Periodic Table & Trends Flashcards
What are the two major factors that contribute to periodic trends?
- As you move from left to right, effective nuclear charge increases
- As you move from top to bottom, radius of the valence shell increases moving further away from the nucleus
Which periodic trends are determined by effective nuclear charge?
- Ionization energy
- Atomic radius
- Electron affinity
What is the atomic radius its trend?
Distance from center of nucleus to exterior of valence electron cloud. Radius decreases as you move up and to the right
What is ionization energy, its units, and its trend? How is its trend different?
Ionization energy is the energy measured in kJ/mol required to remove the outermost electron from an atom. It increases as you move up and to the right. Compared to electronegativity, ionization energy trend is very erratic because it accounts for half-filled and filled orbital stability
What is electron affinity, its units, and its trend?
Electron affinity is the energy (kJ/mol) absorbed (endothermic) or released (exothermic) when an electron is added to the valence shell of an atom. It increases as you move up and to the right
What is electronegativity and its trend?
Electronegativity is the willingness of an atom to gain and retain an electron from a neighboring atom in a covalent bond. It increases are you move up and to the right
What is the general principle behind the exceptions to the general trends? What two trends do they effect?
Half or completely filled subshells - electron affinity and ionization energy
Column with nitrogen vs. column with oxygen: nitrogen has all of its p orbitals half-filled, therefore, it requires greater energy to remove an electron (ionization energy) and when an electron is added less energy will be given off, if any (electron affinity)
What is the general rule regarding the atomic size of cations and ions?
Generally, cations are smaller than neutral and anions due to less electron repulsion. Anions are larger than neutral atoms and cations due to greater electron repulsion
What has a greater atomic radius, hydrogen or helium?
Hydrogen has smaller radius. The electrons in the helium atom are so close together that it causes repulsion
What is the relationship between bond length and atomic radius?
The more tightly held the valence electrons are to the nucleus (shorter atomic radius) the shorter the bond will be between two atoms. Shorter bonds are stronger bonds
What are the two exceptions to ionization energy?
Half or completely filled subshells
What is the relationship between ionization energy and oxidation/reduction potentials?
MORE NEEDED ON THIS
Why is second ionization energy always greater than first ionization energy?
Electrostatics - removal of second electron is more difficult due to stronger
Higher electron affinity is associated with a more negative or positive energy?
Negative energy. A higher affinity means that the atom becomes more stable upon an addition of an electron to its valence shell, thereby releasing more energy (exothermic). Higher electron affinity is associated with a more negative energy
How is electronegativity measured? How is bond determined to be ionic or covalent?
Pauling Scale is measured from 0.9 for Na and 4.0 for F. A bond is determined to be ionic if the electronegativity difference of the atoms is greater than 2.0 and covalent if less than 2. For those bonds that are between 2 and 1.5, they are said to be polar covalent. Below 1.5 is nonpolar covalent
How is chemical reactivity of an atom determined?
Atoms of the same family (column) have similar reactivity because they have the same valence electrons
What is the name of the family containing oxygen
Chalcogens
Why are alkali metals strong reducing agents?
By losing their only valence s electron, they obtain a complete octet, stabalizing the atom.
Why does the reactivity differ between alkali metals? In presence of molecular oxygen, what effect do the differences of reactivity have on the formation of oxides?
Ionization energy decreases as more shells are added to an atom. As you move down the alkali family, its easier to lose an electron thus becoming a more reactive species. As you move down the family/group, the elements become more corrosive/susceptible to oxidation. This can be seen by the different oxide formations and the stoichiometric relationships in the reactions.
What is the product of mixing solid alkali metal and water?
Metal hydroxide + hydrogen gas
What are the three different oxides that alkali metals form and why do they differ?
- 4 Lithium atoms + 1 molecule O2 –> 2 molecules Li2O(s) [oxide[
- 2 Sodium atoms + 1 molecule O2 –> 1 molecule Na2O2 [peroxide]
- 1 K, Rb, Cs(s) atom + 1molecule O2 –> MO2 [superoxide]
Why would diatomic nitrogen corrode lithium metal moreso than diatomic bromine?
Diatomic nitrogen has a stronger reduction potential than bromine does. This is required because, relative to the elements down the alkali family, lithium does not have a strong oxidation potential, requiring a species with a strong reduction potential in order for the reaction to occur.
For bromine to become reduced, which metal would be the better reducing agent?
Because bromine’s reduction potential is not that strong relative to the other halogens, it requires a metal with a strong oxidation potential. Oxidation potential increases as you move down the alkali metal family. Cesium is stronger than Rubidium and Potassium in terms of oxidation potential. Therefore, for bromine to react, Cesium would be the best choice.
Of the alkali metals, which are the stronger reducing agents?
The oxidation potential increases as you move down the alkali family due to increase shielding
