CHEMICAL BONDING

A little background info first…

Elements  Substance that cannot be separated or broken down into simpler substances by chemical means.  Ex’s- any box on the periodic table  Made of only 1 type of atom  The smallest unit of an element that maintains the properties of that element  HUH?

The smallest unit of an element that maintains the properties of that element???  The element sodium has certain properties  11 protons, 11 electrons, etc and that determines properties like boiiling point, etc.

Compounds  Molecules made by atoms of two or more elements bonded together -always in a definite ratio Elements  Molecules made of just one element Na (sodium) NaCl (sodium chloride/salt)

Molecules  Two or more atoms bonded together…  They can be two of the same element or two different elements (compounds)  All compounds are molecules, but not all molecules are compounds.  Ex- O2, NaCl, etc.

Compounds cont…  Substance made of atoms of 2 or more different elements that are CHEMICALLY combined.  Means they are bonded by the electrons!  Elements are combined in a definite way and this changes their properties Na - lethal if ingested Cl- lethal if ingested NaCl- table salt

Let’s start the real notes…

Compound/Molecule  Chemical combination of 2 or more atoms/elements.  Properties of the compound are unlike those of the elements that make it. (table salt ex)  Represented by a formula that gives the ratio of atoms of the elements.  Ex- The formula NaCl tells you that salt is a compound made of one Na and one Cl. The ratio is then 1:1

Chemical Bond  Force which holds atoms together.  3 Types: Metallic Ionic Covalent Polar Nonpolar

Metallic Bonds  Formed between 2 or more metal atoms (elements).  Valence electrons overlap.  The electrons are free to move about all the atoms; therefore, they are good conductors of electricity.  Ex) Mg, Cu, Fe, etc. form these types of bonds

Ionic Bonds (formed in ionic compounds)  IONS are the basic unit (atom with a charge).

How are these ions made?  Reminder…  What charge does an electron have?  So what would happen to the atom if they LOSE one? Would they get more positive or more negative overall???

ION PREDICTION FROM PERIODIC TABLE…

IONS  If you mess with the electrons you change the overall charge of the atom…an atom that is no longer neutral is called an ION.  ANION- has a negative charge  Means you added an electron!  CATION- has a positive charge  Means you lost an electron

Let’s look at our families- What ion will each form?  It all starts with the noble gases… Everyone wants to be NOBLE

These are the “magic numbers”  Each of these atomic numbers will make a “full outer shell”  Other families will lose or gain electrons to get the these “numbers”

Alkali Metals  All (except hydrogen- of course) will lose one electron to form a __________ charge.  (+1)

Alkaline Earth Metals  All will lose two electrons to form a __________ charge.  (+2) Ex- A neutral Mg atom has 12 protons and 12 electrons (+12) + (-12) = 0 A Mg ion has 12 protons and only 10 electrons (+12) + (-10) = +2

Boron Family  All will lose three electron to form a ____ charge.  (+3)

We don’t do much with the Nitrogen and Carbon families in ion formation…you will understand more about why soon…

Oxygen Family  All will gain two electrons to form a __________ charge.  (-2) Ex- A neutral Oxygen atom has 8 protons and 8 electrons (+8) + (-8) = 0 An Oxygen ion has 8 protons and 10 electrons (+8) + (-10) = (-2)

HALOGENS  All will gain one electrons to form a __________ charge.  (-1)

How about those noble gases?  They will NOT FORM IONS!!!

How do ions stick together?  Force of attraction between oppositely charged ions.  (anion & cation)  Ionic bonds are very strong bonds.  Formed between metal & nonmetal atoms (elements).  Electronegativity difference between the atoms is 1.7 or greater. (see table on last page of notes)  Ex) Na & Cl

Ionic Compounds: pack into a pattern (crystal; lattice) have very high melting points.

Ionic Compound Cont… Dissolve in water (H 2 O), and ions are then free to move (dissociate). Conduct electric current.

