Mass Number Definition and Examples

Mass Number Definition and Examples Mass number is an  integer (whole number) equal to the sum of the number of protons and neutrons of an atomic nucleus. In other words, it is the sum of the number of nucleons in an atom. Mass number is often denoted using a capital letter A. Contrast this with the atomic number, which is simply the number of protons. Electrons are excluded from the mass number because their mass is so much smaller than that of protons and neutrons that they dont really affect the value. Examples 3717Cl has a mass number of 37. Its nucleus contains 17 protons and 20 neutrons. The mass number of carbon-13 is 13. When a number is given following an element name, this is its isotope, which basically states the mass number. To find the number of neutrons in an atom of the isotope, simply subtract the number of protons (atomic number). So, carbon-13 has 7 neutrons, because carbon has atomic number 6. Mass Defect Mass number only gives an estimate of isotope mass in atomic mass units (amu).The isotopic mass of carbon-12 is correct because the atomic mass unit is defined as 1/12 of the mass of this isotope. For other isotopes, mass is within about 0.1 amu of the mass number. The reason there is a difference is because of mass defect, which occurs because neutrons are slightly heavier than protons and because the nuclear binding energy is not constant between nuclei.

Christmas Chemistry - Make Peppermint Cream Wafers

Christmas Chemistry - Make Peppermint Cream Wafers Cooking is really an artistic variation of chemistry! Heres a fun and easy Christmas holiday project for the chemistry lab. Make these peppermint cream wafers for a seasonal project or demonstration. Difficulty: Average Time Required: 30 minutes Peppermint Water Materials sucrose (table sugar)concentrated liquid sucrose (or Karo syrup)potassium tartrate (cream of tartar)lactose (we will use milk)food coloringoil of peppermint250 ml beaker or a saucepancandy thermometer or other metal-backed thermometeraluminum foilassorted labware or utensils for stirring, etc. Procedure First, make sure all of the measuring utensils and glassware are clean and dry. If possible, use beakers that have never been used for more tradition chemistry experiments, since residues of chemicals can remain in the glass.Measure and mix the following chemicals in a 250-ml beaker: 1/4 cup or 2 tablespoons or 2 level medicine cups of sugar; 8 ml (1.5 tsp) milk; 10 ml (2 tsp) Karo syrup; 1/4 tsp or pea-sized amount of cream of tartar.Heat the mixture until its temperature reaches 200Â °F, stirring often.Once the temperature reaches 200Â °F, cover the beaker (with foil) and remove it from the heat for 2 minutes.Return the mixture to the heat. Heat and stir until the temperature reaches 240Â °F (soft-ball on a candy thermometer).Remove the mixure from heat and add one drop of peppermint oil and 1-2 drops of food coloring.Stir until the mixture is smooth, but not any longer than that or else the candy could harden in the beaker. Avoid stirring longer than 15-20 seconds.Pour coin-siz ed drops of the mixture onto a sheet of foil. Depending on the size of the drops, you will get 8-12 of them. Allow the candy to cool, then peel the drops off to enjoy your treat! Hot water is sufficient for clean-up. Tips You can use wooden tongue depressors or metal spoons for stirring.Disposable plastic measuring cups, such as those used to dispense liquid medications, work well for measuring the ingredients for a lab of students.The mixture can be heated over a hotplate or a bunsen burner, with a ring stand and wire gauze pad. You could also use a stove.The texture of the finished product depends on the heating/cooling of the sugar mixture. You could get jellied candies or rock candy. Its a nice opportunity to discuss crystal structures.