1. Chapter 20
Chemical Bonds

2. Ions Ex. Sodium: +11 – 10 = +1 p+ - e- = charge
Atoms can gain or lose e- to form ions.
Ion—an atom with a positive or negative charge.
To find the charge, take the number of protons & subtract the number of electrons
p+ - e- = charge
Ex. Sodium: – 10 = +1
Chlorine: +17 – 18 = -1

3. 2 Types of Ions Cations—ions that have a + charge
Form by atoms losing electrons
Losing negative electrons makes it positive
Metals form cations
Anions—ions that have a – charge
Form by atoms gaining electrons
Nonmetals form anions

4. Ion Symbols
Write the symbol of the element with its charge as a superscript
A superscript is a small number in the upper right hand corner
Ex. Na+1 & Cl-1
Polyatomic Ions—ions made of more than one atom. (ex. Sulfate: SO4-2)
Chart on the back of your PT
Write the symbol exactly as it is on the chart

5. Another casualty in the War of the Atoms.

6. Atomic Stability
Atoms combine to form a compound that is more stable than the atoms alone
Want to be like noble gases
Noble gases are already stable and do not form compounds.
Their outer energy level is full.

7. Rule
Atoms gain, lose, or share electrons to get a full valence electron shell like the noble gases.
H, He, Li, B, Be want 2 valence e-
ALL other elements want 8 valence e- (an octet)

8. Ions & Bonding
Atoms don’t gain or lose electrons on their own, it takes more than one.
When an electron is lost by 1 atom it is gained by another.
This makes an ionic bond
Ex.
Sodium has 1 valence e-Chlorine has 7, so it needs 1 more electron to be stable.
If sodium gives its 1 valence e- to chlorine, they are both stable with 8 valence e-

9. Formulas
Chemical Formula—tells what elements a compound contains & the number of atoms of each element.
Ex. NaCl: 1 sodium atom & 1 chlorine atom
A subscript is written after a symbol to tell how many atoms of that element there are. (unless there is just 1)
MgCl2: 1 magnesium & 2 chlorines

10. Rules for Binary Ionic Formulas
Binary = 2 different elements
Write the metal cation 1st. Write the nonmetal anion 2nd.
The net charge (overall charge) is zero.
Na+1 Cl-1 = 0
Use subscripts to show multiple ions.
Write the formula in the lowest whole number ratio. (reduce if needed)

11. Silver Chloride
Cl-1
Ag+1
AgCl

12. Copper (I) Arsenide (Domeykite)
Cu+1
As-3
Cu3As

13. Magnesium Sulfide
Mg+2
S-2
MgS

14. Lead (IV) Sulfide (Galena)
Pb+4
S-2
PbS2

15. Zinc Phosphide
Zn+2
P-3
Zn3P2

16. A trick for ionic formulas
Write both ions with their charges as superscripts.
Crisscross the charges to make the subscripts in the formula
Do not put + or – in the formula
Cu3+ & O2-
Cu2O3

17. Polyatomic Ions Ions that contain more than 1 element.
Use parenthesis to indicate multiple polyatomic ions.
Ex Mg(NO3) Al(OH)3

18. Magnesium Sulfate
Mg+2
SO4-2
MgSO4

19. Copper (II) Nitrate
Cu+2
NO3-1
Cu(NO3)2

20. Strontium Hydroxide
Sr+2
OH-1
Sr(OH)2

21. Ammonium Sulfide
NH4+1
S-2
(NH4) 2S

22. Mistakes to Avoid Charges are not written in the formula
Don’t drop polyatomic subscripts
Hydroxide, OH, needs parentheses to indicate multiples.
K+1Br KBr
CaNO Ca(NO3)2
CaOH Ca(OH)2

23. Write the cation name 1st
Rules for Naming
Binary Ionic with Group A Elements
Write the cation name 1st
Cation name is the same as the element name
Write the anion name 2nd
Change the ending of the element name to –ide. Ex. Oxygen becomes oxide
Chlorine becomes chloride

24. Variable Charged Cations (transition & other metals)
Same rules as for Group A, but…
Name of the cation includes its charge as a Roman Numeral in parentheses
Cu+2 = copper(II) Cu+1 = copper(I)
(none are negative)
No roman numerals are in formulas

