Atoms Ions and isotopes

When atoms lose or gain an electron, the atom turns into an ion. When an atom gains or lose a neutron, it is called an isotope. When either of these two things happen, then we no longer use the term element to describe the atoms. Remember, it is the number of protons that determines what type of atom it is.

Recreate and complete the chart below Atom Atomic Symbol Atomic Number #of Protons Atomic Mass Rounded # of Neutrons #of Electrons Lithium Lithium Ion (Loses an electron) Beryllium Isotope

Recreate and complete the chart below Atom Atomic Symbol Atomic Number #of Protons Atomic Mass Rounded # of Neutrons #of Electrons Lithium Lithium Ion (Loses an electron) Beryllium Isotope Li 3 3 7 4 3 Li+ 3 3 2 7 4 Be 4 4 9 5 4 Be-8 4 4 8 4 4

Write a definition for ion Write a definition for isoptope

When atoms come together, they form molecules and compounds. What is the difference between a compound and a molecule? A molecule is formed when two or more atoms join together chemically. A compound is a molecule that contains at least two different elements. *All compounds are molecules but not all molecules are compounds.

Molecular hydrogen (H2), molecular oxygen (O2) and molecular nitrogen (N2) are not compounds because each is composed of a single element. Water (H2O), carbon dioxide (CO2) and methane (CH4) are compounds because each is made from more than one element. The smallest bit of each of these substances would be referred to as a molecule. For example, a single molecule of molecular hydrogen is made from two atoms of hydrogen while a single molecule of water is made from two atoms of hydrogen and one atom of oxygen.

How do molecules form? Two ways (Well, actually three, but we are only going to look at two.)   As it turns out, atoms bond together for a very simple reason: Atoms like to have full valence shells!

1st way- Covalent Bond: This is when two atoms SHARE an electron. 2 hydrogen atoms equally share electrons to form a covalent bond. Each covalent bond is represented by a line in the Lewis dot structure, so the molecule shown above would be represented as  H-H and the chemical formula would be H2 (the subscript indicates the number of atoms of a single type in a compound). 

Atoms can form multiple covalent bonds if they need more than one electron to complete their valence shells.  Oxygen, for example, bonds with itself to form 2 bonds between the atoms (since each atom needs to share 2 electrons).  The Lewis dot structure would be showing that each oxygen atom has 4 shared electrons (2 per bond) and 4 unshared electrons, giving each a total of 8 and filling the valence shells. If two atoms have equal electron affinities they form covalent bonds.

2nd way- Ionic Boning So, if one atom has a much greater affinity for electrons than another, the two may form an ionic bond.  For sodium to have a full valence shell it can do one of 2 things: pick up 7 new electrons (which is a very difficult thing to do) or give up one.  If sodium gave up the 1 electron in its 3rd shell, this shell would now be empty and the 2nd shell (which is filled with 8 electrons) would become its valence shell.  Thus chlorine and sodium are a perfect match for each other. 

When the chlorine atom gets close enough to the sodium atom, it strips away the sodium's electron and the two ions formed attract each other because of their opposite charges.  Using the Lewis dot structure to represent the reaction we would write:

Covalent share with Non-Metals The compounds which form Covalent Bonds are those that result from a sharing of electrons between Non-Metal Elements (Groups IIIA through VIA of the Periodic Table and Hydrogen (Group IA). Ionic bonds share with metals The compounds which form Ionic Bonds are those that result from an exchange of electrons between Metals (Groups IA, IIA and IB through VIIIB of the Periodic Table) and the Halogens (Group VIIA).

H2 H H H

NaCl Na Cl Na1+ Cl1-

H20 O H O H H

Na 2O O Na Na Na 21+ O 2-

CaCl2 Cl Cl Ca Ca2+ Cl21-

C H4 C H H H H C H

CO2 O C O=C=O

CHCl3 C H Cl H H H H H

TOD For the following elements list: Name of the element #of shells Total # of electrons #of valence electrons Mg N Ar B Na H