Atomic number (Z):
always an integer and is equal to the number of protons in the nucleus
Mass number (A):
equal to the total number of nucleons (protons and neutrons) in a nucleus.
immediately left to the chemical symbol, the mass number and atomic number can be read top to bottom, respectively.
atoms of the same element that have different mass numbers; same number of protons, different number of neutrons;
Isotopes generally exhibit the same chemical properties
generic term used to refer to any radioactive isotope, especially those used in nuclear medicine
The atomic mass of an atom is simply equal to:
its mass number (A)
the mass in grams of one mole of atoms of a given element. Expressed g/mol
Nuclear binding energy is:
the amount of energy that is released when nucleons (protons and neutrons) bind together through strong nuclear force
Mass defect is:
the difference between the mass of the unbound constituents and the mass of the bound constituents in the nucleus
Unbound constituents in the nucleus have:
more energy and more mass than the bound constituents
Mass defect is the amount of mass converted to energy through:
the nuclear reactions of fusion or fission
occurs when small nuclei combine into larger nuclei
occurs when a large nucleus splits into smaller nuclei; rarely spontaneous; when a nucleus absorbs a low energy neutron, a chain reaction can occur
Energy is released in both fusion and fission because:
the nuclei formed in both processes are more stable than the starting nuclei
Alpha decay is:
Loss of a 4-He nucleus (2 protons and 2 neutrons). Mass number decreases by 4 and atomic number decreases by 2.
Beta decay is:
Loss of an electron (e- or β-). Emitted when a neutron in the nucleus decays into a proton and an antineutrino (β-). A neutron is lost and a proton takes its place. Mass number remains the same and atomic number increases by one.
Positron decay is:
when a proton splits into a positron (β+) and a neutron. A proton is lost and the mass number remains the same.
Gamma decay is :
the emission of a gamma photon. The energy of the parent nucleus is lowered, but the mass and atomic number remain the same.
Electron capture is:
When a radionuclide captures an inner electron that combines with a proton to form a neutron. Atomic number is one less and mass number remains the same.
the amount of time required for half of a sample of radioactive nuclei to decay
T1/2 = 0.693/λ
The rate at which radioactive nuclei decay is proportional to:
the number of nuclei that remain
The more binding energy per nucleon released, the more:
stable the nucleus
Equation for exponential decay:
n = noe-λt
Equation to determine the mass lost as binding energy in a nucleus:
E = mc2
where m is the mass of c is the speed of light
When protons and neutrons come together to form the nucleus, they are attracted to each other by:
the strong nuclear force
The most stable atom according to binding energy per nucleon is:
in general, intermediate-sized nuclei are more stable than large and small nuclei