Periodic TrendsPeriodic Trends

Chapter 6 Section 3 Chapter 6 Section 3

pp.163-169pp.163-169

What is a trend?What is a trend?

1. 1. The general direction in which The general direction in which something tends to move.something tends to move.

2. 2. A general tendency or inclination. See A general tendency or inclination. See Synonyms at Synonyms at tendency..

Things to remember…Things to remember…Nuclear chargeNuclear charge Positively charged nucleus pulls electrons Positively charged nucleus pulls electrons

towards ittowards it

Atomic radius is measured in picometersAtomic radius is measured in picometers 1 x 10^-12 meters = 1 pm1 x 10^-12 meters = 1 pm

IonsIons An atom or bonded group of atoms that has a An atom or bonded group of atoms that has a

positive or negative chargepositive or negative charge Occurs when an atom gains or loses an electronOccurs when an atom gains or loses an electron Electrons are charged so you are gaining or losing Electrons are charged so you are gaining or losing

a negative chargea negative chargeAffects the overall charge of the atomAffects the overall charge of the atom

Electrostatic repulsionElectrostatic repulsion Remember like charges repel each other…Remember like charges repel each other…

electrons in orbitals repel/push each other awayelectrons in orbitals repel/push each other away

Energy is needed to overcome the Energy is needed to overcome the attraction between the positive protons and attraction between the positive protons and negative electronsnegative electrons Ionization energy (IE) is the energy required to Ionization energy (IE) is the energy required to

remove an electron from a gaseous atom remove an electron from a gaseous atom (kJ/mol)(kJ/mol)

IE indicates how strongly a nucleus can hold IE indicates how strongly a nucleus can hold onto its valence e-onto its valence e-

High IE= strong hold on e-; less likely to make High IE= strong hold on e-; less likely to make positive ionspositive ions

Low IE= atom can lose valence e- easily; likely Low IE= atom can lose valence e- easily; likely to make positive ionsto make positive ions

More about ionization energy…More about ionization energy…

After removing the 1After removing the 1stst e- it is still possible e- it is still possible to remove additional electronsto remove additional electrons

Second ionization energy:Second ionization energy: The IE needed to remove a second electron The IE needed to remove a second electron

from a +1 ionfrom a +1 ion

Third ionization energy:Third ionization energy: The IE needed to remove a third electron from The IE needed to remove a third electron from

a +2 iona +2 ion

Electro negativityElectro negativity

Characteristic of an element that indicates Characteristic of an element that indicates the relative ability of its atoms to attract the relative ability of its atoms to attract electrons in a chemical bondelectrons in a chemical bond

Units: PaulingsUnits: Paulings

Values are less than 3.98 or lessValues are less than 3.98 or less

Leave out noble gases (they really don’t Leave out noble gases (they really don’t react)react)

Atomic RadiusAtomic Radius

Electron cloudElectron cloud Spherical surface in which there is a 90% Spherical surface in which there is a 90%

probability of finding an e-probability of finding an e- Not physicalNot physical

Atomic size is defined by how closely an Atomic size is defined by how closely an atom lies to its neighboring atomatom lies to its neighboring atom Each atom has different properties so there Each atom has different properties so there

are going to be different sizes…are going to be different sizes… Different sizes in different blocks…Different sizes in different blocks…

Atomic Radius of a MetalAtomic Radius of a Metal

MetalsMetals Atomic radiusAtomic radius

half the distance between adjacent nuclei in a half the distance between adjacent nuclei in a crystal of that elementcrystal of that element

Atomic Radius of a NonmetalAtomic Radius of a Nonmetal

Usually occur as moleculesUsually occur as molecules

Atomic radius:Atomic radius: Half the distance between nuclei of identical Half the distance between nuclei of identical

atoms that are chemically bonded togetheratoms that are chemically bonded together Diatomic moleculesDiatomic molecules

HydrogenHydrogen

BromineBromine

IodineIodine

OxygenOxygen

Ionic RadiusIonic Radius

Losing/gaining electrons affects size of an atomLosing/gaining electrons affects size of an atomGain an electronGain an electron atom becomes negative atom becomes negative atom atom becomes largerbecomes larger Electrostatic repulsion between atom’s outer electrons Electrostatic repulsion between atom’s outer electrons

increaseincreaseForces outer electrons to move further apartForces outer electrons to move further apartMakes radius biggerMakes radius bigger

Lose an electronLose an electron atom becomes positive atom becomes positive atom atom becomes smallerbecomes smaller Electron lost is valence electronElectron lost is valence electron

Can lead to completely empty orbital=smaller radiusCan lead to completely empty orbital=smaller radius Electrostatic repulsion between atoms decrease so they Electrostatic repulsion between atoms decrease so they

can be pulled closer to nucleuscan be pulled closer to nucleus

Periodic Trend ScramblePeriodic Trend Scramble

Break up into your first groupBreak up into your first group Find everyone with the same type of card…all Find everyone with the same type of card…all

kings together, all queens together, etc….kings together, all queens together, etc….

Listen for instructionsListen for instructions

Atomic Radius: Trends in PeriodsAtomic Radius: Trends in PeriodsDECREASE in atomic radii left-to-rightDECREASE in atomic radii left-to-rightIncreasing positive charge in the nucleusIncreasing positive charge in the nucleusPrinciple energy level (n) remains the same Principle energy level (n) remains the same throughout the periodthroughout the period Each successive element the atomic # IncreaseEach successive element the atomic # Increase Add proton and electronAdd proton and electron Electron gets added to same Prin. E level (n)Electron gets added to same Prin. E level (n) No additional electrons come across valence No additional electrons come across valence

electrons and nucleuselectrons and nucleusVal. E- are not shielded from increased nuclear chargeVal. E- are not shielded from increased nuclear chargeTherefore the increased nuclear charge brings the outermost Therefore the increased nuclear charge brings the outermost electrons closer to the nucleus …which means…electrons closer to the nucleus …which means…Smaller atomic radii going Smaller atomic radii going

Atomic Radius: Trends within Atomic Radius: Trends within GroupsGroups

INCREASE as you move down a groupINCREASE as you move down a groupNuclear charge increasesNuclear charge increasesWhat happens to your principle energy level as you What happens to your principle energy level as you move down a group?move down a group?

Therefore…Electrons added to higher principle energy levelsTherefore…Electrons added to higher principle energy levels

Although nuclear charge increased, other factors in play Although nuclear charge increased, other factors in play to overpower increased nuclear charge...to overpower increased nuclear charge...

Outermost orbital increases in sizeOutermost orbital increases in sizeElectrons are farther from the nucleus b/c of bigger orbitalElectrons are farther from the nucleus b/c of bigger orbitalMore resistant to higher nuclear charge b/c of increased distanceMore resistant to higher nuclear charge b/c of increased distance

Principle energy level increasedPrinciple energy level increasedPuts more orbital with electrons between the nucleus and the Puts more orbital with electrons between the nucleus and the outermost electronsoutermost electronsThese electrons in between shield the outermost electrons from the These electrons in between shield the outermost electrons from the pull of the nucleuspull of the nucleus

Solve…Solve…

Which has the largest radius?Which has the largest radius? Magnesium (Mg)Magnesium (Mg) Silicon (Si)Silicon (Si) Sulfur (S)Sulfur (S) Sodium (Na)Sodium (Na)

Which has the smallest radius?Which has the smallest radius?

And the answer is…And the answer is…

Largest: Na (sodium)Largest: Na (sodium)

Smallest: S (sulfur)Smallest: S (sulfur)

Ionic Radius: Trends in PeriodIonic Radius: Trends in Period

What type of ions do you think will be formed on the What type of ions do you think will be formed on the left side of the table?left side of the table? Smaller positive ionsSmaller positive ions

What type of ions do you think will be formed on the What type of ions do you think will be formed on the right side of the table?right side of the table? Larger negative ionsLarger negative ions

General Rule:General Rule: Left-to-right across a period, the size of positive ions Left-to-right across a period, the size of positive ions

gradually decreasesgradually decreases Around 5A and 6A, the size of much larger negative ions Around 5A and 6A, the size of much larger negative ions

gradually decreasesgradually decreases

Ionic Radius: Trends in GroupIonic Radius: Trends in Group

What happens to the principle energy level What happens to the principle energy level as we move down a group?as we move down a group? IncreasesIncreases

Ion’s outer electrons are in a higher Ion’s outer electrons are in a higher principle levelprinciple level This means an increase in ionic sizeThis means an increase in ionic size

Ionic radii increases as we move down a Ionic radii increases as we move down a group for both positive and negative ionsgroup for both positive and negative ions

Ionization EnergyIonization Energy

What type of IE does group 1A have? High or What type of IE does group 1A have? High or low?low? Low IELow IE Likely to form + ionsLikely to form + ions

What type of IE does group 8A have?What type of IE does group 8A have? High IEHigh IE Unlikely to form ionsUnlikely to form ions

From left to right, the IE to remove successive From left to right, the IE to remove successive electrons always increaseselectrons always increases Does not happen smoothly…requires large jump of Does not happen smoothly…requires large jump of

energyenergy

IE continued….IE continued….

Trends in periods:Trends in periods: First IE generally increases as you move left-First IE generally increases as you move left-

to-rightto-right The nuclear charge increases with each The nuclear charge increases with each

successive element…successive element… What does this have to do valence electrons?What does this have to do valence electrons?

Increase the nuclear charge=stronger hold on Increase the nuclear charge=stronger hold on valence electronsvalence electrons

IE continued…IE continued…

Trends within groups…Trends within groups… First IE generally decrease as you move First IE generally decrease as you move

down a groupdown a group What happens to the size of an atom as you What happens to the size of an atom as you

move down a group?move down a group?IncreasesIncreases

This cause decrease in IE This cause decrease in IE

Valence electrons are farther from the nucleusValence electrons are farther from the nucleus

Easier to removeEasier to remove

Octet RuleOctet Rule

What is the electron configuration for sodium?What is the electron configuration for sodium?

What is the new configuration when a sodium What is the new configuration when a sodium atom becomes a +1 sodium atom?atom becomes a +1 sodium atom?

What noble gas does this configuration look What noble gas does this configuration look like?like?

OCTET RULE:OCTET RULE: Atoms tend to gain, lose, or share electrons in an Atoms tend to gain, lose, or share electrons in an

order to acquire a full set of valence electronsorder to acquire a full set of valence electrons First period elements are en exception to the ruleFirst period elements are en exception to the rule This rule helps to determine what kind of ions will This rule helps to determine what kind of ions will

formform

Food for thought….Food for thought….

Do atoms on the right side of the periodic table Do atoms on the right side of the periodic table tend to gain or lose electrons?tend to gain or lose electrons? Gain electronsGain electrons

What type of ions are they likely to form?What type of ions are they likely to form? Negative ionsNegative ions

Do atoms on the left side of the periodic table Do atoms on the left side of the periodic table tend to gain or lose electrons?tend to gain or lose electrons? lose e-lose e-

What type of ions do they form?What type of ions do they form? Positive ionsPositive ions

Electronegativity (EN)Electronegativity (EN)

Fluorine is the most electronegative Fluorine is the most electronegative elementelement Value: 3.98Value: 3.98

Cesium and Francium are the least Cesium and Francium are the least electronegativeelectronegative Values: 0.79 and 0.7Values: 0.79 and 0.7

Atom with greater electronegativity attracts Atom with greater electronegativity attracts electrons in a chemical bond the strongest electrons in a chemical bond the strongest

Electronegativity (EN)Electronegativity (EN)

Trends in periods and groups:Trends in periods and groups: EN decreases as you move down a groupEN decreases as you move down a group Increases as you move left to right on tableIncreases as you move left to right on table

Where are the lowest electronegatives Where are the lowest electronegatives found?found? Lower left side of the periodic tableLower left side of the periodic table

Where are the highest electronegatives Where are the highest electronegatives found?found? Upper right side of the periodic tableUpper right side of the periodic table

AffinityAffinityWhat are some things you have What are some things you have

an affinity for?an affinity for?

Electron AffinityElectron Affinity

The energy change that occurs when an The energy change that occurs when an electron is acquired by a neutral atomelectron is acquired by a neutral atom

Measure in kJ/molMeasure in kJ/mol

Many atoms release energy when they gain an Many atoms release energy when they gain an electronelectron

A + e- A + e- A- + energy A- + energy

A + e- + energy A + e- + energy A- A- Some atoms need energy to be “forced” to gain an Some atoms need energy to be “forced” to gain an

electronelectron Produces unstable ions that lose electron quicklyProduces unstable ions that lose electron quickly