Atoms, Molecules, and Ions

• Atoms contain even tinier particles called subatomic particles.
• The fundamental types of subatomic particles are protons, neutrons, and electrons.
• The electron (e) is a negatively charged particle. It has been assigned a relative electrical charge of -1.
• The proton (p) is a positively charged particle with a relative electrical charge of +1.
• The neutron (n) is a neutral particle (zero charge/does not have electrical properties) with a relative mass of 1 amu.
• Rutherford's Nuclear Atomic Model suggests that each atom consists of a central core or nucleus made of protons and neutrons, and the negatively charged electrons are found outside the nucleus.
• Atomic number (Z): The number of protons in the nucleus and number of electrons in a neutral atom (since an electron has the same charge as the proton but opposite in sign).
• No two elements have the same atomic number.
• No two elements have the same number of protons in the same number of protons in the nuclei of their atoms.
• Mass Number (A): The total number of protons and neutrons in the nucleus of an atom.
• atomic number (Z) = number of protons

  = number of electrons
• mass number (A) = number of protons + number of neutrons

  = atomic number (Z) + number of neutrons
• number of neutrons = mass number - atomic number (protons)
• Isotopes: Atoms of an element with the same atomic number (protons) but different mass numbers (neutrons).
• Isotopes are identified or named in two ways:

  • element name - mass number (e.g., C-12, read as carbon twelve)
  • Isotopic symbol

  
• The number of protons in an atom defines what element the atom is. On the other hand, the number of neutrons in an atom defines an element's isotopes.
• Ion: A charged atom or molecule that has gained or lost electrons.
• Cation: An atom with a positive charge formed by losing electrons.
• Anion: An atom with a negative charge formed by gaining electrons.
• Removing an electron from a neutral sodium atom will yield an ionic notation of (Na+), indicating that the positive charge in the atom is now greater than its total negative charge by one charge unit since one unit of negative charge (from the electron) has been removed from the atom.
• On the other hand, (Cl-) is the notation of an anionic chlorine, which is created when an electron (and, consequently, a negative charge) is added to a neutral chlorine atom.
• Simply, the superscript in the notation of an ion is the charge (no. of atoms) of that ion.
• When atoms interact, the electrons come into play.
• Mendeleev's Periodic Law states that elements with similar properties appear at periodic intervals when the elements are arranged in the order of increasing atomic number.
• Henry G. Moseley's Modern Periodic Law states that elements' physical and chemical properties are periodic functions of their atomic numbers.
• Elements with similar properties are placed in columns called groups or families.

  The elements are arranged in horizontal rows called periods according to their atomic numbers.

  
• In 1985, the International Union of Physical and Applied Chemistry (IUPAC) suggested using Hindu-Arabic numerals 1 to 18 to designate the groups or families of elements.
• Group 1: alkali metals (except for hydrogen)

  Group 2: alkaline earth metals

  Group 3-12: transition metals

  Group 13: boron group/earth metals

  Group 14: carbon group/tetrels

  Group 15: nitrogen group/pnictogens

  Group 16: oxygen group/chalcogens

  Group 17: halogens

  Group 18: noble gases
• Period 6 elements: lanthanides/lanthanoids

  Period 7 elements: actinides/actinoids
• Inner Transition Elements: All elements belonging to the lanthanide and the actinide series (two separate rows at the periodic table's bottom).