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 (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

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- F2

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- Cl2

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.

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: 0-0.3 = nonpolar covalent bond 0.4-1.6= 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 electron away0-0.3 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.