Ch 4 Chemical Bonding

• What is an ion?


  -particle formed when an atom or a group of atoms gains/loses electrons

  -number of protons and neutrons remains the same
• How do you represent calcium that has 2 more protons than electrons?

  2+ after and above the atomic symbol 'Ca' to represent the net charge of +2
• What are isotopes?


  -atoms of same element have the same proton number

  -but have different number of neutrons -> different nucleon number
• Isotopes have the same number of electrons, which allow them to undergo the same chemical reactions but have different physical properties (density, melting point, boiling point)
• what is the average mass number of Chlorine?

  (percentage x [respective mass number of chlorine - which is 35])

  +

  (percentage x [respective mass number of chlorine - which is 37])

  = 35.5
• What is the relationship between electron shells and energy levels?

  -Electrons in innermost shell (closest to nucleus) have the lowest energy

  -Electrons in valence shell (furthest to nucleus) have the highest energy

  electrons occupy lowest energy levels first
• What makes an atom unreactive?


  -full valence shell of electrons - noble gas electronic configuration (elements in group 18)
• electrons in valence shell known as valence electrons
• electronic configuration, electronic structure refers to arrangement of electrons in the electron shell
• What are noble gases?


  gases in group 18, have full valence shells
• Why is helium used to inflate balloons but not hydrogen?

  -Hydrogen does not have full valence shell -> unstable electronic configuration

  -> reactive => flammable

  -Helium has full valence shell ->stable electronic configuration

  -> unreactive / inert
• What is a noble gas electronic configuration?

  -full valence electron shells

  -> chemically unreactive

  -> monoatomic gases => single atoms that do not combine with other atoms
• duplet -> full valence shell of 2 electrons (helium)
• octlet -> full valence shell of 8 electrons (other elements in group 18)
• How do atoms become stable if they do not have a full valence shell?

  -chemically combine to form bonds

  -> loss of electrons

  -> gain of electrons

  -> sharing of electrons
• What are cations?


  -net positive charge

  -noble gas electronic configuration
• What are anions?


  -net negative charge

  -noble gas electronic configuration
• Show a sodium ion (electronic configuration -> 2, 8, 1)

  loses 1 electron -> number of protons is more than number of electrons. Sodium ion has a net charge of +

  
• Show oxygen ion (electronic configuration -> 2, 6)

  gains 2 electrons -> number of protons is fewer than number of electrons. Oxygen ion has a net charge of 2-

  
• What ions are metallic elements?


  cations -> donate/give away/lose electrons
• What ions are non-metallic elements


  anions -> receive / gain electrons
• How can you tell the number of valence electrons of elements?

  group number in the periodic table
• What does Na2O mean?

  2 sodium atoms for every oxygen atom
• What is an ionic bond?


  strong forces of electrostatic attraction between metal and non-metal ions of opposite charges
• Why and how are ionic compounds formed?


  -Transfer of electrons -> how

  -obtain full valence shell -> why

  -achieve noble gas electronic configuration -> why
• Why are bonds formed?

  To achieve a full valence shell and noble gas electronic configuration
• What is a 3-dimensional structure of alternating positive and negative ions in an ionic compound?

  -giant ionic crystal lattice (eg NaCl)

  -uncountably large number of sets (of sodium and chlorine ions) regularly spaced and held together by ionic bonds -> strong forces of electrostatic attraction

  (alternating -> for every Na+ there is 1 Cl - in NaCl)
• What is valency?

  number of electrons lost, gained, shared in order for atom to attain noble gas electronic configuration
• How are different covalent bonds represented?

  -Single - (2 electrons)

  -Double = (4 electrons)

  -Triple =_ (6 electrons)
• What happens when covalent bonds are formed?

  Gives a molecule
• What are the rules to check if 'dot and cross diagram' covalent substances are drawn correctly?

  1)Ensure the number of valence electrons is correct for each atom

  2)Check if noble gas electronic configuration is achieved for each atom of the bonding
• Covalent molecules as simple molecules 


  -countable number of atoms

  -in fixed ratio
• Covalent molecules as giant molecules


  uncountable number of atoms in each molecule
• What is a covalent bond?

  -sharing of electrons between non-metals

  -to achieve noble gas electronic configuration

  -due to strong electrostatic forces of attraction between opposite charges exerted by the nuclei of the sharing atoms
• what does an ionic bond give?

  a compound