Introduction to Atoms, Ions and Isotopes

What are atoms?• The atom is a basic unit of

matter that consists of a dense, central nucleus surrounded by a cloud of negatively charged electrons.

• While all atoms have protons, neutrons and electrons, atoms of different elements have different numbers of these.

Atoms• Each element on the periodic table

has an atomic number, which tells how many protons an atom of that element has.

• Each element also has an mass number.

• Mass number = # of Protons + # of Neutrons

Electrons• Neutral atoms have the same

number of electrons (negative charge) as they do protons (positive charge).

• # of electrons = atomic number

• ONLY IN NEUTRAL ATOMS

Let’s Practice!• Find Boron on the periodic table.• How many protons does an atom of Boron

have?• How many neutrons?

– Assume the mass number is 11• How many electrons?

Ions• An atom or small molecule with an

overall positive or negative charge due to an imbalance of protons and electrons.– # of protons does not change– # of electrons changes.– Positive charge = loss of electrons– Negative charge = gain of electron

Ions Continued…• Ions are represented by a superscript

charge on the element symbol.– Examples: F-, Mg2+, Al3+

Practice:• How many protons, neutrons, and

electrons does Al3+ have?

Isotopes• All neutral atoms of the same

element have the same number of protons, and therefore the same number of electrons.

• The number of neutrons CAN vary.• Isotopes: atoms of an element

that have the same number of protons, but a different number of neutrons.

Average Atomic Mass• The mass shown on your periodic

table as a decimal is the average atomic mass.– Average mass of all isotopes of an atom

in nature.

Example: Lithium• 2 Isotopes are found in nature:

Lithium-6 and Lithium-7 (Lithium-8 is radioactive and quickly decays)

• Atomic mass is listed as 6.94.• How is that possible?

– 94% of Li atoms have an atomic mass of 7, and 6% have an atomic mass of 6.

– Avg. Atomic Mass = (7 x .94) + (6 x .06)

Let’s Review!• ________ are charged atoms.

– _________ ions have LOST electrons.– _________ ions have GAINED electrons.

• An atom of Cu2+ with mass number 63 has:– ________ protons– ________ neutrons – ________ electrons

More Review• ____________ are atoms of the same

element that have different numbers of neutrons in the nucleus.

• What does average atomic mass represent?

Complete Atomic Structure WS #1 Front and Back

Hint: Chromium-52 means Chromium with a mass number of 52. 26Fe means

iron with atomic number 26.

Related Book Work

• Read section 5.1• Pg. 134-143• Answer the following questions on

page 162 1-3, 6, 7, 29, 31, 32, 38, 65, 71-76.