Chemistry Riddle
Q: What is a robber’s least favorite element?
A: Copper!!!

Remember these groups of the periodic table?

The Periodic Law

When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.




Classifying Elements by Electron Configuration
Remember…electrons play the most significant role in determining physical and chemical properties of elements.
Elements are arranged in the table according to their properties.
Therefore, there should be some relationship between the electron configurations of the elements and their placement in the table.

How the configurations of the noble gases similar?
1 s 2
He
2
1s 2 2s 2 2p 6
Ne
10
The outer energy level is completely full!
1s 2 2s 2 2p 6 3s 2 3p 6
Ar
18
1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 Kr
36
1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6
Xe
54
1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10
5p 6 6s 2 4f 14 5d 10 6p 6
Rn
86

H
1 1 s 1
Li
3
1s 2 2 s 1
How are the configurations of the alkali metals similar?
Na
11
K
19
1s 2 2s 2 2p 6 3 s 1
1s 2 2s 2 2p 6 3s 2 3p 6 4 s 1
They all end in s 1 !
Rb
37
Cs
55
Fr
87
1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5 s 1
1s 2 2s
5p 6
2
6
2p s 1
6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10
1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s
2 4f 14 5d 10 6p 6 7 s 1

s
1 s
2
Alkaline earth metals all end in s 2 .
He
 Alkaline earth metals might include He, but He fits better with the noble gases.
 He has similar properties to the noble gases because its outer energy level is completely full.
 How would the halogens all end?
p 5

Periodic Trends

These patterns in electron configurations produce patterns in properties.

These patterns are called Periodic
Trends.

Can be followed either across a period or down a group

Five Trends

Atomic Size

Ion Size

Ionization Energy

Electron Affinity

Electronegativity

Periodic Trends

Influenced by two factors:
1. Energy level

At higher energy levels the electron is further away from nucleus.
2. Charge on nucleus (# protons)

More protons means a greater charge pulls electrons in closer.

Trends in Atomic Size

Problem: Where do you start measuring from?

The electron cloud doesn’t have a definite edge.

This problem is solved by measuring more than 1 atom at a time.

Trends in Atomic Size
Radius

Measure the distance between the two nuclei of a diatomic molecule. Half of this distance is the atomic radius.


Atomic Size - Group Trend
As we go down a group…

Each atom has another energy level

So the atoms get
bigger.
H
Li
Na
K
Rb

Atomic Size - Period Trend
 Going from left to right across a period, the size gets smaller .
 Electrons are in the same energy level.


But, there is more nuclear charge (more protons).
So…outermost electrons are pulled in closer.
Na Mg Al Si P S Cl Ar

Atomic radius decreases
Atomic radius increases

Ion Size
 To form ions, atoms may gain or lose electrons.
 If an atom loses electrons, a positive ion is formed called a cation .
– Metals tend to lose electrons.
 This cation is smaller than the atom from which it formed.
– It now has fewer occupied energy levels.

Ion Size
 When an atom gains electrons, a negative ion is formed called an anion .
– Nonmetals tend to gain electrons.
 This anion is larger than the atom from which it was formed.
 The period and group trends for ions are the same as atomic radius….except in the period trend when you cross the metalnonmetal dividing line.

Ion Size Period Trend
N 3-
B 3+
O 2-
F 1-
Li 1+
Be 2+
C 4+
Cations —Atoms that have lost electrons to become positively charged.
Smaller than the original, but showing the same trend in size.
Anions —Atoms that have gained electrons to become negatively charged.
Larger than the original, but showing the same trend in size.

• The amount of energy required to completely remove an electron from an atom.
• Removing one electron makes a +1 ion
• The energy required to remove the outermost electron is called the first ionization energy.
• Also known as…IE

• As you go across a period…
• The electrons are closer to the positive nucleus and therefore harder to pull off.
• The harder it is to pull off the electron, the higher the ionization energy.

• As you go down a group…
• The electrons are farther away from the positive nucleus and therefore easier to pull off.
• There are more electrons shielding the outer electrons from the positive nucleus, making them easier to pull off.
• The easier it is to pull off the electron, the lower the ionization energy.

(Generally) Increases
Decreases

Ionization Energy Graph

Electron Affinity Trends
 Ability for a neutral atom to acquire an electron is known as it’s
 Trend:
– Increase across the period
 Hence the high reactivity of Halogen
– No general trend for the groups

Increases
Noble
Gases do not have an affinity for electrons.
NO definite pattern

Electronegativity
• The tendency for an atom to attract electrons to itself when it is chemically bonded to another element(s).
• Measures how fair an atom shares electrons.
• Large electronegativity means it pulls the electron toward it strongly.
• Fluorine is the most electronegative element

Increases
Decreases
F Noble
Gases are not electronegative.
Fluorine is the most electronegative element.

Chemistry Riddle
Give this flask to Mel and tell him to put it away where no one can find it.
What is it?
It’s formaldehyde!!

Diatomic
Molecules
1 H
2 Li Be
• 7 elements
• Beginning with element 7
• Form the number 7
(except H)
• Never alone
• If they are not with another element, they bond with themselves.
3 Na Mg
4 K Ca Sc
5 Rb Sr Y
6 Cs Ba La
7 Fr Ra Ac
S
He
C
7
N O F Ne
Al Si P S Cl Ar
T i
V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Z r
Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
H f
Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
R f
Db Sg Bh Hs Mt Ds Rg
Uu b
—
Uu q
— — — —

Chemistry Riddle
Q: What does a doctor do with a sick chemist?
A: He!