The Nuclear Atom

Nuclear Model of the Atom

  • The nuclear model describes the structure of the atom with protons and neutrons in the nucleus and electrons in orbit.

  • It emphasizes that most of an atom's mass is concentrated in the nucleus.

Subatomic Particles

  • Atoms consist of subatomic particles: protons, neutrons, and electrons.

  • Masses and charges of subatomic particles are compared to each other (relative atomic masses and charges).

    • Relative Mass & Charge of Subatomic Particles:

      • Proton: Charge = +1, Relative Mass = 1

      • Neutron: Charge = 0, Relative Mass = 1

      • Electron: Charge = -1, Relative Mass = negligible

  • Example charge values:

    • Charge of electron = -1.602189 x 10^-19 coulombs

    • Charge of proton = +1.602189 x 10^-19 coulombs

Location of Subatomic Particles

  • The nucleus of an atom is positively charged due to protons and dense because mass is concentrated there.

  • Electrons orbit the nucleus, creating a 'cloud' of negative charge due to their electrostatic attraction to the nucleus.

Atomic Structure and Numbers

  • Atomic Number (Z): Number of protons in the nucleus; equals the number of electrons in a neutral atom.

    • Example: Lithium (Li) has atomic number 3 (3 protons, 3 electrons).

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

    • Formula to find number of neutrons:

      • Number of Neutrons = Mass Number - Atomic Number

Protons and Elements

  • The atomic number determines the element.

  • Example:

    • Lithium: Atomic number = 3

    • Beryllium: Atomic number = 4

    • Number of protons = atomic number

Calculating Subatomic Particles in Atoms and Ions

  • For neutral atoms:

    • Number of Protons = Number of Electrons

  • Ions may have different numbers of electrons compared to protons:

    • Positively charged ions lose electrons.

    • Negatively charged ions gain electrons.

Worked Examples on Protons and Electrons

  • Example 1: Mg²⁺ ion - atomic number is 12 (12 protons), therefore has 10 electrons (lost 2).

  • Example 2: Carbon atom - atomic number is 6, so it has 6 protons and 6 electrons (neutral).

  • Example 3: Element X (mass number 63, neutrons 34):

    • Number of protons = 63 - 34 = 29 (element X is Copper).

Neutrons in Ions and Atoms

  • To find number of neutrons:

    • Example for Mg²⁺: Atomic number = 12, mass number = 24.

      • Neutrons = 24 - 12 = 12.

    • Example for Carbon: Atomic number = 6, mass number = 12.

      • Neutrons = 12 - 6 = 6.

    • Element X: Number of protons = 29, mass number = 63.

      • Neutrons = 63 - 29 = 34.

Isotopes

  • Isotopes are different atoms of the same element with varying numbers of neutrons.

    • Example: Carbon-12 (6 neutrons) and Carbon-14 (8 neutrons).

    • Representation:

      • Carbon-12 = 12C or C-12

      • Carbon-14 = 14C or C-14.

Calculating Relative Atomic Mass

  • Relative Atomic Mass (A): Average mass of an atom compared to 1/12 of carbon-12's mass.

    • Calculation method:

      • Total mass of 100 atoms = (% abundance x mass of isotope A) + (% abundance x mass of isotope B)

      • Average = Total mass / 100.

  • Example of calculating relative atomic mass of oxygen with given abundances of isotopes.

Worked Example on Oxygen Isotopes

  • Isotopes: O-16 (99.76%), O-17 (0.04%), O-18 (0.20%).

    • Total mass = (99.76 x 16) + (0.04 x 17) + (0.20 x 18) = 1600.44.

    • Relative atomic mass = 1600.44 / 100 = 16.0044; rounded to 2 decimal points = 16.00.