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Forming Compounds. When two atoms collide, the valence electrons of each atom interact. Elements try to get to the electron configuration of the closest noble gas - full valence shell. Valence Shell. Three ways for an atom to acquire a full valence shell. An atom may give up electrons

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forming compounds
Forming Compounds
  • When two atoms collide, the valence electrons of each atom interact.
  • Elements try to get to the electron configuration of the closest noble gas - full valence shell.
valence shell
Valence Shell
  • Three ways for an atom to acquire a full valence shell.
    • An atom may give up electrons
    • An atom may gain electrons
    • An atom may share electrons
  • When atoms give up and gain electrons in a reaction the resulting compound is known as an ionic compound with an ionic bond.
  • The third way to acquire a full valence shell will be talked about later in the course.
ionic compounds
Ionic Compounds
  • Ionic compounds involve bonds between a metal cation and a non-metal anion.
  • If just two different elements are involved, than you have a binary compound.
  • Binary compounds require that the total charge (sum of the element’s charges) of the compound is equal to zero.
  • We represent the compound by writing down the element symbol for cation first and then the anion
  • Subscripts after each symbol identify how many ions are required for a total charge of zero.
  • The representation of the compound is known as the chemical formula
lewis structures
Lewis Structures
  • Sodium (Na+) and Chlorine (Cl-)
  • Now Chlorine has a full valence shell and the ionic compound NaCl is formed.

Na

Cl

[ ]+

[ ]-

Na

Cl

example
Example
  • NaCl (Table Salt)
  • How do we name this compound?
  • Sodium Chloride
  • The suffix “ide” is put at the end of the name for the element that is the electron acceptor (anion)

Na+ + Cl- NaCl

  • The sodium has a +1 charge and the chlorine has a -1 charge therefore +1 + -1 = 0.
another example
Another Example
  • What would happen if we combined Magnesium and Chlorine?
  • Charges do not add up to zero.
  • Therefore we need more of one of the elements, but which one.
  • Magnesium has a 2+ charge and Chlorine has a 1- charge so we need two Chlorine.
  • MgCl2 (Magnesium Chloride)
  • Can also be done by drawing out the required number of atoms to get a total charge of zero.
polyatomic ions
Polyatomic Ions
  • Polyatomic Ions consist of two or more non-metal atoms grouped together.
  • There is only one common polyatomic cation
    • Ammonium NH4+
  • There are several common polyatomic anions
    • Hydroxide OH-
    • Carbonate CO32-
    • Nitrate NO3-
    • Sulfate SO42-
    • Chlorate ClO3-
    • Phosphate PO43-
polyatomic i ons
Polyatomic Ions
  • Compounds are named the same way
  • Writing the chemical formula is a little different - If more than one polyatomic ion is needed, than brackets must be put around the ion
  • Example: The chemical formula for ammonium oxide is (NH4)2O not NH42O
  • Do not forget the brackets!!!!
polyatomic example
Polyatomic Example
  • Calcium Nitrate
  • Calcium (Ca2+) and Nitrate (NO3-)
  • Need two Nitrate ions to balance charges.
  • Ca(NO3)2
transition metals
Transition Metals
  • Transition metals can form more than one ion - except for silver(+1), zinc (+2) and aluminum (+3).
  • For example Sodium can only produce the Na+ ion. Iron on the other hand can produce two ions.

Fe  Fe2+ or Fe3+

  • A roman numeral is placed after the atom in brackets to identify the charge
  • Iron that produces the +2 ion is iron(II)
  • Iron that produces the +3 ion is iron(III)
examples
Examples
  • 1. Iron(III) Oxide (Rust)

Fe3+ O2-

Fe3+ O2-

O2-

  • Charge of +6 from the iron and -6 from the oxygen. Chemical Formula - Fe2O3
  • 2. CuCl2

Cu Cl-

Cl-

  • Cu must have a +2 charge to balance the -2 from the 2 Cl. Copper(II) Chloride
covalent bonds
Covalent Bonds
  • Two or more non-metallic elements.
  • Electrons must be shared since both atoms are looking to gain electrons.
  • When atoms share electrons they are joined by a covalent bond.
  • A neutral particle that is composed of atoms joined together by covalent bonds is called a molecule.
  • Substances that are composed of molecules are called molecular compounds.
molecular compounds
Molecular Compounds
  • Water (H2O)
  • Two H+ atoms and a O2- atom.

O

H

H

O

H

H

naming molecular
Naming Molecular
  • H2O
  • Start with the element that is farther left on the periodic table (Hydrogen).
  • The rules for the second element still apply, suffix of “ide”.
  • Different is that the elements require prefixes depending on how many are in the compound.
  • So water’s chemical name is dihydrogen monoxide.
prefixes
Prefixes
  • Prefix mono is only used for the second element.
  • “a” or “o” is left off of the prefix when used with an element starting with a vowel
diatomic molecules
Diatomic Molecules
  • Atoms can share electrons with the same atom.
  • These molecules have two of the same atoms joined by a covalent bond.
  • Since there are two of the same atoms the word diatomic is used. (“di” meaning two)
  • Seven elements exist as diatomics:
    • Hydrogen
    • Oxygen
    • Nitrogen
    • Fluorine
    • Chlorine
    • Bromine
    • Iodine
ionic compounds1
Ionic Compounds
  • Ionic compounds form large structures called lattices
  • Attraction between oppositely charged ions is strong.
ionic properties
Ionic Properties
  • Characteristics of an ionic compound:
    • Tend to have relatively high melting and boiling points because of the large amount of energy is needed to break the strong force of attraction in an ionic bond.
    • Conduct electricity when they are liquid or when they are dissolved in water. Melting or dissolving allow ions to move freely. In a solid state the ions are not able to move and therefore cannot conduct electricity.
molecular compounds1
Molecular Compounds
  • Bonds within the molecule are strong but forces of attraction between the molecules is weak.
molecular properties
Molecular Properties
  • Characteristics of a molecular compound:
    • Have relatively low melting points because little energy is needed to break the forces of attraction between molecules.
    • Relatively soft
    • Tend not to conduct electricity when they are in solid or liquid state. Do not conduct when dissolved in water because ions are not formed.
electrolytes
Electrolytes
  • An electrolyte is a substance the dissolves in water to produce a solution that conducts electricity.
  • Ionic substances tend to be electrolytes.
  • Molecular substances tend to be non-electrolytes.
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