4.1 Atomic Theory & Bonding4.1 Atomic Theory & Bonding

What is an Atom?What is an Atom? smallest particle of an element that still smallest particle of an element that still

has the properties of that elementhas the properties of that element An atom = proton(s) + electron(s) + neutron(s) An atom = proton(s) + electron(s) + neutron(s)

(PEN)(PEN)

Fun FactFun Fact: : 50 million atoms, lined up end-to-end = 1 50 million atoms, lined up end-to-end = 1

cmcm

An An ELEMENTELEMENT is made up of one type of atom is made up of one type of atom The element, oxygen, is OThe element, oxygen, is O

IONSIONS are atoms with a charge. are atoms with a charge. The ion of oxygen is OThe ion of oxygen is O2-2-

Atoms can join together to form Atoms can join together to form MOLECULESMOLECULES.. The oxygen molecules are OThe oxygen molecules are O22

COMPOUNDSCOMPOUNDS are made up of several (2+)atoms are made up of several (2+)atoms Hydrogen and oxygen are atoms/elementsHydrogen and oxygen are atoms/elements HH22O is a compoundO is a compound

Structure of an Atom:Structure of an Atom:

The The nucleusnucleus is at the centre of an atom is at the centre of an atom composed of composed of protons protons (positive charge) and (positive charge) and

neutrons neutrons (neutral charge)(neutral charge)

ElectronsElectrons (negative charge)(negative charge) exist in the space exist in the space surrounding the nucleussurrounding the nucleus

Subatomic Particles:Subatomic Particles:

Atoms are made up of smaller particles Atoms are made up of smaller particles known as sub-atomic particles.known as sub-atomic particles.

NameName SymbolSymbol ChargeCharge LocationLocation Atomic MassAtomic Mass

ProtonProton pp 1+1+ nucleusnucleus 1 AMU1 AMU

NeutronNeutron nn 00 nucleusnucleus 1 AMU1 AMU

ElectronElectron ee 1–1– area surrounding area surrounding the nucleusthe nucleus 1/1836 (0)1/1836 (0)

Numbers to Remember :Numbers to Remember :

# of protons = # of electrons in every atom# of protons = # of electrons in every atomAND ONLY IN ATOMS!!! (not ions)AND ONLY IN ATOMS!!! (not ions)

Nuclear chargeNuclear charge = charge on the nucleus = charge on the nucleus = # of protons = # of protons

Atomic numberAtomic number = # of protons = # of protons = # of electrons in atoms= # of electrons in atoms

Families of the Periodic Table:Families of the Periodic Table:

Columns of elements are called Columns of elements are called groupsgroups, or , or familiesfamilies All elements in a family have…All elements in a family have…

similar propertiessimilar properties bond with other elements in similar waysbond with other elements in similar ways have the same number of valence electronshave the same number of valence electrons

Family names (on the periodic table!):Family names (on the periodic table!): Group 1 = alkali metalsGroup 1 = alkali metals Group 2 = alkaline earth metalsGroup 2 = alkaline earth metals Group 17 = the halogensGroup 17 = the halogens Group 18 = noble gasesGroup 18 = noble gases

PeriodsPeriods are horizontal rows on the periodic table are horizontal rows on the periodic table

INC

RE

AS

ING

RE

AC

TIV

ITY

Where are the following?

• Atomic Number

• Period

• Group/Family

• Metals

• Non-metals

• Transition metals

• Metalloids

• Alkali metals

• Alkaline earth metals

• Halogens

• Noble gases

Periodic Table & Ion Formation:Periodic Table & Ion Formation:

Atoms gain and lose electrons to form Atoms gain and lose electrons to form ionsions Metals lose electrons & become positive ions Metals lose electrons & become positive ions

((cationscations)) Some metals can have more than one charge Some metals can have more than one charge

((multivalentmultivalent)) ie. Iron, Fe, loses either 2 (Feie. Iron, Fe, loses either 2 (Fe2+2+) or 3 (Fe) or 3 (Fe3+3+) )

electronselectrons Non-metals gain electrons & become negative ions Non-metals gain electrons & become negative ions

((anionsanions)) Atoms do this in an attempt to have the same Atoms do this in an attempt to have the same

number of number of valence electronsvalence electrons as the nearest noble as the nearest noble gas – to become stablegas – to become stable

Bohr Diagrams:Bohr Diagrams:

