The Elements

Subatomic Particles The atom can be broken down into even smaller parts. The Proton is a positively charged particle that resides in the nucleus of an atom. The Neutron is a neutrally charged particle that adds mass to the nucleus. Electrons are negatively charged particles that orbit the nucleus in the electron cloud.

Es Elements Elements are groups of atoms that are all the same. Elements are defined by how many protons are in their nucleus. The element with 6 protons is known as Carbon. The number of protons is also called the Atomic Number of an element. The atomic number of Einsteinium is 99. This means there are 99 protons in an atom of Einsteinium. 99 Es Einsteinium Note: There are the same number of electrons as protons in every atom.

Elements Another important part of Chemistry is Chemical Symbols. Chemical Symbols are abbreviations used to identify the different elements. Some give clues to what the element is E.g. C-Carbon, He-Helium, F-Fluorine While others are derived from other languages E.g. Na-Sodium, W-Tungston, Pb-Lead Chemical symbols always have the first letter capitalized and the second letter is lower cased.

Elements The Atomic Mass Number of an element is the atomic mass rounded to a whole number It represents the number of protons plus the number of neutrons The Atomic Mass is the weighted average of all the isotopes of an element It is measured in atomic mass units (amu) Note: An isotope is an element with the same number of protons, but a different number of neutrons.

C Elements 6 12.01 Atomic Number Chemical Symbol Atomic Mass *So, the atomic mass number for Carbon would be 12

Elements Isotopes- Calculating the number of neutrons Isotopes have different numbers of neutrons in elements that have the same number of protons. To find the number of neutrons subtract the number of protons from the mass number. Mass number–number of protons = number of neutrons E.g. How many neutrons in Carbon-12 and Carbon-14? 12-6= 6 neutrons 14-6= 8 neutrons Both are carbon, but they do not have the same number of neutrons.

Elements Calculating the atomic mass Atomic mass can be calculated for an atom by multiplying the mass of each isotope by its percent abundance, then adding the results. E.g. The element neon has three isotopic forms: Neon-20 (90.92%), Neon-21 (0.257%), and Neon- 22 (8.82%). What is the atomic mass of neon? (.9092 x 20) + (0.00257 x 21) + (0.0882 x 22) = 20.2 amu Note: Make sure to change your percentage to a decimal. Amu= atomic mass units

Ions During chemical changes, atoms sometimes lose or gain electrons to form charged particles called ions. Atoms that gain electrons have a negative charge. These are called cations Depicted with a + sign and a number. E.g. Li+, Ca+2, Al+3 Atoms that lose electrons have a positive charge. These are called anions Depicted with a – sign and a number E.g. Cl-, O-2, N-3