Journal #11

• How do you find the average age of the students in this classroom?

Current AtomicModel

Subatomic Particles

Charge Mass Location

Proton +1 amu(1/12 of a carbon atom)

Nucleus

Neutron none 1 amu Nucleus

Electron - Almost0 amu

Outside nucleusIn motion

IsotopesDistinguishing Atoms

What makes an atom unique?

• Number of protons• Number of neutrons• Number of electrons

The Atom

Almost every atom is neutral, a balance of positive & negative charges.

FYI: If the nucleus was the size of a pea it would have a mass 250 tons. If the nucleus was the size of a marble, the atom would be the size of a football stadium.

atomic number = # of p+ & e-

• top number• # electrons = # protons (in a neutral atom)

• This number never changes• If it did you would make a different element

12.0107

mass number

= # protons + # neutrons

This is NOT on the periodic table! You round the atomic mass to get the mass number of the most common isotope.

12.0107

Try some

Pb Ag

Na C

How many protons, neutrons & electrons do each of the elements have?

Use the periodic table in the back of your book:

p+= 82

e-= 82

n= 207- 82= 125p+= 11

e-= 11

n= 23- 11= 12

p+= 6

e-= 6

n= 12- 6= 6

p+= 47

e-= 47

n= 108- 47= 61

Stop and practice

Packet page 3

Isotopes

• Different versions of an atom

• # protons is the same– Atomic number is the same

• # neutrons is different– Mass number is different

Chemical Properties of Isotopes

• Chemically, all isotopes are the same since they all have the same number of electrons.

• Electrons determine the chemical properties of an element.

Designating Isotopes

Mass # Symbol 14 CAtomic # 6

---------------------------------------------Hyphen notation:

Name – mass # carbon-14

Nuclear symbol:

Practice

• How many protons, electrons and neutrons make up an atom of bromine-80?– 35 protons, 35 electrons, 45 neutrons

• Write the nuclear symbol for carbon-13– 13

6C

• Write the hyphen notation for the isotope with 15 electrons and 15 neutrons.– Phosphorus-30

Try Some + worksheet

Atomic #

(p+/e-)

Mass #

(p+ + n)

# p+ # n symbol

9 10

14 15

47 25

55 25

Check

Atomic # Mass # # p+ # n symbol

9 19 9 10 F

14 29 14 15 Si

22 47 22 25 Ti

25 55 25 30 Mn

Stop and practice

• Do packet pages 9 & 10

% abundance

• Most elements occur as mixtures of isotopes.• The % of each isotope that occurs for each

element is nearly always the same, no matter where the element is found.

• The percentage at which each element (ISOTOPE) occurs in nature is called the isotope’s % abundance.

Why atomic mass is a decimal

• Average atomic mass is the weighted average mass of atoms in a naturally occurring setting

• To calculate (Isotope mass x % abundance)+ (Isotope mass x % abundance)= average atomic mass

Calculating average atomic mass

• In order to calculate the average atomic mass, you need to know three things1. The number of isotopes

2. The mass of each isotope

3. The natural % abundance of each isotope

Marble Example: You have 100 marbles; 60 black marbles (5g each), 40 red marbles (8 g each).

1) Find the % abundance of each marble isotope?

Marble type x 100 = % abundance Total marbles

60 black marbles x 100= 60% black marbles 100 marbles

40 red marbles x 100= 40 % red marbles 100 marbles

2) What is the average mass of each marble? (Isotope mass x % abundance)

+ (Isotope mass x % abundance)

= average atomic mass

(5 g x 60% black marbles) 3.0g+ (4g x 40% red marbles) 1.6 g= average atomic mass 4.6 g

FYI: 60%= 60 /100=0.60

Atomic Mass of Chlorine

Element % abundance Mass

Chlorine -35 75.77%(divide by 100)

34.969

Chlorine -37 24.23%(divide by 100)

36.966

Atomic Mass

Atomic Mass of Chlorine

Element % abundance Mass

(amu)

Chlorine -35 75.77% x 34.969 = 26.496

Chlorine -37 24.23% x 36.966 = 8.957

Atomic Mass35.453

Determine the Element

• 63X weighs 62.929601 amu and has a % abundance of 69.15%

• 65X weighs 64.927794 amu and has a % abundance of 30.85%

• Find the average atomic mass and then compare to the periodic table.

• What is the element?