Into to chemical bonding

Intro to chemical bonding A mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together

Two types of chemical bonds Ionic bonding Bonding that results from the electrical attraction between large numbers of cations and anions Covalent bonding Results from the sharing of electron pair between two atoms

Wait it’s not that simple Bonding isn’t usually purely ionic or covalent it usually falls somewhere in between. The electronegativity is a measure of an atom’s ability to electrons Therefore more time is spent by the electron around the more electronegative atom.

Two types of covalent bonds Nonpolar-covalent bond This bond is a covalent bond in which the bonding electrons are shared equally by the bonded atoms, resulting in a balanced distribution of electrical charge. NO POLES Polar-covalent bond is a covalent bond in which the bonded atoms have an unequal attraction for the shared electrons. HAS POLES LIKE A MAGNET

Non polar polar H H H H + O + - End 6-1

Molecular compounds with covalent bonding A molecule is a neutral group of atoms that are held together by covalent bonds. A molecular compound is a chemical compound whose simplest units are molecules. A chemical formula indicates the relative numbers of atoms of each kind in a chemical compound by using atomic symbols and numerical subscripts.

More bonding A molecular formula shows the types and numbers of atoms combined in a single molecule of a molecular compound A diatomic molecule is a molecule containing only two atoms.

Why? Chemicals bond because they have a lower potential energy when bonded then when they are alone. Remember atoms want to lowest energy always Different chemicals have different energies so bond length of those molecules may differ Bond length is the distance between tow bonded atoms at their minimum potential energy, that is, the average distance between two bonded atoms.

Can we break the bond Bonds can be broken but it takes energy to do this. This energy is called bond energy. The energy required to break a chemical bond and form neutral isolated atoms. Reported in KJ/mol So what we learned is that bond lengths and energies differ based on what and how atoms are bonded together.

The octet rule What is an octet? What does oct mean? So an octet is a set of how many electrons? These valence electrons are in the outer shell of the atom. Atoms will gain lose or share electrons to fill their outer shells with an octet. As always there are exceptions to the octet rule. These atoms can be happy with more or less than an octet in their outer shell.

Electron-dot notation An electron-configuration notation in which only the valence electrons of an atom of a particular element are shown indicated by dots place around the element’s symbol. Example Fluorine F

Lets do these on the board Carbon Potassium Sulfur Argon Lithium Hydrogen Helium

Lewis Structures Expands on electron-dot notation Lewis structures are formulas in which atomic symbols represent nuclei and inner-shell electrons, dot-pairs or dashes between two atomic symbols represent electron pairs in covalent bonds, and dots adjacent to only one atomic symbol represent unshared electrons In Lewis structures the lone dots represent an unshared pair of electrons. Unshared pair is also called a lone pair. A pair of electrons that is not involved in bonding and that belongs exclusively to one atom

Lets do some Lewis structures CH3I H2O NH3 H2S

Structural formula This is the Lewis formula without the electron pairs Indicates the kind, number, arrangement, and bonds but not the unshared pairs of the atoms in a molecule. Just dashes no dots

Bonds and dashes A single bond is a covalent bond produced by the sharing of one pair of electrons between two atoms. Represented by one dash (-) A double bond is a covalent bond produced by the sharing of two pairs of electrons between two atoms Represented by two dashes (=) A triple bond is a covalent bond produced by the sharing of three pairs of electrons between two atoms. Represented by three dashes(=) Double and triple bonds are reffered to a multiple bonds.

Lets do some multiple bonding CH2O CO2 CO HCN

Resonance structures Refers to bonding in molecules or ions that cannot be correctly represented by a single Lewis structure……. Ozone is one of these O3 Lets do it

Ionic bonding Ionic compound is composed of positive and negative ions that are combined so that the numbers of positive and negative charges are equal. Ionic compounds are represented by a formula unit The simplest collection of atoms from which an ionic compound’s formula can be established.

Characteristics of ionic bonding Remember that molecules want the lowest potential energy. In ionic molecules this means forming a crystal and then those crystals forming a lattice Crystal lattice Form by the attractive forces at work Opposite charges, like charges and electrons Table salt looks like this

More about Lattice structures Lattice structures are three-dimensional arrangements of ions Strengths and sizes of these structure differ by ionic compound Bonds strengths in ionic compounds is known as lattice energy The energy released when one mole of an ionic crystalline compound is formed from gaseous ions.

Ionic vs. Molecular compound Greater attraction between molecules Higher melting points Higher boiling points Do not vaporize at room temperature Hard but brittle Ions cant move making it hard But if they do it breaks Lower attraction between molecules Lower melting points Lower boiling points Most vaporize to gas at room temperature Malleable Compounds can move Bend don’t break

Polyatomic ions These bond covalently and ionic Becomes a charged group of compounds Shown with charges Some Lewis structures of polyatomic ions

Metallic bonding Different than in other types of bonding Give metals their properties Good conductors of electricity This property due to the highly mobile valence electrons of the atoms that make up a metal With empty shells in the P-block and or D-block that overlap The electrons can roam freely Delocalized –not belonging to any one electron The attraction between metal atoms and the surrounding sea of electrons is called metallic bonding

Properties of metals….again Good conductors of heat and electricity Due to the fact the electrons are free to move in the network of metal atoms Shiny (luster) The free electrons absorb energy from light then release it giving metals their shine Malleability and Ductility Due to the fact that metallic bonding is the same in all directions. Atoms can slide past another without encountering any resistance or breaking any bonds

Metallic bond strength Varies with nuclear charge and the number of electrons in the metal’s electron sea Heat of vaporization Atoms in the normal state (usually solid) are converted to individual metal atoms in the gaseous state. The amount of heat required is a measure of the strength of the bonds that hold metal together.

Molecular geometry This is the shape of molecules The three-dimensional arrangement of a molecule’s atoms in space The polarity of each bond along with the shape determines Molecular polarity The uneven distribution of molecular charge

VSEPR Theory Stands for Valence-shell, electron-pair repulsion This theory states Repulsion between the sets of valence-level electrons surrounding an atom causes these sets to be orientated as far apart as possible. Gives us all the different shapes of molecules Linear, bent or angular, trigonal-planar Tetrahedral, trigonal-pyramidal, octahedral, trigonal-bipyramidal

Hybridization The mixing of two or more atomic orbitals of similar energies on the same atom to produce new orbitals of equal energies Hybrid orbitals Orbitals of equal energy produced by the combination of two or more orbitals on the same atom

Intermolecular forces The forces of attraction between molecules Dipole-Dipole forces A dipole is created by equal but opposite charges that are separated by a short distance In polar molecules the attraction between particles are dipole-dipole forces This is what keeps water together These forces raise boiling points

More Intermolecular forces Hydrogen bonding The intermolecular force in which a hydrogen atom that is bonded to a highly electronegative atom is attracted to an unshared pair of electrons of an electronegative atom in a nearby molecule Represented by dotted lines London dispersion forces The intermolecular attractions resulting from the constant motion of electrons and the creation of instantaneous dipoles. Named for Fritz London Only forces acting on noble gases and nonpolar molecules Results in the low boiling points of the noble gases Strength increases with the number of electrons This can be seen in the boiling point of the noble gases They increase down the group