Trends in the Periodic TableTrends in the Periodic Table

trend: direction or pattern

p. 70-75

s, p, d and f blocks of the periodic table

gro

up

s

periods

“Long form” periodic table

• Electronic structures are related to the position of the elements on the periodic table– s-block: s orbitals are filled– p-block: p orbitals are filled, etc.

Zumdahl p. 322

Atomic number

• Increases from left to right (across periods)

• Increases from top to bottom (down groups)

• Period number: number of energy levels containing electrons

• Group: same valence shell electron configuration 1

2

34 56 7 89101112

131415161718

Group names

• 1: alkali metals (1 valence electron)

• 17: halogens (7 valence electrons)

• 18: noble gases (all electron shells filled, little chemical reactivity)

• periodicity: repeating of similar properties because of similar valence electron configuration

117

18Important Groups

Physical Properties in the PTE

Atomic and Ionic Radii

• Atomic radius: half the distance between the nuclei of two touching atoms

• Increases going down a group– Additional filled energy levels of electrons

• Decreases going across a period– More electrons = increased attraction to

positive nucleus

Increasing Atomic Radius

Atomic Radius Increases

Ato

mic R

adiu

s Increases

• Radius of an atom always decreases when it loses an electron (becomes a cation +)– A whole energy level may be lost, or– There is less electron-electron repulsion

(pushing away) between the electrons in different energy levels

• The radius of an atom always increases when it gains an electron (becomes an anion -)– Increased electron-electron repulsion pushes

the valence shell away from the nucleus.

Ionic radius examples

• K

• K+

• Cl

• Cl-

Ionization energy

• The amount of energy that is required to remove an electron from a gaseous atom

• Decreases going down a group– Valence electrons are further from the

nucleus, less “pull” from the protons

- +15 -

- -

-

-

- -

-

-

-

-

-

-

-+15

+13+5

Effective Nuclear Charge

• Charge exerted on each electron by the positively charged nucleus

- +15 -

- -

-

-

- -

-

-

-

-

-

-

-+15

+13+5

Ionization Energy

• Increases going across a period– Electrons on the same energy level are more

strongly “pulled” by the nucleus (which is increasing in positive charge)

+11 +12

Ionization Energy IncreasesIo

niz

atio

n E

ner

gy

Incr

ease

s

Electronegativity

• How strongly an atom attracts other electrons in a chemical bond (electron affinity)

• Decreases going down a group– Valence electrons are further from the nucleus, less

“pull” from the protons– Atoms increase in radius

• Increases going across a period– Electrons on the same energy level are more strongly

“pulled” by the nucleus– Atoms decrease in radius

Electronegativity IncreasesE

lect

ron

egat

ivit

y In

crea

ses

Other Physical Properties

• Melting Point

• Boiling Point

• Density

• Types of bonds formed

Chemical Properties

• Elements in the same group have similar chemical properties

Increasing atomic and

ionic radii

Incr

easi

ng io

niza

tion

ener

gy

Incr

easi

ng

elec

tron

egat

ivity

Increasin

g reactivity

Alkali metals• Soft, malleable (can be shaped) metals• Low melting points

– Can only contribute one electron to a bond – easily broken

• Low density– Largest atomic radius in the period

• Very chemically reactive– One valence electron, easily lost, + ion

• Tarnish quickly• Combine with O, Cl, Br to form ionic compounds

sodium

potassium

rubidium

cesium (l)

• All react with water to form a solution of metal hydroxide and hydrogen

• 2M(s) + 2H2O(l) 2M+(aq) + 2OH-(aq) + H2(g)

• M = alkali metal

sodium potassium

Reaction is alkaline (base)

• What trend in reactivity did you see as we moved down the group?

Increasing atomic and

ionic radii

Incr

easi

ng io

niza

tion

ener

gy

Incr

easi

ng

elec

tron

egat

ivity

Incr

easi

ng

rea

ctiv

ity

Halogens

• Very reactive non-metals– Need only one electron to fill valence shell

• All exist as diatomic molecules– Cl2, Br2, I2 (all colored)

• Slightly soluble in water – non-polar bonds

Halogens – colored diatomic molecules

fluorine pale yellow gas

chlorine yellow-green gas

bromine red-brown liquid

iodine black-purple solid

purple gas

• X2(aq) + H2O(l) H+(aq) + X-(aq) + HOX(aq)

– X = halogen– HOX = acid

• Ex: Chlorine: HOCl (HClO: chloric acid), used as a bleach, toxic to microbes, treats water

• all quite electronegative (high electron affinity)

• easily gain electrons to form anions– halide ions

• Ability to gain electrons decreases going down a group

• reactivity decreases going down a group

• Halogens combine with metals to produce ionically bonded salts containing a halide ion.– white and soluble in water colorless solutions

– insoluble: lead and silver compounds

– lead(II) iodide: bright yellowyellow precipitate

• Test for a halide ion by adding nitric acid, then a solution of silver nitrate– a precipitate indicates Cl-, Br-, or I-

compound color

AgF no precipitate

AgCl white, then purple/black in sunlight

AgBr off-white

AgI pale yellow

silver bromideused to print black and white photos

silver chlorideused to print black and white photos

silver iodideused to “seed the clouds” to make it rain

• Oxidant: In a reaction, a higher halogen will replace a lower halogen.

• NaCl(aq) + Br-

• NaBr(aq) + Cl- NaCl(aq) + Br-(aq)

Ionization Energy Increases

Atomic Radius Increases

Electronegativity Increases

Metallic Character Increases

Your questions…

Answered!

• Q: Why don’t the electrons crash into the nucleus?

• A: Electrons have lots of their own energy. E=hf due to their position around the nucleus. Electrons are constantly moving, very fast.

• This kinetic energy overcomes the positive attraction of the nucleus.

• A: How does temperature affect ionization energy?• Q: Temperature has no affect on ionization energy. Heat is

only powerful enough to change kinetic energy of a particle or molecule.

• Microwaves and radio waves can affect nuclear spin. Gamma rays and X rays can effect the nucleus and the inner electrons.

• Electricity does have an affect on ionization energy.

• Q: How does temperature affect the movement of the subatomic particles, specifically electrons?

• A: Temperature does not have enough energy to affect subatomic particle movement, only molecule movement.

• Q: Where does ionization energy come from?

• A: Electricity

• Q: If there is just one electron in a px orbital, can it be located everywhere, or just on one side of the orbital?

•A: It can be located anywhere. An orbital is an area of probability inside of which the electron will be found. Electrons are constantly moving very fast, and can be anywhere within their orbitals.

• Q: Why does ionization energy increase going across a period? Why, oh Why?!?

• A: The effective nuclear charge DOES change on each valence electron!

+11 +12ENC=+1

ENC=+2

Mid-term

• Tuesday, April 22– 14:40-16:10– Room 407 or 408

• 19 questions – short answer or calculations– 2 definitions

• Answer all parts of all questions• No dictionary/translator• Bring calculator, Periodic Table on test