2.3

2.3

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

Things to know

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 neutrons4 = 2 + 2

Name Atomic massNumber of

protons (Atomic number)

Number of electrons

Number of neutrons

K

V

Cl

So let’s talk about location now!

• So we know how many protons, electrons and neutrons each atom has….

• Well, where do we find them? Can we draw them?

p+ ne

Bohr Diagrams

Bohr models show electron arrangement in shells

See page 64 - 65

Drawing Bohr DiagramsBohr 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 shellso1st shell fills with 2 electronso2nd shell fills with 8 electronso3rd shell fills with 8 electronso4th shell fills with 18 electrons

Kp= 19n=20

Kp= 19n=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

Try: Draw the Bohr diagram for the following

Bohr Model Patterns1) Chemical families on the periodic table have the same

number of valence electrons2) Elements in the same period have the same number of shells3) 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-

ATOMS 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 _____________

SO HOW DO ATOMS BECOME STABLE?

Let us take a look at the noble gases

Noble gases are very unreactive because their atomshave _______ 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.

Atom Stability

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.

See pages 66 - 67

To gain or to lose, that is the question!

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.

ION CHARGESWhen an atom loses electrons, it gets a positive charge. It becomes a positive ion. Ca

When an atom gains electrons, it gets a negative charge. It becomes a negative ion. O

What is the ion charge for?

N

Be

Atom Stability

1. Metals lose electrons to form positive ions2. Non-metals gain electrons to form negative ions3. 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!

See pages 66 - 67

How to figure out ion charges using the

periodic table

Give the ion charges for the following

Ca

Br

O

Na

Homework

Worksheet 2.3