CHEM1011 Lecture Notes - Lecture 9: Avogadro Constant, Molar Mass, Sodium Chloride

-Isotopes are represented by the symbol , where Z is the atomic number, A is the mass number, and E is the elemental symbol. . Write symbol that represents an isotope of nickel that contains 28 protons and 32 neutrons in the nucleus. Isotopes are also represented by the notation: Name-A, where Name is the name of the of the isotope. An example of this isotope notation is magnesium-26. This represents an isotope of The extremely small size of atoms and molecules makes it inconvenient to use their element and A is the magnesium that has a mass number of 26 · actual masses for measurements or calculations. Relative masses are used instead. Relative masses are comparisons of actual masses to each other. For example, if an object had twice the mass of another object, their relative masses would be 2 to 1 . 35 ,1#of protons CI # f neutrons 17 18-20 chioine 3545 #of electrons 17 17 . An is a unit used to express the relative masses of atoms. One atomic mass unit is equal to 1/12 the mass of a carbon-12 atom. A carbon-12 atom has a relative mass of 12 u. . An atom with a mass equal to 1/12 the mass of a carbon-12 atom would have a relative .An atom with a mass equal to twice the mass of a carbon-12 atom would have a relative . The atomic weight of an element is the relative mass of an average atom of the element mass of 1 u. mass of 24 u. expressed in atomic mass units. Atomic weights are the numbers given at the bottom of the box containing the symbol of each element in the periodic table. of nitrogen atoms (N) is 14.0 u, and that of According to the periodic table, the silicon atoms (Si) isu .