🗊Презентация Atomic number, Mass number and Isotopes

Atomic number, Mass number and Isotopes

Information about an element

Let’s take Li atom for an example: Let’s take Li atom for an example:

Atomic number and Mass Number The number of protons in a given atom is called the atomic number, or the proton number, Z. The number of electrons in the atom is also equal to Z because the atom is electrically neutral. The total number of protons and neutrons in an atom is called the mass number, A. The number of neutrons, the neutron number, is A - Z. An electron carries an atomic unit of negative charge, a proton carries an atomic unit of positive charge, and a neutron is electrically neutral.

Atomic number and Mass Number

Number of electrons An atom is neutral. The net charge is zero. Therefore, Number of protons = Number of electrons Atomic number = Number of electrons For chlorine (Cl), Atomic number = Number of electrons = 17

Isotopes同位素 They are atoms of the same element that have different numbers of neutrons. Hydrogen has 3 isotopes.

Isotopes Hydrogen has 3 isotopes.

Isotopes Hydrogen has 3 isotopes.

Cation and Anion An ion is an atom, or group of atoms, that has a net positive or negative charge. cation – ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. anion – ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion.

Cation and Anion A monatomic ion contains only one atom eg. Na+, Cl-, Ca2+, O2-, Al3+, N3- A polyatomic ion contains more than one atom eg. OH-, CN-, NH4+, NO3-

Why does the atomic mass on the periodic table have so many decimal places?

Atomic mass

Calculating a “weighted” average

Calculating a “weighted” average A sample of magnesium collected anywhere in the universe will contain three isotopes of magnesium.

Calculating a “weighted” average

Calculating a “weighted” average Atomic mass of magnesium = 23.985045 x 78.90% + 24.985839 x 10.00% + 25.982595 x 11.10% = 24.30685245 amu

For your reference

Another example Cl-35 is about 75.5 % and Cl-37 about 24.5% of natural chlorine.

Exercise Copper has two isotopes 63Cu (62.9 amu) and 65Cu (64.9 amu). What is the % abundance of isotope 63Cu? (Hint: Check periodic table for atomic mass) 1) 30% 2) 70% 3) 100%

Radioactive isotope Radioactive isotope, also called radioisotope, any of several species of the same chemical element with different masses whose nuclei are unstable and dissipate excess energy by spontaneously emitting radiation in the form of alpha, beta, and gamma rays. Radioactive isotopes have many useful applications. In medicine, for example, cobalt-60 is extensively employed as a radiation source to arrest the development of cancer. In industry, radioactive isotopes of various kinds are used for measuring the thickness of metal or plastic sheets. Other significant applications include the use of radioactive isotopes as compact sources of electrical power—e.g. plutonium-238 in cardiac pacemakers and spacecraft.

Radioactive isotope The table lists some naturally occurring radioactive isotopes. http://www.youtube.com/watch?v=E4B94zCY4ok