11.4 Electron Configurations

And the Periodic Table

11.4 Electron Configurations (p377)

• The electron configuration of hydrogen is “1s1”

• This means there is one electron in the 1s orbital.

11.4 Electron Configurations

• Rule 1: Electrons occupy the lowest orbital energies first.

1s

2s

2p

Energy

First here

Then here

11.4 Electron Configurations

• Rule 2: Pauli Exclusion Principle: Two electrons can occupy the same orbital. – They have different “spins”

1s

2s

2p

Energy

OneTwo

11.4 Electron Configurations

• Rule 3: Electrons will not “pair up” in the same orbital until all energy levels are occupied.

2s

2p

Energy

1s

Example: Sodium (Na)• Start by drawing a dashed line for each

sub-orbital needed in the correct order.

1s 3s2px2s 2pz2py

11.4 Electron Configurations

• Look at your field diagram

• The order of the “seats” is the same as the order of orbitals.

• Notice the 4th energy level has seats closer than some of the 3rd energy level.

• Which orbital fills up first, 4s or 3d?– Yes, 3d.

Electron Configuration

• Quicker way to write the orbital notation

• Example: sodium

• Becomes 1s22s22p63s1

1s 3s2px2s 2pz2py

11.4 Electron Configurations

• Examples: Li (Z=3), N (7), O(8) (See book)• Mg can be written as [Ne]3s2

• Valence electrons are the electrons in the highest principal energy level of an atom. They are involved in bonding with other atoms.

• Nitrogen has electrons in n = 1 and 2. Level 2 is the valence level. 1s22s22p3

• Nitrogen has 5 valence electrons.

11.4 Electron Configurations

• The core electrons are the inner electrons, and are not involved in bonding.

• Question: What elements have the same number of valence electrons as N?

• Where are they on the periodic table? • Elements with the same number of

valence electrons have similar chemical properties.

B. Electron Configurations and the Periodic Table.

p-blockd-blockNumber one less than row number

f-block

Number two less than row number

s-b

lock

Helium actually part of s-block1

3

2

7

4

6

5

Example: Germanium (Ge)

• Do the orbital notation

1s 2s 2p 2p 2p 3s 3p 3p 3p

4s 3d 3d 3d 3d 3d 4p 4p 4p

11.4 C. Atomic Properties and the Periodic Table

• Representative Elements - groups 1A-8A• Ionization – ionization is when an atom

loses an electron.• Remember: ______________ lose

electrons.• _______________ gain electrons.• Going down a group, atoms are more

likely to lose an electron. Cs is more likely to lose an electron than Li.

Metals

Nonmetals

11.4 C. Atomic Properties and the Periodic Table

• Atomic size – decreases going up and right.

• Decreases going up because electrons are closer at lower principal energy levels.

• Decreases going right because the + charge in the nucleus is stronger.

Atomic Size• Size generally decreases

•S

ize

gene

rally

dec

reas

es

11.4 C. Atomic Properties and the Periodic Table

• Ionization energy - the energy required to remove an electron from an atom in the gas phase.– increases up a group– increases to the right

Ionization Energy• increases

•In

crea

ses

Checkpoint

• Which element has a larger atomic size?– Sulfur or chlorine?– Answer: Sulfur

• Which element has the larger ionization energy?– Sodium or potassium?– Answer: Sodium– http://www.mhhe.com/physsci/chemistry/essentialche

mistry/flash/atomic4.swf– http://video.google.com/videoplay?docid=-213426665

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