Periodic Trends

Periodic Trends

Periodic Trends

• "Periodic" = recurring pattern

Open Ended

Give one or two other examples of "periodic trends" that we see or experience?

The Periodic Law

• "When elements are arranged in order of increasing atomic number, there is a periodic repetition of their chemical and physical properties."

• PERIODICITY

Atomic Radius

• One-half the distance between the nuclei of identical atoms that are bonded together.

Multiple Choice

Why can't an atomic radius be measured for a single atom?

• There is no distinct outer boundary since the electrons are constantly moving.

• Atomic radii are simply too small to measure that way.

• The electrons stay on the same orbital but move too fast to measure.

Trend in Atomic Radius

• Decreases from left to right across the period.

• Caused by increasing NUCLEAR CHARGE (addition of protons to the nucleus), so there's a greater pull on electrons.​

• This gets slightly offset by electrons filling the outer orbital which increases the repulsion amongst the electrons.

Group Trend (Atomic Radius)

• In general, it INCREASES as you move down a group.

• A higher energy orbital is added in each period, increasing the outermost distance from the nucleus.

• ​(Compare this to magnets...)

Open Ended

Of the elements magnesium (Mg), chlorine (Cl), sodium (Na), and phosphorus (P), which has the largest atomic radius and which has the smallest? Explain in terms of trends in the periodic table. (Pg. 148-149)

Quick Review on Ions...

• An ion is any atom (or group of bonded atoms) that has lost or gained electrons.

• Lose electron(s) = positive charge

• Gain electron(s) = negative charge

Becoming an ion changes the radius of an atom.

• Adding electrons = increased radius

• larger e^- cloud and less pull on electrons

• Removing electrons = decreased radius

• Smaller e^- cloud and imbalance in nuclear charge

Ionization Energy

• The energy required to remove one electron from a neutral atom.

• Also known as "first ionization energy"

• Used to compare the ease with which atoms of different elements give up electrons.

• High ionization energy = tight hold = a lot of energy is required by OTHER atoms take take the electrons away

• Low ionization energy = weak hold = NOT a lot of energy is required by OTHER atoms to take electrons away

Multiple Choice

(Ionization Energy: The energy required to remove an electron from an atom.) Therefore, a low ionization energy means that an atom

• holds onto its valence electrons very tightly

• loses its valence electrons very easily

Ionization Energy Period Trend

• Increases as you move left to right across the a period

• Due to increasing nuclear charge

• Same reason as the radius getting smaller (the nucleus has a stronger and stronger "pull")

Ionization Energy Group Trend

• Generally decrease down a group.

• Due to increasing distance from the nucleus (more orbitals)

• Due to increased shielding by inner electrons

• The repulsion of inner electrons partially blocks the attraction of the outer electrons and the nucleus.

Multiple Choice

Which electron will be the first to be removed during ionization?

• an electron closest to the nucleus

• a valence (outermost) electron

• a core electron that isn't paying attention to what it's doing

• it's a random occurrence that can't be predicted

Multiple Choice

When an atom loses an electron it forms a(n)

• anion

• cation

• element

• compound

Multiple Choice

When an atom gains an electron its overall charge

• becomes positive

• remains neutral

• becomes negative

Multiple Choice

An atom with more shielding will have a ___ ionization energy than an atom without a lot of shielding.

• lower

• higher

Multiple Choice

If an atom has a strong hold on its own valence electrons, its ionization energy is most likely

• low

• high

Multiple Choice

Which element has the weakest ionization energy?

• Helium (He)

• Carbon (C)

• Sodium (Na)

• Francium (Fr)

Poll

How confident do you feel about describing the periodicity of ionization energy?

• This is making sense. Sit back and relax Mrs. Lambert, I got this.

• I kind of get it; just have to let it all stew for a bit.

• I mostly understand but I have some questions.

• The perio-what of iza-who?

Electron Affinity

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

(Think of it as the atom's likelihood of gaining an electron to become an anion).

​

​Atoms may gain or lose energy while acquiring electrons. MOST lose energy.

Electronegativity

• A measure of the ability of an atom to capture electrons from another atom

• Results in the formation of a compound

• Numbers are arbitrary; 4 is the highest (fluorine). 0.7 is lowest (francium)

Electronegativity

Increases across a period; increased nuclear charge

Decreases down a group; increased number of orbitals and increased shielding

Fluorine is the most electronegative element.

Francium is the least electronegative element.

• The Noble gases aren't even assigned values (NOT zero... simply NO value).

Put it all together!

• Atomic Radii; Decreases across period and increases down group

• Ionization Energy; Increases across period and decreases down group

• Electron Affinity; Increases across period and decreases down group

• Electronegativity; Increases across period and decreases down group

Arrows point in the direction of INCREASE

Multiple Choice

When an electron is added to a neutral atom, energy is

• always absorbed

• always released

• either absorbed or released

• neither absorb nor released

Multiple Choice

The energy required to remove an electron from a neutral atom is the atom's

• electron affinity

• electron energy

• electronegativity

• ionization energy

Multiple Choice

From left to right across a period, ionization energy tends to

• fluctuate

• increase

• decrease

• stay the same

Multiple Choice

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

• ionization energy

• electron affinity

• electronegativity

• depolarization

Multiple Choice

In regard to electron affinity, a negative number represents

• energy being gained by an atom when it acquires an electron

• energy being released by an atom when it acquires an electron

Multiple Choice

Moving from left to right across a period, electron affinty values tend to become

• more negative

• more positive

• neutral

• unequal

Multiple Choice

When electrons repel each other and "block" the attraction between the nucleus and outer electrons.

• shielding

• buffering

• reacting

• neutralizing

Multiple Choice

True or False: In the same period, an atom with a larger atomic number will have a larger radius.

• True

• False