1.1 Everything on Atoms.ppt

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Democritus

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You put sugar it water, it dissolves, you can’t see it, but it’s still

there...leads to the idea of the particle theory of matter.

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400 B.C., the Greek thinker, Democritus

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Aristotle

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Aristotle thought that all matter was ‘continuous’

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This idea was accepted for nearly 2000 years.

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Neither hypothesis, Democritus or Aristotle had experimental

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1700’s

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Chemists accepted that an

element was a substance that

couldn’t be broken down further.

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They also accepted that elements

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1790’s

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Transforming one substance into another occurred by chemical

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Law of Conservation of Mass

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Mass is neither destroyed nor

created during ordinary chemical reactions or physical changes.

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In 1799, Joseph Proust, observed that the In 1799, Joseph Proust, observed that the

composition of water is always 11 percent composition of water is always 11 percent

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Proust studied many other compounds and Proust studied many other compounds and observed that the elements that composed observed that the elements that composed

the compounds were always in a certain the compounds were always in a certain

proportion by mass. This principle is now proportion by mass. This principle is now

referred to as the

law of definite

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A water is a water is a waterA water is a water is a water

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No matter where you are, or how it is, H2O No matter where you are, or how it is, H2O will be the same H2O

will be the same H2O

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2 H’s and 1 O2 H’s and 1 O

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The masses of H’s and O’s are always the The masses of H’s and O’s are always the same, so the compound will always be the same, so the compound will always be the

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Lavoisier’s Experiment p.64 and 65Lavoisier’s Experiment p.64 and 65

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Mercury II oxide yields Mercury + OxygenMercury II oxide yields Mercury + Oxygen

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2 HgO ---2 HgO --- 2 Hg + O 2 Hg + O22

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Law of Multiple Properties

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P.76 P.76

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There are different combinations of There are different combinations of

compounds with the same elements. One compounds with the same elements. One

compound may be totally different from the compound may be totally different from the

other, such as mass. other, such as mass.

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1 1 3 3

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C + O --> CO C + O --> CO

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+ --> + -->

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CO --> C + OCO --> C + O

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--> +--> +

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1 1 4 41 1 4 4

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– Compound I vs Compound II_{Compound I vs Compound II}

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John Dalton

(1766-1844), an English

1844), an English

schoolteacher and

chemist, studied

the results of

experiments by

Lavoisier, Proust,

and many other

scientists.

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1 1 7 7

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Dalton turned Democritus’s hypothesis into a Dalton turned Democritus’s hypothesis into a scientific theory.

scientific theory.

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Dalton’s Atomic Theory

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1. All matter is made up of atoms.1. All matter is made up of atoms.

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2. Atoms are indestructible and cannot be 2. Atoms are indestructible and cannot be divided into smaller particles. (Atoms are divided into smaller particles. (Atoms are

indivisible.) indivisible.)

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3. All atoms of one element are exactly alike, 3. All atoms of one element are exactly alike, but are different from atoms of other elements. but are different from atoms of other elements.

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4. Atoms of different elements can combine to 4. Atoms of different elements can combine to form compounds.

form compounds.

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5. In chemical reactions, atoms are combined, 5. In chemical reactions, atoms are combined, separated and rearranged.

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1 1 9 9

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He got a few things wrong.He got a few things wrong.

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But what he got right was...But what he got right was...

–1. All matter is composed of atoms. _{1. All matter is composed of atoms.}

–2. Atoms of any element has different properties _{2. Atoms of any element has different properties} that atoms of other elements.

that atoms of other elements.

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2 2 0 0

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P. 68 Travels with CP. 68 Travels with C

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Chapter 3.2

The Structure of an

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The Electron

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Because of Dalton’s atomic theory, most scientists Because of Dalton’s atomic theory, most scientists in the 1800s believed that the atom was like a tiny in the 1800s believed that the atom was like a tiny

solid ball that could not be broken up into parts. solid ball that could not be broken up into parts.

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In 1897, a British physicist, J.J. Thomson, In 1897, a British physicist, J.J. Thomson,

discovered that this solid-ball model was not discovered that this solid-ball model was not

accurate. accurate.

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A vacuum tube has had all gases pumped A vacuum tube has had all gases pumped out of it.

out of it.

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At each end of the tube is a metal piece At each end of the tube is a metal piece called an electrode, which is connected called an electrode, which is connected

through the glass to a metal terminal through the glass to a metal terminal

outside the tube. outside the tube.

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These electrodes become electrically These electrodes become electrically

charged when they are connected to a charged when they are connected to a

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Thomson concluded that cathode rays are Thomson concluded that cathode rays are made up of invisible, negatively charged

made up of invisible, negatively charged particles referred to as

particles referred to as electrons_electrons._.

