Atoms and the Atoms and the Periodic TablePeriodic Table

Mr. HolmesMr. Holmes

Russian chemist, Dimitri Mendeleev, Russian chemist, Dimitri Mendeleev, searched for a way to organize the searched for a way to organize the elements in the 1800’s.elements in the 1800’s.

He arranged the elements in order of He arranged the elements in order of increasing mass, which revealed a increasing mass, which revealed a pattern in their chemical properties.pattern in their chemical properties.

Elements are arranged by increasing Elements are arranged by increasing atomic number and chemical atomic number and chemical properties.properties.

In 1800, there were only 31 elements In 1800, there were only 31 elements to organize.to organize.

Elements can appear in three various Elements can appear in three various states:states:– SolidsSolids– Liquids (aqueous)Liquids (aqueous)– Gases (gaseous)Gases (gaseous)

The periodic table is divided into three The periodic table is divided into three different regions (families)different regions (families)– MetalMetal– NonmetalsNonmetals– Metalloids Metalloids

There are two groups within the nonmetalsThere are two groups within the nonmetals– Noble gasesNoble gases– Halogens (are a series of nonmetal elements Halogens (are a series of nonmetal elements

from Group 17) from Group 17)

The horizontal rows of the periodic table The horizontal rows of the periodic table are called are called periodsperiods..

Elements increase by one proton and Elements increase by one proton and one electron as you go from left to right one electron as you go from left to right on the periodic table.on the periodic table.

Each vertical column in the periodic Each vertical column in the periodic table is a group, which make up the table is a group, which make up the families.families.

Each group is given a roman numeral.Each group is given a roman numeral.

Aristotle

Early Greek TheoriesEarly Greek Theories400 B.C. - Democritus thought matter 400 B.C. - Democritus thought matter

could not be divided indefinitely.could not be divided indefinitely.

• 350 B.C - Aristotle modified an earlier theory that matter was made of four “elements”: earth, fire, water, air.

Democritus

• Aristotle was wrong. However, his theory persisted for 2000 years.

fire

air

water

earth

• This led to the idea of atoms in a void.

John DaltonJohn Dalton1800 -Dalton proposed a modern atomic model1800 -Dalton proposed a modern atomic model

based on experimentation not on pure reason.based on experimentation not on pure reason.

• All matter is made of atoms.• Atoms of an element are identical.• Each element has different atoms.• Atoms of different elements combine

in constant ratios to form compounds.• Atoms are rearranged in reactions.

• His ideas account for the law of conservation of mass (atoms are neither created nor destroyed) and the law of constant composition (elements combine in fixed ratios).

Adding Electrons to the ModelAdding Electrons to the Model

1)1) Dalton’s “Billiard ball” modelDalton’s “Billiard ball” model (1800-1900) (1800-1900)Atoms are solid and indivisible.Atoms are solid and indivisible.

2) Thompson “Plum pudding” model (1900)Negative electrons in a positive framework.

3) The Rutherford model (around 1910)Atoms are mostly empty space.Negative electrons orbit a positive nucleus.

Materials, when rubbed, can develop a charge difference. This electricity is called “cathode rays” when passed through an evacuated tube (demos). These rays have a small mass and are negative.Thompson noted that these negative subatomic particles were a fundamental part of all atoms.

Ernest Rutherford Ernest Rutherford (movie: 10 min.)(movie: 10 min.)

Most particles passed through. So, atoms are mostly empty.

Some positive -particles deflected or bounced back!

Thus, a “nucleus” is positive & holds most of an atom’s mass.

Radioactive substance path of invisible

-particles

Rutherford shot alpha (Rutherford shot alpha () particles at gold foil.) particles at gold foil.

Lead block

Zinc sulfide screen Thin gold foil

Atoms are the basic unit of matter.Atoms are the basic unit of matter. Atoms are made of small subatomic Atoms are made of small subatomic

particles: particles: – ProtonsProtons– NeutronsNeutrons– ElectronsElectrons

Protons and neutrons are made up of Protons and neutrons are made up of 3 smaller particles called 3 smaller particles called quarks.quarks.

