Atomic Structure and the

Periodic Table

Atomic Structure

Atoms are made of three particles:

1. Protons = positive

2. Neutrons = neutral

3. Electrons = negative

The protons and neutrons are in the center of

the atom (the nucleus)

Electrons buzz around in a cloud around

the nucleus

Atomic Structure

Periodic Table

Different kinds of atoms make different elements

Elements are organized in the Periodic Table

Printed on a Periodic Table are several important

pieces of information

Periodic Table

Periodic Table

A lot of thought went into how the Periodic Table is

organized

● They are arranged in order of number of

electrons

● Columns (groups) have similar chemical and

physical properties○ Also have same number of valence electrons

● Rows (periods) have the same number of

electron layers

● Elements are also arranged by how metallic

they are○ Metals to the left, non-metals to the right

Periodic Table

Metalloids

Periodic Table

Periodic Table

Atomic

Symbol

Atomic

Number

Protons Neutrons Electrons Atomic Mass

B 5 5 6 5 11

Look at the example below which is completed for the element Boron. For the following, complete the table following this example.

Periodic Table

Atomic

Symbol

Atomic

Number

Protons Neutrons Electrons Atomic Mass

11 24

Complete the missing parts of the table below using the Periodic Table to identify the element symbol and the number of subatomic particles for that element.

Periodic Table

Atomic

Symbol

Atomic

Number

Protons Neutrons Electrons Atomic Mass

31 37

Complete the missing parts of the table below using the Periodic Table to identify the element symbol and the number of subatomic particles for that element.

Atomic Structure

Let’s break that down a bit….

● The classic model of an atom (the Bohr model) has protons and neutrons in

the middle, surrounded by circling electrons

Atomic Structure

● In the Bohr model, electrons stay in rings called “orbitals”

● Each shell (layer of ring outside the nucleus) can only have a certain number of electrons

Atomic Structure

Shells on the Periodic Table. Each ‘shell’ is one full ring around the nucleus. Each

additional shell is a full circle around the outside of the first. The number of shells

depends on the ‘period’ (horizontal row) the element is in on the Periodic Table. Look at

the pictures below. Can you identify how many shells an element in the 4th period down

(light blue) would have?

Atomic Structure

● The outermost shell (ring/orbital) contains special

electrons called valence electrons

● These electrons are very important because they

determine how reactive the atom is (how likely it is to

bond or join with another atom)

○ A full shell means the atom cannot react with another atom

○ Having 8 electrons = a full shell

○ Atoms want to have as many electrons in the outer shell as possible

because they want to be “stable”

Atomic Structure

Valence electrons (electrons in the outer shell) can be identified by the

column number on the Periodic Table, as seen below. Elements in the first

vertical column have ONE valence electron (we do not look at the middle

chunk of elements for this trend).