Atoms, Atomic Number, Mass Number

Atoms Atoms are the building blocks of matter. All elements are made up of one type of atoms. All compounds are made up of two or more types of atoms that are chemically bonded to each other. Atoms consist of three main subatomic particles. These are protons, neutrons and electrons.

A comparative study of the sub-atomic particles Symbol Relative mass Relative charge Location Proton p 1 +1 nucleus Neutron n Electron e 1/2000 -1 outside

The proton Has +1 charge Has a relative mass of 1 Every atom must have at least one proton Atoms do not gain or lose protons in normal chemical reactions. The number of protons in an atom identifies the element

The neutron No charge (neutral or a charge of zero) Has a relative mass of 1 They are found in the nucleus Atoms do not gain or lose neutrons in normal chemical reactions The function of the neutron is to help stabilize the nucleus The PROTONS and NEUTRONS are contained in the middle of the atom in a region known as the NUCLEUS.

The ELECTRON: Has a -1 charge Has a relative mass of 1 / 2000 (mass of electron compared to that of a proton) Electrons circles AROUND the nucleus The Electrons are responsible for the chemical properties of atoms

Atomic Number Atomic Number gives the number of protons in the nucleus of an atom. This is represented by the symbol ‘Z’. This number helps us to identify the element to which the atom belongs.

Mass Number Mass number is the sum of number of protons and the neutrons. This is represented by the symbol ‘A’.

Atomic symbols Atomic symbols represent the atom of an element. The atomic symbol always consists of one or two letters from the name of the element.

Atomic symbols Element Symbol Some elements can be represented using only one letter This is the first letter of their English name. This letter is always written in capital Element Symbol Hydrogen H Phosphorus P Oxygen O Sulfur S Nitrogen N Boron B Carbon C Vanadium V Iodine I Fluorine F

Atomic symbols Symbols of some elements are made of two alphabets. These two may be the first and second or first and third letter of their English name. The first letter is always written in capital, the second is always written in lower case. Element Symbol Helium He Chlorine Cl Beryllium Be Manganese Mn Lithium Li Chromium Cr Calcium Ca Magnesium Mg Aluminum Al Silicon Si

Atomic symbols Some elements have symbols taken from their Latin (usually) names: Element Original Name Symbol Iron Ferrum (Latin) Fe Copper Cuprum (Latin) Cu Lead Plumbum (Latin) Pb Sodium Natrium (Latin) Na Potassium Kalium (Latin) K Silver Argentum (Latin) Ag Gold Aurum (Latin) Au Tin Stannum (Latin) Sn Mercury Hydrargyrum (Latin) Hg

Standard Atomic Notation The Standard Atomic Notation is a way to describe an element showing the elements symbol in the middle, the mass number and atomic number in the left corners (top and bottom).

Standard Atomic Notation For Example, for the element Chlorine, Chlorine is known by the Symbol ‘Cl’ Chlorine has an atomic number of 17 Chlorine has a mass number of 35 This information can be summarized as follows:

Standard Atomic Notation In general, for an element ‘X’ with atomic number ’Z’ and mass number ‘A’, the standard atomic notation is given as: The number of protons is equal to number of electrons in a neutral atom. The number of neutrons can be calculated using the formula (A-Z).

Summary: The ATOMIC NUMBER = # of protons in an Atom The MASS NUMBER = # of protons + neutrons The # of Neutrons = MASS Number – ATOMIC Number

All the above information about an atom of an element can be obtained from the Periodic Table of Elements

atomic # = # of protons = # of electrons (in an atom)

mass # = # of protons + # of neutrons Mass # is obtained by rounding the atomic mass value to a nearest whole number (read from the Periodic Table)

# neutrons = mass # - atomic #

Examples 79 79 118

17 17 38

30 30 35