Chapter 12 Ionic Bonding Transfer of electrons Covalent Bonding Sharing of electrons Metallic Bonding Sea of electrons Intermolecular Forces

BONDING WITH ELECTRONS IONIC BOND is the attraction of a cation (positive ion) to an anion (negative ion) so that the overall charge on the compound is zero. VALENCE ELECTRON are electrons responsible for the chemical properties of atoms and are in the outer energy level. CORE ELECTRON-those in the inner energy levels. Atoms in the same column have the same valence electrons.

BONDING WITH ELECTRONS Easily found by looking up the group number on the periodic table. Only valence electrons involved with bonding. An ionic bond is formed by the transfer of electrons from a metal to a non-metal OCTET RULE: All atoms bonded in a compound get the same number of electrons as the nearest Nobel gas.

LEWIS DOT STRUCTURE Show the outer number of electrons as dots Write the symbol. Put one dot for each valence electron Don’t pair up until they have to X

The Lewis Dot Structure for Nitrogen l Nitrogen has 5 valence electrons. l First we write the symbol. N l Then add 1 electron at a time to each side. l Until they are forced to pair up.

Write the electron dot diagram for Na Mg C O F Ne He

Electron Dots For Cations Metals will have few valence electrons These will come off Forming positive ions Ca Ca +2

Electron Dots For Anions Nonmetals will have many valence.electrons. They will gain electrons to fill outer shell. P P -3

Stable Electron Configurations All atoms react to achieve noble gas configuration. This is called the octet rule. KNOW THIS!!! Noble gases have 8 valence electrons. Except He with 2 which is a full outer level electron shell Ar

Ionic Bonding Anions and cations are held together by opposite charges. The opposite charge is an electrostatic force that holds the ions together. Ionic compounds are called salts. Simplest ratio is called the empirical formula. The bond is formed through the transfer of electrons

Ionic Bonding Na Cl Electrons are transferred to achieve noble gas configuration. Na + Cl -

Properties of Ionic Compounds CRYSTAL LATTICE: A regular repeating arrangement of ions in the solid. Ions are strongly bonded. Structure is rigid. High melting points- because of strong forces between ions. Dissolved in water they conduct.

Ionic solids are brittle Strong Repulsion breaks crystal apart

Covalent bonding Properties of covalent compounds Share electrons so that each element has a full valence level. Low melting and boiling points. Solids, liquids and gases at STP. Not conductors. Some not water soluble, do not form ions in solution.

How does H 2 form? The nuclei repel But they are attracted to electrons They share the electrons ++

Covalent bonds Sharing valence electrons to achieve Nobel gas electron configuration. Nonmetals hold onto their valence electrons. Still want noble gas configuration. Sharing electrons, both atoms get to count the electrons toward noble gas configuration, 8. Shared pair are 2 electrons shared by 2 atoms forming a covalent bond.

Covalent bonding l Fluorine has seven valence electrons l A second F atom also has seven l By sharing electrons l Both end with full orbitals FF 8 Valence electrons

Single Covalent Bond A sharing of two valence electrons, one pair. Only nonmetals and Hydrogen. Each atom now has 8 in valence level, octet rule FF

Multiple Bonds Sometimes atoms share more than one pair of valence electrons. A double bond is when atoms share two pair (4) of electrons. A triple bond is when atoms share three pair (6) of electrons. O O

Electronegativity l A measure of how strongly the atoms attract electrons in a bond. l The bigger the electronegativity difference the more polar the bond. Unequal sharing is a polar bond. l The difference is between the central atom and the atoms bonded to it. l Covalent nonpolar l Covalent polar l >2.0 Ionic (# 2 polar has electronegativity difference >.5 to 1.9)( #7 e. n. diff >.5<2.0)

Water Each hydrogen has 1 valence electron The oxygen has 6 valence electrons 2 H atoms needed to make 8 for O They share 8 to make each other happy H O H

Water The second hydrogen attaches Every atom has full energy levels Calculate electronegativity by subtracting the O number from the H number. Water is polar because the electronegativity is = to 1.4 Water has a dipole because each end has a slight charge. H O H

PROPERTIES OF WATER High boiling point because of H bonding between water molecules. Strong intermolecular (between water molecules) forces keep the molecules from changing phase easily. Universal solvent because of its polar ends. Hydrogen bonds form between molecules when H is bonded to highly electronegative and small atoms. Polar covalent molecule water1.htm

INTERMOLECULAR FORCES between molecules DIPOLE-DIPOLE: Dipole-dipole forces are attractive forces between the positive end of one polar molecule and the negative end of another polar molecule. The partially positive end of a polar molecule is attracted to the partially negative end of another. The closer the molecule, the Stronger the force! The stronger The force, the higher the boiling point.

