How molecules are symbolized Cl 2 2Cl 2Cl 2 Molecules may also have brackets to indicate numbers of atoms. E.g. Ca(OH) 2 O H O H Ca Notice that the.

How molecules are symbolizedCl2 2Cl 2Cl2

• Molecules may also have brackets to indicate numbers of atoms. E.g. Ca(OH)2

O H

O H

Ca• Notice that the OH is a group• The 2 refers to both H and O• How many of each atom are in the following?

a) NaOHb) Ca(OH)2

c) 3Ca(OH)2

Na = 1, O = 1, H = 1Ca = 1, O = 2, H = 2

Ca = 3, O = 6, H = 6

Balancing equations: MgO• The law of conservation of mass states that

matter can neither be created or destroyed• Thus, atoms are neither created or destroyed,

only rearranged in a chemical reaction• Thus, the number of a particular atom is the

same on both sides of a chemical equation• Example: Magnesium + Oxygen (from lab)• Mg + O2 MgO O Mg O+ Mg O

• However, this is not balanced• Left: Mg = 1, O = 2• Right: Mg = 1, O = 1

Balance equations by “inspection”

Hints: start with elements that occur in one compound on each side. Treat polyatomic ions that repeat as if they were a single entity.

5

2 33.52 7 4 6

2 222 63

C2H6 + O2 CO2 + H2O

a) P4 + O2 P4O10

b) Li + H2O H2 + LiOHc) Bi(NO3)3 + K2S Bi2S3 + KNO3

d) C2H6 + O2 CO2 + H2O

From Mg + O2 MgO 2Mg + O2 2MgO is correctMg + ½O2 MgO is incorrectMg2+ O2 2MgO is incorrect

4Mg + 2 O2 4MgO is incorrect

a) Mg + 2HCl MgCl2 + H2

b) 3Ca + N2 Ca3N2

c) NH4NO3 N2O + 2H2O

d) 2BiCl3 + 3H2S Bi2S3 + 6HCl

e) 2C4H10 + 13O2 8CO2 + 10H2O

f) 6O2 + C6H12O6 6CO2 + 6H2O

g) 3NO2 + H2O 2HNO3 + NO

h) Cr2(SO4)3+ 6NaOH 2Cr(OH)3+ 3Na2SO4

i) Al4C3 + 12H2O 3CH4 + 4Al(OH)3

Balance these skeleton equations:

• We have looked at several types of reactions without worrying about balancing

• However, all equations should be balanced• Predict the products and balance these: (recall, metals above replace metals below,

reactions with water yield metal hydroxides)

Cu + Fe2(SO4)3

NR (no reaction)

Zn + Li2CO3

Cu + AlCl3

KNaLiCaMgAlZnFeNiSnPbH

CuHgAgAu

Returning to reaction types

Fe + CuSO4

LiOH + H2Al2O3

2Ni+ NaCl Al+ CuCl2 Li + ZnCO3 Li + H2O Al+ O2

3 3

3 22 32

½2 2 23 24

Discovery of Radioactivity• Radioactivity is the release of energy or

particles when an atom disintegrates (demo)

• Radioactivity was discovered when minerals were exposed to film through an opaque cover

• The 3 types of radioactivity can be shown by passing emissions through an electrical field:

Lead block

Radioactive substance

Phosphorescent zinc sulfide

detection screen

+

– Strong magnetic or electrostatic field

Types of RadioactivityTypes of radiation: 1) , 2) , 3) 1. Alpha () particles are symbolized as 4

2He

2. Beta () particles (essentially electrons) are 0–1e

3. Gamma () rays are symbolized as 00

• You can determine the composition of each: : mass of 4 u, charge of +2 (2 p+, 2 n0, 0 e–)

• Other symbols: proton = 11p, neutron = 1

0n• There are different terms to describe the

different types of nuclear reactions• “alpha decay” means an particle is given off.• Other: beta decay, fusion (meaning to bring

together), fission (meaning to break apart)

Nuclear equationsQ. Write the beta decay for C-14

In all cases, charge and mass must be balanced• Practice: pg. 222-3, Q6, Q3

C14 6 e

0 -1 N

14 7 +

Po209 84 He

4 2 Pb

205 82 +

Q. Write the alpha decay for 209Po

Q. Complete this fission reaction

Kr 94 36U

235 92 n

1 0 Ba

139 56 +n

1 0 + 3 +

6. a) b) c) d) e)

Ra226 88 He

4 2 Rn

222 86 +

Sr9938P

3215 Re

18775 He

42 Tc

9943

3. a)

b)

c)

d)

e)

Br8435 e

0 -1 Kr

84 36 +

Pu242 94 He

4 2 U

238 92 +

N14 7 C

11 6 +p

1 1 + He

4 2

O18 8 F

19 9 +n

1 0 + e

0 -1

a) 2KNO3 2KNO2 + O2

b) 2Pb(NO3)2 2PbO + 4NO2 + O2

c) P4 + 6I2 4PI3

d) 3MgO + 2H3PO4 Mg3(PO4)2 + 3H2O

e) Br2 + 2KI I2 + 2KBr

f) Ca(OH)2 + 2HNO3 Ca(NO3)2 + 2H2O

g) Bi2O3 + 3H2 2Bi + 3H2O

h) 3Fe + 2O2 Fe3O4

i) 2CaO + 5C 2CaC2 + CO2

Here are some more to balance:

Question 3 pg. 252a) 2Li + 2H2O H2 + 2LiOH

b) P4 + 5O2 P4O10

c) 2C2H6 + 7O2 4CO2 + 6H2O

d) CS2 + 3O2 CO2 + 2SO2

e) 2AsCl3 + 3H2S As2S3 + 6HCl

f) 3AgNO3 + FeCl3 3AgCl + Fe(NO3)3

g) 2KClO3 2KCl + 3O2

h) 2SO2 + O2 2SO3

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