Quantitative Chemistry

Atomic Number Tells the number of protons and electrons the element contains

Atomic Mass The average of all the mass numbers of all the isotopes of that element. The unit is amu, stands for atomic mass units

Mass Number The number of protons plus the number of neutrons found in that element

Isotope Atoms of the same element with different numbers of neutrons

LecturePLUS Timberlake7 Calculating Atomic Mass Percent(%) abundance of isotopes Mass of each isotope of that element Weighted average = mass isotope 1 (%) + mass isotope 2 (%) + …

LecturePLUS Timberlake8 Atomic Mass of Magnesium Isotopes Mass of Isotope Abundance 24 Mg =24.0 amu 78.70% 25 Mg = 25.0 amu 10.13% 26 Mg = 26.0 amu 11.17% Atomic mass (average mass) Mg = 24.3 amu Mg 24.3

LecturePLUS Timberlake9 Learning Check AT7 Gallium is a metallic element found in small lasers used in compact disc players. In a sample of gallium, there is 60.2% of gallium-69 (68.9 amu) atoms and 39.8% of gallium-71 (70.9 amu) atoms. What is the atomic mass of gallium ?

LecturePLUS Timberlake10 Solution AT7 Ga amu x 60.2 = 41.5 amu for 69 Ga 100 Ga-71 (%/100) 70.9 amu x 39.8 = 28.2 amu for 71 Ga 100 Atomic mass Ga = 69.7 amu

LecturePLUS Timberlake11 Finding An Isotopic Mass A sample of boron consists of 10 B (mass 10.0 amu) and 11 B (mass 11.0 amu). If the average atomic mass of B is 10.8 amu, what is the % abundance of each boron isotope?

LecturePLUS Timberlake12 Assign X and Y values: X = % 10 B Y = % 11 B Determine Y in terms of X X + Y = 100 Y = X Solve for X: X (10.0) + (100 - X )(11.0) = Multiply through by X X = 1080

LecturePLUS Timberlake13 Collect X terms 10.0 X X = X = -20 X = -20 = 20 % 10 B Y = X % 11 B = % = 80% 11 B

LecturePLUS Timberlake14 Learning Check AT8 Copper has two isotopes 63 Cu (62.9 amu) and 65 Cu (64.9 amu). What is the % abundance of each isotope? (Hint: Check periodic table for atomic mass) 1) 30%2) 70%3) 100%

LecturePLUS Timberlake15 Solution AT8 2) 70% Solution 62.9X X = X = -140 X = 70%

Ratio Is the mathematical relationship between two quantities in the form of a fraction or percentage

Ratio Analysis is essentially concerned with the calculation of relationships

Law of Conservation of Mass States that in any reaction, the same amount of mass must be found on both sides of the equation.

Significant Figures When making measurements, it is the size of the measurement needed to be precise.

Sig. Fig. Rule 1)Non-zero numbers are always significant 2)Zeros between non-zero numbers are always significant. 3)All final zeros to the right of the decimal place are significant.

Sig. Fig. Rule 4)Zeros that act as placeholders are not significant. 5)All numbers in calculations should have same sig. fig. go with the smallest sig. fig. number 6)Counting numbers and defined constants do not change.

What’s the Sig. Fig X

Scientific Notation Expresses numbers as a multiple of two factors-a number between 1 and 10, and 10 raised to a power or exponent; makes it easier to write a really big number or really small number.

Round to 3 sig. fig

Rounding Rules If digit after sig # is above 5, then round up If digit after sig # is below 5 then leave as is If digit after sig # is 5 and # after 5 is not zero, then round up If digit after sig # is 5 and # after 5 is zero; if sig # is odd round up and if even then leave as is.

10 18 exa E peta P tera T 10 9 giga G 10 6 mega M 10 3 kilo k 10 2 hecto h 10 1 deka da deci d centi c milli m micro µ nano n pico p femto f atto a

Dimensional Analysis A problem solving method that focuses on the units that are used to describe matter.

System International Units (SI Units) Units are a name tag that lets you know what measurement the number is for. The SI Units are the standard units use throughout the world.

SI Units Time= second (s) Length= meter (m) Mass= kilogram (kg) Temperature= Kelvin (K) Volume= liter (L) or cubic centimeter (cm 3 ) Density= g/cm 3