25. Compounds Containing Polyatomic Ions
Cation name:
If the cation is a polyatomic ion, name it just as it is written on the back of your P.T.
If cation is 1 element, use previous rules

26. Anion name:
If the anion is a polyatomic ion, name it just as it is written on the back of your P.T.
DO NOT change the ending.
Most end in –ate or –ite
If anion is 1 element, use previous rules

28. Ionic VS Covalent Ionic Electrons are transferred
The bond is held together by the attraction between the + and -
Covalent/Molecular
Electrons are shared
Atoms are physically attached by sharing electrons

29. Covalent/Molecular Compounds
Ionic compounds contain a metal & a nonmetal
Covalent: 2 or more nonmetals or metalloids
Composed of molecules—NOT IONS—no charges!

30. Single, Double, & Triple Bonds
Single Covalent Bond—2 shared electrons (1 pair)
Double Covalent Bond—4 shared electrons (2 pairs)
Triple Covalent Bond—6 shared electrons (3 pairs)

31. Covalent e- dot diagrams
In e- dot diagrams a line represents a single bond
A double line represents a double bond, and a triple line represents a triple bond + + +

33. Covalent/Molecular Compounds
Unlike ionic compounds, 2 Nonmetals or Metalloids can combine in more than 1 way!
CO2: the gas we breathe out.
CO: colorless, odorless, deadly gas
Both are carbon oxides, but it is important to distinguish between them.

34. Naming Covalent (Molecular) Compounds
Prefixes tell the number of each element in the compound.
The 2nd element: change the ending to -ide
1-mono
2-di
3-tri
4-tetra
5-penta
6-hexa
7-hepta
8-octa
9-nona
10-deca
Examples:
CO2 is carbon dioxide
CO is carbon monoxide

35. IMPORTANT: The mono prefix is left off if the first element has 1
IMPORTANT: The mono prefix is left off if the first element has 1. Otherwise ALL parts of the name have a prefix.
Sometimes the vowel at the end of a prefix is dropped so the name sounds better.
Monoxide—not Monooxide

36. Formulas of Covalent Compounds
The prefixes tell you the subscripts of elements in the formula.
Example: tetraiodine octoxide
I4O8
Do not reduce molecular formulas

37. Lets try some examples N2O PCl3 SF6 Dinitrogen monoxide
Given the formula, name the following molecular compounds.
N2O
PCl3
SF6
CS2
C4O5
Dinitrogen monoxide
Phosphorus trichloride
Sulfur hexafluoride
Carbon disulfide
Tetracarbon pentoxide

38. More examples Carbon tetrafluoride Disulfur dichloride CF4
Given the name, what’s the formula for the following compounds.
Carbon tetrafluoride
Disulfur dichloride
Dinitrogen tetroxide
Phosphorus pentafluoride
Trihydrogen Mononitride
CF4
S2Cl2
N2O4
PF5
H3N

40. Ionic Covalent Type of elements Metal + Nonmetal
(& polyatomic ions)
2 or more nonmetals/metalloids
Smallest particle
Ions (charges)
Molecules (no charges)
How bonds form
Electrons are transferred
Electrons are shared
Formulas
Balance the charges
Use prefixes to tell subscripts
Name
Some have Roman Numerals
Don’t change polyatomic ions
2nd element ends in –ide
NO PREFIXES!!
Prefixes tell how many
2nd element ends in -ide

41. Ionic or Covalent Quiz Number 1-10 and answer I or C
Metal + Nonmetal
Nonmetal + Nonmetal
Metalloid + Nonmetal
NO2
Mg(OH)2
NaI
CH4
Calcium Phosphate
Nitrogen trifluoride
Sand (silicon dioxide)

42. Properties of Compounds
When elements combine, the compounds are more stable than the elements alone.
Compounds have different properties than their elements
Na: soft metal, explodes in water
Cl: toxic gas
Salt (NaCl): edible crystal

43. Properties of Ionic & Covalent
Ionic Bonds: held together by the attraction of a + and - charges
Weak bonds
Covalent Bonds: sharing electrons is a strong bond. (single, double, or triple)
Can be Polar or Nonpolar

44. Polar vs Nonpolar
Polar: is slightly (―) on one end & slightly (+) on the other.
e- are pulled closer to the larger nucleus
water is polar
Nonpolar: e- are shared equally
Oxygen gas (O2) is nonpolar