Chapter 6 Section 1 - 4 Chemical Bonding

Chemical Bond… A mutual __________ attraction between the _________ and __________________ of different atoms that binds the atoms together. Most atoms are at a __________ energy state when bonded to other atoms rather than as independent particles

Types of chemical bonds: Covalent Covalent-network Ionic Metallic

Ionic bonding Results from the ____________ attraction between large numbers of _______ (+ ions) and ___________ (- ions) Covalent bonding Results from the ____________ of electron pairs between 2 atoms

Ionic Bonding Δ electronegativity > ________ _____________ differences in electronegativity values between atoms: One atom attracts an e- so strongly that it actually PULLS IT AWAY from the other atom…electron is _______________ Δ electronegativity > ________

Nonpolar Covalent Bond Bonding electrons are shared ____________ by the bonded atoms, resulting in a balanced distribution of electrical charge Δ electronegativity: ____________ (roughly)

Polar-covalent bond Bonding electrons are shared ____________ because one atom pulls, although not very strongly, more on the electron pair than the other atom Δ electronegativity: ______________ Still relatively small differences, so no atom really “wins” & e- is shared

Why would nature favor forming a covalent bond?

Attraction: nucleus of one atom to ______________ Repulsion: both _____ repel…as do both _________ As atoms approach, ____________ increases and potential E goes down Beyond a certain point, ________________increases and E goes up ∴ bottom of valley on E curve is where there is a _______ between attraction & repulsion

MOLECULE: neutral group of atoms held together by _________________ bonds MOLECULAR COMPOUND: a cmpd that is made of molecules MOLECULAR FORMULA: shows the _____________ & ______________ of atoms making up a molecule i.e. H2O DIATOMIC MOLECULE: molecule containing only ________ atoms i.e. H2

Characteristics of the Covalent Bond Bond Length: average distance between 2 bonded atoms (min potential E) In the H2 molecule, the 1s orbitals overlap and result in a increased electron density between the nuclei.

Bond energy: Energy required to ___________ a chemical bond and form neutral isolated atoms Measured in __________________ ________ value Bond energy and bond length values will vary depending on what atoms an element is bonded to…ave values found on tables P.168)

Octet Rule Chemical cmpds tend to form so that each atom, by gaining, losing or sharing electrons, has an ________________ of electrons in its highest (outermost) energy level Example of exceptions: H: only has 2 valence e-s required to reach stability B: only has 6 valence e-s “ “ Some elements have > 8 (occurs when atom bonds with highly electroneg elements & some “d” e-s are involved in bonding

Electron Dot Diagrams Electron configuration notation in which only the valence electrons of an atom of a particular element are shown, indicated by dots placed around the element’s symbol F:

“other” dot diagram format Mg: [Ne]3s2 “paired” electrons are shown as a pair

Lewis Structures Formulas in which…. atomic symbols are represent ___________________________________ Dot-pairs or dashed between 2 atoms represent _____________________________ Dots adjacent to only one atomic symbol represent _____________________________

Lewis structure Structural Formula: indicates the kind, number, arrangement,and bonds .. but NOT the unshared pairs of the atoms in a molecule

Lewis structure Single bond: covalent bond produced by the sharing on ONE pair of electrons between 2 atoms

Draw the Lewis structure for the following molecules: IBr CH3Br F2O SiCl4 C2HCl (????)

Multiple Covalent Bonds DOUBLE BOND sharing of ___ pairs of electrons between 2 atoms TRIPLE BOND sharing of _____ pairs of electrons between 2 atoms Bond Energies triple double single …..triple bonds are _________ and _______

Resonance Structures bonding in molecules or ions that cannot be correctly represented by a single Lewis structure

Covalent-network Bonding Covalent bonding exists throughout a large network of atoms…will be discussed in chapter 12 i.e. carbon atoms in a diamond

Ionic Compound composed of positive and negative ions that are combined so that the number of positive charges are equal to (cancel out) the number of negative charges Na+1Cl-1 Mg+2Cl2-1 (Mg+2Cl-1Cl-1) Not called “molecules”…but called _____________________________

Formation of Ionic Cmpds Atoms form ions when they ______________ e- in order to attain _________________________ Ions reach a ____________ potential E through the electrical forces of attraction between oppositely charged particles when they combine in an orderly arrangement known as a _____________ Forces of repulsion (like-charged ions, adjacent e- clouds) _____________ the forces of attraction (opp-charged ions, nuclei-electron of adj. ions)

Sodium chloride, NaCl The chemical formula of an ionic cmpd is the simplest formula of the cmpd…it does NOT represent a discrete GROUP of separate atoms like a molecule does Covalent bonding: simplest unit is a ________________ Ionic bonding: simples unit is a _________________________

“belong” to any one neighbor “Molecules” – discrete gps of atoms covalently bonded “Formula units” – simplest collection of atoms within an ionic cmpd i.e. NaCl..Na+1 doesn’t “belong” to any one neighbor

Lattice Energy Term used to describe ___________ in ionic cmpds Energy ____________________ when one of an ionic crystalline cmpd is formed from gaseous ions _________ value indicates that E is ________ The __________ the value, the more E released, the more stable the bonding will be (true also for bond E) i.e. NaCl –787.5 kJ/mol

Which ionic cmpd has a higher melting point….MgO or CaO ?

Ionic vs. Covalent Properties strong force that holds _________________ stronger forces of attraction _____________ ions ∴_________ melting & boiling pts; don’t vaporize at room temp MOLECULAR strong covalent bond ____________________________________ _______ F of attraction ___________ molecules ∴melt at __________ temps & many vaporize at room temp

Other ionic properties… ________________: tough for one layer to slide past another layer ______________: if ionic layers DO shift, they “snap” when part of their crystal lattice is shifted

Ionic vs. Covalent Properties non-conductors in solid state because _________________ conductors in ______________ state conductors when _________________ MOLECULAR non-conductors in ________________

Polyatomic Ions A ______________ group of ____________ bonded atoms Combine with ions of opposite charge to form __________________ cmpds

Draw the Lewis structure for the phosphate ion

Metallic Bond Model Metals have _______________ electrons in their highest E level Metals frequently have many _________________________________ Vacant orbitals of adjacent atoms overlap which allows _________________________________

Metallic Bond Model (con’t) “_________________ electrons” - e-s don’t stay in one locality like… covalent bonding: stay in the ________________________________ Ionic bonding: e-s are bound to ________________________________ mobile electrons form a “________ of electrons”

Metallic Bonding the chemical bonding that results from the attraction between ___________________________________ ______________ sharing of many e-s where each atom contributes its valence e-s which are then free to move about the mostly vacant outer orbitals of all the metal atoms

Metallic Properties __________ electrical & thermal conductivity due to high mobility and delocalization of e-s _____________ (shine) metals absorb E and become “excited” very easily because many of their orbitals are separated by extremely small ∆E…shine occurs when photons are emitted when excited e-s return to ground state

Metallic Prop. (con’t) _______________________ (ability to be hammered/beaten into thin sheets) and ____________________ (ability to be drawn, pulled, or extruded to produce wire) because metallic bonding is the same in all directions and a shift in layers of atoms is inconsequential

Metallic Bond Strength Expressed in the _________________ value where the bonded atoms in the metallic solid state are converted into ___________________ metal atoms in the gaseous state (usually↑heat of vap, the ____ the bond strength) Determined by ___________________________________