Chemistry Riddle

Q: What is a robber’s least favorite element?

A: Copper!!!

Introduction to Periodic Trends

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.

He2

Ne10

Ar18

Kr36

Xe54

Rn86

1s2

1s22s22p6

1s22s22p63s23p6

1s22s22p63s23p64s23d104p6

1s22s22p63s23p64s23d104p65s24d105p6

1s22s22p63s23p64s23d104p65s24d10

5p66s24f145d106p6

How the configurations of the noble gases similar?

The outer energy level is completely full!

1s1

1s22s1

1s22s22p63s1

1s22s22p63s23p64s1

1s22s22p63s23p64s23d104p65s1

1s22s22p63s23p64s23d104p65s24d10 5p66s1

1s22s22p63s23p64s23d104p65s24d105p66s2

4f145d106p67s1

H1

Li3

Na11

K19

Rb37

Cs55

Fr87

How are the configurations of the alkali metals similar?

They all end in s1!

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.

s2s1

He

Alkaline earth metals all end in s2.

How would the halogens all end?

p5

Periodic TrendsThese 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 TrendsAtomic SizeIon SizeIonization EnergyElectron AffinityElectronegativity

Periodic Trends

Influenced by two factors:1. Energy levelAt 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.

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

Trends in Atomic Size

Measure the distance between the two nuclei of a diatomic molecule. Half of this distance is the atomic radius.

}Radius

Atomic Size - Group Trend

As we go down a group…

Each atom has another energy level

So the atoms get bigger.

HLi

Na

K

Rb

OBVIOUS!!

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

NOT SO OBVIOUS!!

Atomic radius decreases

Atomic radius increases

Periodic Trends, Cont.

Ion SizeIonization EnergyElectronegativityElectron Affinity

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 metal-nonmetal dividing line.

Ion Size Period Trend

Li1+

Be2+

B3+

C4+

N3-O2-

F1-

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.

Ionization Energy• 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

Ionization Energy Trends• 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.

Ionization Energy Trends• 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.

Ionization Energy Trends(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

Electron Affinity

Electron Affinity TrendsIncreases

NO definite pattern

Noble Gases do not have an affinity for electrons.

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

Electronegativity TrendsIncreases

Decreases

Noble Gases are not electro-negative.

F

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 He

2 Li Be S C N O F Ne

3 Na Mg Al Si P S Cl Ar

4 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

5 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe

6 Cs Ba La   Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn

7 Fr Ra Ac   Rf Db Sg Bh Hs Mt Ds Rg Uu

b — Uuq — — — —

7

• 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.

Chemistry Riddle

Q: What does a doctor do with a sick chemist?

A: He!