Flashcards in Chapter 25 - Periodic Properties Deck (27):
Who published the first periodic table? What did it show
Dmitri Mendeleev - showed the ordering of elements according to atomic weight producing a pattern where similar properties periodically recurred
Who reorganized the period table? Based on what?
Henry Moosely - based on increasing atomic number
What is the periodic law?
States that the chemical properties of the elements are dependent, in a systemic way, upon their atomic numbers
How is there periodic table organized today?
- What do they represent?
- What does the Roman numerals represent?
In periods (rows) and groups (columns)
- There are 7 periods that represent the principal quantum numbers n = 1 to n = 7 and each period is filled sequentially; groups represent elements that have the electronic configuration in valence shell and share similar chemical properties
- They are located above each group and represent the number of valence electrons
What are representative and non-representative/transition elements?
1) Representative: Have s or p sub-levels as their outermost orbitals - Groups IA through VIIA which have incompletely filled s or p sub-shells
2) Non-representative/Transition: Have partly filled d sub-levels, and the lanthanide and actinide series, which have partly filled f sub-levels
What do all elements seek to do?
Gain or lose electrons to achieve a fully filled formation possessed by the inert or noble gases of Group VIIIA
What are the two trends exhibited in the periodic table?
* What does Zeff show?
1) From left to right across a period, protons are added one at a time and the electrons of the outermost shell experience an increasing degree of nuclear attraction, becoming closer and more tightly bound to the nucleus
- Net positive charge from the nucleus is called the effective nuclear charge (Zeff)
2) From top to bottom down a given column, the outermost electrons become less tightly bound to the nucleus because the number of filled principle energy levels increases downward within each group
*Together, the trends show that Zeff is at a maximum for elements top-right and at a minimum for those in the bottom-left
What is the atomic radius equal to?
One-half the distance between the centres of two atoms of that element that are just barely touching each other
What is the trend for atomic radius?
Atomic radius decreases across a period from left to right and increases down a given group
- Largest = bottom-left
What happens to an atom from left to right in regard to atomic radii?
Electrons are added left to right one at a time to the outer energy shell
- Electrons within the same shell do not shield one another from the attractive pull of protons, therefore since the number of protons are increasing left to right, the effective nuclear charge of Zeff increases as well
- The greater positive charge experienced by the valence electrons, the closer those electrons are pulled toward the nucleus and the smaller the atomic radius
What happens from top to bottom in regard to atomic radii?
The number of electrons and filled electron shells increase from top to bottom in a group
- Although the number of valence electrons within a group remain the same, these valence electrons are found further and further from the nucleus as they are in larger energy shells
- Zeff becomes smaller with distance, so valence electrons in higher energy shells will feel less pull from the nucleus
- More electrons comes increased repulsion from the additional negative charge
- Atomic radii increases
What is ionic radius?
The radius of a cation or anion
- Cations = smaller since they possess fewer electrons creating less repulsion
- Anions = larger since they have greater number of electrons creating greater repulsion = larger distance between electrons and larger atomic radius
What is ionization energy?
Energy required to completely remove an electron from a gaseous atom or ion which requires an input of energy (endothermic)
- The closer and more tightly bound an electron is to the nucleus, the more difficult it is to remove and the higher the ionization energy
What is the first ionization energy? Second?
Energy required to remove one valence electron from the parent atom
- It is the energy needed to remove a second valence electron from the univalent ion to form the divalent ion, and so on
Is the second ionization energy always greater than the first? Why?
Yes - they grow increasing larger with each ionization energy
What is the ionization energy trend?
Increases left to right across as period as Zeff increases
Moving down a group, decreases as Zeff decreases
Why does Group IA have low ionization energy?
Because the loss of an electron results in the formation of a stable, noble-gas configuration
What is electron affinity?
- What is Zeff effect on affinity?
The energy change occurs when an electron is added to a gaseous atom, and it represents the ease with which the atom can accept and electron
- The higher the Zeff, the greater the electron affinity will be
There are two sign conventions used in discussing electron affinity, which is the more common?
States that a positive electron affinity value represents energy release when an electron is added to an atom
Ex. X(g) + e- = X- (g)
What is the less common sign convention in regard to electron affinity?
A negative electron affinity represents a released of energy
What are some generalizations about electron affinity?
- Group IIA (alkaline earth metals) have low electron affinity values because they are relatively stable due to their s sub-shell being filled
- Group VIIA (halogens) have high electron affinity because the addition of an electron results in a completely filled shell; a stable configuration
- Group VIIIA (noble gases) have electron affinity of zero because they possess a full shell and cannot accept electrons
What is electronegativity?
A measure of the attraction an atom has for electrons in a chemical bond - the greater it is, the greater the attraction for bonding electrons
- Trend: Increases from left to right across periods and decreases from top to bottom down a group
What is the Pauling electronegativity scale?
- Low Zeff?
- High Zeff?
Ranges from 0.7 (most electropositive - Ce) to 4.0 (more electronegative - F)
- Low Zeff = low electronegativity because nuclei does not attract electrons strongly
- High Zeff = high electronegativity because of the strong pull the nucleus has on electrons
List the types of elements
Review the nomenclature of cations and anions
Describe ion charges of metals and non-metals
Metals: Generally form positive ions
Non-metals: Generally form negative ions