How Atoms Differ

2

• What are the subatomic particles?

• What are their charges?

• Where are they located?

• What are their sizes?

2

Properties of Subatomic Particles

Particle Symbol Location RelativeCharge

Relative mass

Actual mass (g)

Electron

e- or In the space

surrounding the

nucleus

1-_1__1840

9.11 x 10-

28

Protonp+ or

In the nucleus 1+ 1

1.673 x 10-24

Neutronn0 or In the

nucleus 0 11.675 x 10-24

4

• What makes a carbon atom a carbon atom?

• What number represents the number of protons?

• How do we use the atomic number?

Atomic NumberA. The atomic number is the number of protons or electrons

in a neutral atom

B. Remember that atoms are neutral thus:1. Atomic number = Number of protons = number

of electrons

C. Each element has a unique number of protons

D. The periodic table is organized by increasing atomic number (number of protons)

E. Only protons determine the type of atom present and will never change for an element.

Question Time

• What does the atomic number represent?

• Why are there an equal number of protons and electrons in a neutral atom?

• How many protons and electrons are in aluminum (Al)?

• An atom contains 28 protons, what element is it? How many electrons does it have?

• How is the periodic table organized?• What subatomic particle determines

the type of element?

8

• What is something that can be different from one atom of the same element to the next?

• How would we figure out the mass of an atom?

8

Isotopes and Mass Number

A. Isotopes are atoms of the same element that have the same number of protons but different number of neutrons

B.Mass number represents the sum of the number of protons and neutrons in the nucleus

C. So, # of neutrons = mass number – atomic number

What could isotope mean? Do you know any other words that begin with iso-?

Representing IsotopesA. In Ag-107, the 107 represents the

mass number (neutrons + protons)B. In Ag-109, the 109 represents the

mass number (neutrons + protons) How many neutrons

are there?

Question Time• What are isotopes?

• What is the mass number?

• What is the mass number in carbon-14?

• What is the mass number and atomic number in Fe?

• How many protons, neutrons, and electrons are in potassium-41, whose symbol is K?

• How many protons, electrons, and neutrons are in

Ne?

• What is the difference between hydrogen ( H), deuterium ( H), and tritium ( H)?

2210

5626

11

21

31

12

• Could we use grams to measure the mass of an atom?

• What could we use?

• If there are multiple isotopes, how would we figure out the mass for the element?

Atomic MassA. The mass of an atom is so small it is difficult to

work with, so chemists have developed an atomic standard to compare all the masses to

B. The standard is the atomic mass unit (amu) is defined as 1/12 of the mass of a carbon-12 atom

C. If the mass of an element is not close to a whole number, it is because the atom has several isotopes

D. The atomic mass is the weighted average of the isotopes of that element.

Example

A. Silver has two naturally occurring isotopes. Ag-107 has an abundance of 51.82% and mass of 106.9 amu. Ag-109 has a relative abundance of 48.18% and a mass of 108.9 amu. Calculate the atomic mass of silver.

Question Time

• Rubidium is a soft, silvery-white metal that has two common isotopes, Rb and Rb. If the abundance of 85Rb is 72.2% and the abundance of 87Rb is 27.8%, what is the average atomic mass of rubidium?

8537

8737

Vocabulary to Know

A. Atomic #-

B. Mass #-

C. Isotopes-

D. Atomic mass-

146

same # of protons & electrons

protons + neutrons written 2 ways: Carbon-14 or C

same # of protons, different # of neutrons

weighted average mass