Unit 3: Atoms, Elements and Compounds

3.1 Atomic Structure and Periodic Table

Introduction: All Substances are made of Atoms

A substance that has only kind (type) of atoms is called an Element

Atoms are made up of three fundamental particles: Protons, Neutrons and Electrons.

An atom consists of a small central nucleus (Protons & Neutrons) and around the nucleus you will find electrons which are revolving around the nucleus in shell/orbits.

Atoms are neutral (Have no charge) because the number of protons = the number of electrons

Created and Published by Mayur PatelDepartment of Chemistry (2013-2014)High School Attached to Harbin Institute of Technology

Symbols: All atoms are represented by a symbol

- Some have a capital letter

- Some have a Capital letter followed by a small case letter

Created and Published by Mayur PatelDepartment of Chemistry (2013-2014)High School Attached to Harbin Institute of Technology

Protons:

- Protons have a positive charge

- Atoms of the same element have the same number of protons

- In a Neutral atom, the number of protons = number of electrons

Neutrons:

- Neutrons have no charge

- Atoms of the same elements can have different number of neutrons

- So, atoms that have the same number of protons but different number of neutrons are called ISOTOPES

Created and Published by Mayur PatelDepartment of Chemistry (2013-2014)High School Attached to Harbin Institute of Technology

Electrons:

- Electrons have a negative charge

- They are outside the nucleus in the shells

- Electrons are responsible for the chemical properties of an element

- Every shell can have a certain maximum number of electrons

Created and Published by Mayur PatelDepartment of Chemistry (2013-2014)High School Attached to Harbin Institute of Technology

Electronic Configuration:

The arrangement of electrons in an atom is called Electronic Configuration

Eg: the electronic configuration of Calcium is 2,8,8,2

Eg: The electronic configuration of Magnesium is 2,8,2

Electron Configuration

Electron configuration up to 20 electrons

1st2nd

3rd4th

Nucleus

ElectronsShells

1st Shell: 2 electrons2nd Shell: 8 electrons3rd Shell: 8 electrons4th Shell: 2 electrons

Created and Published by Mayur PatelDepartment of Chemistry (2013-2014)High School Attached to Harbin Institute of Technology

Noble Gas Configuration

Atoms that have a completely filled outermost orbit are called Noble Gases/ Inert Gases/ Non Reactive Gases. Eg: He, Ne, Ar……….

Valence Electrons

The electrons in the outermost shell are called valence electrons.

Created and Published by Mayur PatelDepartment of Chemistry (2013-2014)High School Attached to Harbin Institute of Technology