grade 11 chemistry part 1

8/8/2019 Grade 11 Chemistry Part 1

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CHAPTER .1. The Electronic Structures of Atoms, Periodic Table

and Chemical Bonds

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1.Atomic Structure (or) Structure of an atom ( 1.1.

Fundamental Particles of Atoms ()Atoms: All materials are made up of tiny particles called atoms. The

atom of any element consists of three basic types of particles. They are

electrons , protons and neutrons .

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Electrons: are tiny, very light particles that have a negative electrical

charge (-).

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Protons: are much larger and heavier than electrons and have a positive

charge (+).


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Neutrons: are large and heavy like protons, however neutrons have no

electrical charge (or) neutral.

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1.2. Arrangement of Fundamental Particles in Atoms ( )Nucleus: is the centre of atom. The nucleus of the atom is composed of

two particles called neutrons and protons and one or more electrons are

surrounding the nucleus. Every neutral atom has an equal number of protons

and electrons.So, the whole of atom is just empty space (or) neutral.

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1.3. Atomic number ()The number of protons in the nucleus of an atom is called the atomic

number. It is represented by the symbol Z . The atomic number of an element

never changes, meaning that the number of protons in the nucleus of every

atom in an element is always the same.

Z


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1.4. Mass number()The mass number is the total number of neutrons and protons in the

nucleus of the atom. It is also called the nucleon number. It is represented by

the symbol A.

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A

The atomic number and the mass number of an element is usually written

in the following way. For Example, The oxygen atom has a atomic number of 8

and mass number of 12.


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1.5. Nucleon Number ( () )Protons and neutrons, also called nucleons, are located in the nucleus of

the atom. So,the total number of protons and neutrons in an atom is called

nucleon number. For example, the sodium atom has 11 protons and 12

neutrons.So, the nucleon number for the sodium atom is 11 + 12 = 23.

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1.6. Find the number of protons, electrons and neutrons( )To find the number of protons, electrons and neutrons in an atom, just

follow these easy steps:

Step 1 - Gather Information:The first step you will need to do is

find some information about your element. Go to the Periodic Table of

Elements and you can select your element from this table. Example, lets see in

the following element for krypton.

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Step 2 - The Number of Protons: The atomic number is the

number of protons in an atom of an element. Example, krypton's atomic

number is 36. This means that an atom of krypton has 36 protons in its nucleus.

There is that every atom of krypton contains 36 protons. If an atom doesn't

have 36 protons, it can't be an atom of krypton. Adding or removing protons

from the nucleus of an atom creates a different element. For example, removing

one proton from an atom of krypton creates an atom of bromine.

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Step 3 - The Number of Electrons: Atoms have no overall electrical

charge. That means that there must be a balance between the positively charged

protons and the negatively charged electrons. Every neutral atom has an equal


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number of protons and electrons. For example, the krypton atom has 36 protons

and 36 electrons and there is no overall charge.

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Electrons are arranged around atoms in a special way. An atom can gain

or lose electrons, becoming what is known as an ion. An ion is nothing more

than an electrically charged atom. Adding or removing electrons from an atom

does not change which element it is, just its net charge.

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Net Charge

For example, removing an electron from an atom of krypton forms a

krypton ion, which is usually written as Kr+. The plus sign means that this is a

positively charged ion. It is positively charged because a negatively charged

electron was removed from the atom. The 35 remaining electrons were

outnumbered by the 36 positively charged protons, resulting in a charge of +1.


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Kr+

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+1

Step 4 - The Number of Neutrons: The number of neutrons in an

element can also vary, and if two atoms of the same element have different

numbers of neutrons, then they are called isotopes.

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The any element is usually written as36

Kr , and when using the symbol

for the element instead of its full name: 36Kr or 12C or 26Al. The number is

called the mass number, and the mass number is equal to the sum of the

number of protons.


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36Kr

36Kr or 12C or 26Al

So if you want to find the number of neutrons, subtract the mass number

from the atomic number, and then you will get the number of neutrons. For

krypton atom, this equation becomes: Number of Neutrons = Mass Number -

Atomic Number = 84 - 36 = 48.

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=

=-=.

In this case, to find the number of protons, electrons and neutrons in an

atom, just remember these following methods.


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1.7. Isotopes ( Atoms of the same element with different numbers of neutrons (or)

masses are called isotopes. For example, the oxygen atoms naturally occur in 3

types of isotopes and they are all stable (non-radioactive). lets see in thefollowing table for three types of isotopes in an oxygen atoms.

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Table 1.1 Three types of isotopes in an oxygen atoms

isotopes p+ e Z n0 A

o816 8 8 8 8 16

o817 8 8 8 9 17

o818 8 8 8 10 18


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The notation of isotopes are usually written like this: XZA . Where, X isthe chemical symbol for the element, Z is the atomic number, and A is the

number of neutrons and protons combined, called the mass number.

() XZA

X

() Z A
http://www.colorado.edu/physics/2000/isotopes/iso_notation.htmlhttp://www.colorado.edu/physics/2000/periodic_table/atomic_number.htmlhttp://www.colorado.edu/physics/2000/periodic_table/atomic_number.htmlhttp://www.colorado.edu/physics/2000/isotopes/iso_notation.html

grade 11 chemistry part 1

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