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 a mass number.

• Mass number = # of Protons + # of Neutrons

# of electrons in atoms

• 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 0.94) + (6 x 0.06) = 6.94 amu (atomic mass units)

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.

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?

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.