An element having symbol 20X40 answer the following questions Write the atomic mass of an element
Answers
Atoms are the basic building blocks of everything around us. They come in different kinds, called elements, but each atom shares certain characteristics in common. All atoms have a dense central core called the atomic nucleus. Forming the nucleus are two kinds of particles: protons, which have a positive electrical charge, and neutrons, which have no charge. In addition to protons and neutrons, all atoms have electrons, negatively charged particles that move around in the space surrounding the positively-charged nuclear core. Electrons are usually depicted in drawings as much smaller than protons or neutrons because their mass is so much smaller. This mass comes from the nucleus. Each proton and neutron has about the same amount of mass, measured in daltons, or atomic mass units (amus). Because the unit of measure is defined by one proton, 1 proton = 1 neutron = 1 dalton = 1 amu.
1) Look Up Atomic Mass on the Periodic Table
If it's your first encounter with chemistry, your instructor will want you to learn how to use the periodic table to find the atomic mass (atomic weight) of an element. This number usually is given below an element's symbol.
2) Sum of Protons and Neutrons for a Single Atom
To calculate the atomic mass of a single atom of an element, add up the mass of protons and neutrons.
Example: Find the atomic mass of an isotope of carbon that has 7 neutrons. You can see from the periodic table that carbon has an atomic number of 6, which is its number of protons. The atomic mass of the atom is the mass of the protons plus the mass of the neutrons, 6 + 7, or 13.
3) Weighted Average for All Atoms of an Element
The atomic mass of an element is a weighted average of all the element's isotopes based on their natural abundance. It is simple to calculate the atomic mass of an element with these steps.
Typically, in these problems, you are provided with a list of isotopes with their mass and their natural abundance either as a decimal or percent value.
Multiply each isotope's mass by its abundance. If your abundance is a percent, divide your answer by 100.
Add these values together.
The answer is the total atomic mass or atomic weight of the element.
Example: You are given a sample containing 98% carbon-12 and 2% carbon-13. What is the relative atomic mass of the element?
First, convert the percentages to decimal values by dividing each percentage by 100. The sample becomes 0.98 carbon-12 and 0.02 carbon-13. (Tip: You can check your math by making certain the decimals add up to 1. 0.98 + 0.02 = 1.00).
Next, multiply the atomic mass of each isotope by the proportion of the element in the sample:
0.98 x 12 = 11.76
0.02 x 13 = 0.26
For the final answer, add these together:
11.76 + 0.26 = 12.02 g/mol
Advanced Note: This atomic mass is slightly higher than the value given in the periodic table for the element carbon. What does this tell you? The sample you were given to analyze contained more carbon-13 than average. You know this because your relative atomic mass is higher than the periodic table value, even though the periodic table number includes heavier isotopes, such as carbon-14.
Over time, you may notice the atomic mass values listed for each element on the periodic table may change slightly.
Because of their shared negative charge, electrons repel one another if they get too close. At the same time, electrons are attracted to the positive charge of the nucleus. Although electrons have plenty of space, they all want to be closest to the positive nuclear charge that is attracting them. This space is called the first energy shell. If there are three electrons in an atom, the first two will be found in the first energy shell. The third electron will have to settle for the second energy shell, a three-dimensional space a little farther from the nucleus, where it will be alone. In this example, the lone electron is called a valence electron, and the outermost energy shell that contains any electrons is called the valence shell.
The second energy shell is big enough to hold as many as eight electrons, grouped in pairs inside four electron orbitals, or spaces where electrons spend most of their time.When an energy shell is incompletely filled, the electron(s) in that shell are not as stable and are more likely to react.