CHEMICAL BONDINGp. 144-156

REMEMBER….THERE ARE TWO KINDS OF PURE SUBSTANCES

ElementsCompounds

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, reactivity, etc.

Compounds cont… Substance made of atoms of 2 or more

different elements that are CHEMICALLY combined.

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- this would be a compound

All compounds are molecules, but not all molecules are compounds.

Ex- O2, NaCl, etc.

Compounds Molecules made

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

Elements Molecules made

of just one element

Na (sodium)NaCl (sodium chloride/salt)

Let’s start the new notes…

Compound/Molecule

Chemical combination of 2 or more elements.

Properties of the compound are unlike those of the elements that make it.

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). 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).

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.

Covalent Bonds (formed in molecular/covalent compounds)

Atoms are the basic unit. Covalent bonds are firm, but

molecules not strongly held together. Force between atoms that share

electrons.

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.

Nonpolar Covalent bonds:

Electrons are shared equally in the bond. Does not have (+) and (-) end to the bond. Formed between 2 or more of the same

nonmetal. Electronegativity difference between the atoms

(elements) is 0. (see table on last page of notes) Ex) Cl & Cl

Polar Covalent bonds: Electrons are NOT shared equally in the bond. Has a (+) and (-) end to the bond. Formed between 2 different nonmetals. Electronegativity difference between the atoms

(elements) is 0.1-1.6 (see table on last page of notes)

Ex) H & O C & O

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: 0= nonpolar covalent bond 0.1-1.6= polar covalent bond

1.7 & up= ionic bond 

Electronegativity Differences summary…

If difference is: 0.1-1.6Electronegativities 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 eletron away

0 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 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 Metals Both the same

metal

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.