covalent & ionic bonds and polarity

covalent bond

a bond where two nuclei of nonmetals are bonded together by their mutual attraction to the same pair of electrons

how does a covalent bond occur?

• two nonmetal atoms collide so that the nuclei are closer than two times the radius

• the electron pair is drawn to the internuclear distance where they can create a concentration of charge

• side ways repulsion increased

• mutual attraction to same pair of electron bonds atoms together

• creates a covalent bond

differences between ionic and covalent bonds

ionic:

• attraction from ions in all directions

• non localized and non directional

• all ions pack together

• forms ionic crystal lattice

covalent

• attraction is localized to the internuclear distance

• attraction is directional along internuclear distance

• ex. in a H₂ bond, another extra hydrogen will not bond as no attraction is available

• forms molecule

How and why do ionic compounds form?

• a non metal and metal must physically collide with enough energy that an electron from the metal is dislodged

• the metal has low IE, easier to remove electron

• the non metal has high EA, the dislodged electron is attracted to the non metal

it is always true that…

丨IE丨 (energy required) > 丨EA丨 (energy released) therefore the electron transfer from metal to nonmetal always requires energy and the ions are less stable than the neutral atoms

how does an ionic crystal lattice form?

• the positive and negative ions attract

• every cation surrounded by a number of anions and so on to maximize attraction

• a great amount of energy is required to create the crystal lattice, but much more is needed to break it apart, so it is stable

• ionic compound is more stable than neutral elements due to high attraction necessary to break apart

endothermic vs exothermic

• Endothermic: Process that absorbs/requires energy 

• Exothermic: releases energy 

Why does covalent bonding result in molecules and not ionic crystal lattices?

• ionic bond: sodium can attract chloride as long as they are relatively close, it is non directional and non localized, which is why they pack together to create a crystal lattice

• covalent bond: the attraction is localized and directional to the internuclear distance and not just anywhere, so ions cannot pack together

what type of bond is this?

single bond

what type of bond is this?

double bond

polarity

uneven distribution of netgative charge in a bond

Partial charges: δ ⁺ or δ^-

• used to indicate the polarity of a covalent bond

• detla positive on less EN element

• detla negative on more EN element

how do you predict what kind of bond will form between elements in a compound?

use differences in electronegativity

electronegativity differences and type of bond

• 0≤ Δ EN≤ 0.4, non-polar or slightly polar

• 0.4 < Δ EN < 1.7, polar covalent bond

• Δ EN ≥ 1.7, ionic compound