Lesson 9: Periodic Trends

Do Now 7Hg, B, Pb, Zr 11.13.18• Take HW out.

• Copy info down from CJ board.

• On Do Now page 5, copy and answer:

1. A neutral atom of chlorine has ____ unpaired and ____ valence electrons.

2. Longhand e-config for Potassium: ____________________

3. What’s wrong with these e-configs?a) 1s22s23s22p6

b) 1s22s22p63s23p63d44s2

Important Dates (write down in CJ)

• Tuesday Nov. 20th: Quiz corrections due; use form and turn into the slot on the white bookshelf.

• Wednesday Dec. 5th: GP2 Bonus Projects Due

• Monday Dec. 10th: Late work (for work that was due Oct. 29th

– Dec. 9).

• Thursday Dec. 20th: Late work (for work that was due Dec. 10 –Dec. 19th)

Reminder: Expectations after Absences

• Absent 1 day = HW that was due should be turned in before class on the first day you return.

• Extended absences = your responsibility to come talk to me and figure out a makeup plan. This includes the plan to make up any quiz/test.

• It’s your responsibility to turn work in after an absence on time. If not, it’ll be marked as late and receive partial credit.

Bonus Project for GP2Due Wed. Dec. 5th

• Make a *video* to demonstrate a concept we’ve covered in Chemistry• Lab safety• Human-scale “particle diagrams” to show matter• Show-and-tell / teaching style• Anything else creative

• You may work with students from other classes.

• Submit with a flash drive or send a link via email.

• Submission must be clearly labeled with names and elements of students involved.

Lesson 9: Periodic Trends

Do Now 7Zr 11.15.18• Take graphs out to be checked.

• Copy info down from CJ board.

• On Do Now page 5, copy and answer:

1. Classify each of the following as an element, a compound, or a mixture:

a) Copper f) Sulfurb) Water g) Baking sodac) Nitrogen h) Mercury oxided) Air i) Sucrosee) Brass j) Diatomic fluorine

HW: Graphing Review

Atomic Radius

Atomic Radius (Covalent Radius)

one-half the distance between the nuclei of two

identical atoms when they are joined by a covalent

bond

Atomic Radius (Covalent Radius)

As we go down a group, n increases by one for each

element and electrons are being added to a region of

space that is increasingly distant from the nucleus.

As we go across a period, there is a stronger pull (higher

effective nuclear charge) experienced by electrons on the

right side of the periodic table draws them closer to the

nucleus, making the covalent radii smaller.

Atomic Radius (Covalent Radius)

Effective nuclear charge, Zeff

Zeff: the pull exerted on a specific electron by the nucleus, taking into account any electron–electron repulsions

Hydrogen: only one electron so the nuclear charge (Z) and the effective nuclear charge are equal.

All other atoms: the core electrons partially shield the outer electrons from the pull of the nucleus

Effective nuclear charge, Zeff

Effective nuclear charge, Zeff

Nuclear charge

Zeff = Z − shielding

Determined by the probability of another electron being between the electron of interest and the nucleus and electron-electron repulsion

K

The valence electrons are easiest to remove because they have the highest energies, are shielded more, and are farthest from the nucleus.

Atomic Radius The general trend is that radii increasedown a group and decrease across a period.

DECREASES ACROSS A PERIOD

INCREASES D

OW

N

A G

ROUP

Sort by Atomic Radius

• Predict the order of increasing covalent radius for Ge, Fl, Br, Kr.

Radius increases as we move down a group, so Ge < Fl .Radius decreases as we move across a period, so Kr < Br < Ge.

Putting the trends together: Kr < Br < Ge < Fl.

First Ionization Energy

First Ionization Energy (IE1)

• The amount of energy required to remove the most

loosely bound electron from an atom in its ground state

• The energy required to form a cation with +1 charge

• Energy is always required to remove electrons from atoms

or ions, so IE values are always positive.

K

How much energy would it take to remove the red electron?

Cl

How much energy would it take to remove the red electron?

First Ionization Energy (IE1)

• For larger atoms, the most loosely bound electron is

located farther from the nucleus and so is easier to remove.

• As size (atomic radius) increases, the ionization energy should

decrease.

• First ionization energies decrease down a group and increase

across a period.

INCREASES ACROSS A PERIOD

First Ionization Energy

DECREASES D

OW

N

A G

ROUP

Do Now 7Hg, Zr 11.16.18• Take graphs out to be checked.

• Copy info down from CJ board.

• On Do Now page 5, copy & answer:

1. (Just) draw two boxes and arrows to show the trends for atomic radius and first ionization energy.

2. Define 1st ionization energy.

3. Which is greater – 1st or 2nd ionization energy?

Exceptions to the Trend: First Ionization Energy

Draw electron Box diagrams for:

Be vs. B

N vs. O

Group 2A Group 3A

Be B

IE1 = ___________ IE1 = ___________

Group 5A Group 6A

N O

IE1 = ___________ IE1 = ___________

• each time a new subshell begins• an s electron is harder to remove from an atom than a p

electron in the same shell

• as orbitals become more than one-half filled• removing one electron will eliminate the electron–electron

repulsion caused by pairing the electrons in the 2p orbital and will result in a half-filled orbital

Exceptions to the Trend: First Ionization Energy

• an electron in the “s” sublevel is capable of shielding electrons in the “p” sublevel of the same principal energy level due of the spherical shape of the “s” orbital.

Removing an electron from a cation is more difficult than removing an electron from a neutral atom because of the greater electrostatic attraction to the cation

successive ionization energies for one element always increaseNotice anything?

First Ionization Energy Practice

• Which has the lowest value for IE1: O, Po, Pb, or Ba?

Ionic Radius

Ionic Radius

• Ionic radius is the measure used to describe the

size of an ion

• A CATION always has fewer electrons and the same

number of protons as the parent atom; it is smaller than

the atom from which it is derived

Li Li+

Na Na+

1.52 Å 0.60 Å

1.86 Å 0.95 Å

K K+

2.31 Å 1.33 Å

In cations, there are fewer

electrons but the same amount

of protons. The remaining

electrons feel a greater

electrostatic force toward the

positively-charged nucleus.

The radii of the cation is

always smaller than its neutral

atom.

Atomic radii measured in Å (10−10 m)

• An ANION (negative ion) is formed by the addition of one

or more electrons to the valence shell of an atom.

• Result? Greater repulsion among the electrons and a

decrease in Zeff per electron.

• The radius of an anion is larger than that of the parent atom

Ionic Radius

O2-O

S2-S

1.40 Å0.66 Å

1.04 Å 1.84 Å

F-F

0.64 Å 1.36 Å

In anions, there are more

electrons but the same amount

of protons. The electrons feel a

smaller electrostatic force toward

the positively-charged nucleus.

The radii of the anion is always

larger than its neutral atom.

Atomic radii measured in Å (10−10 m)

Isoelectronic

•Atoms and ions that have the same electron configuration

• Examples• N3–, O2–, F–, Ne, Na+, Mg2+, and Al3+ (1s22s22p6)• P3–, S2–, Cl–, Ar, K+, Ca2+, and Sc3+ ([Ne]3s23p6)

• The number of protons determines the size• The greater the nuclear charge, the smaller the radius in a

series of isoelectronic ions and atoms

Electronegativity

Electronegativity

• a measure of the tendency of an atom to attract

electrons (or electron density) towards itself.

• determines how the shared electrons are distributed

between the two atoms in a bond.

• the more strongly an atom attracts the electrons in its

bonds, the larger its electronegativity.