Structure of the Atom CHEM

Basic Parts of the Atom nucleus –the positively charged center of the atom nucleus –the positively charged center of the atom protons – positive charged particle with a relative mass of 1 protons – positive charged particle with a relative mass of 1 neutrons – neutrally charged particle in the nucleus with a relative mass of 1 neutrons – neutrally charged particle in the nucleus with a relative mass of 1 electron cloud – negatively charged, mostly empty space electron cloud – negatively charged, mostly empty space electrons – negatively charged particles with a relative mass of 1 / 1840 electrons – negatively charged particles with a relative mass of 1 / 1840

Atomic Structure

Forces in Atoms Electromagnetic Force: Electromagnetic Force: Like charges repel, opposite charges attract. Like charges repel, opposite charges attract. Strong Force: Strong Force: Opposes the electromagnetic force between protons in the nucleus. Opposes the electromagnetic force between protons in the nucleus. The strongest of the four forces, but only acts over short distances. The strongest of the four forces, but only acts over short distances. Weak Force: Weak Force: The force responsible for radioactive decay. The force responsible for radioactive decay. Gravity: Gravity: The force of attraction between all objects in the universe. The force of attraction between all objects in the universe. The weakest of the four forces. The weakest of the four forces.

Atomic Number The atomic number is equal to the number of protons in the nucleus of an atom This number is expressed as a whole number on the periodic table. This number is expressed as a whole number on the periodic table. Since + and - charges are equal in atoms, it is also the number of electrons Since + and - charges are equal in atoms, it is also the number of electrons

Mass Number The mass number is equal to the sum of the protons and neutrons in the nucleus of an atom. This number is expressed as a This number is expressed as a Number of neutrons in a atom = (mass number, as a whole number) - (atomic number) Number of neutrons in a atom = (mass number, as a whole number) - (atomic number) How many neutrons are in an atom of zinc? = 35 neutrons in Zn How many neutrons are in an atom of zinc? = 35 neutrons in Zn

Atomic Number and Mass Number

Isotopes Atoms which have the same number of protons with different amounts of neutrons. Carbon-12 has 6 neutrons, while Carbon- 14 has 8 neutrons. Carbon-12 has 6 neutrons, while Carbon- 14 has 8 neutrons. The mass number for an element on the periodic table represents the average for all the isotopes in a sample of the element. The mass number for an element on the periodic table represents the average for all the isotopes in a sample of the element.

Hydrogen has 3 common isotopes Carbon also has 3 common isotopes nuclide name 1)6p, 6nmass # = 12carbon )6p, 7nmass # = 13carbon )6p, 8nmass # = 14carbon

Isotopes

Atomic Mass The average mass of the mixture of an elements isotopes Atomic mass is measured in Atomic Mass Units where 1amu = (1/12) mass of carbon measured in grams. Atomic mass is measured in Atomic Mass Units where 1amu = (1/12) mass of carbon measured in grams. In order to find this average you need to know: In order to find this average you need to know: 1. number of stable isotopes of the atom 2. mass of isotopes 3. percent abundance in nature of isotopes

Atomic Mass Example: A sample of cesium is 75% 133 Cs, 20% 132 Cs, and 5% 134 Cs. Example: A sample of cesium is 75% 133 Cs, 20% 132 Cs, and 5% 134 Cs. What is its average atomic mass? What is its average atomic mass? Answer:.75 x 133 = Answer:.75 x 133 = x 132 = x 134 = 6.7 Total = amu Total = amu