Electrons have a negative chargeElectrons have a negative charge Protons have a positive charge Protons have a positive charge Neutrons have no chargeNeutrons have no charge Protons and neutrons make up the Protons and neutrons make up the

nucleusnucleus Electrons surround the nucleusElectrons surround the nucleus

The AtomThe Atom

Protons and Protons and neutrons are neutrons are the same size the same size and mass .and mass .

Electrons are Electrons are much smaller much smaller and lighter and lighter than protons than protons and neutronsand neutrons

Atomic numbers, Mass numbersAtomic numbers, Mass numbersThere are 3 types of subatomic particles. We There are 3 types of subatomic particles. We

alreadyalready knowknow aboutabout electronselectrons (e(e––)) && protonsprotons (p(p++). ). Neutrons (nNeutrons (n00) were also shown to exist (1930s).) were also shown to exist (1930s).

They have: no charge, a mass similar to protonsThey have: no charge, a mass similar to protonsElements are often symbolized with their Elements are often symbolized with their mass mass

numbernumber and and atomic numberatomic numberE.g. Oxygen: O16

8These values are given on the periodic table.These values are given on the periodic table.For now, round the mass # to a whole number.For now, round the mass # to a whole number.These numbers tell you a lot about atoms.These numbers tell you a lot about atoms.

# of protons = # of electrons = atomic number# of protons = # of electrons = atomic number # of neutrons = mass number – atomic number# of neutrons = mass number – atomic number

Calculate # of eCalculate # of e––,, nn00, p, p++ for Ca, Ar, and Br. for Ca, Ar, and Br.

35354545353580803535BrBr

18182222181840401818ArAr

20202020202040402020CaCa

ee––nn00pp++MassMassAtomicAtomic

3 p+

4 n02e2e–– 1e 1e––

Li shorthandLi shorthand

Bohr - Rutherford diagramsBohr - Rutherford diagramsPutting all this together, we get B-R diagramsPutting all this together, we get B-R diagramsTo draw them you must know the # of protons, To draw them you must know the # of protons,

neutrons, and electrons (2,8,8,2 filling order)neutrons, and electrons (2,8,8,2 filling order)Draw protons (pDraw protons (p++), (n), (n00) in circle (i.e. “nucleus”)) in circle (i.e. “nucleus”)Draw electrons around in shellsDraw electrons around in shells

2 p+

2 n0

He

3 p+

4 n0

Li

Draw Be, B, Al and shorthand diagrams for O, Na

11 p+12 n°

2e2e– – 8e8e– – 1e1e––

Na

8 p+8 n°

2e2e–– 6e 6e––

O

4 p+5 n°

Be

5 p+6 n°

B

13 p+14 n°

Al

The groups of the periodic table also The groups of the periodic table also tell you the number of valence tell you the number of valence electrons of each atom.electrons of each atom.

The periods tell the valence shell of The periods tell the valence shell of the element.the element.

1A

2A 3A 4A 5A 6A 7A

8A

Isotopes have the same number of Isotopes have the same number of protons but differ in their number of protons but differ in their number of neutrons.neutrons.

Boron, for example, naturally Boron, for example, naturally appears as B-11. An isotope of B-11 appears as B-11. An isotope of B-11 would be B-10 and B-12would be B-10 and B-12

IsotopesIsotopes

Which of the following is an Which of the following is an isotope?isotope?

a.a. Li-8Li-8

b.b. Mg-24Mg-24

c.c. N-14N-14

d.d. C-13C-13

Compounds Compounds

A substance formed by the chemical A substance formed by the chemical combination of two or more elements combination of two or more elements in definite proportions.in definite proportions.

Compounds are formed by forming Compounds are formed by forming chemical bondschemical bonds

Bond formation involves the Bond formation involves the electrons that surround each atomic electrons that surround each atomic nucleus.nucleus.

Types of Chemical BondsTypes of Chemical Bonds

Covalent Bonds Covalent Bonds – Sharing of electrons between moleculesSharing of electrons between molecules

Ionic BondsIonic Bonds– Transfer of electrons between moleculesTransfer of electrons between molecules

Van der Waals ForcesVan der Waals Forces– Intermolecular forces of attraction Intermolecular forces of attraction

between moleculesbetween molecules