Bohr diagrams show how many electrons Bohr diagrams show how many electrons appear in each electron shell around an appear in each electron shell around an atom.atom. Each shell holds a maximum number of Each shell holds a maximum number of

electrons (2, 8, 8, 18, 18)electrons (2, 8, 8, 18, 18) Electrons in the outermost shell are called Electrons in the outermost shell are called

valence electronsvalence electrons Except for the transition elements, the last digit Except for the transition elements, the last digit

of the group # = # of valence electronsof the group # = # of valence electrons

Note: Think of the shells as being 3D like spheres, not 2D like circles!Note: Think of the shells as being 3D like spheres, not 2D like circles!

What element is this?

Bohr Diagrams

•It has 2 + 8 + 8 = 18 electrons, and therefore 18 protons

•It has 8 electrons in the outer (valence) shell

18 p

22 n

Argon!

Note: The noble gas elements have full electron shells, and are very stable.

Bohr Diagrams for the first 20 elements

Covalent Bonds:Covalent Bonds: Formed between two or more non-metalsFormed between two or more non-metals Electrons are shared between atomsElectrons are shared between atoms

Hydrogen Fluorine

+

Electrons are shared

Hydrogen fluoride

When two atoms get close together, their When two atoms get close together, their valence electronsvalence electrons interact. interact.

Bonding Types:Bonding Types:

Ionic Bonds:Ionic Bonds:

Metals give electrons to non-metals (transfer of Metals give electrons to non-metals (transfer of electrons)electrons)

cations (+ ions) and anions (- ions) formcations (+ ions) and anions (- ions) form For example, lithium and oxygen form an ionic For example, lithium and oxygen form an ionic

bond in the compound Libond in the compound Li22OO

Lithium Oxygen

+

Electrons are transferred from the cations to the anion

Li+ O2- Li+

Lithium oxide,Li2O

Lewis Diagrams:Lewis Diagrams:

Like simplified Bohr diagramsLike simplified Bohr diagrams Only valence electrons are shownOnly valence electrons are shown Dots representing electrons are placed around Dots representing electrons are placed around

the element symbols (on 4 sides, imagine a box the element symbols (on 4 sides, imagine a box around the symbol)around the symbol)

Electron dots are placed singularly, until the fifth Electron dots are placed singularly, until the fifth electron is reached, then they are paired.electron is reached, then they are paired.

Example: Nitrogen atom

Lewis Diagrams:Lewis Diagrams:

NoteNote: the Lewis diagrams are the same : the Lewis diagrams are the same (except for the symbols) for elements in the (except for the symbols) for elements in the same family because they have the same same family because they have the same number of valence electronsnumber of valence electrons

Lewis Diagrams for Ions:Lewis Diagrams for Ions:

For positive ions:For positive ions: one electron dot is removed one electron dot is removed from the valence shell for each positive charge from the valence shell for each positive charge of the ion.of the ion.

For negative ions:For negative ions: one electron dot is added to one electron dot is added to each valence shell for each negative charge of each valence shell for each negative charge of the ion. the ion.

Square brackets and the charge are placed Square brackets and the charge are placed around each ionaround each ion

Example: Nitrogen ion

Lewis Diagrams For Covalent Bonds:Lewis Diagrams For Covalent Bonds:

valence electrons are drawn to show sharing of valence electrons are drawn to show sharing of electrons.electrons.

Remember: All atoms “like” to have a full valence shellRemember: All atoms “like” to have a full valence shell The shared pairs (“bonding pairs”) of electrons are The shared pairs (“bonding pairs”) of electrons are

usually drawn as a straight lineusually drawn as a straight line ““lone pairs” are the electrons not sharedlone pairs” are the electrons not shared

Be Cl• •

• •

• •

• •Each beryllium has two electrons to transfer

away, and each chlorine wants one

more electron

BeCl Cl• •

• •

• •

• •

• ••

••

•

• •

• ••

••

•

• •

BeCl Cl• •

• •

• •

• •

• ••

••

•

• •

• ••

••

•

• •Since Be2+ wants to donate 2 electrons and

each Cl– wants to accept only one, two

Cl– ions are necessary

The ionic compound Beryllium chloride is

formed

2+–• ••

••

•

• •

–

Lewis Diagrams For Ionic Bonds:Lewis Diagrams For Ionic Bonds: