How do you determine overall polarity of a molecule?
Two things need to be considered to determine if a molecule is polar or not. The first thing that needs to be determined is if the bonds within the molecule are polar. To determine whether or not a bond is polar, you need to find the difference in electronegativity values of the atoms in each bond. Although the cut off values for polarity is not set (they can be a little different depending on the textbook), generally if the electronegativity difference is 0.4 or less, the bond is non-polar. If the value is greater than 0.4, the bond is said to be polar. The next thing that needs to be determined is the shape of the molecule. Once the shape has been determined, you will need to look at whether the shape is symmetrical or asymmetrical. If symmetrical and all the bonds are the same polarity, the compound will be non-polar. If the polarities are not the same, the overall molecule will be polar. If the molecule is asymmetrical and has polar bonds, it will be a polar molecule.
How do you find the number of protons, neutrons, and electrons in an isotope?
In a neutral isotope, the number of protons and electrons will be the same. This number can be found on the periodic table. The atomic number (the whole number with each element) gives the number of protons in each element. The number of neutrons can be found by subtracting the atomic number from the mass number. When given an isotope, you should also be given a number with the name of the element (for example, Uranium-235). This number is the mass number and is equal to the number of protons plus the number of neutrons.
What is the difference between a mixture and a pure substance?
The main difference between the two types of matter is the types and numbers of particles. In a mixture, there are more than one type of particle and in a substance there is only one type of particle. There are two different types of mixtures, heterogeneous and homogeneous. In a heterogeneous mixture the different types of particles are easily distinguished and usually separated (for example as in Italian dressing). In a homogeneous mixture the particles are distributed evenly and difficult to easily distinguish from each other (for example as in salt water). There are also two different types of pure substances, elements and compounds. In an element, there is only one type of particle that can not be broken down further except through nuclear reactions. There are currently 118 different types of elements. These are all listed on the periodic table. Compounds are made up of two or more elements that are chemical bonded together and can only be separated by a chemical reaction. An example of a compound is common table salt, sodium chloride.