutron
    c. Electron
    d. Ion

Atomic Number and Mass Number

Objectives

  • To explain what atomic number and mass number indicate about an atom’s nucleus.

  • To describe how isotopes of an element differ from one another.

Description of Atomic Number and Mass Number

  • Each atom of a particular element possesses the same number of protons.

  • Atomic Number:

    • Defined as the number of protons in an atom.

  • Mass Number:

    • Defined as the total of protons and neutrons in an atom.

    • Example calculations:

    • Sulfur (S): 16 protons + 16 neutrons = mass number 32.

    • Aluminum (Al): 13 protons + 14 neutrons = mass number 27.

Atomic Notation

  • Atomic notation is employed to designate the number of protons and neutrons in an atom.

    • Example format: 714N_{7}^{14}N

    • Atomic Symbol: N

    • Atomic Number: 7 (indicating the number of protons)

    • Mass Number: 14 (indicating the sum of protons and neutrons).

Isotopes

  • Isotopes have identical atomic numbers (number of protons) but differ in mass numbers due to varying numbers of neutrons.

Periodic Table

Definition and Structure

  • The Periodic Table is a comprehensive list of elements organized by increasing atomic number.

  • Information provided for each element includes:

    • Atomic Number

    • Symbol

    • Atomic Weight (e.g., C: 12.011, 6)

Classification of Elements

  • Elements can be categorized into three main groups:

    1. Metals

    2. Nonmetals

    3. Semimetals (metalloids)

Metals

  • Located on the left side of the Periodic Table.

  • Properties include:

    • Good conductors of heat and electricity.

    • Typically solid at room temperature, with the exception of mercury (Hg).

    • Have lustrous (shiny) surfaces when freshly cut.

    • Properties include malleability (can be hammered into thin sheets) and ductility (can be drawn into wires).

Nonmetals

  • Located on the right side of the Periodic Table.

  • Properties include:

    • Poor conductors of heat and electricity.

    • Nonlustrous and brittle when in solid state.

Semimetals (Metalloids)

  • Positioned between metals and nonmetals on the Periodic Table.

  • Exhibit properties that are intermediate between metals and nonmetals.

  • Typically act as semiconductors, which have applications in electronics.

Groups and Periods

Groups (Vertical Columns)

  • Characteristics of groups include:

    • Atomic size increases as you move down a group.

    • Atoms become more metallic as you descend a group.

    • Specific groups have conventional names: Alkali metals, Alkaline earth metals, Halogens, and Inert (Noble) gases.

Question on Group Characteristics

  • Question: Elements of group 2A are known as?
    a. Alkali metals
    b. Alkaline earth metals
    c. Transition metals
    d. Noble gases

Periods (Horizontal Rows)

  • Characteristics of periods include:

    • Atomic size typically decreases when moving from left to right within a period.

    • Elements furthest to the left are generally the most metallic, while those to the far right are the most nonmetallic.

Question on Period Characteristics

  • Question: Which element has the smallest atomic radii?
    a. Fluorine (F)
    b. Francium (Fr)
    c. Lithium (Li)
    d. Astatine (At)