The periodic table and atomic theory

Today we will analyze atoms, see how many protons they have, how many electrons, neutrons and so on….in science this is referred to as: Atomic Analysis
Atomic Analysis = finding the number of protons, neutrons, and electrons in an atom of an element

 Atomic number =
= number of protons (He = 2) number of electrons (He = 2)
Electrons=protons only and onllllllly in a neutral atom .
How do you know it’s neutral? It does NOT have any ion charge!!!
 Atomic mass = number of protons + number of neutrons
4 = 2 + 2

Name Atomic mass
Number of protons
(Atomic number)
Number of electrons
Number of neutrons
K
V
Cl

• So we know how many protons, electrons and neutrons each atom has….
• Well, where do we find them? Can we draw them?
p+ n e

See page 64 - 65
Bohr models show electron arrangement in shells

Drawing Bohr Diagrams
Bohr diagrams map out the number of protons, neutrons, and electrons in an atom.
Step 1: Draw the nucleus with the number of protons and neutrons
Step 2: Draw the electrons in their shells o 1st shell fills with 2 electrons o 2nd shell fills with 8 electrons o 3rd shell fills with 8 electrons o 4th shell fills with 18 electrons
K p= 19 n=20
K p= 19 n=20
 The outside shell is called the valence shell
 The electrons in the valence shell are called valence electrons

Together: Draw the Bohr diagram for the following

Draw the Bohr diagram for the following

1) Chemical families on the periodic table have the same number of valence electrons
2) Elements in the same period have the same number of shells
3) Period number indicates the number of electron shells
See page 66

Valence Electrons: Total number of electrons in the most outer shells that can participate in a chemical bond.
Atom
Group
K
I
Ca
2
Ga
13
Ge
14
As
15
Se
16
Br
17
Kr
18
# of valence e-

A TOMS LIKE TO BE AS STABLE AS POSSIBLE

All the elements on the periodic table are neutral atoms. Meaning, they have not gained or lost any electrons.

However, all these elements tend to lose or gain electrons to become as stable as possible!

When neutral atoms lose or gain electrons, they become _____________

S O HOW DO ATOMS BECOME STABLE ?
Let us take a look at the noble gases
Noble gases are very unreactive because their atoms have _______ valence shells.
Filled shells make atoms __________
Filled means the atom has 2,8, or 18 electrons in the valence shell!
But atoms with unfilled shells tend to lose or gain electrons to become filled.

See pages 66 - 67
Atoms, other than the noble gases, gain or lose electrons in order to achieve the stability of noble gases.
Gaining or losing electrons makes atoms into ions .

If an atom has 1,2,3 electrons in the valence shell, it will tend to _____ electrons to become stable.
If an atom has 4,5,6,7 electrons in the valence shell, it will tend to ______ electrons to become stable.
If an atom has 8 electrons ?
Wellllll…it’s already stable!!!  unreactive! Like all the noble gases.

When an atom
, it gets a positive charge. It becomes a positive ion .
Ca
When an atom
, it gets a negative charge. It becomes a negative ion .
O

N
Be

See pages 66 - 67
1. Metals lose electrons to form positive ions
2. Non-metals gain electrons to form negative ions
3. Ions have a similar electron arrangement to the nearest noble gas
There is a nice trend on the periodic table to help you out  let’s see what it is!

Ca
Br
O
Na

Worksheet 2.3