INTERMOLECULAR FORCES between molecules HYDROGEN BONDING: Hydrogen bonding is a special type of dipole-dipole attraction between molecules, not a covalent bond to a hydrogen atom. It results from the attractive force between a hydrogen atom covalently bonded to a very electronegative atom such as a N, O, or F atom and another very electronegative atom. INCREASES BOILING POINT! H-bonding between small atoms With high electronegativities.

INTERMOLECULAR FORCES between molecules DISPERSION FORCES Force between molecules made up of atoms with no imbalance in electronegativity (non-polar molecules). Non-polar molecules act like dipoles. Caused by slight imbalance in electron cloud.

The melting and boiling points of noble gases are very low in comparison to those of other substances of same atomic masses. This indicates that only weak dispersion forces or are present between the atoms of the noble gases in the liquid or the solid state. The dispersion force increases with the increase in the size of the atom; the boiling and melting points increase from He to Rn.

ORDER OF BOND STRENGTH IONIC METALLIC POLAR COVALENT COVALENT INTERMOLCULAR FORCES HYDROGEN BOND DIPOLE -DIPOLE DISPERSION FORCE

LEWIS DOT STRUCTURE Represents the valence electron = ELECTRON DOT DIAGRAM Electrons from the valence level are represented around the symbol for the element. Count up the total number of valence e- Write down the symbols Make a trial drawing. The # of e- should = what you counted in step 1. Too few pairs to equal 8? Maybe it has a multiple bond. Some will not follow the octet rule, they may have a coordinate covalent bond. Exceptions to the octet rule occur and the central atom may have more or less than 8.

Examples NH 3 N - has 5 valence electrons wants 8 H - has 1 valence electrons wants 2 N will attach to 3 H atoms. N now has 8 and each H has 2 N H H H

What element is in the center? H and O are rarely if ever in the center. Paired e- pairs before unpaired e- pairs. C and Si always at the center The atom with the lowest electronegativity is usually the center.

l CO 2 - Carbon is central atom Carbon has 4 valence electrons Attaching 1 oxygen leaves the oxygen 1 short and the carbon 3 short l The only solution is to share more l Requires two double bonds l Each atom gets to count all the atoms in the bond O CO 8 valence electrons

Another way of indicating bonds Often use a line to indicate a bond Called a structural formula Each line is 2 valence electrons HHO = HHO

Structural Examples C has 8 electrons because each line is 2 electrons Same for N6 electrons in bonds and 1 lone pair Lone Pair is a pair of electrons on the atom not attached to another atom H CN C O H H

HCN l Put in single bonds l Need 2 more bonds l Must go between C and N l Uses 8 electrons - 2 more to add l Must go on N to fill octet NHC

POLYATOMIC IONS IONS FORMED FROM NON-METALS THAT SHARE A SINGLE CHARGE OF -1,-2, OR -3 OVER THE ENTIRE GROUP OF ATOMS. COVALENTLY BONDED NON-METALS THAT GAIN A CHARGE FROM THE TRANSFER OF ELECTRONS. Covalently bonded polyatomic ions will form an ionic compound with another ion.

SHAPES OF MOLECULES VSEPR: Valence shell electron pair repulsion Electrons repel each other and determine the shape of the molecule.

METALLIC BONDS Between metal atoms electrons freely move around (metal atoms close together) to form a bond between all of the metals. This type of bonding is what makes metals so strong, malleable, conductible, and often shiny (metallic luster). This strong bond is also why there is such a high boiling point and melting point for most metals.

BOND COMPARISON Ionic Bond Covalent BondMetallic Bond The transfer of electrons between two atoms having different electro negativities forms this bond. This bond is formed by the mutual sharing of electrons between same or different elements. This bond is formed due to the attraction between nuclei and the mobile electrons in a metal lattice. This is a strong bond due to electrostatic force of attraction. This is also a fairly strong bond because the electron pair is strongly attracted by two nuclei. This is a weak bond due to the simultaneous attraction of the electrons by a large number of nuclei This bond makes substances hard and brittle. This bond can be polar or non- polar. This bond makes substances malleable and ductile.

“LIKE DISSOLVES LIKE” Polar substance will dissolve polar substances. Non-polar substances will dissolve non-polar substances. Oil will not dissolve in water because water is polar and oil is non-polar