Ch 5.3 Electron Configuration and Periodic Properties

Atomic and Molecular Structure

1. The periodic table displays the elements in increasing atomic number and shows how periodicity of the physical and chemical properties of the elements relates to atomic structure. As a basis for understanding this concept:

b. Students know how to use the periodic table to identify metals, semimetals, non-metals, and halogens.

c. Students know how to use the periodic table to identify alkali metals, alkaline earth metals and transition metals, trends in ionization energy, electronegativity, and the relative sizes of ions and atoms.

f.* Students know how to use the periodic table to identify the lanthanide, actinide, and transactinide elements and know that the transuranium elements were synthesized and identified in laboratory experiments through the use of nuclear accelerators.

g.* Students know how to relate the position of an element in the periodic table to its quantum electron configuration and to its reactivity with other elements in the table.

Science Content Standards for California Public Schools

Atomic Size

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

}Radius

#1. Atomic Size - Period Trends Going from left to right across a

period, the size gets smaller. Electrons are in the same energy

level. Outermost electrons are pulled closer.

Na Mg Al Si P S Cl Ar

#1. Atomic Size - Group trends As we increase

the atomic number (or go down a group), each atom has another energy level.

Valence electrons get further from the nucleus.

So the atoms get

bigger.

HLi

Na

K

Rb

Trend in Atomic Radius

An ion is an atom (or group of atoms) that has a positive or negative charge

Atoms are neutral because the number of protons equals electrons◦Positive and negative ions are formed when electrons are lost or gained between atoms

Ions

Ions therefore get bigger as you go down, because of the additional energy level.

#2: Ionic Group trends

Li1+

Na1+

K1+

Rb1+

Cs1+

Across the period from left to right, they get smaller.

Ionic Period Trends

Li1+

Be2+

B3+

C4+

N3-O2- F1-

Ionization energy is the amount of energy required to completely remove an electron (from a gaseous atom).

The energy required to remove 1 electron is called the first ionization energy.

#3. Trends in Ionization Energy

The second ionization energy is the energy required to remove the second electron.◦Always greater than first IE.

The third IE is the energy required to remove a third electron.◦Greater than 1st or 2nd IE.

Ionization Energy

As you go down a group, the first IE decreases because...◦The electron is further away from the attraction of the nucleus, and

◦There is more shielding.

Ionization Energy - Group trends

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

So IE generally increases from left to right.

Ionization Energy - Period trends

Metals tend to LOSE electrons, from their outer energy level◦Sodium loses one electron.◦There are now more protons (11) than electrons (10), and thus a positively charged particle is formed = “cation”

◦The charge is written as a number followed by a plus sign: Na1+

◦Now named a “sodium ion”◦Lost an electron, so a decrease in size from atom to ion.

Ions

Nonmetals tend to GAIN one or more electrons◦Chlorine will gain one electron◦Protons (17) no longer equals the electrons (18), so a charge of -1

◦Cl1- is re-named a “chloride ion”◦Negative ions are called “anions”◦Gained an electron so increase in size from atom to ion.

Ions

Valence Electrons

The electrons available to be lost, gained, or shared in the formation of chemical compounds.

Main group elements: valence electrons are in the outermost s and p orbitals.

Electronegativity is the tendency for an atom to attract electrons.

It decreases as it goes down a group because electrons get farther away from the nucleus.

Metals (left side)They let their electrons go easilyLow electronegativity

Nonmetals (right side).They want more electrons.Try to take them away from others

High electronegativity.

Electronegativity Period Trend

Summary of Trends

Atomic and Ionic Radius

Ionization Energy and Electronegativity

Additional Assessment QuestionsAdditional Assessment Questions

For each of the following pairs, predict which atom is larger.

Question 1

a. Mg, Sr

b. Sr, Sn

c. Ge, Sn

d. Ge, Br

e. Cr, W

Topic 5Topic 5

Answers

a. Mg, Sr

b. Sr, Sn

c. Ge, Sn

d. Ge, Br

Sr

Sr

Sn

Ge

e. Cr, W W

Topic 5Topic 5

Additional Assessment QuestionsAdditional Assessment Questions

For each of the following pairs, predict which atom or ion is larger.

Question 2

a. Mg, Mg2+

b. S, S2–

c. Ca2+, Ba2+

d. Cl–, I–

e. Na+, Al3+

Topic 5Topic 5

Additional Assessment QuestionsAdditional Assessment Questions

Answers

a. Mg, Mg2+

b. S, S2–

c. Ca2+, Ba2+

d. Cl–, I–

Mg

S2–

Ba2+

I–

e. Na+, Al3+ Na+

Topic 5Topic 5

Additional Assessment QuestionsAdditional Assessment Questions

For each of the following pairs, predict which atom has the higher first ionization energy.

Question 3

a. Mg, Na

b. S, O

c. Ca, Ba

d. Cl, I

e. Na, Al

f. Se, Br

Topic 5Topic 5

Additional Assessment QuestionsAdditional Assessment Questions

Answers

a. Mg, Na

b. S, O

c. Ca, Ba

d. Cl, I

Mg

O

Ca

Cl

e. Na, Al Al

f. Se, Br Br

Topic 5Topic 5

Additional Assessment QuestionsAdditional Assessment Questions