Atomic Structure

Junior Science

Matter Refresher

•Matter is anything that takes up space and has mass.

• All matter is made of Atoms.

• Atoms are the building blocks of matter, like bricks are the building blocks of houses.

What are elements?

• Elements are the alphabet to the language of molecules.

• To make molecules, you need elements.

• Elements are made of atoms.

• Atoms have different weights and organisation, but they are all built in the same way.

So far we know…..

• Everything in existence is made up of tiny

particles called ATOMS.

• Substances which are made up of only one

type of atom are called ELEMENTS.

• Atoms of elements can join together to

form groups called COMPOUNDS and

MOLECULES.

And we know that…..

• Atoms are made smaller particles called

subatomic particles.

• In the middle of every atom is the NUCLEUS, which contains two types of subatomic particles called PROTONS and NEUTRONS.

• A third type called ELECTRONS (- charge) moves around the nucleus.

And we know that…..

• These subatomic particles have mass measured in Atomic Mass Units (AMU) and a charge.

• PROTONS 1 amu (+ charge)

• NEUTRONS 1 amu (0 charge)

• ELECTRONS 0 amu (- charge)

The Electron

• Electrons are negatively charged particles that surround the atom's nucleus.

• Electrons were discovered by J. J. Thomson in 1897.

• Electrons determine properties of the atom. Chemical reactions involve sharing or exchanging

electrons.

The Nucleus

• The nucleus is the central part of an atom. It is composed of protons and neutrons.

• The nucleus contains most of an atom's mass.

• It was discovered by Ernest Rutherford in 1911.

The Proton

• Protons are positively charged particles found in the atomic nucleus. Protons were discovered by Ernest Rutherford.

• Experiments done in the late 60's and 70's showed that protons are made from other particles called quarks. Protons are made from two 'up' quarks and one 'down' quark.

The Neutron

• Neutrons are uncharged particles found in the atomic nucleus.

• Neutrons were discovered by James Chadwick in 1932.

• Similar to protons neutrons are made from quarks. Neutrons are made from one 'up' quark and two 'down' quarks.

Atomic Number

• Atoms of different elements have different numbers of protons in their nucleus.

The number of PROTONS (+) in the nucleus of an atom is called the

ATOMIC NUMBER.

• The Atomic Number is a like a barcode for the element.

The smaller number always give the Atomic

Number

C6

12

Atomic Number

Atomic Mass Number

C 6

12

C6

12

Atomic Mass Number

• The more protons and neutrons in an atom the greater its mass.

The total number of protons (+) and neutrons (0) in an atom is called the

ATOMIC MASS NUMBER.

Atomic Nucleus

Electric Charges

• The sub-atomic particles which make up the atom are held together by

electric charges.

• PROTONS (+) ELECTRONS(-) NEUTRONS (0)

Atoms usually have the same number of (+) and (-) charges, so they are

electrically neutral.

Around the nucleus….

• Electrons exist at different energy levels, called SHELLS.

• Each shell holds a definite number of electrons.

How Many Electrons?

Energy Level Shell Letter Electron

Capacity

1 K 2

2 L 8

3 M 18

4 N 32

5 O 50

6 P 72

How many electrons fit in each shell

around an atom?The maximum number of electrons that can occupy a

specific energy level can be found using the following

formula:

Electron Capacity = 2n2

Bohr’s Energy Levels -Nitrogen

Nucleus of Nitrogen

7 Protons

7 Neutrons

7 protons (+ charge)

Therefore

7 electrons (- charge)

N= 2

8 Electrons

N= 1

2 Electrons

N7

14

EC = 2,5

Summary

• Atoms consist of Protons, Neutrons and Electrons.

• Protons and Neutrons are found in the nucleus of the Atom and have a mass of 1amu

• Electrons are found in shells or energy levels around the nucleus and have no mass.

• Protons have a positive charge (+), electrons have a negative (-) charge and neutrons have no charge (o).

• An atom will always have the same number of protons as electrons and thus will be electrically neutral.