Subatomic ParticlesAtomic Number | Isotopes | Ions

Learning Objectives• Understand the importance of atomic

numbers• Find the numbers of subatomic particles in a

given isotope • Calculate the average atomic mass of an

element using isotopic composition• Determine the charge of an ion based on

numbers of subatomic particles

Subatomic Particles

• Neutrons– Neutral charge, 0– 1 amu

• Protons– Positive charge, +1– 1 amu

• Atomic number – the number of protons in an atom, which determines the identity of an element– Modern periodic table is arranged by atomic

number• Ex) All atoms containing 6 protons are carbon atoms

Atomic Number

• Isotopes – the atoms of the same element that contain different numbers of neutrons and therefore have differing masses

• Mass number – the sum of the number of neutrons and the number of protons in an isotope

Isotopes

• Isotopic notation– Mass number written as a superscript in front of

the element’s symbol– Atomic number written as a subscript in front of

the element’s symbol

Isotopes

Finding the Number of a Subatomic Particle

Ex) How many neutrons does contain?  

IV. Conversions needed? V. Intermediates needed? VI. Solve

VII. Does the result make sense?

I. StrategyII. Given and unknown

III. Formula

so

No.No.

Yes.

• Value given for element’s mass on periodic table

• Isotopic composition – the relative amounts of each isotope of an element found in a sample

• Percent abundance – the percentages that describe isotopic compositions

Average Atomic Mass

• Average atomic mass – the weighted average of the masses of all stable isotopes of an element

• Atomic mass unit (amu) – a unit of mass equal to one-twelfth the mass of a carbon-12 atom

Average Atomic Mass

Finding Average Atomic Mass

Step 1 Change the given percent abundances into decimal form.

Step 2 Multiply the given mass of each isotope by its percent abundance in decimal form.

Step 3 Find the sum of these values.

Finding Average Atomic Mass Example Step 1

Ex) Use the information in the data table to find the average atomic mass of silver.

Step 1 Change the given percent abundances into decimal form.

Isotope Percent Atomic Mass (amu)

Silver-107 51.839% 106.91Silver-109 48.161% 108.90

Finding Average Atomic Mass Example Step 2

Ex) Use the information in the data table to find the average atomic mass of silver.

Step 2 Multiply the given mass of each isotope by its percent abundance in decimal form.

Isotope Percent Atomic Mass (amu)

Silver-107 51.839% 106.91Silver-109 48.161% 108.90

Finding Average Atomic Mass Example Step 3

Ex) Use the information in the data table to find the average atomic mass of silver.

Step 3 Find the sum of these values.

Does the result make sense?

Isotope Percent Atomic Mass (amu)

Silver-107 51.839% 106.91Silver-109 48.161% 108.90

Yes.

• Electrons– Outside nucleus– Negative charge, –1

• Atoms containing equal numbers of protons and electrons are neutrally charged

• Ion – an atom that has an overall charge because it does not contain the same number of protons and electrons– Cation – a positively charged ion formed when an

atom loses one or more electrons– Anion – a negatively charged ion formed when an

atom gains one or more electrons– Charge equals sum of charges of protons and

electrons

Ions

Finding the Charge of an Ion

Step 1 Find the sign of the charge by determining whether protons outnumber electrons or electrons outnumber protons in the ion.

Step 2 Find the magnitude of the charge by determining the difference between the number of protons and electrons

in the ion.

Finding the Charge of an Ion

Ex) What is the charge on an ion that contains 53 protons and 54 electrons?

Step 1 Find the sign of the charge by determining whether protons outnumber electrons or electrons outnumber protons in the ion.

Electrons outnumber protons, so this is an anion. The ion will be negatively charged.

Step 2 Find the magnitude of the charge by determining the difference between the number of protons and electrons in the ion.

There is one more electron than proton, so the magnitude of the charge is 1. The charge of the ion is –1.

Does the result make sense?

Yes.

Learning Objectives• Understand the importance of atomic

numbers• Find the numbers of subatomic particles in a

given isotope • Calculate the average atomic mass of an

element using isotopic composition• Determine the charge of an ion based on

numbers of subatomic particles

Subatomic Particles