ch. 4 - atomic structure i. subatomic particles (p.113 - 114)

Ch. 4 - Atomic Structure

I. Subatomic Particles(p.113 - 114)

Subatomic Particle Properties

Particle Symbol Location Charge Relative Mass (amu)

Actual Mass (g)

electron

proton

neutron

e-

p+

n0

Electron cloud

nucleus

nucleus

–

+

0

1/1840

1

1

9.11 x 10-28

1.67 x 10-24

1.67 x 10-24

approx 0

Symbols

Elements are listed by their chemical symbols

Symbols are usually either one capital letter like C for Carbon, or one capital and one lowercase letter like Ne for Neon

Periodic Table

The periodic table gives much information we need to learn more about the atom of each element

Atomic Number

Atomic number = # of protons in an atomWhole number shown on periodic tablePeriodic table is arranged by atomic

number

Atomic Mass

The average atomic mass is the number at the bottom of this square

Found by averaging the natural abundances of its isotopes

Atom Math

Protons Electrons

Protons Neutrons

# n0 = Atomic mass – Atomic number

Subatomic Particles

POSIT IVECHARG E

PROT ONS

NEUT RALCHARG E

NEUT RONS

NUCLEUS

NEG AT IVE CHARG E

ELECT RONS

AT OM

Most of the atom’s mass.

NUCLEUS ELECTRONS

PROTONS NEUTRONS NEGATIVE CHARGE

POSITIVE CHARGE

NEUTRAL CHARGE

ATOM

#n0 = Atomic mass- Atomic #

equal in a neutral atom

Atomic Numberequals the # of...

Ch. 4.3 - Atomic Structure

II. How Atoms Differ (p. 114 - 121) Mass Number Isotopes Relative Atomic Mass Average Atomic Mass

A. Mass Number

mass # = protons + neutrons

always a whole number

NOT on the Periodic Table!

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B. Isotopes

Atoms of the same element with different numbers of neutrons

C126

Mass #

Atomic #

Isotope notation:

Isotope name: carbon-12

Element name Mass #

B. Isotopes

Chlorine-37

atomic #:

mass #:

# of protons:

# of electrons:

# of neutrons:

17

37

17

17

20

Cl3717

Isotope notation:

Natural Abundances of Isotopes

Most elements are found as mixtures of isotopes

Relative abundance of each isotope is the same in each source

Ion: an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative charge.

Cation: has a positive charge, due to the loss of electrons

Anion: has a negative charge, due to the gain of electrons

C. Relative Atomic Mass

12C atom = 1.992 × 10-23 g

1 p = 1.007276 amu

1 n = 1.008665 amu

1 e- = 0.0005486 amu

© Addison-Wesley Publishing Company, Inc.

atomic mass unit (amu)

1 amu = 1/12 the mass of a 12C atom

D. Average Atomic Mass

weighted average of all isotopeson the Periodic Table

100

(%)(mass(mass)(%) )

Avg.AtomicMass

Avg.AtomicMass


EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O.

100

(18)(0.20)(17)(0.04))(16)(99.76 16.00amu

Avg.AtomicMass


EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37.

100

(37)(20)(35)(80)35.40 amu

Atomic Theory

Development of our understanding

of the atom

Early ModelsBattle of Philosophers

Aristotle vs. Democritus-Matter is infinite - Matter is composed of

extremely small particles

-4 Basic ‘elements’ - Called these particles ‘atoms’

- Earth (From ‘atmos’ meaning invisible)

-Air

-Fire *Eventually after many years

-Water Democritus is proven right

Early Models Dalton’s model was the “Billiard Ball”

Published an Atomic Theory1. All matter is composed of atoms that are

indivisible (did not know about protons, electrons, or neturons)

2. Atoms of a given element have same size, mass and chemical properties and are different from those of another element (no longer true, b/c of isotopes)

3. Different atoms combine in whole number ratios to form compounds and are separated, combined and rearranged in chemical reactions

4. In chemical reactions atoms can combine or separate, but are neither created or destroyed

Law of Definite Proportions Law of Definite Proportions Each compound has a specific ratio of Each compound has a specific ratio of

elementselements It is a ratio by mass It is a ratio by mass Water is always 8 grams of oxygen for Water is always 8 grams of oxygen for

each gram of hydrogen each gram of hydrogen

Law of Multiple ProportionsLaw of Multiple Proportions if two elements form more than one if two elements form more than one

compound, the ratio of the second compound, the ratio of the second element that combines with 1 gram of element that combines with 1 gram of the first element in each is a simple the first element in each is a simple whole number.whole number.

What?What? Water is 8 grams of oxygen per gram of Water is 8 grams of oxygen per gram of

hydrogen.hydrogen. Hydrogen Peroxide is 16 grams of Hydrogen Peroxide is 16 grams of

oxygen per gram of hydrogen.oxygen per gram of hydrogen. 16 to 8 is a 2 to 1 ratio16 to 8 is a 2 to 1 ratio True because you have to add a whole True because you have to add a whole

atom, you can’t add a piece of an atom. atom, you can’t add a piece of an atom.

