Chapter 2: Periodic Table

Periodic law

The chemical and physical properties of the elements are dependent in a periodic way upon their atomic numbers

Arrangement of periodic table

Periods are rows

• 7 periods representing the principle quantum numbers n=1 through n=7

Groups are columns

• Contain elements that have same electronic configurations in their valence shells

A elements

Representative elements and are included in groups IA-VIIA

• Valence electrons in the orbitals of either s/p sub shells 

• ex: in group VA, there is 5 valence electrons 

B elements 

Nonrepresentative elements 

• Transition metals: valences e- in the s and d sub shells 

• Lanthanide and actinide series which have valence electrons in the s and f sub shells 

• May have unexpected electron configurations 

Metals

Found on the left and middle of the periodic table

Active, transition, lanthanide and active series metals

Qualities:

• lustrous solids except for mercury

• high melting points and densities except lithium

• Malleable and ductile (can be pulled into wires)

Atomically:

• Low electronegativity, large atomic radium, small ionic radius, low ionization energy, low electron affinity

• Easily gives up electrons

Why are metals good conductors for heat and energy

Have two or more oxidation states (charges when forming bonds)

• valence electrons are loosely held, they are free to move

Valence electrons in metals

Active: found in the s subshell

Transition metals: found in s and d sub shells

Lanthanide and actinide: found in s and f sub shells

Nonmetals

Found predominantly on the upper right side of the periodic table 

• Qualities: 

  • Brittle in the solid state and are not metallic

  • high ionization energy, electron affinities, and electronegative

  • small atomic radius and large ionic radius

  • poor conductors of heat due to inability to easily give up electrons

Metalloids

Also semimetals cause they have properties of both metals and nonmetals

• reactivity depends on the elements which they are reacting with

• stair-step group of elements 

• electronegativity and ionization energies of metalloids lie between metals and nonmetals, making physical properties widely varied and can be combined 

• make good semiconductors 

What is z_eff or the effective nuclear charge and what periodic trend is seen relating to this charge?`

The electrostatic attraction between the valence shell electrons and the nucleus that includes positively charged protons

Trend:

• For elements in the same period, Zeff increases from left to right

• As one moves down the elements of a given group, Zeff remains constant, as with an increase in protons comes an increase in separation with valence electrons, meaning electrons are held less tightly

What trend is seen with noble gases?

Elements can gain or lose an electron in order to achieve a stable octet formation representative of the noble gas

Definition of atomic radius of an element and trends seen through periodic table

Equal to ½ of the distance between centers of two atoms pf an element that are briefly in contact with each other

Trend: Electrons are being added to the outermost shell while protons are being added, increasing the pull between the nucleus and the outer shell, decreasing the atomic radius as one moves across a period from left to right

• left → right, atomic radius decreases

• top → bottom, atomic radius increases as Zeff remains constant but there are a greater number of inner shells as you move down

Generalizations made about the relations between metals and electrons and how that impacts ionic radii

• Metals lose electrons and become more positive

  • Metals closer to the metalloid line have more electrons to lose to achieve electron configuration seen in group 19, so the radii of metals closer to the metalloid line will have a smaller ionic radius

• Non metals gain electrons and become more negative

  • Non metals close to the metalloid line require more electrons than other nonmetals to achieve electronic configuration seen in group 18, so they possess a larger ionic radius that their counterparts closer to group 18

• Metalloids tend to follow the trend based on what side they are of the metalloid line

Define ionization energy and describe the trend seen 

Energy required to remove an electron from a gaseous species 

• endothermic process as it requires an input of heat 

• the greater an atoms Zeff is, the more tightly the electrons are bound, requiring more energy 

Trend: Left → right, ionization energy increases as Zeff increases 

top → bottom, ionization energy decreases 

Second ionization energy

energy necessary to remove the second electron from the univalent cation to form the divalent cation

• requires an increasing amount of energy because the removal of more than one electron means the electron is being removed from an increasingly cationic species (positive)

First ionization energy

Energy necessary to remove the first electron

Active metals

Found in groups 1 and 2, have such a low ionization energy that they do not exist in their neutral forms

Define electron affinity and the period trend

The energy dissipated by a gaseous species when it gains an electron

• exothermic process

• the stronger the electrostatic pull, higher Zeff, the greater the release will be when the atom gains electrons

Trends:

• left → right, electron affinity increases

• top → down, electron affinity decreases

However, for noble gases they have an electron affinity of 0 because they already have a stable octet

Define electronegativity and the trend

Measure of the attractive force that an atom will exert on an electron in a chemical bond

• greater the electronegativity, the more it attracts electrons within a bond

• proportional to ionization energies except first 3 noble gases

Trends:

• left → right, increasing electronegativity

• top → bottom, decreasing electronegativity

Alkali metals 

Group 1

• low densities but majority of metal properties 

• only one loosely bound electron 

• Zeff values are low, having a large atomic radius 

• readily react with nonmetals, especially halogens 

• high reactivity with water and air 

• active metal with group 2

Alkaline earth metals

Group 2

• Possess many characteristics of metals

• two electrons in their valence shell, which are easily removed to form divalent cations

• active metal with group 1

Chalocogens

Group 16

• group of nonmetals and metalloids

• each have six electrons in their valence electron shell

• generally have small atomic radii and large ionic radii

• important for biological functions, ex: oxygen

Halogens

Group 17

• highly reactive nonmetals with seven valence electrons

• desperate to complete octets by gaining one additional electron

• especially reactive towards alkali and alkaline earth metals

• normally found as halides, diatomic molecules

Noble gases 

Minimal chemical reactivity due to their filled valence shells 

• high ionization energies, little tendency to gain or lose electrons 

• low boiling points and exist at room temperature 

Transition elements

Groups 3-12

• Metals have such low electron affinities, low ionization energies, and low electronegativities

• very hard and high melting and boiling points

• malleable and good conductors due to loosely held electrons that progressively fill the d-orbitals in their valence shells

• can have different charged forms or oxidation states, which often correspond to different colors, so they can form many different ionic compounds

• tend to associate in solutions either with water or nonmetals

• forms complexes that splits the d-orbitals into two, enabling many complexes to absorb frequencies of light, and reflect frequencies to give characteristic colors