Electron Configurations - part III - Short hand notation - Valence electrons

Electron Configurations- part III

- Short hand notation- Valence electrons

Essential questions

Is there a way to write electron configuration even easier?

I’ve heard the valence electrons are the important – what are they and why?

Valence Electrons Valence electrons are the electron’s

located in the highest energy level These are the electrons that determine

the chemical properties of an element And these are the electrons involved in

chemical reactions and bonding!

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Valence ElectronsValence Electrons Valence electronsValence electrons = electrons in = electrons in ALLALL

the subshells with the highest the subshells with the highest principal energy shell (outermost principal energy shell (outermost shell)shell)

Core electronsCore electrons = = in lower energy in lower energy shellsshells

Atoms will try to either gain or lose electrons in order to get to a full or empty outer most shell

Shorthand NotationShorthand Notation A way of abbreviating long electron A way of abbreviating long electron

configurationsconfigurations Since we are only concerned about Since we are only concerned about

the outermost or valence electrons, the outermost or valence electrons, we can skip to the closest we can skip to the closest noble gasnoble gas and then finish the configurationand then finish the configuration

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The Noble Gas The Noble Gas Electron ConfigurationElectron Configuration

The noble gases have The noble gases have 88 valence electrons valence electrons except for He, which has only 2 electronsexcept for He, which has only 2 electrons

Noble gases are especially Noble gases are especially unreactiveunreactive He and Ne are practically inertHe and Ne are practically inert

Reason noble gases are unreactive is that Reason noble gases are unreactive is that the electron configuration of the noble the electron configuration of the noble gases is especially gases is especially stablestable

Shorthand NotationShorthand Notation Step 1: It’s the Showcase Showdown!Step 1: It’s the Showcase Showdown!

Find the closest Find the closest noble gasnoble gas to the atom (or ion), to the atom (or ion), WITHOUT GOING OVER the number of WITHOUT GOING OVER the number of electrons in the atom (or ion). Write the noble electrons in the atom (or ion). Write the noble gas in brackets [ ].gas in brackets [ ].

Step 2: Find where to resume by finding the next Step 2: Find where to resume by finding the next energy levelenergy level

Step 3: Resume the configuration until it’s Step 3: Resume the configuration until it’s finished.finished.

Step 4: Check by counting the Step 4: Check by counting the total numbertotal number of of electrons!electrons!

Shorthand NotationShorthand Notation Let’s try chlorineLet’s try chlorine

Step 1Step 1Step 2Step 2Step 3Step 3Step 4Step 4

Energy LevelsEnergy LevelsEnergy LevelsEnergy Levelsn = 1n = 1

n = 2n = 2

n = 3n = 3

n = 4n = 4

Let’s Practice

Work with a partner to write the electron configurations for the first 20 elements on your blank periodic table.

The first 2 has been done for you You can use the noble gas notation for

elements after Neon

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Electron Configurations andElectron Configurations andthe Periodic Tablethe Periodic Table

Take aways for shorthand Electron configurations

1. The number of protons equals the atomic number which equals number of electrons

2. The number of the highest energy level occupied by electrons equals the period number of the element.

Take aways for shorthand Electron configurations

3. The number of electrons in the highest used energy level (valence level) equals the roman numeral group number.

4. We can break up the periodic table in blocks that correspond to the ending configuration orbitals.

Orbitals and the Orbitals and the Periodic TablePeriodic Table

Orbitals grouped in s, p, d, and f orbitalsOrbitals grouped in s, p, d, and f orbitals

s orbitalss orbitals

p orbitalsp orbitals

d orbitalsd orbitals

f orbitalsf orbitals

What about valence electrons for transition metals? The general method for counting valence

electrons is generally not useful for the d-block transition metals.

Therefore, we will focus on s and p block elements.

Valence Electrons

Go back and write the number of valence electrons for each of first 20 elements you wrote the configuration for in the upper left corner of the box and circle it.

Li

Ions

Can you predict if the atoms will want to gain or lose electrons for fail to react chemically?

All atoms want to have full outermost energy levels

Go back and write the ion most likely to form in the upper right corner of each box.

See any trends?

Check for understandingCheck for understanding

carbon: 1scarbon: 1s222s2s222p2p22 = = 44

chlorine: 1schlorine: 1s222s2s222p2p663s3s223p3p55 = = 77

How many valence electrons does each How many valence electrons does each atom have?atom have?

magnesium: 1smagnesium: 1s222s2s222p2p663s3s22 = 2= 2

gallium: 1sgallium: 1s222s2s222p2p663s3s223p3p66 4s4s22dd10104p4p1 1 = 3= 3

Practice more

Let’s COMPLETE WORKSHEET 5-6 together

Electron Dot Notation

• If you want to see how atoms of one element will react, it is handy to have an easier way to represent the atoms and the electrons in their outer energy levels.

• An electric dot diagram is the symbol for the element surrounded by as many dots as there are valence electrons.

• # of dots = # of valence electrons

Electron Dot Diagrams

G.N. Lewis Also known as Lewis Dot Structures Named after G.N. Lewis, an American

chemist who developed the method while teaching chemistry class in 1902.

• Start by writing one dot to the right of the element symbol, then work your way around clockwise adding dots to the bottom, left, and top.

• Add a fifth dot to the right to make a pair. Continue in this manner until you reach eight dots to complete the level.

How to write them N

1. Electrons are now known to swarm around the nucleus of an atom in a configuration known as the _______.

A. electron circleB. electron cloudC. electron configurationD. electron swarm

The answer is B. The “cloud” includes all the regions where an electron might be found.

Check for understanding

What information can you learn from this diagram?

It tells you that nitrogen contains five electrons in its outer energy level.

Question 2

The _______ an energy level is from the nucleus, the ______ electrons it can hold.

A. closer, moreB. closer, lessC. farther, lessD. farther, more

The answer is D. The farthest shells contain the greatest number of electrons.

Question 3

Question 4

a. Write the shorthand electron configuration for arsenic (atomic number 33)

b. What block is it in?

c. How many valence electrons does it have?

d. Write the electron dot diagram.

Question 4

a. [Ar] 4s2 3d10 4p3

b. p-block

c. 3 valence electrons

d.

Work on your own

Write the electron dot diagrams for the first 20 elements on the periodic table in your packets.

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