Understanding the Atom

4-3: Elements, Isotopes, and Ions – How Atoms Differ

Vocabulary

elementatomic numbermass numberisotopeaverage atomic massion

Different Elements – Different Numbers of Protons

An element is a pure substance that can be identified by the number of protons in the nucleus of its atoms.Each atom of a particular element has the same number of protons in its nucleus. This number is called the element’s atomic number.

Atomic Number and the Periodic Table

In a chart called the Periodic Table of the Elements, elements are arranged horizontally by increasing atomic number and vertically in columns of elements with similar chemical properties.Elements in the periodic table are mostly metals, but also include nonmetals and semimetals (or metalloids)

Atomic Number and the Periodic Table (cont’d)

Isotopes – Different Numbers of Neutrons

All atoms of an element have the same number of protons. Different atoms of the same element can have different numbers of neutrons.The mass number of an atom is the total number of neutrons and protons in the atom.To calculate the number of neutrons, subtract the atomic number from the mass number.

Concepts in Motion (revisited)

Isotopes – Different Numbers of Neutrons (cont’d)

Atoms of the same element that contain different numbers of neutrons are called isotopes.

Isotopes – Different Numbers of Neutrons (cont’d)

The average atomic mass of an element is the weighted average of the mixture of an element’s isotopes.Some isotopes of certain elements are radioactive, meaning they spontaneously decay and release particles and/or energy.Hydrogen has three isotopes, called protium, deuterium, and tritium.

Isotopes – Different Numbers of Neutrons (cont’d)

Name Protium Deuterium Tritium

Symbol H-1 H-2 H-3

Atomic Number

1 1 1

Mass Number

1 2 3

Radioactive?

No No Yes

Atomic Structure

Ions – Gaining or Losing Electrons

An atom can gain or lose electrons.It no longer has the same number of protons (+) and electrons (-)An ion is an atom that no longer is neutral because it has gained or lost electrons.

Ions – Gaining or Losing Electrons (cont’d)

If an element loses an electron, it then has more protons than electrons and has a positive charge. An atom with a positive charge is called a positive ion.

Ions – Gaining or Losing Electrons (cont’d)

When an atom gains an electron, it has more electrons than protons.The atom has a negative charge and is called a negative ion.

Positive ions and negative ions attract each other and form compounds.

4-3 Lesson Review Questions

The carbon element has several isotopes. How is carbon-14 different from carbon-13?

A Carbon-14 has a positive charge.

B Carbon-13 has a positive charge.

C Carbon-14 has one more neutron than carbon-13.

D Carbon-14 has one less neutron than carbon-13.

4-3 Lesson Review Questions

What is the number of protons in an element called?

A isotope

B atomic number

C atomic mass

D radiotope

4-3 Lesson Review Questions

How does a neutral atom become a negative ion of the same element?

A It gains a proton.

B It loses a proton.

C It loses an electron.

D It gains an electron.

Homework

Answer the three multiple choice Lesson Review questions.Draw the three isotopes of Hydrogen: Protium, Deuterium, and Tritium. Be sure to label each.