CHEMICAL BONDING

THERE ARE TWO KINDS OF PURE SUBSTANCES

ElementsCompounds

Let’s start the new notes…

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 boiling point, etc.

Forming a Compound Compounds- have properties unlike

those of their elements ex. Na-shiny, soft, grey metal Cl- green-yellow gas NaCl- forms table saltChemical formula- tells what elements it

contains & the ratio of the atoms of those elements

ex. H2O, Na+1Cl-1 Subscript-indicates #atoms

Superscript-indicates charge

Compounds cont…

Substance made of atoms of 2 or more different elements that are CHEMICALLY combined. Means they are bonded by the valence electrons!

Elements are combined in a definite way and this changes their properties

Na- lethal if ingested Cl- lethal if ingested

NaCl- table 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 Molecules made

by atoms of two or more elements bonded together -always in a definite ratio

Elements Made of just one

type of atom Ex. Sodium is

only made of Na atoms

Na (sodium)NaCl (sodium chloride/salt)

Chemical Bond

Force which holds atoms together. 2 major types:

 Ionic Covalent

Why Bond??

Chemically stable- if an atom’s outer energy level is completely filled with electrons

-most are filled when they contain 8 electrons (OCTET RULE) (exceptions- He, H, Li, Be) ex. Noble gases- inert; chemically

stable So, atoms will try to form compounds by

doing chemical reactions and therefore forming bonds.

REMEMBER: ATOMS DON’T LIKE TO BE ALONE!

Why Bond??

Chemical bond- force that holds together the atoms in a substance

*Losing, gaining, and sharing of valence electrons are the means that atoms use to become stable & form chemical bonds.

ex. LiF- Li loses 1 electron F gains 1 electron

Ionic Bonds (formed in ionic compounds)Formed between metal & nonmetal atoms (elements).

IONS are the basic unit (atom with a charge). CATION = ion that has a + charge (lost e-‘s) ANION = ion that has a – charge (gained e-‘s)

How are these ions made?

Can you mess with protons? Would messing with neutrons

do anything to the charge? What must you mess with??? 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???

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). One atom gives an electron to

another atom (remember it’s the losing and gaining of electrons)

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 (H2O), 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

Ionic Bonds

Sodium atom, Na, that lost an electron is now a sodium ion, Na1+

Chlorine atom, Cl, that gained an electron is now a chlorine ion, Cl1-

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

Types of Bonds

Covalent bond – bond that forms b/w atoms when they share electrons

-occurs between 2 nonmetals -types- single (shares 1 pair of e) double (shares 2 pairs of e) triple (shares 3 pairs of e) Usually forms liquids/gases at room

temp. *REMEMBER HYDROGEN IS A

NONMETAL AND FORMS COVALENT BONDS!!!

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- F2

Lewis Dot Diagrams…

Covalent bonds

H2-hydrogen gas-sharing of electrons

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- Cl2

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

How do you know which type of bond will form? Use two rules:

Calculation using electronegativity values on a periodic table:

 Subtract the values of the 2 elements (larger minus smaller)

If difference is: 0-0.3 = nonpolar covalent bond >0.3-1.7= polar covalent bond

1.7 & up= ionic bond 

Electronegativity Differences summary…

If difference is: >0.3-1.7Electronegativities are not

different enough to steal the electron away, but

there will be a “bully” who hugs the electrons closer

If difference is 1.7 & up

Electronegativities are so

great that one atom will

steal the electron away

0-0.3 differenceElectronegativities 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 nonmetal = ionic bond

Nonmetal and nonmetal = covalent

Rule of thumb summary…

A metal with a nonmetal

Two Nonmetals

Covalent/ Molecular Compounds:

Not packed into a pattern. Have low melting points. May not dissolve in water (H2O), but some can. Do not conduct electricity; do not dissociate.