Atoms & Molecules

Atom and Molecules

Prepared By: Fahad And Arsalan

ATOM • An atom is the smallest unit that maintains the characteristics of an element – Nucleus- The center of the atom, contains protons and neutrons – Electron Cloud – Region surrounding the nucleus containing the

The Nucleus Proton- A positively charged sub-atomic particle (+).The number of protons is the same as the atomic number

Neutrons– A sub-atomic particle in the nucleus. Neutron do not have a charge (0)

3

Li 7

The Atomic Symbol The atomic massmass The atomic

The Electron Cloud • Electrons• • • •

The number of electrons equals the number of protons Sub-atomic particle with a negative charge (-) Mass of an electron is negligible Electrons behave as if in a 3-D orbit

• Valence Electrons – The outer most electrons – Valence electrons are responsible for bonding

Bohr Model • The first shell can have 2 electrons • The second can have 8 electrons

Shells and the Electron Cloud

Let’s look at a few elements…

Hydrogen

1= Proton 1= electron

Let’s look at a few elements… 3=protons

Lithium

4=neutrons 3=electrons

Let’s look at a few elements…

Argon

18=protons 22=neutrons 18=electrons

Isotopes 

Atoms of the same element with different number of neutrons

Isotopes of Hydrogen

Molecules

Molecules 

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A molecule is defined as a stable neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds . It can also be defined as a unit of two or more atoms held together by covalent bonds.

Types Of bonding 

Ionic Bond: Ionic bonds are formed when atoms become ions by gaining or losing electrons.

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Covalent Bond:

Covalent bonds form when atoms share electrons. Since electrons move very fast they can be shared, effectively filling or emptying the outer shells of the atoms involved in the bond. Such bonds are referred to as electron-sharing bonds.

 Guess

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