The Structure of the Atom and the Periodic Table

Chapters 4 and 5

Atomic Theories- Ancient •Ancient times identify 4 elements:

•Fire

•Water

•Wind

•Earth

•They thought that these elements could be converted into each other through a cycle

end

Atomic Theories- Ancient

Democritus

•1st to propose that there is a smallest particle

•Matter was made up of atomos

•Atoms cannot be created, destroyed, or divided

Aristotle

•Opposed Democritus’ view

•Did not agree with the concept of empty space

•Destroyed Democritus’ theory

end

Atomic Theories- Modern

John Dalton

•English Quaker Schoolteacher

•Father of modern atomic theory

•Spent a great deal of time studying the behavior of gasesHe noticed that in every sample the ratio of the elements was always the same

end

Atomic Theories- Modern

Dalton's Atomic Theory: All elements are made of atoms Atoms of the same element have the same mass

This was later proved wrong- Isotopes Atoms of different elements have different masses Atoms combine in whole number ratios

You can't have half of an atom in a compound

Dalton's Atoms

•Dalton went back to Democritus' view. •All matter is made up of individual particles called atoms, which cannot be divided

•Atoms are little spheres•Like marblesend

Atomic Theories- Modern

Atom The smallest particle of an element that

retains the properties of the element

end

Atomic Theories- ModernJ. J. Thomson

•Performed cathode ray tube experiments

•Discovered the electron

•Proved that atoms can be broken up

•Dalton was wrong

•Created the Plum Pudding Model

When electricity moves through a gas it produces a glowing beam (neon signs)

When a magnetic field was applied the beam went toward the positive plate

end

Atomic Theories- Modern

Thomson had to come up with a new model to explain the electrons

•The Plum Pudding Model

•Large area of positive charge

•Small packets of negative charge

•Think: Chocolate Chip Cookies

end

Atomic Theories- ModernErnest Rutherford

•Conducted the Gold Foil Experiment

•Shot particles at thin pieces of gold foil

•Expected to see particles pass straight through

•Some particles bounced almost straight back

end

Atomic Theories- Modern

His experiment showed that the Plum Pudding Model was wrong

Rutherford came up with a new model of an atom A small, dense, positive nucleus Electrons are outside the nucleus Atoms are mostly empty space

+

Nucleus

Electrons are somewhere in this area

end

Structure of the Atom

Protons, electrons, and neutrons are subatomic particles They make-up an atom

You must be able to identify them by mass, charge, and location

end

Structure of the Atom

The Nucleus

Small dense region in the center of an atom Contains all of an atom’s positive charge And almost all of its mass. Contains protons and neutrons

end

Structure of the Atom

Proton (p+) Found inside the nucleus Charge of +1 Same mass as a neutron If you change the # of protons you get a different

element

end

Structure of the Atom

Electron (e-) Charge of -1 Found outside the nucleus Almost no mass compared to the proton If you change the # of electrons you get a ion

end

Structure of the Atom

•Neutron (n0)

•No charge

•Same mass as a proton

•Found in the nucleus with the proton

•If you change the # of neutrons you get different isotopes

end

Review

Particle Symbol Location Relative Mass

Relative Electrical Charge

Change in Number

Electron e- Outside the

Nucleus

1/1840Basically = 0

-1 Ions

Proton p+ Nucleus 1 +1 Elements

Neutron n0 Nucleus 1 0 Isotopes

end

Isotopes

Isotopes Atoms of the same element Have different numbers of neutrons

Which means different mass numbers

All elements have isotopes In nature the elements occur as a mixture of

isotopes

end

Structure of the Atom

Mass Number The relative mass of each atom The number of protons + the number of neutrons Different isotopes have different mass numbers

Changes the # of neutrons!

Mass# = (Atomic#) + (# of neutrons)

end

Structure of the Atom

Atomic Number The number of protons in the element This defines each element Equals the number of electrons in a neutral atom

Atomic Number

end

Structure of the Atom

• Atomic Symbols– 1 or 2 letters– The 1st letter is always capitalized the 2nd is

always lowercase• Make sure to write your letters correctly!!!!!

