Review sheet – Chapter 2
Understand that living organisms are made up of 25 chemical elements
Be able to identify the elements that make up ~96% of the weight of the human body (O,C,N,H)
Be able to recognize elements that fall within the “remaining 4%” category
Be able to identify and recognize a trace element from the examples given
Understand that elements combine to form elements
Be able to recognize an example of a compound
Understand that compounds are more common than pure elements (why???)
Understand the definition of an atom
Understand the components of an atom (proton, neutron, electron)
Know and understand the definition of atomic number and mass number; be able to identify
the number of protons, neutrons and electrons if given a period table or mass number or atomic
number
Understand the definition of an isotope
Be able to calculate the number of neutrons and protons if given the mass number of different
elements
Understand the difference between stable and radioactive isotopes
Understand the function of a “PET” (positron-emitting tomography)
Understand that the number of electrons in the outermost electron shell determines the
chemical properties of an element/atom
Understand that the innermost electron shell contains 2 electrons, and the outermost can
contain up to 8 electrons
Be able to calculate the number of electrons in the outermost shell if given the atomic number
Understand the consequences of having an incomplete outer electron shell – will the element
want to share or give up/receive an electron with/from another element?
Understand that when atoms gain or lose electrons, they also gain or lose electrical charge;
understand that a charged atom is called an ion
Understand that an ionic bond results from the transfer of electrons and the resulting electrical
charges between the two ions
Understand that NaCl is an example of a compound that is ionically bonded
Understand that a covalent bond results from the sharing of electrons between 2 atoms
