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Compounds and Chemical Formulas
Compound– Two or more elements
chemically combined
Chemical Formula– Chemical “short hand”– Shows what ELEMENTS a
compound contains– Shows HOW MANY ATOMS
of each element
H2O
C6H12O6
2 atoms of Hydrogen1 atom of Oxygen
6 atoms of Carbon12 atom of Hydrogen6 atoms of Oxygen
Common Chemical Compounds
Can you tell what elements are present and HOW MANY atoms of each element are present in each compound?
Why do elements form compounds?– All atoms want a full outer
electron shell – FULL Outer Shell = stable
atom (less reactive)
EXAMPLES:• H and He need 2 electrons to
become Full/stable• Groups 1 – 18 need at least 8
electrons to be full/stable
Chemical Bonds
ATOMS WILL FORM BONDS in order to fill the outer electron shell…to become more stable
Chemical Bond = Attraction between atoms when electrons are gained, lost or shared
2 types of bonds• Ionic• Covalent
What happens when an atom Gains or Loses an electron just to be stable?
The atoms become IONS(Charged particles)
IONSATOM Loses electron (-)BECOMES MORE POSITIVE
ATOM Gains electron (-) BECOMES MORE NEGATIVE
The + or – Charge of the ion is equal to the NUMBER of electrons
lost or gained
PRACTICEFor each of the following compounds, LIST the elements present AND the number of atoms of each element
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
For each of the following elements, state the VALENCE electrons.
11) Nitrogen (N)
12) Hydrogen (H)
13) Potassium (K)
14) Calcium (Ca)
15) Carbon (C)
16) Argon (Ar)
17) Aluminum (Al)
18) Silicon (Si)
19) Lithium (Li)
20) Beryllium (Be)
In your notebook, write the problem and the solution
For each of the following atoms, write the NEW ION that is formed AND its charge
21) Calcium loses 2 e-
22) Sodium loses 1 e-
23) Chlorine gains 1 e-
24) Lithium loses 1 e-
25) Magnesium loses 2 e-
26) Bromine gains 1 e-
27) Aluminum loses 3 e-
28) Sulfur gains 2 e-
29) Iron loses 2 e-
30) Potassium gains 3 e-
Lewis Dot StructureStructure that shows the valence electrons for a given atom; helps predict how one atom might combine with another atom to form a compound.
PRACTICE ELEMENT Chemical Symbol
Total number of Electrons
Valence Electrons
Dot Diagram
Potassium K
Nitrogen N
Carbon C
Beryllium Be
Neon Ne
Sulfur S
NOW…Try to predict the chemical formulas
Elements Dot Diagram for EACH Element
Dot Diagram for Compound
Chemical Formula
Na and F
Br and Br
Mg and O
Complete the following tables in
your notebook
Ionic Compounds
IONS ARE FORMED+Cation– Metals– Lose electrons– Carry a (+) oxidation
number
-Anion– Nonmetals– Gain electrons– Carry a (-) oxidation
number
Oxidation NumberNumber of electrons gained, lost or shared to become stable(NEGATIVE means that electrons will be gained;POSITIVE means that electrons will be given away)
THIS IS NOT VALENCERECOGNIZE THE DIFFERENCE???
Using RED pen/pencil Write the Oxidation Number for each group on the chart.
Covalent Bonds– Attraction between atoms when
they share electrons
– Sharing occurs between 2 or more NON-METALS
– Can have equal or unequal sharing
– Equal sharing = no charge or neutral compound also called Non-Polar
– Unequal sharing = POLAR MOLECULE (EX: Water)
PRACTICE
Before moving forward students must understand…1. What are Valence Electrons2. How to complete an Electron dot diagram for an
element3. How to create an electron dot diagram for a
compound4. Difference between Ionic and Covalent bonds5. How to find the oxidation number for a given
element
STEPS TO Create compounds from combinations of elements:
1) Are the elements METALS or NON-METALS (This determines
whether they will form ionic or covalent bonds)
2) What is the Valence
3) What will the Element need to fill its outermost shell?
4) Will you need additional atoms of the element to satisfy the
outermost shell requirements; if so, how many?
5) Draw the Electron Dot Diagram showing either transferred
electrons or shared electrons.
6) What is the chemical formula for the compound?
Writing & Naming Compounds
BINARY compound is a compound composed of two elements
REMEMBER: Oxidation number tells us how many electrons an atom has Lost, Gained, or shared to become stable.
Ionic Compounds: elements themselves become ions
Ions have a charge, but the net charge of the compound is ZERO.
Shortcut to Writing Binary Ionic Compounds
1. Write oxidation numbers above symbols
2. Criss-cross oxidation numbers writing them as subscripts (small numbers at the
bottom right of the element)
3. The metal is ALWAYS written first
4. Will always be between (+) and (-) ions
PRACTICE:
Metal Cation(+) NonMetal Anion (-) Compound Formula
Sodium Na+1 Oxygen O-2 Na2O
Aluminum Sulfur
Magnesium Phosphorus
Potassium Selenium
Naming Binary Ionic Compounds
1. Write the name of the metal/cation first
2. Drop the end of the nonmetal
3. Add “ide” to the nonmetal
Practice NAMING Binary Ionic Compounds
Metal Cation(+) NonMetal Anion (-) Compound Formula
Compound Name
Sodium Na+1 Oxygen O-2 Na2OSodium oxide
Aluminum Al+3 Sulfur S-2 Al2S3Aluminum
sulfide
Magnesium Mg+2 Phosphorus P-3 Mg3P2Magnesium phosphide
Potassium K+1 Selenium Se-2 K2Se Potassium selenide
Writing Covalent Compounds
– Add prefixes to show HOW MANY atoms of each element are in the compound
– Compound Ends in -ide
Polyatomic Ions
• Polyatomic Ions– Positively or negatively
charged– Covalently bonded– Contains two or more
atoms
Polyatomic Ions to Know . . . .Charge Name Formula
1 + Ammonium NH₄
1 - Acetate
Chlorate
Hydroxide
Nitrate
C₂H₃O₂
ClO₃
OH
NO₃
2 - Carbonate
Sulfate
CO₃
SO₄
3 – Phosphate PO₄
POLYATOMIC IONS• Positive or Negative
Compounds• COVALENT Bonds
(sharing electrons)• Contain 2 or MORE atoms