Lecture 5 9/9/05

Quiz 2

1. Which of the following has the highest temperature?

30 °C 80 °F 300 K

2. How many protons and neutrons does an atom of potassium-40 have?

F32)F(TF9

C5)C(T C15.273)C(T)K(T

1 mole =the amount of substance that contains as many particles (atoms, molecules) as there are in 12.0 g of 12C.

1 mole =the amount of substance that contains as many particles (atoms, molecules) as there are in 12.0 g of 12C.

THE MOLE

1 mole = 6.02214199 x 1023 particles = Avagadro’s number

MOLAR MASS

sum of the atomic weights of all atoms in the

molecule molecular weight in grams/mole

1 mol of 12C = 12.00 g of C = 6.022 x 1023 atoms of C

12.00 g/mol is the molar mass of 12C

12.011 g/mol is the molar mass of carbon (taking into account all of the isotopes of C)

Mass to Moles

gramsmole 1

gramsMoles

mole 1/grams

gramsMoles

mass Molar

MassMoles

How many moles of Mg is represented by 0.200 g? How many atoms?

How many moles of Mg is represented by 0.200 g? How many atoms?

Mg has a molar mass of 24.3050 g/mol.

0.200 g • 1 mol

24.31 g = 8.23 x 10-3 mol

8.23 x 10-3 mol • 6.022 x 1023 atoms

1 mol

= 4.95 x 1021 atoms Mg

How many atoms in this piece of Mg?

Dmitri Mendeleev (mid-19th cen)Periodic Table

Lined up elements in horizontal rows with increasing atomic weight

Started new rows when properties seemed similar

Left space in table where he predicted new elements would be discovered

HGJ Moseley (1913)Discovered a method to determine atomic

numberRealized Periodic Table should be organized

by atomic number

Law of Chemical Periodicity:Properties are periodic functions of atomic #

Periodic Table