Let’s Draw Some:  Do you remember how to draw a bohr model?  Draw one for Sodium and one for Chlorine  What do you think will happen?

Bond Diagrams  Ionic Bond- -lose & gain electrons  Ex. NaCl

Lets make some Lewis Dot diagrams!!!  Draw a Lewis Dot for Na & Cl.  Draw an arrow to show what the electron will do  Finally draw the ions in the bond.

Let’s put it all together…

Lewis Dot Diagrams 

Try some more…  Ca + O  Na + O  Subscripts = __________________________

Covalent Bonds (formed in molecular/covalent compounds)  Atoms are the basic unit. (atoms bond to form them)  Covalent bonds are firm, but molecules not strongly held together.  Force between atoms that share electrons.

Let’s draw some!  Remember covalent bonds SHARE electrons, so there is no drawing arrows.  Ex- F 2

Lewis Dot Diagrams…

Steps to help you…  Draw the lewis of each kind of atom in the compound.  Highlight/circle which electrons will be shared  When you draw your molecule-  Draw the center atom in the molecule with all 8 valence electrons (use two “types” like x’s and o’s to show where they came from)  Draw in your other atoms and their valence electrons  Circle each atoms’ “8 electrons”- they will overlap each other where they share

Ex- Cl 2

Covalent/ Molecular Compounds: Not packed into a pattern. Have low melting points. May not dissolve in water (H 2 O), but some can. Do not conduct electricity; do not dissociate.

Kinds of Covalent Bonds  Can share different number of electrons: Single- share ONE pair of electrons Double- share TWO pair of electrons Triple- share THREE pairs of electrons  Can be polar covalent or nonpolar covalent bonds.

Polar vs Nonpolar Covalent Bonding

How do you know which type of bond will form? Use two rules:  Calculation using electronegativity values on a periodic table: (Note: if they are both/all metals, automatically, it is a metallic bond!)  Subtract the values of the 2 elements (larger minus smaller)  If difference is: = nonpolar covalent bond = polar covalent bond 1.7 & up= ionic bond

Electronegativity Differences summary… If difference is: Electronegativities are not different enough to steal the electron away, but there will be a “bully” who hugs the electrons closer If differenc is 1.7 & up Electronegativities are so great that one atom will steal the electron away difference Electronegativities are the same, so the atoms will share nicely

A second way… “rule of thumb”  2) Periodic table/metal, nonmetal rule (Rule of thumb):  Metal and Metal = metallic bond  Metal and nonmetal = ionic bond  Nonmetal and nonmetal = covalent All same nonmetal = nonpolar covalent bond Different nonmetals = polar covalent bond

Rule of thumb summary… Two different nonmetals A metal with a nonmetal Two Nonmetals Both the same nonmetal

Naming Rules:  Naming Chemical Compounds  Ionic Compounds:  Ionic compounds are formed when a metal atom donates one or more electrons to a nonmetal atom. This forms an anion and a cation. Which one is which?  The metal will form a _______________.  The nonmetal will form a ________________.

Below are the rules for naming ionic compounds:  1. Write the metal (cation) name first. (It does not change)  2. Write the nonmetal (anion) name next but make a slight change: Take off the end of the name and add “–ide” instead.  Ex- Chlorine becomes “Chloride,” Oxygen becomes “Oxide” 

Covalent Compounds:  Covalent compounds are formed when two nonmetals share electrons.  Rules 1. The first element is named first, using the elements name.  2. Second element is named as an Anion (suffix "-ide")  3. Prefixes are used to denote the number of atoms  4. "Mono" is not used to name the first element  Note: when the addition of the Greek prefix places two vowels adjacent to one another, the "a" (or the "o") at the end of the Greek prefix is usually dropped; e.g., "nonaoxide" would be written as "nonoxide", and "monooxide" would be written as "monoxide". The "i" at the end of the prefixes "di-" and "tri-" are never dropped.