Atomic Mass Number

The average atomic mass of the element takes the variations of the number of neutrons into account, and tells you the average mass per atom in a typical sample of that element. For example, the element silver (Ag) has two naturally occurring isotopes: Ag-107 and Ag-109 (or 107 Ag and 109 Ag). If you have mass number and atomic number, subtract the atomic number from the mass number to get the number of neutrons. ('Mass number') - ('atomic number')='number of neutrons'. There are: 9 protons 9 electrons 10 neutrons Fluorine is the element in question, as its atomic number is 9. You would name this particular isotope using the mass number. The atomic mass of Hydrogen is 1.00797 amu and the atomic mass of Carbon is 12.011 amu. The atomic mass is typically listed in the periodic table below the element's name. Since isotopes have a different number of neutrons, thier mass numbers and atomic masses differ. Periodic Table of Elements - The periodic table is a very useful listing of all 118 elements by symbol, atomic number, and atomic mass and molecular mass. Elements with similar chemical properties are called groups. Visit BYJUS to learn more about it. This two minute video shows how to read the periodic table. The terms 'atomic number' and 'atomic mass' are also defined. Find more free tutorials, videos.

Atomic Number and Mass Number

When you study the periodic table, the first thing that you may notice is the number that lies above the symbol. This number is known as the atomic number, which identifies the number of protons in the nucleus of ALL atoms in a given element.

The symbol for the atomic number is designated with the letter Z. For example, the atomic number (z) for sodium (Na) is 11. That means that all sodium atoms have 11 protons. If you change the atomic number to 12, you are no longer dealing with sodium atoms, but magnesium atoms. Hence, the atomic number defines the element in question.

Recall that the nuclei of most atoms contain neutrons as well as protons. Unlike protons, the number of neutrons is not absolutely fixed for most elements. Atoms that have the same number of protons, and hence the same atomic number, but different numbers of neutrons are called isotopes. All isotopes of an element have the same number of protons and electrons, which means they exhibit the same chemical behavior. Because different isotopes of the same element haves different number of neutrons, each of these isotopes will have a different mass number(A), which is the sum of the number of protons and the number of neutrons in the nucleus of an atom.

Mass Number(A) = Number of Protons + Number of Neutrons

The element carbon (C) has an atomic number of 6, which means that all neutral carbon atoms contain 6 protons and 6 electrons. In a typical sample of carbon-containing material, 98.89% of the carbon atoms also contain 6 neutrons, so each has a mass number of 12. An isotope of any element can be uniquely represented as ^A_ZX, where X is the atomic symbol of the element, A is the mass number and Z is the atomic number. The isotope of carbon that has 6 neutrons is therefore ¹²₆C. The subscript indicating the atomic number is actually redundant because the atomic symbol already uniquely specifies Z. Consequently, it is more often written as ¹²C, which is read as “carbon-12.” Nevertheless, the value of Z is commonly included in the notation for nuclear reactions because these reactions involve changes in Z.

When an atom has an atomic number of 6 and a mass number is 14 how many electrons and neutrons are in the atom?