ch3: atomic structure

• an atom is the smallest particle of a substance. it has a nucleus containing protons and neutrons and an electron shell containing the electrons.
• an atom has an equal number of protons and electrons, it is electrically neutral.
• we use nuclide notation to represent the number of neutrons and protons in an atom.
• electronic configuration is the arrangement of electrons in an atom
• written electronic configuration can be shown as 2,8,8
• valance electrons are the electrons that are found in the outermost shell of an atom
• when an atom has maximum number of electrons in the valence shell, it is stable and unreactive. it has a stable electronic configuration and are called noble gases. they are inert and exist as monoatomic elements.
• an ion is a charged particle formed when an atom loses or gains electrons
• when an atom loses electrons, it becomes a positive ion
• when an atom gains electrons, it becomes a negative ion
• metals lose electrons to form cations. non mentals gain electrons to form anions. cations are positive ions and anions are negative ions.
• electrons are responsible for the chemical properties of an atom.
• valency electrons are the number of valence electrons involved in forming chemical bonds through gaining, losing or sharing
• the noble gases have full outer shells so they do not react with other elements as their electron configuration is stable
• sub atomic particles

  electrons, protons, neutrons
• innermost shell of an atom has the least energy while the outermost has the highest.
• group 18 in the periodic table have NGCs, they are noble gases which exist as monoatomic ( 1 atom ) elements
• duplet electronic configuration: 2 electrons max

  octet electronic configuration: 8 electrons max
• when an atom loses or gains electrons, the number of protons is no longer equal to the number of electrons hence is no longer electrically neutral. a charged particle called an ion is formed
• formation of ions

  metals lose electrons to form cations while non metals gain electrons to form anions. during this, proton and nucleon number remain unchanged.
• valency electron can be used to deduce chemical formulas.

  magnesium atoms lose 2 electrons so their valency is 2. chlorine atoms gain 1 electron so their valency is 1. chemical formula is MgCl2
• all atoms have a number of protons equal to electrons
• how is an ion formed?

  when an atom loses or gains electrons
• proton

  • relative mass: 1
  • relative charge: +1
  • found in: nucleus
• neutron

  • relative mass: 1
  • relative charge: 0
  • found in: nucleus
• electrons

  • relative mass: 1/1840
  • relative charge: -1
  • found in: electron shells
• nuclide notation

  A) mass

  B) protons

  C) neutrons

  D) element

  E) atomic

  F) protons

  
• 1-3 valence electrons: metal

  4-8 valence electrons: non metal
• isotopes are the same elements with the same number of protons but different number of neutrons, this results in the nucleon number changing
• nucleon number: number of protons + number of neutrons
• isotopes have similar chemical properties but different physical properties
• electrons are responsible for the chemical properties of an ion
• how to deduce chemical formula using valence electrons

  • Magnesium has 2 valence electrons while Chlorine has 7
  • Mg atoms lose 2 electrons, Cl atoms gain 1 electron
  • MgCl2