Chemical Bonding

Atoms & Bonding

Ionic Bonds

Covalent Bonds

Additional Info: Metallic Bonds

I really hate to tell you this but you have a lot of notes to

take today over some stuff that can get confusing. You really need to pay attention

and askMrs. Taylor questions if you

don’t understand.

19.1 Atoms & BondingWhat does it mean to “bond”?Think about the types of “bonds” that you might befamiliar with, for example:

I am bonded to my husband by

I am bonded to my paintball buddies by a sense of camaraderie, together we are one team.2008_149[1].JPG2008_150[1].JPG.

How does this idea relate to “Atoms & Bonding”?

Together weare one.

LOVE

When you use glue to hold two things together they arebonded.

A Little ReviewYou should remember the parts of an atom.

The proton

+p n

The neutron The electron

Of these three particles, which is the only one that hasthe ability to move from one place to another?

The -e

You should also recall that atoms are the smallest particle of an element and a molecule is the smallestparticle of a compound.

-e

An Important Piece of Information

You need to always remember this. Each energy levelwill hold only a certain number of electrons.

n 2 8 1832

You need to remember 2 – 8 – 18 (only the first 3 )

You need toremember alsothat an energylevel must be fullbefore the next one will hold -e

Count the levelsfrom the nucleusout. There area total of 7.

Chemical Bonds Means you should writethis in your notes.

When atoms chemically combine, they create achemical bond. A chemical bond is an attractive force that holds atoms or ions together to form a molecule.

Of the three main parts of an atom, only the –e isinvolved in forming the bond.

Why is this true? Remember, it is the only onethat can move.

When chemical bonding occurs, electrons from oneatom may be transferred to another atom or theymay be shared by atoms.

Why does transfer or sharing of –e occur?

In order for an atom to be “satisfied” in nature, italways tries to achieve having 8 –e in its outer energylevel. This is called “stability”

YOU MUST ALWAYS REMEMBER THE NUMBER

8, EIGHT, & VIII.In order to achieve “stability” atoms will gain, lose, orshare the electrons in their outer energy level only. The -e in levels below the outer cloud are not involved inchemical bonding.

19.2 Ionic Bonds What is an “ion”?

Remember from previous lessons that atoms appear innature as neutral particles. This means that even though their outer energy levels may not have 8 –eand they are not stable, they do have the same numberof +p in the nucleus as they have –e in their electronclouds. For each + charge in the nucleus they have a

- charge in the clouds to balance out the charge, thusthey are neutral.

If an atom loses or gains electrons in its OEL it willnow have an imbalance of charges, either + or -.When the charges are not balanced the atom is called an ION.

The three types of bonds:

Let’s look at how an ionic bond is formed betweenSodium (Na) and Chlorine (Cl) when NaCl (salt) isformed.

Na has 11 +pin its nucleusand 11 – e (neutral atom)

Cl has 17 +p in its nucleusand 17 –e(neutral atom)

If Na can transfer its 1 OEL –e to Cl, its 3rd level will disappear and it will then have 8. If Cl will gain that 1 –e (it already has 7)it will have 8 and both will be stable or “satisfied”.

11+p10-e 1 + ion

?17+p18-e 1 - ion

+ -Sodium ion chlorine ion

Electromagneticforce holds the Na and Cl togetheras NaCl molecule

NaCl

Let’s look at magnesium (Mg) bonding with fluorine (F)to make magnesium fluoride

Mg F

12 +p13n

9+p8n

Will these two atoms bond?Why not?

9+p8n

Both Mg –e need a place to go. 1 F atom can only take 1-e

There must be 2 F atoms for the 2 – e that Mg must lose.

Now F can transferboth its OEL –e. Itis now stable. BothF’s get up to 8 intheir OEL andbecome stable

12+p10 –e 2 + ion

9 +p10 –e 1- ion

9+p10-e 1- ion

What wouldthe formula be formagnesium fluoride?

MgF2

What holds themtogether?electromagnetic force2+

1-

1-

The CRYSTAL LATTICEA three dimensional pattern that repeats itself over andover again. (go.com) search

crystal atomic lattice viewer

TheSodiumChlorideCrystalLattice.

NaCl

CRYSTAL LATTICE STRUCTURE OF QUARTZSiO2

Crystal lattice structure of Diamond

Just checking to see how you are doing. Get ready for the

hard stuff.

IONSIon is a charged atom. Remember, if an atom loses –eIt becomes a + ion, if it gains –e it becomes a – ion.

Metals tend to lose electrons and form + ions

Non metals tend to gain electrons and form – ions.

Electromagnetic force (+/- attraction) holds two ionstogether in a molecule of an ionic compound.

Crystals are formed by ionic compounds. The shape of the crystal is determined by how the ions arrange them-selves in the crystal lattice.

Ionic bonds are formed between metals and nonmetals.

