Periodic Trends, Bond Polarity, Formal Charge, Octet

Question 1

Electronegativity

Answer 1

• the tendency of an atom to attract a pair of bonding electrons from another atom
• atoms with a greater Eneg attract e density from other atoms but also hold their valence electrons closer to their nucleus
• Eneg is a function of atomic size and effective nuclear charge
• Eneg increases go left to right across the periodic table and UP the periodic table
• F>O>N>Cl>Br>I>S>C>H

Question 2

Atomic Radius

Answer 2

• half the distance between the nuclei of two atoms bonded together
• increases as you go DOWN the periodic columns and increases as you go right to left

Question 3

Bond order

Answer 3

• the number of covalent bonds shared by two atoms
• single bonds=1, double bonds = 2 (1 pi, 1 sigma), triple bonds= 3 (2 pi, 1 sigma)
• the greater amount of s character an atom possesses, the shorter the bond it will make

Question 4

Bond length

Answer 4

• the distance between the nuclei of the two bonded atoms once they have reaches their bond energy minimum

Question 5

Bond strength

Answer 5

• the energy required to homolytically break a bond; corresponds to bond length

Question 6

Bond Dipole

Answer 6

• the polarization of a covalent bond towards one atom created by a difference in Eneg between the 2 atoms
• indicated by partial charges
• they point in direction of the more Eneg atom

Question 7

Dipole moment

Answer 7

• the magnitude of a charge on either atom in a bonding interaction multiplied by the distance between the two charges
• they are a product of the directionality and magnitude of individual bond dipoles that reinforce each other

Question 8

Polar molecule

Answer 8

• a compound that possesses a molecular dipole moment

- dipoles reinforce each other and have overall directionality, creating a defined region of positive and neg density

Question 9

Non-polar molecule

Answer 9

• a compound that lacks a molecular dipole moment
• they either have no notable bond dipoles or they possess symmetrical bond dipoles
• a non polar molecule can possess individual bond dipoles but existing bond dipoles will cancel out

Question 10

Formal Charge

Answer 10

• the number of valence electrons minus the number of electrons the atom directly possesses
• valence = electrons in the outermost shell
• possessed = all lone pair electrons and half the number of electrons in bonding interactions

Question 11

Bonding capacity and exceptions

Answer 11

• the max number of distinct bonds an atom naturally makes to other atoms/groups
• atoms in the same periodic column will have a similar bonding capacity
• exceptions:
• — sulfur (S) - can take on 6 covalent bonds and remain neutral but it can also be neutral with only 2 covalent bonds
• — phosphorus (P) can take on 5 covalent bonds and remain neutral but also be neutral with only 3 covalent bonds
• — boron (B) and aluminum (Al) make 3 bonds when neutral and possess an empty p orbital (sp2 hybridized) and they will take on a formal negative charge when they take on a 4th bond

Question 12

neutral bonding capacity of some atoms

Answer 12

C - 4 bonds 
N - 3 bonds, 1 lone pair
O - 2 bonds, 2 lone pair
Halogens - 1 bond, 3 lone pairs 
B and Al - 3 bonds, no lone pairs

Question 13

Octet rule

Answer 13

• atoms will share, accept, or donate electrons to fill or achieve an outer shell with 8 electrons
• add up all the electrons an atom is sharing in covalent bonds plus lone pairs to determine whether or not it possesses a full octet
• atoms can possess a formal charge and still have a full octet (ex. O in H3O+ or N in NH4+)