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These electrons had to come from the These electrons had to come from the

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Atoms weren’t just neutral spheres, but had Atoms weren’t just neutral spheres, but had electrically charged particles.

electrically charged particles.

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There must be more to an atom than just There must be more to an atom than just electrons.

electrons.

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Matter isn’t electrically charged, atoms can’t Matter isn’t electrically charged, atoms can’t be negatively charged.

be negatively charged.

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If atoms contained extremely light, If atoms contained extremely light,

negatively charged particles, then they must negatively charged particles, then they must

also contain positively charged particles— also contain positively charged particles—

probably with a much greater mass than probably with a much greater mass than

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2 2 9 9

1909 - American Physicist

Robert A. Millikan

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Showed that the mass of an electron is two-Showed that the mass of an electron is two-thousandths the mass of a proton (hydrogen thousandths the mass of a proton (hydrogen

atom). atom).

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An electron’s mass is 9.109 x 10An electron’s mass is 9.109 x 10-31-31 Kg Kg

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Scientists thought atoms were made

up of equal numbers of electrons

and protons. However, in 1910,

Thomson discovered that neon

consisted of atoms of two different

masses.

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3 3 1 1

Discovery of the Nucleus

1911- New Zealander

Ernest Rutherford

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3 3 3 3

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alpha particles = 4 times heavier than a alpha particles = 4 times heavier than a proton/hydrogen atom.

proton/hydrogen atom.

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1/8000 would bounce back.1/8000 would bounce back.

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He said it was “as if you had fired a 15 inch He said it was “as if you had fired a 15 inch artillery shell at a piece of tissue paper and artillery shell at a piece of tissue paper and

it came back and hit you.” it came back and hit you.”

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He thought about for 2 years...He thought about for 2 years...

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Then came up with the nucleus idea. Then came up with the nucleus idea.

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3 3 5 5

The Nucleus

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If the nucleus was the size of a marble, the If the nucleus was the size of a marble, the size of the atom would be about the size of size of the atom would be about the size of

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Chapter 3-3

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3 3 7 7

Atomic #

(Z)(Z)

= # of protons

within the nucleus of an element

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3 3 8 8

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The chemical properties of an atom are determined by The chemical properties of an atom are determined by the number of protons in the nucleus--the

the number of protons in the nucleus--the atomic _atomic

number

number, abbreviated Z. The Z number also , abbreviated Z. The Z number also

gives an indication of the how effectively X-rays are

absorbed--the greater the Z number the greater the

absorption of X-rays.

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Bones show up in X-rays relatively well because they Bones show up in X-rays relatively well because they contain large amounts of calcium and phosphorus

contain large amounts of calcium and phosphorus

while most of the rest of the

while most of the rest of the body consists of organic _{body consists of organic}

compounds containing C, H, N and O and water (H

compounds containing C, H, N and O and water (H22O) O)

which have smaller Z numbers. Explain why the

difference in composition is important for

radiographers

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3 3 9 9

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The chemical elements are named on the basis of The chemical elements are named on the basis of their Z number.

their Z number.

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1 hydrogen H1 hydrogen H

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2 helium He2 helium He

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3 lithium Li3 lithium Li

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4 beryllium Be4 beryllium Be

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5 boron B5 boron B

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6 carbon C6 carbon C

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7 nitrogen N7 nitrogen N

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8 oxygen O8 oxygen O

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9 fluorine F9 fluorine F

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4 4 0 0

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Most of the symbols are easy to remember, but Most of the symbols are easy to remember, but some are based on the original Latin used by

some are based on the original Latin used by

alchemists. Examples:

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SymbolSymbol Latin nameLatin name

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sodiumsodium Na Na natrium natrium

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potassiumpotassium K K kalium kalium ironiron Fe ferrum

Fe ferrum

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copper Cu cuprumcopper Cu cuprum

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tin Sn stannumtin Sn stannum

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silver Ag argentumsilver Ag argentum

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gold Au aurumgold Au aurum

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mercury Hg hydrargyrummercury Hg hydrargyrum

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Atoms of an element that are chemically Atoms of an element that are chemically alike but differ in mass are called

alike but differ in mass are called

isotopes

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Symbol

Mass Number

Atomic Number

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4 4 5 5

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Atomic number = #protons = #electronsAtomic number = #protons = #electrons

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If atomic number = 55 If atomic number = 55 There are 55 protons and There are 55 protons and 55 electrons

55 electrons

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Mass number = sum of protons and neutronsMass number = sum of protons and neutrons

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if mass number is133 and atomic 55if mass number is133 and atomic 55

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133 – 55 = 78133 – 55 = 78

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There are 78 neutronsThere are 78 neutrons

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4 4 6 6

• If you look in the periodic table, the atomic mass is 6.9, which is 9/10 of the way between If you look in the periodic table, the atomic mass is 6.9, which is 9/10 of the way between 6 and 7, i.e. it is the weighted average of the different isotopes found in nature. 90% of the

6 and 7, i.e. it is the weighted average of the different isotopes found in nature. 90% of the

Li atoms are Li-7 and about 10% are Li-6

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4 4 7 7

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There are 3 isotopes of carbon:

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12 13 14

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C C C

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6 6 6

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% isotope

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in nature 99% 1% very small

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# of neutrons: ____ ____ ______

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The last isotope is the basis for Carbon-14 dating

and has been used to date on many archeological

specimens and the shroud of Turin.

