Periodic Table and Periodic Periodic Table and Periodic Trends NotesTrends Notes

Mendeleev’s Periodic TableMendeleev’s Periodic Table By the mid-1800s, about 70 By the mid-1800s, about 70

elements were known to existelements were known to exist Dmitri Dmitri MendeleevMendeleev – a Russian – a Russian

chemist and teacherchemist and teacher Arranged elements in order of Arranged elements in order of

increasing increasing atomic massatomic mass

“ “Periodic Table”Periodic Table”

MendeleevMendeleev He left blanksHe left blanks for yet for yet

undiscovered elementsundiscovered elements• When they were discovered, he When they were discovered, he

had made good predictionshad made good predictions In 1913, Henry In 1913, Henry MoseleyMoseley – –

British physicist, British physicist, arranged arranged elements according to elements according to increasing increasing atomic numberatomic number

The arrangement used todayThe arrangement used today

ALLALL Periodic Table Trends Periodic Table Trends Influenced by three factors:Influenced by three factors:

1. 1. Energy LevelEnergy Level• Higher energy levels are further away Higher energy levels are further away

from the nucleus.from the nucleus.

2. 2. Charge on nucleusCharge on nucleus (# protons) (# protons)• More charge pulls electrons in closer. More charge pulls electrons in closer.

(+ and – attract each other)(+ and – attract each other) 3. 3. Shielding effectShielding effect

Atomic SizeAtomic Size

Measure the Atomic Radius - this is half the Measure the Atomic Radius - this is half the distance between the two nuclei of a diatomic distance between the two nuclei of a diatomic molecule.molecule.

}Radius

##1. 1. Atomic SizeAtomic Size - Group trends - Group trends As we increase the As we increase the

atomic number (or go atomic number (or go down a group). down a group).

each atom has each atom has another energy level,another energy level,

so the atoms get so the atoms get

biggerbigger..

HLi

Na

K

Rb

#1. #1. Atomic SizeAtomic Size - Period Trends - Period Trends Going from left to right across a period, the size Going from left to right across a period, the size

getsgets smallersmaller.. Electrons are in the Electrons are in the same energy levelsame energy level.. But, there is more But, there is more nuclear chargenuclear charge.. Outermost electrons are pulled closer.Outermost electrons are pulled closer.

Na Mg Al Si P S Cl Ar

IonsIons Some compounds are composed Some compounds are composed

of particles called “ions”of particles called “ions”• An An ionion is an atom (or group of atoms) is an atom (or group of atoms)

that has a that has a positive or negative chargepositive or negative charge AtomsAtoms are neutral because the number are neutral because the number

of protons equals electronsof protons equals electrons• Positive and negative ions are formed Positive and negative ions are formed

when electrons are when electrons are transferredtransferred (lost or (lost or gained) between atomsgained) between atoms

Metals tend to Metals tend to LOSE electronsLOSE electrons, from , from their outer energy leveltheir outer energy level• Sodium loses one: there are now Sodium loses one: there are now

more protons (11) than electrons (10), more protons (11) than electrons (10), and thus a charge of +1and thus a charge of +1

• The charge is written as a number The charge is written as a number followed by a plus sign: Nafollowed by a plus sign: Na1+1+

• Now named a “Now named a “sodium ionsodium ion””• positively ions are called “positively ions are called “cationcation””

Nonmetals tend to GAINNonmetals tend to GAIN one or one or more electronsmore electrons• Chlorine will gain one electronChlorine will gain one electron• Protons (17) no longer equals the Protons (17) no longer equals the

electrons (18), so a charge of -1electrons (18), so a charge of -1• ClCl-1-1 is re-named a “chloride ion” is re-named a “chloride ion”• Negative ions are called “Negative ions are called “anionsanions””

#2. Trends in Ionization Energy#2. Trends in Ionization Energy Ionization energy is the amount of Ionization energy is the amount of

energy required to energy required to completely remove completely remove an electronan electron (from a gaseous atom). (from a gaseous atom).

Removing one electron makes a 1+ ion.Removing one electron makes a 1+ ion. The first electron is the easiest to The first electron is the easiest to

remove.remove.

Symbol First Second ThirdHHeLiBeBCNO F Ne

1312 2731 520 900 800 1086 1402 1314 1681 2080

5247 7297 1757 2430 2352 2857 3391 3375 3963

11810 14840 3569 4619 4577 5301 6045 6276

What factors determine IEWhat factors determine IE The greater the nuclear charge, The greater the nuclear charge,

the the greatergreater IE. IE. Greater distance from nucleus Greater distance from nucleus

decreasesdecreases IE IE Filled and half-filled orbitals have Filled and half-filled orbitals have

lower energy, so achieving them lower energy, so achieving them is easier, lower IE.is easier, lower IE.

Shielding effectShielding effect

ShieldingShielding The electron on the The electron on the

outermost energy outermost energy level has to look level has to look through all the other through all the other energy levels to see energy levels to see the nucleus.the nucleus.

Second electron has Second electron has samesame shielding, if it shielding, if it is in the is in the same periodsame period

Ionization Energy - Group trendsIonization Energy - Group trends As you go down a group, the As you go down a group, the

first IE decreases because...first IE decreases because...• The electron is further away from The electron is further away from

the attraction of the nucleus, andthe attraction of the nucleus, and• There is more shielding.There is more shielding.

Ionization Energy - Period trendsIonization Energy - Period trends

All the atoms in the same period All the atoms in the same period have the same energy level.have the same energy level.

Same shielding.Same shielding. But, increasing nuclear chargeBut, increasing nuclear charge So IE generally So IE generally increasesincreases from left from left

to right.to right. Exceptions at full and 1/2 full Exceptions at full and 1/2 full

orbitals.orbitals.

#3. Trends in Electronegativity#3. Trends in Electronegativity Electronegativity is the tendency Electronegativity is the tendency

for an atom to for an atom to attract attract electrons electrons to itself when it is to itself when it is chemically chemically combinedcombined with another element. with another element.

An element with a big An element with a big electronegativity means it pulls electronegativity means it pulls the electron towards itself the electron towards itself strongly!strongly!

Electronegativity - Group TrendElectronegativity - Group Trend The further down a group, the The further down a group, the

farther the electron is away from farther the electron is away from the nucleus, plus the more the nucleus, plus the more electrons an atom has.electrons an atom has.

Thus, more willing to share.Thus, more willing to share. Low electronegativityLow electronegativity.. Electronegativity decreases down Electronegativity decreases down

a groupa group

Electronegativity - Period TrendElectronegativity - Period Trend Metals are at the left of the table.Metals are at the left of the table. They let their electrons go easilyThey let their electrons go easily Thus, low electronegativityThus, low electronegativity At the right end are the nonmetals.At the right end are the nonmetals. They want They want moremore electrons. electrons. Try to take them away from othersTry to take them away from others High electronegativityHigh electronegativity.. Electronegativity increases from left to Electronegativity increases from left to

rightright

•Ionization energy increases

•Electronegativity increases

•atomic size decreases

•IE decreases

•Electronegativity decreases

•Atomic size increases