Figure 3.9: A nuclear atom viewed in Figure 3.9: A nuclear atom viewed in cross section.cross section.

The Nucleus

• The nucleus forms the central dense core of the atom (ca. 10-13 cm diameter). It consists of particles referred to as nucleons. There are two types of nucleons: protons and neutrons.

• A nucleus consists of at least one proton.

• Most nuclei also consist of one or more neutrons.

p

p

n

n

n

p

Atomic StructureAtomic Structure

The # of protons determine the type of The # of protons determine the type of element it is and it’s chemical/physical element it is and it’s chemical/physical characteristicscharacteristics

There are three characteristics that can be There are three characteristics that can be discussed about each particlediscussed about each particle– ChargeCharge– MassMass– LocationLocation

Atomic StructureAtomic Structure

Protons have a positive charge (+), an Protons have a positive charge (+), an atomic mass of 1.0073 and are found in the atomic mass of 1.0073 and are found in the nucleus nucleus

Electrons have a negative charge (-), an Electrons have a negative charge (-), an atomic mass of 0.000549 and are found in atomic mass of 0.000549 and are found in the electron cloudthe electron cloud

Neutrons have no charge (Neutrons have no charge (ø), an atomic ø), an atomic mass of 1.0087 and are found in the nucleus mass of 1.0087 and are found in the nucleus

Properties of Subatomic Properties of Subatomic ParticlesParticles

The Structure of the Atom, The Structure of the Atom, continuedcontinued

Surrounding the nucleus is a region occupied by Surrounding the nucleus is a region occupied by negatively charged particles called negatively charged particles called electrons.electrons.

Protons, neutrons, and electrons are often referred Protons, neutrons, and electrons are often referred to asto as subatomic particlessubatomic particles..

Composition of the Atomic Composition of the Atomic NucleusNucleus

Except for the nucleus of the simplest type of hydrogen atom, all Except for the nucleus of the simplest type of hydrogen atom, all atomic nuclei are made of atomic nuclei are made of protons protons and and neutrons.neutrons.

A proton has a positive charge equal in magnitude to the negative A proton has a positive charge equal in magnitude to the negative charge of an electron.charge of an electron.

Atoms are electrically neutral because they contain equal numbers of Atoms are electrically neutral because they contain equal numbers of protons and electrons.protons and electrons.

A neutron is electrically neutral.A neutron is electrically neutral.

Composition of the Atomic Composition of the Atomic Nucleus, Nucleus, continuedcontinued

The nuclei of atoms of different elements differ in their The nuclei of atoms of different elements differ in their number of protons and therefore in the amount of positive number of protons and therefore in the amount of positive charge they possess.charge they possess.

Thus, the number of protons determines that atom’s identity.Thus, the number of protons determines that atom’s identity.

Composition of the Atomic Composition of the Atomic Nucleus, Nucleus, continuedcontinued

When two protons are extremely close to each other, there is a strong attraction between them.When two protons are extremely close to each other, there is a strong attraction between them.

Forces in the Nucleus

The short-range proton-neutron, proton-proton, and neutron-neutron forces that hold the nuclear particles together are

referred to as nuclear forces.

A similar attraction exists when neutrons are very close to each other or when protons and neutrons are very close

together.

Atomic NumberAtomic Number

Atoms of different elements have different numbers of protons.Atoms of different elements have different numbers of protons.

Atoms of the same element all have the same number of Atoms of the same element all have the same number of protons.protons.

The The atomic number atomic number (Z) of an element is the number of (Z) of an element is the number of protons of each atom of that element.protons of each atom of that element.

Atomic NumberAtomic Number

Mass NumberMass Number

The The mass numbermass number is the total number of protons and is the total number of protons and neutrons that make up the nucleus of an isotope.neutrons that make up the nucleus of an isotope.

Mass NumberMass Number

IsotopesIsotopes

IsotopesIsotopes are atoms of the same element that have different masses. are atoms of the same element that have different masses.

The isotopes of a particular element all have the same number of The isotopes of a particular element all have the same number of protons and electrons but different numbers of neutrons.protons and electrons but different numbers of neutrons.

Most of the elements consist of mixtures of isotopes.Most of the elements consist of mixtures of isotopes.

Figure 3.10: Two isotopes of Figure 3.10: Two isotopes of sodium.sodium.

