Electron ConfigurationsChemistry 1d - Students know how to use the periodic table to determine the number of electrons available

for bonding.

Review...How to identify an element: - Look at the protonsHow to find protons:- Look at the atomic numberHow to find neutrons:- Subtract atomic mass from atomic number (the #

of protons)How to find electrons in a neutral (no charge) atom :- Always equals the number of protons

• Atomic number tells us how many electrons an atom has in a neutral atom

• Valence electrons (the outermost e-) are known by looking at the elements’ family/group

The Periodic Table and Electrons

But how do we know where all

an element’s electrons are

found?

• Arrangement of the periodic table which tells us where each electron in an atom is located (which energy level and sublevel) and explains how electrons fill an atom

Electron Configurations

-Nucleus

Which Orbital do I go to?

Negative electron

Energy Levels• Rows/Periods = Energy

Levels (7 on PT)• Energy levels are divided

into sublevels (s, p, d, f)• Sublevels are divided into a

shape of space called orbitals

• Each orbital/shape can ONLY hold 2 electrons!

s, p, d, f Blocks• The periodic table can be divided into sections

called blocks (energy sublevels)• 4 blocks/sublevels = s, p, d, f• s, p, d, f sublevels are divided into orbitals• s = 1 shape • p = 3 shapes • d = 5 shapes • f = 7 shapes

Remember…S, P, D, & F blocks refer to the shape of the

orbital in which electrons are

found!

Helium is moved over by Hydrogen s-BLOCK p-BLOCKd-BLOCK

f-BLOCK

s-BLOCK p-BLOCKd-BLOCK

f-BLOCK

How many electrons can fit in each Orbital?

Just Count the # of Elements in each

Block!

s-BLOCK

d-BLOCK

f-BLOCK

p-BLOCK2 ELECTRONS

6 Electrons

10 Electrons

14 Electrons

How many electrons are in each block?

• s-block = 2 electrons• p-block = 6 electrons• d-block = 10 electrons• f-block = 14 electrons

Just count the # of

elements in each block!

1. N = 1 (1st row/energy level): • Smallest energy level• Can only hold 2 electrons (2 = s-block)2. N = 2 (2nd row/energy level): • A little larger than the first• Can only hold 8 electrons (2 = s-block; 6 = p-

block)

How many electrons per energy level (row)?

3. N = 3 (3rd row/energy level): • A little larger than the second• Can hold 18 electrons (2 = s-Block; 6 = p-Block;

10 = d-Block)4. N = 4 (4th row/energy level): • Larger than the third energy level• Can hold 32 electrons5. N = 5 (5th row/energy level): • Larger than the fourth energy level• Can hold 50 electrons

6. N = 6 (6th row/energy level): • Larger than the 5th energy level• Can hold 72 electrons 7. N = 7 (7th row/energy level): • Largest energy level• Can hold 98 electrons

The rule for determining the number of electrons is 2(n2) The

number of energy levels in represented in N.

2n2

2(6)2

2(36) = 72

sp

d

f

1S2S3S4S5S6S7S

4F5F

3D4D5D6D

2P3P4P5P

6P7P

The S-Block always fills first!

D-Block ONE Row Behind!

F-Block TWO Rows Behind!

How Electrons Fill Orbitals(The Order of fill)

1s2s3s4s5s

2p3p

3d 4p4d 5p

6s 5d 6p4f7s 6d 7p5f

Putting it all together….1

2

345

67

s

d

p

f

Steps for Finding Electron Confi gurati ons for an Element

1. Find the element. 2. List the energy levels, orbitals (blocks), and

number of electrons in each block as you make your way to the element that you are trying to find the configuration for.

Cerium 1s2 2s2p6 3s2p6d10 4s2p6d10f1 5s2p6d1 6s2

1

2

345

67

s

d

p

f

He1s2

What is the Atomic Number of Helium?

1

2

345

67

s

d

p

f

Cl1s22s22p63s23p5

1s22s22p63s23p5

Energy Levels

1s22s22p63s23p5

Orbitals

1s22s22p63s23p5

Electrons

Check work by counting number

of electrons!

For this presentation, thenucleus of the atom is atthe center of the three axes.

x

y

z

The “1s” orbital is asphere, centeredaround the nucleus

The 2s orbital is alsoa sphere.

The 2s electrons have a higher energy than the 1selectrons. Therefore, the 2selectrons are generally moredistant from the nucleus,making the 2s orbital largerthan the 1s orbital.

1s orbital

2s orbital

2px

x

y

z

2px and 2pz

x

y

z

The three 2p orbitals,2px, 2py, 2pz

x

y

z

once the1s orbitalis filled,

the 2s orbitalbegins to fill

once the 2sorbital isfilled,

the 2p orbitalsbegin to fill

each 2p orbitalintersects the2s orbital andthe 1s orbital

each 2p orbitalgets one electronbefore pairing begins

once each 2p orbitalis filled with a pairof electrons, then

the 3s orbitalgets the nexttwo electrons

the 3s electronshave a higher energythan 1s, 2s, or 2pelectrons,

so 3s electrons aregenerally foundfurther from thenucleus than 1s,2s, or 2p electrons