1. Atoms, Atomic Number, Mass Number

2. 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.

3. 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

4. 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

5. 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.

6. 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

7. 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.

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

9. 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.

10. 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

11. 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

12. 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

13. 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).

14. 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:

15. 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).

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

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

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

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

21. # neutrons = mass # - atomic #

22. Examples 79 79
118

23. 17 17 38

24. 30 30 35