Chapter 2: The Periodic Table

Modern Periodic Table

• Each box on the periodic table has the symbol, in order of increasing atomic number, and has the atomic mass below it
• each row is called a period which has 2-32 elements
• each column is called a group with similar chemical and physical properties
  • the close they are, the more similar they are

Atomic Symbols

• Symbols can be abbreviations of the element name or come from latin names
  • Sodium: Na, Potassium: K, Iron: Fe, Tin: Sn
• When an isotope is being specified, the superscript will be the charge (A) and the subscript is the atomic number (Z)

Electron, Protons, and Neutrons

Protons

• Protons are always equal to the atomic number
• Number of protons = Z

Electrons

• The number of electrons is always equal to the atomic number
• Number of electrons = Z

Neutrons

• Number of neutrons depends on the specific isotope
• Number of Neutrons = A-Z

Radioactivity

• Radioactivity is the spontaneous emission of particles or energy from the nucleus of an unstable atom. This process occurs in order for the atom to become more stable. The emitted particles or energy can take the form of alpha particles, beta particles, or gamma rays. Radioactivity can occur naturally, as in the case of radioactive isotopes found in rocks and soil, or it can be artificially induced through processes such as nuclear fission.

Mass Spectrometry

• Mass spectrometry is a technique used to determine the mass of atoms or molecules in a sample. It works by ionizing the sample, then separating the ions based on their mass-to-charge ratio. The resulting mass spectrum shows the relative abundance of each ion, allowing for identification of the sample's components.

Periodic Properties of the Elements

• Differentiating electrons are the electrons in the outermost shell of an atom that are involved in chemical reactions. These electrons are also known as valence electrons. The number of valence electrons determines the chemical properties of an element. For example, elements with the same number of valence electrons tend to have similar chemical properties. The valence electrons are important in bonding because they are the electrons that are shared or transferred between atoms to form chemical bonds.

Physical Properties of the Elements

Metals and Metalloids

• most common element on the periodic table
• elements that border the line between metals and nonmetals are called metalloids
• metallic character is stronger at the top of a group

Allotropes

• Allotropes are different forms of an element that exist in the same physical state. These forms have different arrangements of atoms and different properties.
  • For example, carbon can exist as diamond, graphite, or fullerenes, which are all allotropes of carbon.

Atomic Radii

• Atomic radius is larger as you go down a group
• left to right the atomic radius decreases because of an increase in effective nuclear charge

Effective Nuclear Charge

• Effective nuclear charge is the net positive charge experienced by an electron in an atom. It is the difference between the number of protons in the nucleus and the number of shielding electrons in the inner energy levels. The shielding electrons reduce the attraction between the positively charged nucleus and the outer electrons, making the effective nuclear charge less than the actual nuclear charge.
• The effective nuclear charge increases across a period in the periodic table due to the increasing number of protons, while it remains relatively constant down a group due to the increasing number of shielding electrons.

Ionization Energy

• Ionization energy is the energy required to remove an electron from an atom or ion. It is measured in units of energy per mole, such as kilojoules per mole (kJ/mol).

• The ionization energy generally increases as you move from left to right across a period in the periodic table.

  • This is because the number of protons in the nucleus increases, which makes it harder to remove an electron.

• The ionization energy generally decreases as you move down a group in the periodic table.

  • This is because the electrons are farther from the nucleus and are shielded by inner electrons, making them easier to remove.

• The first ionization energy is the energy required to remove the first electron from an atom or ion. The second ionization energy is the energy required to remove the second electron, and so on.

Photoelectron Spectroscopy

• Photoelectron spectroscopy (PES) is a technique used to study the electronic structure of atoms, molecules, and solids.
• PES involves shining a beam of high-energy photons onto a sample, which causes electrons to be ejected from the sample's surface.
• The kinetic energy of the ejected electrons is measured, which can be used to determine the binding energy of the electrons in the sample.
• The binding energy is related to the electronic structure of the sample, and can be used to identify the elements present and their chemical environment.
• PES can be used to study the valence electrons of atoms and molecules, as well as the electronic structure of solids.
• PES can also be used to study the energy levels of defects and impurities in materials.

Electron Affinity

• Electron affinity is the amount of energy released when an electron is added to a neutral atom to form a negative ion. It is a measure of how much an atom "wants" an additional electron. The higher the electron affinity, the more likely an atom is to gain an electron. Electron affinity is influenced by factors such as atomic size, nuclear charge, and electron configuration.

Electronegativity

• Electronegativity is a measure of an atom's ability to attract electrons towards itself in a chemical bond.
• The electronegativity of an atom is influenced by its atomic number, the distance between its valence electrons and the nucleus, and the shielding effect of inner electrons.
• The most electronegative element is fluorine, with a value of 4.0 on the Pauling scale, while the least electronegative element is francium, with a value of 0.7.
• Electronegativity is important in predicting the polarity of chemical bonds and the behavior of molecules in chemical reactions.
• The difference in electronegativity between two atoms in a bond can be used to determine the type of bond (ionic, polar covalent, or nonpolar covalent) and the degree of polarity.

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