Basics of Chemical Bonding and the Energetics of Chemical Bonding

A few main ideas about bonding and energy…. A chemical bond is a ________1_________ that holds two atoms together. Chemical bonds involve the ____2____ or ____3_____ of one or more electrons between two atoms. There are 3 main types of chemical bonds: _____4____, _____5____, and ____6____. Nature prefers __7__ energy. Low ____8_____ energy equals high ___9______. Chemical bonding allows each atom involved to reach a lower potential energy state and achieve greater stability.

A physical analogy to better understand the energetics of chemical bonding… Ball at top of hill – high potential energy, low stability i.e. unstable Ball at base of hill – lower potential energy, higher stability i.e. more stable Increasing Potential Energy

The main point here is that ….. Through the process of chemical bonding (which allows atoms to achieve stable octets/duets in the ____10____ shell), atoms get to a lower chemical potential energy state. Chemical potential energy is stored within the matter by virtue of the ______11_____ of its particles and via the chemical bonds between particles. Thus, chemical bonding of atoms to form compounds is always an ______12______ process! It releases energy from the ___13____ to the _____14______.

Video Clip – The formation of NaCl NaCl sodium chloride is an ionic compound formed via the chemical reaction: 2Na(s) + Cl2(g)  2NaCl “Two moles of sodium atoms react with one mole of chlorine gas molecules to form 2 moles of sodium chloride formula units”

The Basics of an Ionic Bond An ionic bond is an attraction between oppositely charged ___15___. In an ionic bond, a ____16____ atom gives away one or more electrons from its valence shell to form a ____17____. A _____18_____ atom steals these same electrons to complete its valence shell and form an ____19____. The oppositely charged ions that form then ____20____ together to form the ionic compound..

Flowchart of the Ionic Bond Formation Process

Diagramming Ionic Bond Formation with Electron Dot Diagrams

Basics of the Ionic Bond - Continued The essence of the ionic bond is the ______21______ (postive-negative) attraction between the newly formed cations and anions after electron ____22____ has occurred. The resulting pure substance, made of metallic and nonmetallic atoms bonded together, is called an ________23_________. The number of ____24____ charges balances the number of ____25____ charges so that the ionic compound is ____26____ or charge- ____27_____. It is neither positive or negative as a whole, though it is made of __28__ inside!

Ionic Compounds – Crystal Lattice Structure NaCl (sodium chloride) MgBr2 (magnesium bromide)

Ionic Compounds - Structure When cations and anions join together, they never form ____29_____. Instead, they join up as a continuous, 3-d, geometric structure known as a ______30________. In the crystal lattice, each ___31___ is surrounded only by neighboring ___32___ and vice versa. This is necessary in order to prevent + + or - - repulsions that would break the lattice apart.

Ionic Compounds – Structure and Representative Particles The representative particle of an ionic compound is a _______33_______. It tells us what the lowest, whole-number ___34___ of cations to anions is in the crystal structure. The simplest repeating, piece of any crystal lattice is a _____35_____. It is also represented by a formula unit.

Lattice Energies of Ionic Compounds Lattice energy is the amount of energy _____36______ when one __37__ of an ionic compound forms a crystal lattice structure during a chemical reaction between the constituent metallic and nonmetallic atoms. (Units of kJ/mol) Since energy is released from the chemical system to the surroundings (i.e. exothermic), the sign for lattice energy is always ____38____!

Lattice Energies of Ionic Compounds (continued) In order to break apart a crystal lattice back into the constituent atoms, we would need to put that energy back into the chemical system. Thus, breaking bonds is _____39_____! (It always takes energy to break things!) The energy to break bonds is called ______40_______. For ionic compounds, the bond energy per mole of the compound is equal to the lattice energy but _____41_____ in sign.

Illustrating Lattice Energy vs. Bond Energy

What can we infer from lattice energies of ionic compounds? Attribute of the crystal lattice structure If lattice energy is more negative…. If lattice energy is less negative…. Sizes (radii) of ions present Charges of ions present Strength of the ionic bonds between ions Stability of the ionic compound crystal lattice structure Melting point of the ionic compound