atomic theory

ATOMIC THEORY

IN THE BEGINNING

Atoms originally named by Democritus

Believed the a substance could be divided over and over again only to a point

If divided further it would not be that substance anymore

His atoms were solid, _________________________

LAVOISIER: LAW OF CONSERVATION OF MASS

Precisely measured masses of reactants and products of chemical rxns

Law of conservation of __________- mass is neither created or destroyed in chemical rxn Mass of reactants equals the mass of the

products

PROUST: LAW OF DEFINITE PROPORTIONS

All samples of a particular compound have the same _______________ Elements have the same proportion by mass in

each sample

DALTON: LAW OF MULTIPLE PROPORTIONS

If two or more compounds containing the same two elements are examined (for example: CO and CO2) Then the ratio of masses of the element that

changes in both compounds (in our example: O) is a small whole number

Law of Multiple Proportions (cont.)

Four different oxides of nitrogen can be formed by combining 28 g of nitrogen with: 16 g oxygen, forming Compound I 48 g oxygen, forming Compound II 64 g oxygen, forming Compound III 80 g oxygen, forming Compound IV

Compounds I–IV are N2O, N2O3, N2O4, N2O5

What is the ratio 16:48:64:80 expressed as small whole numbers?

JOHN DALTON

Proposed atomic theory in 1803 Four ideas

All matter is composed of indivisible particles called atoms.

All atoms of one element are alike in mass and other properties, but the atoms of one element are different that the atoms of other elements.

Compounds are formed when atoms of elements unite in fixed proportions.

No atoms are created, destroyed, or broken apart in chemical reactions. Atoms are just rearranged

His atom is also a solid, _____________________

Dalton’s Theory Satisfies Laws

Six fluorine atoms and four hydrogen atoms before reaction …

… six fluorine atoms and four hydrogen atoms after reaction.

Mass is conserved.

HF always has one H atom and one F atom; always

has the same proportions (1:19) by mass.

J.J. THOMSON AND CATHODE RAYS

Worked with cathode ray tubes (made by Sir William Crooke) in the late 1800’s

Found that all matter had negative particles (___________________)

Calculates _______________ ratio of e-

J.J. THOMSON’S MODEL Atoms have negative particles, but overall they are

neutral His atom has a positive sphere with negative

particles embedded (often called the _______________________)

Robert Millikan’s Oil Drop Experiment

Calculated the charge of an e-

Made it possible to calculate the mass of the e-

Charged droplet can move either up or down, depending on the charge

on the plates.

Radiation ionizes a droplet of oil.

Magnitude of charge on the plates lets us calculate the charge on the droplet.

RUTHERFORD’S EXPERIMENT

Often called the ____________ experiment Expected almost all particles to pass

straight through the gold Although many did, some particles were

reflected back

RUTHERFORD’S CONCLUSION

Atom must have positive particles (_______________) concentrated in the center

Center is called the ______________ Electrons gravitate around the nucleus A lot of _________________ between nucleus

and electrons

JAMES CHADWICK

Discovered neutrally charged particles (_________________)

Particle was also found in the ______________

NIELS BOHR

Refined Rutherford’s atom model Put the electrons in fixed _______ (like

planets orbiting around the sun) Electrons could temporarily get excited and

jump levels

MODERN ATOMIC MODEL

Electron behave like _________________________ Can’t be tied down to a orbit like a planet Instead scientist show where an electron is

likely to be a any one point in time Forms an electron __________

COMPARING THE PARTICLES

In the nucleus Protons

Charge= ________ Mass = ___________________

Neutrons Charge= ______ Mass= ______________________

Surrounding the nucleus Electron

Charge= ________ Mass= _______________________

ELEMENTS

Composed of only one type of _________ Identity is based on ___________ number Atomic number (___)- number of protons

found in that atom (ID number for elements) Elements are ordered in periodic table according

to this number Mass Number (___)- mass of atom in atomic

unit Really the mass of the __________________________ Electrons are so tiny that they don’t count

CALCULATING PNE (GROUND STATE)

# of protons= __________________

# of electrons= _________________

# of neutrons= _______________________________

ISOTOPES

Different forms of the same atom type Differ by number of ____________ (so therefore

differ by mass as well) Isotope names- element name – mass

number Lithium-6 Lithium-7 Lithium-8

Atoms that lose or gain ___________ form ions Ions have a charge

Cation- ion with a ____________ charge Anion- ion with a _____________ charge

IONS

Forms when atoms _________ electrons

CATIONS

Forms when atoms __________ electrons

ANION

Cations “Name of the element” ion For example, Ca+2 is calcium ion

Anions “Name of the element with ending changed to –

ide” ion

For example Cl

- is chloride ion

NAMING IONS

CALCULATING PNE (IONS)

# of protons= atomic number

# of electrons = atomic number – charge for cations Atomic number + charge for anions

# of neutrons= mass number – atomic number

ATOMIC MASSES ON THE PERIODIC TABLE

Atomic masses on periodic table are an average of all naturally occurring ___________ based on their abundance

Calculating Atomic Mass

Need Mass of each isotope Fractional abundance of each isotope (must

change to fraction if given as %) For each isotope

Multiple the mass and the fractional abundance Add all of the answers together to get the atomic

mass

Proposed period table (1869)

Arranged elements according to ________________

Grouped elements by similar properties

Left holes for undiscovered elements and predicted their properties

Elements are arranged by _____________________

Elements occur in rows (or _________)- 7 periods in all

Elements occur in columns (or ___________________) with similar chemical properties- 18 in all

______________ law- elements can be organized into patterns in the table based on chemical and physical properties

The two series actually belong in the table like this, but we put them at the bottom to save space

Metal Good conductor of

electricity Malleable Ductile Shiny

Nonmetal Poor conductor of heat

and electricity Often gas or dull, brittle

solid Metalloid

Properties in between the other two

Most occur as solids

Br and Hg can occur as a liquid

Other occur as gas

Many elements can exist in different forms naturally

Carbon Both graphite and diamond are carbon, the

atoms are just arranged differently

Element occurs naturally in pairs 7 elements

Hydrogen (H2) Nitrogen (N2) Oxygen (O2) Fluorine (F2) Chlorine (Cl2) Bromine (Br2) Iodine (I2)