CHAPTER 2

AP

CH

EM

2.2 REVIEW

1. Atomic Number, Mass Number, Atomic Symbol

Atomic number, Z, is the number of protons

An atomic symbol represents the element

The mass number is equal to protons +neutrons

2.3 ISOTOPESDefinition: Two or more forms of the

same element containing different numbers of neutrons. Isotopes of an element have the same chemical properties but differing mass numbers.

Examples:

3. Mass Spectrometer and percent abundance

A device that measures both the individual mass numbers and the percentages of each isotope that exist in a sample of an element.

The percentage an isotope makes up of the entire isotope that exists in nature.

2.4 ATOMIC WEIGHT

1. Atomic mass or Atomic weight

one amu (atomic mass unit) = exactly 1/12 of the mass of a carbon-12 atom

Atomic weight (mass) is the weighted average of the masses of an elements’ isotopes

*in chemistry the terms atomic weight and atomic mass are used interchangeably

EX2.1 Boron exists in two naturally, occurring isotopes. B-10

( 10.016 amu) makes up 18.83% of each natural sample of this element. The remaining 81.17% of the sample is B-11 (11.013 amu). What atomic mass would be calculated for this mixture of isotopes?

Solve by multiplying isotope mass by %

Boron -10 (10.016) (0.1883) = 1.8860

Boron -11 (11.013) (0.8117) = +8.9393

10.825 amu

Keep 5 sig figs – consider percent as exact number

EX2.2The two natural isotopes of Lithium are 6Li (6.01512

amu) which accounts for 7.42% of the total and 7Li which accounts for the remaining amount. If the mass of lithium is shown as 6.942 on the periodic table, what is the mass of the Li -7 isotope? (answer = 7.016 amu)

4. MOST ABUNDANT NATURAL ISOTOPEHydrogen is the most abundant natural

isotope

2.5 ATOMS AND THE MOLE1. Definition: the amount of a substance

that contains as many “representative particles” ( atoms, molecules, or other particles) as there are atoms in 12grams of carbon-12 atoms.

1 mole = 6.022045 x 1023 r.p.’s

ANALOGY

Bakery count 1 dozen = 12 donuts

Chemists use moles like dozens to make things more manageable

http://www.youtube.com/watch?v=g_BelGwRxG8

3. Avogadro’s Number

1 mole = 6.022 x 1023 particles

4. Second DefinitionThe mass of 1 mole of atoms of a pure element in grams is equal to the atomic mass of that element in amu

EX 2.3One mole of sulfur contains 6.022 x 10 23 atoms of

sulfur and has a mass of 32.06 grams. What is the mass of one atom of sulfur? (Use 32.1 to determine sig. figs.) (answer = 5.33x10-23 g)

EX 2.4How many sulfur atoms are present in 1.00

grams of sulfur? (answer = 1.88x1022 atoms S)

EQUIVALENCIES AND CONVERSION FACTORS

Formula Formula mass (amu) Molar Mass (g)

H 1.00794 amu 1.00794 g/mole

H2 = g/mole

H2O = g/mole

H2SO4 = g/mole

SAMPLE MOLE PROBLEMSEx2.5 How many moles are equivalent to 5.00 g CaCO3?

(Add molar masses of calcium, oxygen and carbon present to get the molar mass)

5.00 grams CaCO3 1 mole CaCO3 = 0.0500 moles CaCO3 100.1 g CaCO3

Ex2.6 A microchemical experiment requires 0.0100 moles of Al(NO3)3. How many grams is this? (answer = 2.13 g)

MORE MOLE PROBLEMSEx. 2.7 For exactly 1.000 g of carbon disulfide (CS2), how many

molecules are present? How many atoms of sulfur?

1.000 g CS2 1 mole CS2 6.022 x 1023 molecules CS2 = 7.903 x1021 molc. CS2

76.2 g CS2 1 mole CS2

7.903 x1021 molc. CS2

Ex2.8 A sample of sulfur hexafluoride (SF6) contains 1.69 x 1022

atoms of fluorine. What is the mass of the sample? (answer = 2.48x1047 g SF6)

THE PERIODIC TABLE1.History

Mendeleev, 1869 - developed the first periodic table by identifying similarities among the elements; based on increasing atomic mass

Periodic Law – The properties of elements repeat when arranged by atomic number (updated after Moseley’s work)

Moseley, 1913 - organized the P.T. by atomic number

THE PERIODIC TABLE

Groups or families – columns down the P.T.

Periods or series – rows across P.T.

Metals - on the left side of the staircase , metalloids - along the staircase, nonmetals - on the right side of the staircase

Main group elements – the “A” groups of P.T.

Transition metals – in the middle

Lanthanides and Actinides – bottom double rows

Specific Family Names to Memorize:

Specific Family Names to memorize:

Group 1 – Alkali metalsGroup 2 – Alkaline Earth metalsGroup 17 (7A) – HalogensGroup 18 (8A) – Noble gases

PERIODIC TABLE

http://www.youtube.com/watch?v=SmwlzwGMMwc

Coulomb’s Law – a helpful tool in explaining P.T. trends• Page 93 of the textbookThe magnitude of the electrostatic force of interaction between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distances between them.

Two charges of the same sign=repulsive force; Two charges of opposite sign=attractive force; At least one is neutral=no force• Like charges repel

• opposite charges attract

Coulomb’s Law

• video

The Equation

1 2

1 22

( )

( )e

e

where F is force Newtons , q and q represent charge (Coulomb's),

d is distance meters between electrons, and k is Coulomb's constant

q qF k

d

Applying Coulomb’s Law to P.T.

• Throughout our study this year, we will apply Coulomb’s Law to support observed properties such as melting point and boiling point

• The product of the charges and the force of attraction is directly proportional

• The square of the distances and the force of attraction is inversely proportional

HOMEWORK CHAPTER 2

HW#1 -21, 23, 25, 27, 29, 47 Composition Atoms, Isotopes

HW#2 - 31, 33, 35 Atomic Symbols Wkst

HW #3 – 37, 39, 59, 61, 62, 63

HW #4 - Mole Relationships Wkst.

HW #5 - 43, 45, 57 PT