6.2 chemical building blocks

Chemical Building Blocks

6.2.1 Models to Explain the Building Blocks of Matter

• The understanding of the ‘building blocks’ of matter, termed atoms, is a relatively recent development, with much of it emerging within the last 100 years.
      - The concept that matter consists of atoms was first introduced approximately 2500 years ago by philosopher Democritus.
      - Over time, theories and models regarding the atom have evolved, leading to various acceptance, rejection, and modification of ideas.
      - Figure 6.2 presents a timeline that highlights significant milestones in atomic theory.

• Atoms are extremely small:
      - Even the largest atoms measure less than one billionth of a meter across.
      - Correspondingly, one billionth of a meter equals one millionth of a millimeter.
      - The diameter of the finest human hair is compared to the atom’s size.

• The nucleus constitutes a small fraction of an atom's diameter:
      - If an atom were represented as the size of the Melbourne Cricket Ground, the nucleus would be the size of a grain of rice.

• Atoms are mainly empty space:
      - For instance, a hydrogen atom is approximately 99.9999999999996% empty space.

6.2.2 The Structure of Atoms

• The prevailing atomic model includes:
      - A small, dense nucleus consisting of protons and neutrons.
      - Surrounding the nucleus are electrons that occupy energy shells or orbits (referred to as electron clouds).

• Learning Intention:
      - By the lesson's conclusion, learners will:
          - Comprehend the composition of atoms as formed by subatomic particles (protons, neutrons, electrons).
          - Analyze experimental evidence that led to the identification of these particles.
          - Compare the characteristics of protons, neutrons, and electrons based on their mass, charge, and locational attributes.

• Table 6.1: Subatomic Particles and Their Properties
      | Subatomic Particle | Charge | Relative Mass | Location |
      |--------------------|----------|---------------|----------------------------------|
      | Proton | Positive | +1 | Nucleus |
      | Neutron | Neutral | 0 | Nucleus |
      | Electron | Negative | -1 | Energy shells (electron cloud) |

6.2.3 Elements

• Distinct types of atoms have been recognized:
      - Current count stands at 118 types of atoms.

• Definition of Elements:
      - Elements are pure substances that consist exclusively of one type of atom.
      - Example: Pure oxygen consists solely of oxygen atoms, and pure lead consists solely of lead atoms.
      - An element is defined primarily by the number of protons found in its nucleus.

Investigation 6.1: Exploring Models of the Atom

• Aim: Investigate Rutherford’s experiment.

• Science Inquiry Skills: Repeatability enhances the accuracy of results and boosts confidence in scientific conclusions.

Discussion on Models of the Atom

• Reflection on the evolution of atomic models over the past century prompts inquiries:
      - Have we attained complete understanding of the atom?
      - What improvements could still be made based on historical learning?

Representing Elements

• Each element is denoted by a specific element symbol and is characterized by its atomic number and mass number:
      - Most element symbols derive from the initial letters of their names (e.g., C for carbon, Cd for cadmium).
      - Certain symbols stem from ancient Greek or Latin (e.g., Au for gold, originating from "aurum").

• Atomic Number:
      - Defines the number of protons in an atom’s nucleus.
      - It also represents the number of electrons in a neutrally charged atom, where positive and negative charges balance.
      - Example: Oxygen, with an atomic number of 8, encompasses eight protons and eight electrons.

• Mass Number:
      - Defined as the sum of protons and neutrons within an atom.
      - Protons and neutrons share comparable mass, while an electron's mass is negligible in comparison.
      - Overall atom mass is contingent only on the particles found in the nucleus.

6.2 Quick Quiz

• Q1: Label the atom with the correct terms (Neutron, Proton, Shell, Electron, Nucleus).

• Q2: Match definitions to correct terms:
      - Atomic Symbol
      - Mass Number
          - Definition: Total number of protons and neutrons in the nucleus of a specific atom.
      - Element
          - Definition: A pure chemical species comprising only one type of atom.
      - Subatomic Particles
          - Definition: The particles existing within an atom — electrons, protons, and neutrons.
      - Atomic Number
          - Definition: The number of protons within an atom's nucleus.

• Q3: (Content not provided)

• Q4: Identify which information does not exclusively determine an element:
      - A. Atomic Symbol
      - B. Mass Number
      - C. Number of Protons
      - D. Atomic Number

• Q5: What is the name of the element with an atomic number of 9?
      - A. Carbon
      - B. Fluorine (Correct)
      - C. Oxygen
      - D. Beryllium

Historical Models of the Atom

• Arrange the following developments leading to the current atomic model:
      - Lord Rutherford's nuclear model:
          - Atoms are predominantly empty space; a dense nucleus with positively charged protons exists at the center, while negatively charged electrons orbit the nucleus.
      - John Dalton's atomic theory:
          - Same-element atoms are identical; varying mass among different element atoms; atoms combine in simple whole number ratios.
      - Sir James Chadwick's neutron discovery.
      - Democritus articulated the concept of atoms as indivisible particles.
      - JJ Thompson proposed the plum pudding model:
          - Atoms contain negatively charged electrons within a positively charged matrix, likening them to fruit in plum pudding.

TABLE 6.2: Symbols, Subatomic Particles, Atomic and Mass Numbers for the First 12 Elements

Resources

• eWorkbook: Chemical Building Blocks (ewbk-12424)

• eWorkbook: How Big Is an Atom? (ewbk-12426)

• eWorkbook: Top Ten Elements (ewbk-12428)