Parts of AtomsParts of Atoms J. J. Thomson - English physicist. 1897J. J. Thomson - English physicist. 1897 Made a piece of equipment called a Made a piece of equipment called a

cathode ray tube.cathode ray tube. It is a vacuum tube - all the air has been It is a vacuum tube - all the air has been

pumped out.pumped out.

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Vacuum tube

Metal Disks


Voltage source

+-

Passing an electric current makes a Passing an electric current makes a beam appear to move from the negative beam appear to move from the negative to the positive endto the positive end


Voltage source

+-

Passing an electric current makes a Passing an electric current makes a beam appear to move from the negative beam appear to move from the negative (cathode) to the positive end (anode)(cathode) to the positive end (anode)


Voltage source

+-

Voltage source


By adding an electric field By adding an electric field

Voltage source


By adding an electric field By adding an electric field

+

-

Voltage source


By adding an electric field he found By adding an electric field he found the ratio of electrical charge to mass (e/m) for an electron

The e/m ratio is (negative) 1.76 x 108coulombs per gram (or C/g in SI units).

+

-

Thomsom’s ModelThomsom’s Model Thomson always found the same Thomson always found the same

value for the value for the e/me/m ratio no matter ratio no matter what the tube materials or the gas what the tube materials or the gas inside.inside.

Reinforced the notion that the Reinforced the notion that the electrons are a fundamental electrons are a fundamental component of mattercomponent of matter..

‘ ‘Plum Pudding’ model: a thin Plum Pudding’ model: a thin positive fluid, which contains most positive fluid, which contains most of the mass, w/ negative electrons of the mass, w/ negative electrons embedded to balance the chargeembedded to balance the charge

Millikan used oil drop experiment Would spray a fine mist of oil droplets above a

pair of parallel plates. Some of the oil drops would pass through the hole in the top plate.

He then used X-rays to knock electrons off of the air molecules in the barrel and some of those electrons attached themselves to the oil drops. The oil drops, which were now negative, could now be affected by the electrical field. He then could now measure the charge of the oil drops.

Millikan found that all the values he obtained were whole-number multiples of -1.60 x 10-19 coulomb. This value must be the charge of an electron.

The electron’s charge was -1.60 x 10-19 coulombs Using two values and solving for m

- 1.60 x 10-19 coul = - 1.76 x 108 coul/g

m m = 9.11 x 10-28 grams (a negligible mass even in the smallest atom)

Confirmed the negative charge of an electron Determined mass of the electron

Rutherford’s experimentRutherford’s experiment Ernest Rutherford English physicist. (1910)Ernest Rutherford English physicist. (1910) Believed in the plum pudding model of the Believed in the plum pudding model of the

atom.atom. Wanted to see how big they are using Wanted to see how big they are using

radioactivityradioactivity Alpha particles - positively charged pieces Alpha particles - positively charged pieces

given off by uranium given off by uranium Shot them at gold foil which can be made a Shot them at gold foil which can be made a

few atoms thick few atoms thick

Lead block

Uranium

Gold Foil

Florescent Screen

He ExpectedHe Expected The alpha particles to pass through The alpha particles to pass through

without changing direction very muchwithout changing direction very much BecauseBecause The positive charges were spread out The positive charges were spread out

evenly. Alone they were not enough to evenly. Alone they were not enough to stop the alpha particlesstop the alpha particles

What he expected

Because, he thought the charge was evenly distributed in the atom

What he got

How he explained it

+ Atom is mostly emptyAtom is mostly empty Small dense,Small dense, positive piecepositive piece at at

center (nucleus) center (nucleus) Proposed planetary model… (not as refined as the Proposed planetary model… (not as refined as the

solar sytem model)solar sytem model) Refined the concept of the nucleus & concluded it was Refined the concept of the nucleus & concluded it was

composed of positively charged particles called protonscomposed of positively charged particles called protons James Chadwick: discovered a neutral James Chadwick: discovered a neutral atomic atomic particle particle

with a mass close to a proton. Thus was discovered the with a mass close to a proton. Thus was discovered the neutron. neutron.

Moving Forward… Neils Bohr said electrons move in orbits

Found in energy levels Explains bright-line spectrum Called “Solar System Model” where

Electrons move in orbits around the nucleus

What we believe nowHeisenberg/Schrodinger

Heisenber Uncertainty Principle: You can know either the eˉ position or velocity

but not both Schrodinger said the eˉ are located in orbitals,

(regions of probability) around the nucleus… not orbits

“Electron Cloud” model

ch. 4 - atomic structure i. subatomic particles (p.113 - 114)

Documents

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