University:
University of Arkansas
Course:
CHEM 1053 | Chemistry in the Modern World
Academic year:

2023
Views:

101

Pages:

1
Author:

madeleinejames20

Different elements are distinguished by the number of protons in the atom, which is called the element's atomic number. In the periodic table, elements are ordered according to increasing atomic number. Each element also has a chemical symbol representing the element. The chemical symbol can be one or two letters. The first letter is always capitalized and the second letter, if it's present, is lowercase. This periodic table shows the atomic number at the top, the chemical symbol in the middle, and the name of the element underneath. Many periodic tables will also include the atomic mass for an element. Remember that most of the atom's mass is found in the nucleus, which is composed of protons and neutrons. The electrons are much, much smaller. So the mass number for an atom is the sum of the protons and neutrons in the atom and is a rough estimate of the atom's mass. We said that the number of protons in the atom defines the element. Two atoms of the same element with different numbers of neutrons are called isotopes. We can represent isotopes in a few different ways. One way lists the mass number as the superscript and the atomic number as a subscript to the left of the chemical symbol. Sometimes the atomic number is also left off in this notation since the chemical symbol can be used to determine the number of protons in the atom from the periodic table. The second method lists the chemical symbol, then a dash, then the mass number. If electrons are added or removed from a neutral atom, the atom becomes an ion with either a positive or negative charge. In chemistry, we can only change the number of electrons an atom has; we cannot change the number of protons to make it into an ion. If we remove electrons from a neutral atom, it becomes a positively charged ion, or cation, since electrons are negative. If we add electrons to a neutral atom, it becomes a negatively charged ion, which is called an anion.