Wake-up

1. Explain the relationship between the following: atomic number, mass number, protons, neutrons, and electrons.

2. How do you find the number of electrons of an element?

3. How do you find the number of neutrons of an element?

Isotopes and Relative Abundance

What is an isotope?What is relative abundance?

Examine the information of hydrogen below and answer the following questions. Do not

round the mass number!

What element and chemical symbol is shown?

Hydrogen and H

What is the atomic number for this element?

1

What is the atomic mass for this element? Don’t round

1.00794

List the number of protons, electrons, and neutrons (in that order)

1 p+, 1 e-, 0 n0

What is an ISOTOPE?• Isotope = atoms that have the same number of

PROTONS but different number of NEUTRONS.• Chemically alike but with varying mass numbers

APPLE VARITIES

Examine the mass number of the various elements on the periodic table. Very few are even. This is

due to isotopes. The mass number is better known as the Atomic Mass or Atomic Unit. This number represents the AVERAGE mass of all the naturally

occurring isotopes of an element.

Atomic MassAverage of the masses of an elements (atom)

naturally occurring isotopes

Relative Abundance

The abundance isotopes of an element as naturally found on a planet (%)

Relative abundance of elements on

Earth’s surface

Review NotationsHyphen notation: Write the element name and

the mass number

Hydrogen - 1

Review NotationsNuclear notation: See diagram below

In other words, all the isotopes of the same element (atom) have the SAME

but DIFFERENT

Atomic Number (p+ and e-)

Mass Number (specifically n0)

Isotope: Hydrogen-1Name: Protium

(Most common isotope of Hydrogen has a 99.985% relative abundance)

Isotope: Hydrogen-1

# of Protons: 1# of Electrons: 1# of Neutrons: 0

Isotope: Hydrogen-2Name: Deuterium

(Relative Abundance: 0.015% of Hydrogen)

Isotope: Hydrogen-2

# of Protons: 1# of Electrons: 1# of Neutrons: 1

Isotope: Hydrogen-3Name: Tritium

(Relative Abundance: Very small amounts of Hydrogen)

Isotope: Hydrogen-3

# of Protons: 1# of Electrons: 1# of Neutrons: 2

Calculating Average Atomic MassFormula:

(% abundance #1)(Mass #1) + (% abundance #2)(Mass #2)100

Calculating Average Atomic Mass #1

You have a box containing two sizes of marbles.

• 25% of the marbles have a mass of 2.0 g.

• 75% of the marbles have a mass of 3.0 g.

Calculate the average weight of the marble.

Example #2: Rubidium has two common isotopes, 85Rb and 87Rb. If the abundance of 85Rb

is 72.2% and the abundance of 87Rb is 27.8%, what is the average atomic mass of rubidium?

Example #3: The element boron has two stable isotopes. Boron-10 has an atomic mass

of 10.0129 and a percentage in nature of

19.78% The atomic mass of boron-11 is

11.0093 and its percentage in nature is

80.22% What is the average atomic mass

for boron?