Figure 3.9: A nuclear atom viewed in 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. n p p n n p
Atomic Structure The # of protons determine the type of element it is and it’s chemical/physical characteristics There are three characteristics that can be discussed about each particle – Charge – Mass – Location
Atomic Structure Protons have a positive charge (+), an atomic mass of 1.0073 and are found in the nucleus Electrons have a negative charge (-), an atomic mass of 0.000549 and are found in the electron cloud Neutrons have no charge (ø), an atomic mass of 1.0087 and are found in the nucleus
The Structure of the Atom, continuedSurrounding the nucleus is a region occupied by negatively charged particles called electrons.Protons, neutrons, and electrons are often referred to as subatomic particles.
Composition of the Atomic Nucleus Except for the nucleus of the simplest type of hydrogen atom, all atomic nuclei are made of protons and neutrons. A proton has a positive charge equal in magnitude to the negative charge of an electron. Atoms are electrically neutral because they contain equal numbers of protons and electrons. A neutron is electrically neutral.
Composition of the Atomic Nucleus, continued The nuclei of atoms of different elements differ in their number of protons and therefore in the amount of positive charge they possess. Thus, the number of protons determines that atom’s identity.
Composition of the Atomic Nucleus, continued Forces in the Nucleus When two protons are extremely close to each other, there is a strong attraction between them. A similar attraction exists when neutrons are very close to each other or when protons and neutrons are very close together. The short-range proton-neutron, proton-proton, and neutron- neutron forces that hold the nuclear particles together are referred to as nuclear forces.
Atomic Number Atoms of different elements have different numbers of protons. Atoms of the same element all have the same number of protons. The atomic number (Z) of an element is the number of protons of each atom of that element.
Isotopes Isotopes are atoms of the same element that have different masses. The isotopes of a particular element all have the same number of protons and electrons but different numbers of neutrons. Most of the elements consist of mixtures of isotopes.
Designating Isotopes Hyphen notation: The mass number is written with a hyphen after the name of the element. uranium-235 Nuclear symbol: The superscript indicates the mass number and the subscript indicates the atomic number. 235 92 U
Designating Isotopes, continued The number of neutrons is found by subtracting the atomic number from the mass number. mass number − atomic number = number of neutrons 235 (protons + neutrons) − 92 protons = 143 neutrons Nuclide is a general term for a specific isotope of an element.
Designating Isotopes, continuedSample Problem AHow many protons, electrons, and neutrons are there in an atom ofchlorine-37?
Designating Isotopes, continued Sample Problem A Solution Unknown: numbers of protons, electrons, and neutronsGiven: name and mass number of chlorine-37 Solution: atomic number = number of protons = number of electrons mass number = number of neutrons + number of protons
Designating Isotopes, continued Sample Problem A Solution, continuedmass number of chlorine-37 − atomic number of chlorine =number of neutrons in chlorine-37 mass number − atomic number = 37 (protons plus neutrons) − 17 protons = 20 neutrons An atom of chlorine-37 is made up of 17 electrons, 17 protons, and 20 neutrons.
Isotopes Practice List the number or Protons, Neutrons, and Electrons for each isotope. Mg2512 Al2713200 Hg80 Fe5726
Review and Terms There are different names given to different arrangements of protons, neutrons and electrons A nuclide is an atom that has a specific combination of neutrons and protons (i.e. U-238) Ions – are atoms which have either a positive or negative charge (+ or -) Isotopes are atoms with different #’s of neutrons
Atomic Structure Atomic # - is the number of protons in the nucleus of an atom, it is also how we find elements on a periodic table ( Z ) The Neutron number is given as ( N ) Atomic Mass – is the number of protons 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 the nucleus
Describing a Nuclide A nuclide can be described by specifying:1. The number of protons. ( Z )2. The number of neutrons ( N )3. The total number of protons and neutrons. Also known as the atomic mass ( A ) – A=Z+N
Describing a Nuclide Atomic Mass A ZM Symbol for the chemical Atomic Number element For simplicity, it is more common to ignore the atomic number and follow the symbol for the element with the mass number M-A
Symbolizing a NuclideExamples: 12 6 protons and 6 neutrons, referred to as C carbon twelve, also symbolized C-12 6 13 6 protons and 7 neutrons, referred to as C carbon thirteen, also symbolized C-13 6 14 6 protons and 8 neutrons, referred to as C carbon fourteen, also symbolized C-14 6