1. Unit 2- Measurements- Significant Figures & Scientific Notation

2. Significant Figures
Figures (values) that indicate precision of a measurement.
Recording Sig Figs
Sig figs in a measurement include the known digits plus a final estimated digit
2.35 cm

3. Counting Sig Figs Count all numbers EXCEPT: Leading zeros:
Trailing zeros without a decimal point:
2,500  2 sig figs

4. Atlantic-Pacific Method
Pacific Ocean
“_________”
Atlantic Ocean
“ _______”
PRESENT
ABSENT

5. Atlantic-Pacific Method:
Decimal point is PRESENT:
count significant figures from the LEFT (Pacific side)
Decimal point is ABSENT:
count significant figures from the RIGHT (Atlantic side)
Start counting significant figures at the first nonzero number and don’t stop until there are no more digits.

6. Practice Counting Sig Fig
4 sig figs
3 sig figs
3. 5,280
3. 5,280
3 sig figs
2 sig figs
4 sig figs

7. Practice Counting Sig Fig
Round the number at left to the number of significant figures stated in each column
Number
4 sig figs
3 sig figs
2 sig figs
1 sig fig
80.405
29,350
80.41
80.4
80. 80
29,350
29,400
29,000
30,000

8. Multiplying & Dividing :
Calculating Rules:
Multiplying & Dividing :
The # with the fewest sig figs determines the # of sig figs in the answer.
(13.91g/cm3)(23.3cm3) = g
3 SF
4 SF
3 SF
324 g

9. Calculating Rules: Adding & Subtracting:
The # with the lowest decimal value determines the place of the last sig fig in the answer.
3.75 mL mL
7.85 mL
3.75 mL mL
7.85 mL
224 g
+ 130 g
354 g
224 g
+ 130 g
354 g
 7.9 mL
 350 g

10. Significant Figures Practice Problems
85.6 cm
38 g
1.13 g

11. M x 10n 1 ≤ M < 10 +n: large # -n: small # Scientific Notation
In science, numbers can be very small & very large (confusing!)
Numbers can be expressed in Scientific Notation:
M x 10n
1 ≤ M < n: large # -n: small #

12. Scientific Notation 65,000 kg  6.5 × 104 kg
To convert into Sci. Notation:
Move decimal until there’s 1 digit to its left. (# of places moved = exponent)
Large # (>1)  positive exponent Small # (<1)  negative exponent
Only include sig figs.
65,000 kg 
6.5 × 104 kg

13. Scientific Notation Practice Problems
1. 2,400,000 mg kg
3. 7  10-5 km
 104 mm
2.4  106 mg
2.56  10-3 kg km
62,000 mm

14. Calculating with Scientific Notation
(5.44 × 107 g) ÷ (8.1 × 104 mol) =
Type on your calculator:
2nd EE
2nd EE
5.44 7
8.1 4 ÷
ENTER =
= 670 g/mol
= 6.7 × 102 g/mol