Unit 2Unit 2Chemistry and Chemistry and RadioactivityRadioactivity

Chapter 4:Chapter 4: Atomic theory explains Atomic theory explains the formation of the formation of compoundscompounds

Words to Know:Words to Know:atomic numberatomic number Bohr diagramBohr diagram

compoundcompound covalent bondingcovalent bonding

ionic bondingionic bonding ionsions

Lewis diagramLewis diagram moleculemolecule

valence electronsvalence electrons

Chapter 4.1Chapter 4.1 - Atomic Theory and - Atomic Theory and Bonding 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

Pure Substances:Pure Substances: Elements and Compounds are Elements and Compounds are PURE PURE

SUBSTANCESSUBSTANCES Have their own unique properties that are always the Have their own unique properties that are always the

samesame

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

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

Chemical ChangesChemical Changes::

occurs when the arrangement of atoms in occurs when the arrangement of atoms in compounds changecompounds change

results in a new compoundresults in a new 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 Relative MassRelative Mass

ProtonProton pp 1+1+ nucleusnucleus 18361836

NeutronNeutron nn 00 nucleusnucleus 18361836

ElectronElectron ee 1–1– area surrounding area surrounding the nucleusthe nucleus 11

Numbers to Numbers to RememberRemember : : # of protons = # of electrons in every atom# of protons = # of electrons in every atom

AND 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= # of electrons

The Periodic Table:The Periodic Table:

The periodic table organizes the elements.The periodic table organizes the elements. elements are listed in order by atomic numberelements are listed in order by atomic number metals are on the leftmetals are on the left non-metals are on the rightnon-metals are on the right metalloids form a “staircase” in the middle.metalloids form a “staircase” in the middle.

Rows of elements (across) are called Rows of elements (across) are called periodsperiods all elements in a period have their electrons in the all elements in a period have their electrons in the

same valence shell (we’ll talk about this later!)same valence shell (we’ll talk about this later!)

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:Family names: 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

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 and Periodic Table and Ion Formation:Ion Formation:

Atoms gain and lose electrons to form Atoms gain and lose electrons to form ionsions - - electrically charged particles.electrically charged particles. Metals lose electrons and become positive ions (called Metals lose electrons and become positive ions (called

cations)cations) Some metals (multivalent) lose electrons in different waysSome metals (multivalent) lose electrons in different ways ie. Iron, Fe, loses either 2 (Feie. Iron, Fe, loses either 2 (Fe2+2+) or 3 (Fe) or 3 (Fe3+3+) electrons) electrons

Non-metals gain electrons and become negative ions Non-metals gain electrons and become negative ions ( called anions)( called anions)

Atoms do this in an attempt to have the same number of Atoms do this in an attempt to have the same number of valence electronsvalence electrons (electrons furthest from the nucleus) as (electrons furthest from the nucleus) as the nearest noble gas.the nearest noble gas.

Bohr Diagrams:Bohr Diagrams:

Bohr diagrams show how many electrons appear in each electron shell Bohr diagrams show how many electrons appear in each electron shell around an atom.around an atom. Each shell holds a maximum number of electrons (2, 8, 8, 18, 18)Each shell holds a maximum number of electrons (2, 8, 8, 18, 18) Electrons in the outermost shell are called Electrons in the outermost shell are called valence electronsvalence 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 3 electron shells, so it is in period 3

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

18 p

22 n

Argon!

Remember :Remember :

Electrons appear in shells in a very Electrons appear in shells in a very predictable manner.predictable manner.

There is a maximum of 2 electrons in the There is a maximum of 2 electrons in the first shell, 8 in the 2nd shell, and 8 in the 3rd first shell, 8 in the 2nd shell, and 8 in the 3rd shell.shell. The period # = # of shells in the atom.The period # = # of shells in the atom. Except for the transition elements,Except for the transition elements, the last digit of the group # = # of electrons the last digit of the group # = # of electrons

in the valence shellin the valence shell

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

Forming Compounds:Forming Compounds:

When two atoms get close together, their valence When two atoms get close together, their valence electrons interact.electrons interact. If the valence electrons can combine to form a low-If the valence electrons can combine to form a low-

energy bond, a compound is formed.energy bond, a compound is formed. Each atom in the compound attempts to have the Each atom in the compound attempts to have the

stable number of valence electrons as the nearest stable number of valence electrons as the nearest noble gas.noble gas.

Metals may lose electrons and non-metals gain Metals may lose electrons and non-metals gain electrons, (electrons, (ionic bondionic bond))

OROR Atoms may share electrons (Atoms may share electrons (covalent bondcovalent bond))

Bonding Types:Bonding Types:

Ionic bondsIonic bonds form when electrons are form when electrons are transferred from cations to anionstransferred from cations to anions Cations want to donate an electron (+) and Cations want to donate an electron (+) and

anions want to accept more electrons (-)anions want to accept more electrons (-)

Covalent bondsCovalent bonds form when electrons are form when electrons are shared between two non-metalsshared between two non-metals Electrons stay with their atom, but overlap Electrons stay with their atom, but overlap

with other shellswith other shells

Ionic Bonds:Ionic Bonds:

Formed between cations (+ ions) and anions (- Formed between cations (+ ions) and anions (- ions)ions)

Generally, this is a metal (+) and a non-metal (-)Generally, this is a metal (+) and a non-metal (-) 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

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

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 singly, until the fifth Electron dots are placed singly, 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 are placed around each ion to Square brackets are placed around each ion to indicate a charge on the elementindicate a charge on the element

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 Lewis Diagrams For Covalent Bonds:Covalent Bonds: Like Bohr diagrams, valence electrons are drawn Like Bohr diagrams, valence electrons are drawn

to show sharing of electrons.to show sharing of electrons. All atoms “like” to have a full valence shellAll atoms “like” to have a full valence shell The shared pairs of electrons are usually drawn The shared pairs of electrons are usually drawn

as a straight lineas a straight line