• An element’s properties are related to An element’s properties are related to electron arrangementelectron arrangement

• An element’s location on the PT An element’s location on the PT predicts many properties.predicts many properties.–Atomic radius Atomic radius – Ionic SizeIonic Size–Ionization energy Ionization energy –ElectronegativityElectronegativity–Chemical reactivityChemical reactivity

Periodic Trends Ch# 6 in text

• Atomic radius of an atom is defined by Atomic radius of an atom is defined by the edge of its last energy level.the edge of its last energy level.–However, this boundary is fuzzyHowever, this boundary is fuzzy

• An atom’s radius is the An atom’s radius is the measured measured distancedistance between the nuclei of 2 between the nuclei of 2 identical atoms chemically bonded identical atoms chemically bonded together - together - divided by 2divided by 2..

Periodic Trends ~ Atomic radius

• As we examine atomic radius from left to right As we examine atomic radius from left to right across the PT we see a grad-ual across the PT we see a grad-ual decrease in decrease in atomic sizeatomic size..– As eAs e-- are added to the are added to the s and p sublevelss and p sublevels in the in the

same energy level, they are gradually pulled same energy level, they are gradually pulled closer to the closer to the highly positive nucleushighly positive nucleus

• The more eThe more e--’s in the atom the less dramatic ’s in the atom the less dramatic

this trend looksthis trend looks

Periodic Trends ~ Atomic radius

• The change in atomic radii across the PT is The change in atomic radii across the PT is due to edue to e-- shieldingshielding or to the or to the effective nuclear effective nuclear chargecharge– As we move across the PT As we move across the PT

we are adding ewe are adding e-- into the same into the same

general vol. in which case they general vol. in which case they

will will shield or interactshield or interact with each with each other (other (repulsionrepulsion) )

Periodic Trends ~ Atomic radius

–We are also adding protons into the We are also adding protons into the nucleus which increases the pnucleus which increases the p++-e-e-- interaction (attraction)interaction (attraction)

• So the nucleus gains strength while the So the nucleus gains strength while the ee-- aren’t gaining much distance, so the aren’t gaining much distance, so the atom is drawn in closer and closer to the atom is drawn in closer and closer to the nucleus.nucleus.

–Decreasing the overall radius of the Decreasing the overall radius of the atomatom

Periodic Trends ~ Atomic radius

• How does the size of an atom change when How does the size of an atom change when electrons are added or removed?electrons are added or removed?

As an Atom loses As an Atom loses 1 or more 1 or more electrons electrons (becomes (becomes

positivepositive), it loses ), it loses a layer therefore, a layer therefore,

its radius its radius decreases.decreases.

Periodic Trends ~ Ionic radius

• How does the size of an atom How does the size of an atom change when electrons are change when electrons are added or removed?added or removed?

As an Atom gains As an Atom gains 1 or more 1 or more electrons electrons

((negativenegative), it fills ), it fills its valence layer, its valence layer,

therefore, its therefore, its radius increases.radius increases.

Periodic Trends ~ Ionic radius

• Elements in a group tend to form ions Elements in a group tend to form ions of the same charge.of the same charge.–Modeled by electron configurations.Modeled by electron configurations.

Periodic Trends

Periodic Trend of Ionic Charges

Periodic Trend of Ionic Charges

Tend to lose Tend to lose electrons to electrons to

become become positivepositive

Tend to gain Tend to gain electrons to electrons to

become become negativenegative

• Another periodic trend on the table is Another periodic trend on the table is ionization energyionization energy (a.k.a. potential) (a.k.a. potential)–Which is the energy needed to Which is the energy needed to

remove one of an atoms eremove one of an atoms e--s.s.–Or a measure of how strongly an Or a measure of how strongly an

atom holds onto its atom holds onto its outermost eoutermost e--s s ((Valence electronsValence electrons))..

• If the eIf the e--s are held strongly the atom will s are held strongly the atom will have a have a highhigh ionization energy ionization energy

Periodic Trends ~ Ionization energy

•The ionization energy is The ionization energy is generally measured forgenerally measured for one one electron at a timeelectron at a time

•You can also measure the You can also measure the amount of energy needed to amount of energy needed to reach in and pluck out additional reach in and pluck out additional electrons from atoms.electrons from atoms.

– There is generally a There is generally a large jumplarge jump in energyin energy necessary to necessary to remove additional electrons remove additional electrons from the atom.from the atom.

Periodic Trends ~ Ionization energy

the amount of energy required to the amount of energy required to remove a remove a 2p e2p e–– (an e (an e- - in a full in a full

sublevel) from a Na ion is almost 10 sublevel) from a Na ion is almost 10 times greater than that required to times greater than that required to

remove the sole remove the sole 3s e3s e--

• There is simply not enough There is simply not enough energy available or released to energy available or released to produce an Naproduce an Na2+2+ ion to make the ion to make the compndcompnd NaClNaCl22– Similarly MgSimilarly Mg3+3+ and Al and Al4+4+ require require

too much energy to occur too much energy to occur naturally.naturally.

• Chemical formulas should Chemical formulas should always describe compounds that always describe compounds that can exist naturally the most can exist naturally the most efficient way possibleefficient way possible

Periodic Trends ~ Ionization energy

• An atoms ability to lose an eAn atoms ability to lose an e-- or gain an or gain an ee-- can be used to understand the can be used to understand the Octet Octet RuleRule

• Octet Rule: atoms tend to gain, lose, Octet Rule: atoms tend to gain, lose, or share electrons in order to acquire a or share electrons in order to acquire a full set of valence electronsfull set of valence electrons..–2 e2 e-- in the outermost s sublevel + 6 e in the outermost s sublevel + 6 e––

in the outermost p sublevel= a full in the outermost p sublevel= a full valence shellvalence shell

Periodic Trends

• ElectronegativityElectronegativity is a key trend. is a key trend.–It reflects the ability of an atom to It reflects the ability of an atom to

attract electrons in a chemical bond.attract electrons in a chemical bond.–FF is the most electronegative element is the most electronegative element

and it decreases moving away from and it decreases moving away from F.F.

• Electronegativity correlates to an Electronegativity correlates to an atom’s ionization energy and electron atom’s ionization energy and electron affinityaffinity

Periodic Trends ~ Electronegativity

Reactivity refers to how likely or vigorously an atom is to react with other substances. This is usually determined by how easily electrons can be removed (ionization energy) and how badly they want to take other atom's electrons (electronegativity) because it is the transfer/interaction of electrons that is the basis of chemical reactions. Metals

Reactivity

Metals

Period - reactivity decreases as you go from left to right across a period.

Group - reactivity increases as you go down a group

Why? The farther to the left and down the periodic chart you go, the easier it is for electrons to be given or taken away, resulting in higher reactivity.

Non-metals

Period - reactivity increases as you go from the left to the right across a period.

Group - reactivity decreases as you go down the group.

Why? The farther right and up you go on the periodic table, the higher the electronegativity, resulting in a more vigorous exchange of electron.