Atomic Structure and Properties

• Atoms form all materials
• Atoms contain a nucleus with protons and neutrons
• Electrons orbit the nucleus of an atom
• Elements’ emission and absorption spectra provides proof that electrons are in specific energy levels
• Emission/absorption spectra are used to identify elements

Atomic and Mass Number

• Atomic and mass numbers give data about the amount of subatomic particles in an atom.
• Atoms are the foundational units of matter, containing a nucleus with protons and neutrons surrounded by orbiting electrons.
• Elements consist of only one type of atom.
• Compounds feature two or more elements combined in a fixed ratio.

Atomic Charge and Subatomic Particles

• Atoms possess a neutral charge due to an equal number of protons and electrons.
• Protons have a charge of +1 and are located in the nucleus, and a relative mass of 1
• Neutrons have a charge of 0 and are located in the nucleus, and a relative mass of 1
• Electrons have a charge of -1, are located surrounding the nucleus, and a relative negligible mass

Electron Configuration

• Electron configuration displays the arrangement of electrons in an atom.
• Electrons orbit the nucleus within shells.
• The formula 2n² determines the maximum number of electrons each shell can hold, where n is the shell number:
• Shell 1 (K) holds a maximum of 2 electrons.
• Shell 2 (L) holds a maximum of 8 electrons.
• Shell 3 (M) holds a maximum of 18 electrons.
• Shell 4 (N) holds a maximum of 32 electrons.
• Electrons will fill the lower shell before the next shell.
• Sodium has 11 electrons, with an electron configuration of 2, 8, 1.
• Lower shells are filled before higher shells unless there are exceptions.
• Configuration for Potassium-40 is 2, 8, 8, 1
• Configuration for Scandium-45 is 2, 8, 9, 2

Atomic Composition and Isotopes

• The atomic number (Z) indicates the number of protons in an atom.
• The mass number (A) indicates the total number of protons and neutrons in an atom.
• To find the number of neutrons (N), subtract the atomic number from the mass number: N = A - Z.
• Isotopes are atoms of the same element but have different mass numbers due to a different amount of neutrons.
• Isotopes of an element share identical chemical properties but have varying physical properties due to differences in mass.
• Isotopes are identified by the element name followed by the mass number, like Hydrogen-3 for Tritium.

Emission Spectra

• Emission and absorption spectra determine a material's composition and electron arrangement in distinct energy levels.
• 1000+ years ago, chemists determining that chemical elements emit certain colours when exposed to a flame.
• Kirchhoff invented the spectroscope which splits emitted light into a spectrum using a prism, resulting in line emission spectra for each element.
• Bohr suggested electrons orbit around the nucleus in specific orbits, where each has a specific energy level
• Electrons may move between energy levels via absorption/emission of light
• The difference in energy is based on the amount of energy released/absorbed
• Emission spectra’s bright lines show the emitted light’s wavelengths when electrons go from a higher to a lower energy level. The wavelength is related to the difference in energy between those two energy levels.

Absorption Spectra

• Absorption spectra is produced when a continuous spectrum of visible light is passed through a vaporized or gaseous sample
• The atoms in the sample absorb certain wavelengths, resulting in a series of dark lines
• Each line shows a specific wavelength absorbed by the electrons as they move from lower to higher energy levels
• Each element’s energy levels determine a unique spectrum

Practice Questions

• Q1-The image shows an emission spectrum
• Q1-The lines are specific wavelengths of light. They have been emitted by helium atoms when electrons transition from higher to lower energy levels
• Q2-Hydrogen atoms and oxygen atoms have their own, unique electron energy levels, so the emitted photons from hydrogen and oxygen atoms are different
• Q2-The difference in energy relates to the energy of the photon emitted, and the wavelength will be different

Electron Configuration - Subshells

• Subshells exist within an atom's shells and hold a maximum number of electrons.
• Electrons fill lower energy subshells first, this is the Aufbau principle.
• Subshell notation displays both shells and subshells in an atom, with the number of electrons each subshell holds

Exceptions to the Aufbau Principle

• Exceptions happen where atoms arrange electrons unexpectedly
• Copper and Chromium are exceptions with only one electron in 4s
• Chromium configuration: 24Cr: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵
• Copper configuration: 29Cu: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