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4 4 8 8

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235 238235 238

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U UU U

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92 9292 92

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% of isotope in nature: 0.7% 99.3%% of isotope in nature: 0.7% 99.3%

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# of protons# of protons ______ _____ ______ _____

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# of neutrons: _____ ____# of neutrons: _____ ____

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# of electrons: ______ _____# of electrons: ______ _____

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Only the U-235 is fissionable in nuclear reactors. Naturally occurring uranium is commonly Only the U-235 is fissionable in nuclear reactors. Naturally occurring uranium is commonly enriched in U-235 before being used in the US nuclear power plants. The residue is mostly U-238

enriched in U-235 before being used in the US nuclear power plants. The residue is mostly U-238

and is called depleted uranium (Question: what is depleted??). Because of its very high density (D =

18.7 g/cc), depleted uranium has been used in tank armour, and also in high tech “bullets” to pierce

tank armour and the like. There has been concern about the health effects of depleted uranium left

in the field.

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_{In the 1930’s, the}_{In the 1930’s, the}

Neutron

_was_was confirmed.

confirmed.

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Differences in mass led scientists to believe Differences in mass led scientists to believe there was a third particle.

there was a third particle.

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That nucleus has neutrons

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Like charges repel (- and - or + and +)Like charges repel (- and - or + and +)

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Opposites attract (- and +)Opposites attract (- and +)

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Since protons are positive, how are they all Since protons are positive, how are they all sticking next to one another in the nucleus? sticking next to one another in the nucleus?

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Another particle, Another particle, neutrons neutrons might help.might help.

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Nuclear forces hold nuclear particles Nuclear forces hold nuclear particles

together (p’s and n’s, p’s and p’s, n’s and together (p’s and n’s, p’s and p’s, n’s and

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5 5 1 1

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99.985% 0.015% very small %99.985% 0.015% very small %

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Tin has 10 stable isotopes (the most of any Tin has 10 stable isotopes (the most of any element).

element).

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Isotopes have a neutral charge (-’s and +’s Isotopes have a neutral charge (-’s and +’s are equal).

are equal).

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5 5 2 2

Mass Number

Protons + Neutrons

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Mass # - Atomic # = # of neutronsMass # - Atomic # = # of neutrons

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Uranium has a 235 massUranium has a 235 mass

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It’s atomic number is 92 (so 92 protons)It’s atomic number is 92 (so 92 protons)

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How many neutrons?How many neutrons?

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235 - 92 = 143235 - 92 = 143

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Different number of P’s and N’s means what?Different number of P’s and N’s means what?

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Isotope! Isotope!

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5 5 3 3

Designating Isotopes (nuclides):

The number means MASS.

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Uranium-235Uranium-235

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Hydrogen-3Hydrogen-3

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Helium-4Helium-4

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How many many protons, electrons and How many many protons, electrons and neutrons does Sodium-24 have?

neutrons does Sodium-24 have?

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H

Hydrogen

1

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Na

Sodium

23

11

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Rhenium

Re

186

75

Protons: 75

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Rhenium isotope

Re

187

75

Protons: 75

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EXAMPLE

How many protons, neutrons and electrons are found in an atom of

133

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5 5 9 9

What is the Atomic Mass?

Why does it have decimals?

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The

atomic mass

of an element is

the average of all the atomic

masses of the isotopes.

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an isotopes contribution is

determined by its relative

abundance.

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6 6 0 0

• The mass of an element is the mass of the element The mass of an element is the mass of the element compared to an isotope of carbon Carbon 12.

compared to an isotope of carbon Carbon 12.

• _{Carbon 12 is assigned an atomic mass of 12.00 g.}_{Carbon 12 is assigned an atomic mass of 12.00 g.} • 12.00 is one atomic mass unit_{12.00 is one atomic mass unit}

• The number of protons and neutrons in an atom is its The number of protons and neutrons in an atom is its mass _mass number

number._.

• Atomic numbers are whole numbersAtomic numbers are whole numbers

• Mass numbers are whole numbersMass numbers are whole numbers

• The The atomic mass_{atomic mass} is not a whole number. is not a whole number.

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Atomic Mass Units = amu

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Protons = 1Protons = 1

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Neutrons = 1Neutrons = 1

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Electrons = 0Electrons = 0

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