Designating IsotopesDesignating Isotopes

Hyphen notation: The mass number is written with a hyphen after Hyphen notation: The mass number is written with a hyphen after the name of the element.the name of the element.

uranium-235uranium-235

Nuclear symbol: The superscript indicates the mass number and the Nuclear symbol: The superscript indicates the mass number and the subscript indicates the atomic number.subscript indicates the atomic number.

235 92 U

Designating Isotopes, Designating Isotopes, continuedcontinued

The number of neutrons is found by subtracting the atomic The number of neutrons is found by subtracting the atomic number from the mass number.number from the mass number.

mass number mass number atomic number = number of neutrons atomic number = number of neutrons 235 (protons + neutrons) 235 (protons + neutrons) 92 protons = 143 neutrons 92 protons = 143 neutrons

Nuclide Nuclide is a general term for a specific isotope of an element.is a general term for a specific isotope of an element.

Designating Isotopes, Designating Isotopes, continuedcontinued

Sample Problem ASample Problem AHow many protons, electrons, and neutrons are there in an atom of How many protons, electrons, and neutrons are there in an atom of chlorine-37?chlorine-37?

Designating Isotopes, Designating Isotopes, continuedcontinued

Given:Given: name and mass number of chlorine-37 name and mass number of chlorine-37

Solution: atomic number = number of protons = number of electronsmass number = number of neutrons + number of protons

Unknown: numbers of protons, electrons, and neutrons

Sample Problem A Solution

Designating Isotopes, Designating Isotopes, continuedcontinued

mass number of chlorine-37 mass number of chlorine-37 atomic number of chlorine = atomic number of chlorine = number of neutrons in chlorine-37number of neutrons in chlorine-37

An atom of chlorine-37 is made up of 17 electrons, 17 protons, and 20 neutrons.

mass number atomic number = 37 (protons plus neutrons) 17 protons = 20 neutrons

Sample Problem A Solution, continued

Isotopes PracticeIsotopes PracticeList the number or Protons, Neutrons, and Electrons List the number or Protons, Neutrons, and Electrons

for each isotope.for each isotope.2525MgMg1212

2727AlAl1313

200200HgHg8080

5757FeFe2626

Write the symbol notation for Carbon-14, Sodium-24, and Calcium-40Write the symbol notation for Carbon-14, Sodium-24, and Calcium-40

Review and TermsReview and Terms

There are different names given to different There are different names given to different arrangements of protons, neutrons and arrangements of protons, neutrons and electronselectrons

A nuclide is an atom that has a specific A nuclide is an atom that has a specific combination of neutrons and protons (i.e. combination of neutrons and protons (i.e. U-238)U-238)

Ions – are atoms which have either a Ions – are atoms which have either a positive or negative charge (+ or -)positive or negative charge (+ or -)

Isotopes are atoms with different #’s of Isotopes are atoms with different #’s of neutronsneutrons

Atomic Structure Atomic Structure

Atomic # - is the number of protons in the Atomic # - is the number of protons in the nucleus of an atom, it is also how we find nucleus of an atom, it is also how we find elements on a periodic table ( Z )elements on a periodic table ( Z )

The Neutron number is given as ( N )The Neutron number is given as ( N ) Atomic Mass – is the number of protons Atomic Mass – is the number of protons

and neutrons found in an atom ( A ) and neutrons found in an atom ( A ) – 1 amu =1/12 mass of C-12

99.99% of the mass of an atom is found in 99.99% of the mass of an atom is found in the nucleusthe nucleus

Describing a Nuclide Describing a Nuclide

A nuclide can be described by specifying:A nuclide can be described by specifying:

1.1. The number of protons. ( Z )The number of protons. ( Z )

2.2. The number of neutrons ( N )The number of neutrons ( N )

3.3. The total number of protons and neutrons. The total number of protons and neutrons. Also known as the atomic mass ( A )Also known as the atomic mass ( A )

– A = Z + NA = Z + N

Describing a Nuclide Describing a Nuclide

For simplicity, it is more common to For simplicity, it is more common to ignore the atomic number and follow the ignore the atomic number and follow the symbol for the element with the mass symbol for the element with the mass number number

M - AM - A

MA

ZSymbol for the chemical element

Atomic Mass

Atomic Number

Symbolizing a Nuclide

Examples:

C12

6

6 protons and 6 neutrons, referred to as carbon twelve, also symbolized C-12

C13

6

6 protons and 7 neutrons, referred to as carbon thirteen, also symbolized C-13

C14

6

6 protons and 8 neutrons, referred to as carbon fourteen, also symbolized C-14