– The element’s name is just below the symbol

Atomic Symbol

Element’s Name

end

Structure of the Atom

• Atomic Mass– Weighted average mass for all isotopes of each

element– NOT the same as the Mass Number

Atomic Mass

end

Structure of the Atom

• Writing Atomic Symbols– Since every element has isotopes scientists have

write symbols so the know which one they are talking about

– There are 3 ways to write the symbols:

Carbon- 12 C- 12

Name and Mass Number

Symbol and Mass Number

C126

Symbol

Mass Number

Atomic Number

end

Structure of the Atom

Name Symbol Protons Neutrons Electrons Atomic Number

Mass Number

Carbon-12

136C

15 45

44 34

36 15

end

Atomic Theories- Modern

Rutherford's model was good, but it didn't talk about the electrons

Bohr Model (Solar System Model) Took Rutherford's model and put electrons into

energy levels Electrons change energy levels when they either

gain or lose energy• Electrons cannot be between levels

Electrons can move more than 1 level at a time

end

Atomic Theories- Modern

• In the Bohr Model:– Protons and Neutrons form a nucleus– Electrons are placed in rings around the

nucleus• Each energy level can only hold a certain

number of electrons

Energy Level # of electrons1 2

2 8

3 18

4 32

end

Atomic Theories- Modern

Lets draw H-1

p = 1

n = 0

e = 1

Lets draw He-4

p = 2

n = 2

e = 2

Lets draw Li-6

p = 3

n = 3

e = 3

Lets draw Na-22

p = 11

n = 11

e = 11

end

Atomic Theories- Modern

Electrons want to be in the lowest energy level possible

Ground state All electrons are in the lowest possible energy levels The most stable

Excited state At least 1 electron is not in the lowest possible

energy level

end

Atomic Theories- Modern

Bohr's model was good, but it had problems We can never be sure of exactly where

electrons are located Electron Cloud Model

With some fancy math, we figured out an area around the nucleus where the electrons are going to be 95% of the time This area is known as an Orbital Each orbital can only hold 2 electrons

end

The Periodic Table

By 1860 scientists had discovered 63 elements But there was no good way to organize them Scientists just had to memorized everything about

every element This changed when Mendeleev created a

way to classify the elements

end

The Periodic Table

Mendeleev’s Periodic Table: Elements with similar properties were placed in

the same column The mass of the elements increased along

each row

end

The Periodic Table

Mendeleev left several blank spaces in his periodic table These spaces were for elements that had not

been discovered yet Mendeleev predicted what properties these

elements would have based on the elements around them

end

The Periodic Table

The Modern Periodic Table: Based on Mendeleev’s table Elements with similar properties are in the

same column Columns are called GroupsNumbered 1 to 18 (from left to right)

Atomic Numbers (# of protons) increase going across the table

Rows are called PeriodsNumbered 1 to 7 (from top to bottom)

end

The Periodic Table•This is the full Periodic Table

• As you can see it is REALLY long

• Way too long to fit on a page

end

The Periodic Table

•In order to make everything fit on 1 page, we take out the Lanthanides and Actinides.

•They are moved to the bottom of the table end

The Periodic Table

Metals Left of the stair-step line Francium (Fr) is the most reactive

Moving away from Fr, metals become less reactive Good conductors of electricity and heat Mostly solids at room temperature

High melting and boiling points Malleable and ductile

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The Periodic Table

NonmetalsRight of the stair-step lineFluorine (F) is the most reactive nonmetal

Moving away from F, nonmetals become less reactive

Poor conductors of heat and electricityMostly gases at room temperature

Low melting and boiling points

Not malleable and not ductile

end

The Periodic Table

Metalloids Touching the stair-step line Have properties that fall between those of metals

and nonmetalsThis depends on the temperature

end

The Periodic Table

Alkali Metals Group 1 EXTREMELY REACTIVE!

Alkaline Earth Metals Group 2

end

The Periodic Table

• Transition Metals– Groups 3 to 12– Have a wide variety of properties

• Lanthanide and Actinide Series– At the bottom of the table– All are radioactive

end

The Periodic Table

Halogens Group 17 Highly Reactive

Noble Gases Group 18 Extremely Unreactive

THEY DO NOTHING!

end

The Periodic Table• Atomic Size

– Francium (Fr) is the largest atom– Helium (He) is the smallest atom– The closer to Fr, the larger the atom

• Valence Electrons– Electrons in the highest energy level– These give elements their chemical properties

Group: 1 2 13 14 15 16 17 18

# of 1 2 3 4 5 6 7 8

Valence:

end