Covalent BondsUnlike ionic bonds, atoms involved in covalent bondingdo not transfer their OEL –e to other atoms to form achemical bond.

What does the prefix “co-” mean?

Most colleges are “coeducational”, what does that mean? That both males and females go there, or more thanone gender go to school there. So, “co-” means morethan one.

“valent” refers to the OEL –e or valence electrons. (thoselocated in the outer energy level)

In a covalent bond, -e in the OEL of atoms are SHARED between two atoms.

The simplest covalent bonds happen between atoms That appear in nature as diatomic molecules. Diatomic molecules are two atoms of the same element that are Bonded together.

IMPORTANT INFORMATION THAT YOU WILLNEED TO KNOW FOR THE REMAINDER OF THISCLASS

These elements always appear in their pure form as diatomic molecules: H2- hydrogen, O2- oxygen, N2- nitrogen,

F2-fluorine, Cl2- chlorine, Br2-bromine, I2-iodine, At2- astatine.

Diatomic Elements

H H

Shared electrons

O O

How does this work?

Let’s look at the simplest covalent bondfirst. H2

H H

Since hydrogen has only one energy leveland since that level is satisfied with only2 –e,

if each H atom shares its 1 –e with the other then both are satisfied.

Shared electrons

Diatomic Chlorine

17+p 17+pCl has 17 –e with 7 inits OEL. It needs 8 tobe stable, so each atomshares 1 –e with the other in a covalent bond..

Shared electrons ( )

Hydrogen forms onlycovalent bonds

The Metallic Bond

How are the atoms held together in a piece of metalsuch as a copper wire?

Metal atoms have a tendency to lose their OEL –e’s.

nn

n

n

n

n

nn

n

n

nn

n

nnn

n

n

-e -e -e -e -e -e -e -e -e - e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e-e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e -e - e -e -e -e -e -e -e

When metals form a “metallic crystal” they simplydump their valence –e into a “sea of electrons”to beshared by all the nuclei of all the atoms in the metal

Remember the –e are the only particles that can move so theyare free to travel anywhere in the piece of metal.

Bonds and PropertiesThe type of bond formed between atoms of differentelements determine many of the properties of thecompound formed.

IONIC BONDS are the strongest bonds because ofelectromagnetic force. This bond accounts for:

high melting point hardnessbrittleness shape (crystals)

COVALENT BONDS are the weakest bonds.

low melting points dull finish

METALLIC BONDS

ductility malleabilityconductivity luster

Predicting Types of Bonds

By type of element:Metal + Nonmetal Ionic BondNonmetal + Nonmetal Covalent BondMetal + Metal Metallic Bond

By location on PTLeft + Right Ionic BondRight + Right Covalent BondLeft + Left Metallic Bond

By lose/gain –eLose + Gain Ionic BondGain + Gain Covalent BondLose + Lose Metallic Bond

All of this isimportant

REVIEWChemical bonding – the attractive force that holds atomstogether when they combine to form a compound .Only –e are involved in forming chemical bonds. Why?

Ion – a charged atom How is a + ion formed, a – ion ?Metals form +ions when they lose –e’s.Nonmetals form – ions when they gain –e’s.

Ionic bonds are held together by __________________.Electromagnetic force

Ionic bonds are the strongest bonds.

Atoms become “stable” (satisfied) when they have ____-e’s in their OEL.

8Ionic bonds are formed when –e’s are ____________from one atom to another.

transferred

COVALENT BONDS are formed when atoms ________-e’s.

share

Covalent bonds are the weakest type of bond.

Diatomic molecules are two atoms of the same elementbonded together by a covalent bond.Diatomic elements are: H2, O2, N2, F2, Cl2, I2, At2

The simplest covalent bond is the hydrogen bond ina diatomic molecule of hydrogen - H2. Why?

Metallic bonds are formed when metal atoms _______their valence –e’s into a “sea of electrons”.

dump

The type of bond accounts for properties.IONIC – high melting points, crystals, hardness, brittleness, lusterCOVALENT - low m.p., dullnessMETALLIC – malleability, ductility, conductivity, luster

QUIZ A HARD ONE!!

1. An atom is stable when it has ______ -e in its OEL.2. When –e are transferred to another atom, a(n) ______

bond is formed.1. If a metal atom loses –e it forms a _____________ion.2. When two atoms of the same element are bonded together you

have a _____________ molecule. (ex: H2)1. In covalent bonds, -e are ______________ between two atoms.2. The simplest covalent bond is between two atoms of_________.3. In metallic bonds –e are _____________.4. True / False The first energy level can hold up to 8 –e’s.5. Ionic bonds result in _____________force holding the atoms

together.1. If a sulfur atom gains 2 –e’s, it will form a ______ ion.

(use a number and a sign to answer 10)

The Answers

1.82.Ionic3.Positive4.Diatomic5.Shared6.Hydrogen7.Dumped8.False9.Electromagnetic10. 2-